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G has a "swell" time kayaking

G has a "swell" time kayaking
G has a "swell" time on Lake Michigan in an inflatable canoe

Dawn on the Gulf of Mexico

Dawn on the Gulf of Mexico
Dawn on the Gulf of Mexico

Warren Dunes Sunset

Warren Dunes Sunset
Warren Dunes Sunset
Showing posts with label Lithium Batteries. Show all posts
Showing posts with label Lithium Batteries. Show all posts

Wednesday, October 30, 2019

Coach Batteries - AGM versus Lithium Ion Update


AGM Lead Acid batteries in my 210P. Mounted outside. 

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Here's an update on lead acid sealed AGM batteries versus Lithium Ion (LiFePo4) as coach batteries in my Roadtrek. If you have a Chevy based Roadtrek, you probably have two 6-Volt 220Ah AGM batteries as I do.

Note: 1. I'll post an article about what we can expect from our batteries and my experience powering the stuff in my Roadtrek with AGM batteries since December 2013.

When we compare batteries, we usually look at these three types:
  1. 6V type GC2 golf cart batteries. These lead-acid batteries, are not sealed, and do require addition of distilled water from time to time. They also do vent gasses.
  2. 6 V type AGC2 AGM batteries. These are also lead-acid batteries, but they are sealed and require no maintenance.
  3. 12V LiFePO4 Lithium-Ion batteries. These are radically different than the golf cart and AGM batteries. 
So which is the best type? That requires considering the trade-offs which depends upon your use, and how much money you are willing to spend, and warranties.  Our 210P has an Onan generator and I added limited solar too.  If we are not on shore power we need battery power to get through the night, and then we recharge. If battery power is low we can run the Onan generator, or the chassis engine. We use the inverter sparingly to give us 120VAC. So we don't need a lot of battery power. We also have propane for the stove top and for the hot water heater. Your situation might be different.

Trick question: Should one invest in LiFePo4 batteries or in Solar Panels?  I won't attempt to answer that in this post.  The answer lies in how much electrical power do you need to get through the night, when batteries are important, or use a generator.

In fact the real issue is making a useful comparison of electrical energy sources when off the grid. These include batteries, my Onan generator, and my solar panels.   This is a somewhat unequal comparison, because my Onan can provide 2,800 watts of continuous power. That's sufficient to run my Air Conditioner and the Onan consumes about 25 ounces of gasoline per hour at low power and 55 ounces per hour at full power.

My point is, we are comparing energy sources, and the costs of those sources.  This post will not compare the cost of solar panels and batteries to other sources.

Here is a quick comparison of batteries. I use Battle Born Battery as the Lithium-ion comparison because they seem to be a well made battery with a "10 year warranty".  These would also work with the TrippLite inverter charger in my Roadtrek, with a change in settings to "Gel", because according to Battle Born "the battery prefers to bulk charge at 14.4 volts and float at 13.6 volts".
  1. GC2 and AGM batteries are both lead-acid batteries. One of the characteristics of these batteries is they should not be repeatedly discharged below 50% to get maximum life.  So, my 220 Ah batteries can only really provide about 110 Ah of electrical energy if I want to get maximum life from my batteries. 
  2. LiFePO4 type Lithium-ion batteries are radically different technology. So they are significantly lighter in weight than any lead-acid battery of similar capacity. They can be repeatedly discharged 75 to 80% without decreasing the life of the battery. They also can tolerate more charge-discharge cycles than the lead acid batteries. A 200Ah LiFePO4 battery can provide 160 Ah of useful electrical energy. 
So why haven't we all switched to Lithium-ion batteries? It is because even if we consider the advantages, the lithium batteries also have some disadvantages.

  1. LiFePO4 batteries cannot be charged if they are below freezing temperatures.
  2. LiFePO4 batteries are significantly more expensive than AGM batteries.

Here are some cost comparisons. I'm going to use two different AGM batteries and compare them to a "drop-in" Lithium-Ion battery replacement made by Battle Born Battery company:

  1. Amstron AP-GC2 6V AGM Deep Cycle Battery. This is rated 210 AH and is currently available for $209.99 at atbatt.com. List at $299.99. Two required to achieve 12V at list = $599.98.
  2. Deka 8AGC2 (8AGC2M) 6V Deep Cycle battery. Made in USA. This is rated 220 Ah and is currently available for $389.70 via Amazon. Two required to achieve 12V = $779.40.
  3. Battle Born 12V 100 Ah "drop-in" battery list $949 each. Two would provide 160 Ah of electrical energy versus 110 Ah for lead acid.  This is considering a 80% discharge versus 50%  discharge, which are the recommended maximums for these batteries. Price per battery $949 or $1,898 for two, which is required to achieve 200 Ah.  However, if you are an Escapees RV Club member, you can currently get a 15% discount.

So what are the issues? A couple of years ago, I looked at the replacement of my two 6-V AGM batteries with Lithium Ion batteries.  These were the issues I considered then:

  1. Available power. The Lithium-ion batteries can provide more electrical energy and more discharge-charge cycles.  My AGM batteries can provide 110 Ah of useful electricity while Lithium-Ion which occupies the same space can provide 160 Ah. This is not trivial if one wants to boondock and could be an incentive to consider Lithium-Ion batteries.   
  2. Temperature Restrictions. When I evaluated Lithium-Ion batteries a couple of years ago, I discovered that they should not be charged if the battery temperature is below freezing 32F (0 C).  My 210P carries the batteries in an outside compartment. Because we do trek when it is below freezing, that was a serious impediment. The Battle Born batteries have a low temperature charging limit of 25F.  The batteries are prevented from charging below 25F. However, they can continue to discharge until they reach a "low voltage limit" which is below 10 volts. 
  3. Alternative Location. I even considered moving the Lithium-ion batteries inside of the coach as a means to get them above freezing, but that would displace useful space and add to the installation cost.
  4. Cost. Comparing the Deka AGM to the Battle Born the difference is about $1,118. Comparing the Armston the difference is $1,199.96.
  5. Weight. The Battle Born batteries are about one-half the weight of the AGM batteries. If weight is an issues, that reduction of about 60 lbs could be a significant factor. 
  6. Warranty. Most AGM batteries can be expected to have a life of 5 years, or more. Some Lithium-Ion battery manufacturers offer a 10-year warranty. That means that one set of Lithium batteries is the equivalent of two sets of AGM batteries.  This should be considered when evaluating batteries. 
  7. Temperature and voltage affects - AGM. AGM battery specifications are under "ideal" conditions. These include an ambient temperature of about 77F, discharging to no more than 50% and then immediately recharging.  That may not happen in the real world. AGM batteries do experience reduced capacity in cold weather. AGM battery life will also be reduced at higher temperatures. In other words, that 110 Ah available will decrease as the ambient temperature decreases and may be 25% less at 32F and 20 A discharge rate.  Under high discharge rates the capacity is further reduced. There is a lot of data about AGM and other lead acid batteries because there are so many manufacturers and they have been in use for many decades. 
  8. Temperature and voltage affects - Lithium ion batteries. Using Battle Born Battery data for their "drop-in" 100 Ah battery, they state that the "Output voltage is flat during most of the discharge cycle". Furthermore can provide "100 Amp Continuous Current".  The company states that the batteries have low and high automatic temperature protection which shuts down the battery if temperature falls to 25F or a high temperature of 135F is reached. 
  9. Lifespan. The AGMs in my Roadtrek are designed for about 1200 charge/discharge cycles if they are not discharged below 50%. According to Battle Born the lithium ion batteries "Approximately 75-80% of the battery capacity will remain after 3000 cycles in applications recharging at 0.5C or lower". The recharge "C" rating for a 200Ah battery is 0.5 x 200 A, or a charging rate of 100A. The lithium ion batteries will have much more life remaining than the AGMs after a couple of years of normal use. My AGMs should give good service for about 5 years, or longer. The Battle Born batteries will exceed that. 
  10.  "Useful Life". Lead-acid batteries experience a reduction in capacity as they are charged and discharged because of internal changes, primarily sulfation. This reduction can be significant. After a year of use, my AGMs experienced about a 10% reduction. So, my useful 110 Ah decreased to about 99 Ah. Since then my batteries have leveled out, based upon voltage after a moderate period of discharge. The lithium ion batteries retain their capacity for a longer period of time. That can be important if one needs every bit of electricity available in the batteries when new. 
When I looked into replacing my AGM lead acid batteries with Lithium-ion, I also considered space requirements:
  1. Inside LiFePo4. I would have to give up some under the bed space, because the Lithium Ion batteries should not be charged if below freezing. In fact, the Battle Born battery internal battery management system prevents charging below 25F.
  2. Inside AGM. If I kept my two outside AGM batteries and added two inside, that would provide me with 220 AH of energy versus 160 Ah for the Lithium Ion batteries. In other words, I'd get about 38% more energy from four 6-V AGM batteries. However, those four batteries would weigh about 272 pounds. Two Battle Born batteries would weigh about 62 pounds. 
  3. Inside AGM and Battle Born comparison. The above with four AGM batteries provides about 220 Ah at the best case at 272 pounds. If I added one Lithium Ion battery to total of three, that would increase the energy available to about 240 Ah. The weight would be about 93 pounds. 

The show stopper:
When I considered AGM versus Lithium-ion, I had these issues and yours might be different:
  1. I wasn't willing to mount the LiFePO4 batteries inside the coach, because I didn't want to give up that space. That would be to keep the batteries above 25F while cold weather trekking. 
  2. If I compare the normal life of AGMs (5 years or so) to the Battle Born LiFePo4 (10 year warranty) this changes the costs. To get 10 years of use from AGM batteries would probably require replacement after 5 years. In 10 years the two changes of AGMs is $779.40 each, for a total cost of $1,558.80 for Deka versus $1,878 for Battle Born. 
  3. If I needed more overnight DC power, the Battle Born could be worth that extra $319. After all, considering the 10 year "warranty" life of the batteries, that's only about $32 per year. 

For more about Battle Born Lithium Batteries:

https://battlebornbatteries.com/





Copyright (C) 2019 Norman Retzke, "All Rights Reserved"

Original material:  https://roadtrek210.blogspot.com/

Tuesday, March 20, 2018

Lithium Battery and RV DC Power System Developments


Watt "Imperium" (tm) Fuel Cell Propane Consumption


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September 10, 2021.  Because Roadtrek took down the Watt video, I added a link to the website.
October 10, 2018. Added Roadtrek video on the Watt propane generator

Originally Posted March 20, 2018


Class B RV battery systems continue to evolve. Recently Winnebago announced a new version of the Travato with high voltage lithium-ion (LiB) coach batteries. This sparked some conjecture and interest on social media. WGO is joining Roadtrek and Advanced RV in providing Li-ion battery systems in Class B's. Coachmen has an announced Li-ion system for their Galleria. Not all Class B manufacturer's are on board and some of the new systems may not achieve long term expectations. There is reason for buyers to be cautious with these higher power, somewhat expensive and technically sophisticated systems.  Nevertheless, there is a trend to larger battery powered systems in Class B coaches.

This post builds upon my recent ones about solar, AGM batteries, Li-ion batteries (LiBs) and charging systems.  See the "Important Notes" at the end of this post.

The Only Constant is "Change"
Lithium-ion batteries (LiBs) are a "work in progress" and there are a number of changes coming which may further improve these systems. LiBs will be getting more powerful, and soon.

This post focuses on some of the things that are going on, will be here soon, some of the approaches, some issues and provides some comparisons.  Expanded and larger battery systems may be a necessity if RV manufacturers replace propane fueled devices including refrigerators, hot water heaters, furnaces and range tops with DC electrics. The total available portable energy in these coaches may not be changing, but is shifting to electricity as the primary power source.

Because these are expensive systems, I suspect some buyers will overspend, getting features (power ratings) they don't need or seldom use. Components such as inverters and converters may only have 3-year warranties, or less. It will be up to the RV manufacturers to decide how much warranty they are willing to provide for these systems and owners will have to decide how much financial risk they are willing to take. See the "System Comparison Caveats" at the end of this post for important information about ratings, etc.

However, the core information is very positive for these systems. It seems there is continuing divergence as different technologies appear and each has inherent advantages and disadvantages. For my personal use I will be comparing this to alternatives, including standard AGMs and carbon foam battery technology. A lot of that data has been put into earlier posts. "This really isn't rocket science" although these are systems of varying complexities. Manufacturers and tekkies may use jargon and other terms which can confuse the casual reader. I'm sure I'm guilty of that, too. There are also "apples to oranges" comparisons about systems and ratings. These can confuse, particularly when statements rely upon presenting the "best" case.

I assume you are a casual, but interested, reader and this may be helpful to you.   I've spent a lot of time in advanced technology systems for industrial applications and after years "on the leading edge" and some experience "on the bleeding edge"  I am cautious and I have no interest in being an early adopter, and I will avoid certain types of experiments with my Class B. However, there are others who are far more adventurous than I am.

Meanwhile, for an alternative reality using Propane Fuel Cells

Hymer Group (Roadtrek) announced a propane fuel cell. The Roadtek video has since been taken down.  I am replacing it with a link to the manufacturer's website (Sept. 10, 2021).  "WATT Imperium’s™ quiet, always-working operation is about as loud as a ceiling fan or normal background conversation (45 dB at 3ft.), and won’t cause interruptions or distractions. You can now replace cumbersome and noisy conventional gas generators that emit toxic exhaust fumes with Imperium’s™ state-of-the-art compact, quiet and clean power generator":


Here is the original press announcement by Hymer:
"CAMBRIDGE, Ontario, March 6, 2018 /PRNewswire/ -- Erwin Hymer Group North America, Inc. has signed an exclusive supply and engineering cooperative agreement with WATT Fuel Cell Corporation located in Mount Pleasant, Pennsylvania, to introduce the WATT Fuel Cell technology into the RV market........The integration of the WATT Imperium™ Fuel Cell allows the use of propane to create clean electricity and heat, and allows Erwin Hymer Group North America, Inc. to affordably put in place a method of creating clean electricity."

October 10, 2018: 

"One of the leading manufacturers of class B motorhomes in North America, EHGNA placed their first order with WATT after a successful pilot of the Imperium on board their E-Trek autonomous recreational vehicle earlier this year. The Imperium will provide clean power on demand, allowing EHGNA customers to automatically create, access and manage power for all their on-board appliances and devices wherever their adventures take them.........Manufactured at WATT’s facility in Southwestern Pennsylvania, the Imperium is a hybrid SOFC power management system that creates small-scale power, 500W to 1.5kW, from readily available and easily accessible fuels and manages renewable energy sources. The Imperium SOFC system delivered to EHGNA will utilize the hybrid power manager to integrate the fuel cell with solar generation while optimizing on-board energy storage. It will create power efficiently and quietly from propane and solar energy with little to no engine noise or harmful exhaust."

https://www.wattfuelcell.com/news/imperium-shipments-erwin-hymer-group/




Improved Li-ion batteries (LiBs) are Coming. 
Tesla has begun using improved Lithium batteries in the Model S electric car. These batteries reportedly extend range by 6%.  How was this accomplished? By changing the battery construction to include silicon anodes. That change, which sounds simple but in fact is not, allows more lithium in the batteries and that increases power capacity. Graphite (crystalline carbon)  does not meet the high energy demands of electric vehicles.

It has been predicted that within two or three years manufacturer's will be shifting to this more powerful silicon anode battery construction.  Experts suggest that we'll be seeing improvement in the range of 10 to 15%.  This approach may soon provide some batteries capable of 10 to 30% more power. These improved LiBs will be used in applications ranging from smart phones to laptops to electric vehicles. It remains to be seen if these technologies will make it to Class B RVs at an affordable price.

A few years more distant there are even better batteries. These will have primarily silicon anodes which will have the possibility of improving energy storage by up to 40% over todays Lithium-Ion batteries.

However, it might  be best to keep in mind the actual numbers which Tesla Motors has achieved with silicon in the anodes. There is a huge difference between a 40% potential improvement and a realized 6% improvement.

There are serious hurdles to be overcome to get above the 15% improvement, so don't hold your breath. A few companies involved in this include Angstron Materials, Enovix, Enevate, MilliporeSigma, Panasonic and Sila Nanotechnologies.

Larger Batteries
RV manufacturers are now providing larger capacity battery systems, even in smaller RVs, such as Class Bs.  These use existing LiB battery technology. Not long ago Class B's came with 2.4kW (220Ah AGM batteries) or less, and this can be compared to the LiB technology offerings, which generally provide two times the battery power, and upwards.  Here are a few of the recent battery packs based upon LiB technology in Class Bs. Note that specifications are published by RV manufacturers and are subject to change, as is the information they provide:
  • Roadtrek: Ecotrek 400, 400Ah or about 4.8kW (and upwards beyond 800Ah).
  • Winnebago Travato,  725Ah or about 8.7kW at about 50V.
  • Coachmen Li3, 600Ah or about 7.2kW
  • Advanced RV, 400 to 800 Amp hours at 12V (4.8kW to  9.6kW).
Charging Issues and Requirements
Those larger batteries need a lot of power to recharge them. This has led to larger underhood generators and larger shore power chargers. Using solar to recharge those batteries? Consider that in a typical day we might only get about 8 hours of bright sunlight at an angle to the solar panels sufficient to provide maximum charging.  Solar is limited because of daylight hours and rooftop space. 400W of rooftop solar provides only about 33A at peak charging amperes. A 200W solar array provides half that. Consider that a 100W solar array provides 0.1kW of power. That's useful for augmenting or reducing dependence upon batteries, but with 4.8kW and larger battery systems, that 0.1kW solar is going to be a trickle battery charger.

The problem can be exemplified by the Tesla Model S electric automobile, which is normally charged on a high ampere 240V AC circuit. However it can be charged on a 120V circuit. Such a circuit limits charging amperes to 15-20  (about 2.4kw max charging power drawn from "shore power").

How far can a Model S go after an all night charge at such reduced charging?
  • Answer: about 30 miles after an overnight charge at 120V! Yet, the Model S has a normal  battery range of 249-315 miles. (According to Tesla the 60-kwh battery provides a range of up to 232 miles (the EPA pegs it at 208 miles), and the 85-kwh battery (a $10,000 option) provides up to 300 miles (the EPA puts it at 265 miles).
  • It would seem that the best the Tesla can do on a 120V circuit overnight is to get about 6-8kW of charge. 
The problem now being faced by RVers is similar to the above. How to get enough power to "quickly" charge those large coach batteries, and from where?

Here are a few typical choices available as coach battery power recharge sources:
  1. 120VAC "shore power" circuit with standard 12V charger: 45A = 540W (e.g. Tripp-lite).
  2. 120VAC "shore power" circuit with high capacity charger: Up to 30A at 120VAC = 3600W (Volta).
  3. Onan gasoline/propane 120V generator: powers "shore power" charger, above. 
  4. Underhood 12V generator (e.g. Roadtrek GU):  300A max. at fast idle = 3600W.
  5. Solar: e.g. 200W panel about 17A = 200W.
Note: There are conditions for each of the above. Here are a few:
  1. For the underhood generator the engine must be at a fast idle to provide sufficient power from the alternator. That will use about 0.6gph of fuel according to some sources.  That's more than a gasoline generator, but what vehicle engine RPMs are required to provide those quoted "peak" alternator charging rates? However, underhood generators can provide more DC power at peak alternator speeds.. 
  2. The Onan gasoline generator (2.8kW) in my 210P can provide a maximum 23.6A at 120V. If charging batteries at maximum using the Tripp-Lite, the other AC consumption in the coach must be limited to 13.6A or less (about  1.6kW). Generator power output decreases above 1,500 ft elevation and temperatures above 85F. "Typical" gasoline consumption at full load: 0.43gph; at half load: 0.3 gph.
  3. Solar charging is determined by the size of the panels in watts as well as the type of charge controller. MPPT type will outperform PWM type. Temperature and amount of sunlight also determines how much energy can be "harvested" from the sunlight striking the panel(s). 200W is probably the maximum roof real estate that can be provided for solar panels on a Class B, but there will always be exceptions. Rooftop solar has one large limitation for those parking and charging; the RV must be in full sun to get full benefit. That sometimes turns the metal can into an oven. Using portable solar panels may overcome this, but they might have a tendency to "walk."
  4. A Tripp-Lite "Powerverter" inverter-charger includes "load sharing" settings, to limit the charging current when running off of an AC circuit. If not used, AC input of 10A or 1200W may occur for charging batteries at 45A.  This is the device in my Roadtrek 210P. 
  5. LiBs can charge faster than AGM batteries. However, charge times are determined not only by battery chemistry but also by charging power available. 
The Problem in a Nutshell
From the above, the problem facing RV manufacturers for their large, LiB systems can be summarized simply:
  • It takes a lot of power to quickly recharge those large battery packs!
  • Solar, small underhood generators, and other charging systems may be inadequate to fully charge the batteries in the time available. 
  • Going to higher battery voltages requires DC/DC converters and to get fast "shore power" charging will require larger "shore powered" chargers. 
  • As power requirements of RVers increase, so does the need for larger inverters to change that DC power into 120VAC.
  • All of the above equipment adds weight. So there are trade-offs. 
Inverters, 100% Electric Coaches and Load Shedding
Inverters are required to change battery voltage to 120 VAC power. These have peak efficiencies of about 90%, but as AC loads decrease so does the efficiency of the inverter, which can be as low as 50% at light loads. In other words, 250W in and only 125W output power This can create a dilemma. To get maximum use of the batteries requires running inverters at higher efficiencies.  To do so means using more battery power, and using more power requires larger batteries. Eventually we reach a point where the battery systems are approaching the ability to replace that 30A shore power, at least for a few hours a day.

Manufacturers are moving away from propane/electric coaches. This may be for economic reasons and it may also be a result of those larger coach batteries. An example is replacing absorptive refrigerators with compressor refrigerators. Some compressor refrigerators operate on 12VDC (or 24VDC) and require a 15A dedicated circuit (180W maximum).

If 12V DC refrigerators are used on 12V battery systems, then there are no converter losses. If 12V DC refrigerators are used on 48VDC battery systems there will be converter losses. If 120V compressor refrigerators are used, then there are inverter losses.

"There is no free ride."  LiB battery prices can be $2,000 per 2.4kW.   As RV manufacturers embrace "all electric" approaches, the battery requirements increase.

My personal trekking experience a few years ago in an "100% electric, solar powered" Class B RV gave me some insights and I do have some concerns about recent trends. There is a movement away from multi-fuel systems such as propane/electric to all electric coaches. This places larger demands on the electrical power systems of the coach. However, most battery power systems are not up to full replacement of shore power on a continuous basis. That would require battery systems capable of providing up to 3.6kW continuous electrical energy, ignoring inefficiencies of any inverters or converters.

There are methods in use on some larger RVs to control peak power consumption. These are "load shedding" systems which monitor the coach power demands and automatically turn off features based upon priorities so as not to trip circuit breakers, overload inverters, converters, etc.

For example, in an all electric coach there may be a resistance heater stove top, a microwave/convection oven, a coffee pot, a compressor refrigerator, an electric hot water heater and environmental heat and air conditioning. Vehicle engine heat may be used to augment heating/hot water.

Only the larger battery systems can power all of these, which may even overpower the 30A shore power capabilities of a Class B if an attempt is made to use hot water, air conditioning and do cooking at the same time.

It is relatively easy to automatically turn off, or "shed" some of these loads on a priority basis. For example when using the electric range, other appliances may be prevented from powering up. However, I don't see Class B manufacturers doing this. It is also easy to manually turn off certain features, if the coach is so equipped. Using circuit breakers to manually shed loads is not a good approach. Circuit breakers are not intended to be used as "off-on" switches.

Higher Voltage DC Systems:
There is some interest in higher voltage DC battery systems. The moving force for these has been electric vehicles and marine applications. Some Class B RVs offer batteries and underhood generators at higher voltages.  Typically 24 or 48VDC (peak 58VDC). An example is the Volta System, which is the basis for the Winnebago Travato Li-Ion battery system. 

The higher voltage systems may use a variety of chemistries and LiB construction. Lithium Iron Phosphate(LiFePO4) is most common in 12VDC LiB systems. The higher voltage systems depart from this.

Higher voltage battery packs in electric vehicles may use Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) which is also called "NMC" or they may use Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) also called "NCA".

LiFePO4 is generally used in 12-24V systems. "NMC" seems to be more preferred in the higher voltage systems such as 48VDC. There are differences between each of these battery systems which yield different power per unit weight. In other words, some battery packs are lighter than others, even with the same power ratings. The weight and power density varies with the technology used.

Are Higher DC Voltages Better?
I have seen some apparent confusion about the lower versus higher voltages. The bottom line is straightforward with comparison of the copper conductors and the alternators.  As we move into alternative battery chemistries, the density (power per unit volume and the weight) also changes.  Keep in mind that higher voltage DC systems do require a "converter" to get 12VDC from the 48V alternator and batteries. That 12VDC is required for standard RV DC power systems.

Be aware that every time we change voltages, there are losses, or "inefficiencies".  These inefficiencies are inherent in the power conversion, and they usually show up as waste heat. Wonderful in the winter, but unwelcome in the summer. Those converters  probably lose upwards of about 10% of the battery power put into them.

When considering efficiencies, we need to consider the weight of batteries and the weight of alternators and wiring, but also the weight of inverter/chargers and converters (e.g. 48V to 12V DC).  Stationary weight is not a consideration, but increasing accessory weight does displace other things we can carry within the chassis weight limits.

Another term sometimes used for this is "overhead." Whatever term we choose to use, not all of that battery power may get to the appliance, and there are weight differences, which lower the vehicle MPG and may limit the useful carrying weight of the vehicle.

How much inefficiency is there? It is reasonable to use 10% as the minimum inefficiency of a converter. In practical terms, that means that a 7.0kW high voltage battery system will only provide 6.3kW of useable 12VDC power, or less.  Of course inverters which change DC battery power to 120VAC power also have inefficiencies.

One advantage of a 48V alternator is size and weight. Such an "underhood generator" will be smaller and lighter than a 12V alternator providing the identical power. The 48V generator will also require smaller conductors (wires) to convey its power to the batteries. However, the trade-off is the weight of the converter required to change that higher voltage to 12VDC. Volta's Z5104200-0121250 converter weighs 42 pounds and provides 1500 continuous watts of 12VDC.

Of course, under hood generators are less weight than a gasoline generator. An Onan "microlite" 2.8kW generator weighs 113 pounds.

The 12VDC demands may decrease as RV manufacturers juggle and size the voltages of appliances and power requirements. This may allow smaller, lighter and less powerful converters. Transferring requirements from 12VDC to 120VAC will increase the inverter size and weight. Volta's weighs 68 lbs and can provide 3000 watts of continuous 120VAC power.  It can functionally replace the 30A "shore power" connection for as long as there is sufficient battery power available.
Underhood Generators (Alternators)
Here's a comparison of the power ratings of several underhood generators. These alternators require a minimum RPMs to provide usable power. That means that the vehicle engine must run at a "fast idle" and higher to provide sufficient power.  Alternators generally put out low amperes at normal idle (actual output is determined by the speed of the alternator, and increases dramatically once we get above fast idle).  Very low quoted charging times may require highway speeds to get the underhood generator to peak power:
  • Roadtrek GU: 300A at 12VDC, rated 3,600W (3.6kW) at ?? RPM. 
  • Volta 120FTAN-58:  160A at 48V, rated 6,000 W (6.0kW) at 4,000 alternator RPM.
  • Volta 160GM92V-58: 120A at 48V,  rated 8,000 W (8.0kW) at 7,500 alternator RPM.

Projected Lifespan, Warranties and Opportunity Costs 
There are a variety of figures published about the lifespan of these battery systems. Some say 10 years, with the ability to provide 80% of the published power over that period of time. Ultimately, the only thing one can count upon is the RV builders warranty. Equipment manufacturers may only provide 1-3 years. This makes the RV builder's warranty very important.

Justification of these high power battery systems requires long lifespans. For example, the "opportunity cost" of a $10,000 system which operates reliably and provides at least 80% of published power will be:
  • $1,000 per year if the system provides 10 years of service.
  • $2,000 per year if the system provides 5 years of service. 
System Comparison Caveats
The weight and capabilities of these systems varies considerably. In general, here are some things to keep in mind:
  1. LiB batteries weigh substantially less than AGM equivalents. Comparing 12VDC battery packs, for example: 200A Roadtrek "Ecotrek" modules weigh about 80 lbs. 200A AGM batteries weigh about 126 lbs. This gives LiBs a weight advantage if we consider only the batteries.
  2. To compare these different systems, we should consider the useable kW. However, "useable" makes some assumptions, and manufacturer's use this in their published data.  For maximum lifespan, LiBs should probably not be discharged below 80%, but this does vary with battery chemistry and there are some differences of opinion. For maximum lifespan, AGMs should not be discharged below 50%. However, alternative AGM technology reputedly allows discharge to 80%.  Comparing discharge cycles a 2.4kW LiB battery can provide about 1.9kW while an 2.4 kW AGM can provide  about 1.2kW. Alternative Carbon AGM technology batteries rated 2.4kW can reputedly provide 1.9kW.
  3. Losses and inefficiencies are important, too. A 12VDC battery system powering a 12VDC appliance has zero "conversion" losses. A high voltage battery system using a converter will have about 10% conversion loss. In other words, the available 2.4kW of such a system will decrease to 2.16kW useable for appliances. 
  4. Inverters which change battery DC to 120VAC also have inefficiencies. We never get 100% of that DC power to the AC appliances. At lighter loads, inverter efficiency is less and as the load on the inverter increases, the efficiency improves. Generally, inverter manufacturers will state "maximum" efficiency, which occurs at higher AC loads. So, for example, a 2.4kw battery with a highly loaded, 90% efficient inverter can only provide about 2.16kW of AC power; of course at those loads we can quickly draw down batteries. But at lighter loads the actual efficiency may fall to 50%, In other words, half of the battery power may be lost when changing DC to AC with lighter loads. So at lighter loads, we get longer battery availability, but the actual kW available will be less than that at the higher efficiencies. Confusing, isn't it? 
  5. Efficiencies can be difficult to figure out in the "real world" using batteries to power DC appliances and 120VAC appliances, with varying loads and if augmented by solar, with varying sunlight. Which is why there are statements made all over the map. We do make assumptions when specifications are stated (even engine rpm changes the battery charge time using that underhood generator). So it is not surprising to me that it is difficult to come to some idea of what we can actually achieve with these different systems. 
  6. When comparing systems, it is necessary to compare battery costs. By comparing the cost of equivalent kWs of batteries, LiBs win. Comparing usable kW costs and disregarding battery lifespans, the differences change significantly.  Here's a post which provides a comparison:   A comparison of AGM batteries to Lithium-ion
  7. Manufacturers may be inclined to stretch the projected life spans, abilities and so on, as well as to make other statements to justify the costs to buyers.  
  8. To determine the weight of a system requires adding the weight of all of the following:
  • Generator
  • Batteries
  • Inverter/Charger
  • Converter
  • Solar Panel
  • Solar Controller
  • Wiring
  • Mounting Hardware
Volts, Amperes and Wiring (Conductors)
In higher voltage battery systems the conductors required to carry power will also be smaller than they would be in a 12V system providing the identical power (kW).. The actual size of the conductors will be determined by the current (amperes) they are required to carry as well as the allowable voltage drop.

All wires have resistance. That creates "voltage drop" which is wasted power and it is dissipated as heat. Voltage drop reduces the DC voltage available to the appliances, etc. on the circuit. Here's an example in which we want the voltage drop not to exceed 3%. In a 12VDC circuit, a 3% drop means that with a battery voltage of 12.0 we'll see 11.64V at the end of the wire when carrying the rated amperes :
  • For a 30A circuit, we would use a #10AWGwire for a circuit up to 10 ft. in length.
  • For a 30A circuit with lengths of 15 ft. we would use a #8AWG conductor.
  • At 20 ft. we'd go to #6AWG.  
  • etc.
Note: The smaller the AWG number the larger in diameter and current carrying capacity is the conductor. AWG = American Wire Gauge.

So what do we gain with higher DC voltages? To use those higher power alternators (underhood generators) requires either larger conductors or increasing the voltage. The significance is this:
  • At 12V a 30A circuit carries 360 watts.
  • At 48V the same 30A circuit carries 1,440 watts (four times more "power" than the 12V circuit). 
Ultimately it is the power that matters, not the voltage or the amperes.
  • DC power (watts) = volts x amperes. 
Important Notes:
  1. All trademarks, etc. belong to the respective equipment and RV manufacturers.
  2. Information presented here is from the equipment manufacturer's and RV manufacturer's published sources. No effort has been made to certify the validity or accuracy of that information. 
  3. All information is "subject to change" by the respective manufacturers.
  4. This post is Copyright (c) 2018 Norman Retzke "All Rights Reserved"
  5. I don't work for any RV or battery manufacturer, nor am I compensated in any way by them. These posts are  provided with the intention to provide factual and useful information. Nevertheless, they are my personal opinion.
  6. I have no inherent preference for any of the LiB systems in this post. At the time of this writing I am trekking in a Class B which is equipped with an Onan gasoline generator, 220AH AGM batteries and an inverter/charger. I added a supplemental solar panel to assist in charging the coach batteries when I am parked off the grid. 
  7.  It has been reported that global lithium-ion battery revenue is expected to expand to $53.7 billion in 2020, up from $11.8 billion in 2010.
  8. Tech Note: Silicon (Si) has attracted substantial attention as an improved LiB battery material because of "its specific capacity of 4,200 mAhg-1, volume capacity of 9,786 mAh cm-3,  relatively low working potential (0.5 V vs. Li/Li+), the abundance of the element Si and the environmental benignity of Si."
Original material:  https://roadtrek210.blogspot.com/


Monday, August 7, 2017

Comparing AGM and Lithium RV Battery Systems



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Comment added August 10, 2017; see the notes at the bottom of this post, in particular #5.

A couple of years ago, I considered swapping my AGM batteries for Lithium (LiFePO4). I looked again in January 2017 and I again decided against doing that.

What's the problem? It's simply dollars and sense.




As can be seen above, running both 200AH lithium and AGM battery systems to 80% depth of discharge (DoD) the cost of the AGMs is sufficiently less. So, while the lithium batteries are more "elegant" from an engineering perspective they may not provide more benefits and at a higher cost. Read on for the details.

Here's the background:

Battery life: Lithium 2000 cycles at 80% DoD. AGM 700 cycles at 80% DoD.

Cost for 200 AH: Lithium with BMS = $1,939. AGM = $450.

As can be seen above, here is the arithmetic:

AGM: 2100 cycles at 80% DoD requires (3) sets of batteries, or 3 x $450 = $1,350.
Lithium: 2000 cycles at 80% DoD requires (1) set of batteries at $1,939.

Conclusion: use AGM batteries, install a better battery monitor and run the batteries to 80% DoD. Compared to Lithium, save $589 while getting about the same performance and none of the low temperature headaches.

Other Considerations: 
  1. AGMs weigh more than LiFEPO4 batteries, so if I needed more than 200AH of battery capacity (more than 10 hours @ 16.8A) then I should re-evaluate an alternative to the 200AH of AGMs I have. 
  2. Installing lithium ion batteries will also require additional electronics, including a charger and an Energy Management System, at additional cost.  My AGM system includes the necessary electronics, I added a digital Volt/Ammeter, so all I have to do is replace the batteries at the required time.
  3. AGM batteries can be charged at below 32F. LiFEPO4 batteries have to be heated to be charged at 32F and below. In my case (AGM), that means no heaters and no wasted electrical energy warming up lithium ion batteries prior to charging. In my case, that makes installations simpler. I can keep the 200AH of AGM batteries in the outside compartment. I had decided that if I chose lithium ion batteries that I would install them inside the coach. I would have had to give up valuable real estate (square footage) to do that. 
  4. Because Lithium ion batteries weigh less than AGM batteries, if I really needed 400AH or so, I'd look at the volume and weight differences. But that is not currently an issue for me. 
  5. Over on social media, putting info about the relative merits of AGM batteries versus Lithium (LiFePO4) usually causes a bit of a stir. Here is my response to one social media rebuttal:  "I agree about the "light duty", but that also changes the cycles for AGMs and what' the point of buying a lot of capacity not to use it? What is missing in the chart you provided is remaining capacity and that does make a difference. The charts for the AGMs I'm using indicate about 60% capacity remaining after 80% DoD and 700 cycles. It is a known AGM characteristic that capacity does gradually decline, and by 700 cycles capacity decrease to 50-60% is usual. That certainly can have an impact on [battery] selection. Specifics may vary from manufacture to manufacturer. I used the table of the AGM battery manufacturer in my coach, and it might be accurate or not. I also based cost on the actual cost of the batteries (AGM's in my coach and the current price of the LiFePO4's I was considering). The lithiums don't include installation, which would definitely not be drop in. One other issue to beware of in AGMs is full discharge. The battery numbers vary based upon "relative" DoD. In other words, some battery specs go all the way down to 10.5 volts, which is a dead AGM battery. Other charts use relative terms in which the 0% AGM charge is 11.66V or so, which is actually about 20% DoD. Everything I've seen indicates that AGMs when fully charged generally have about 80-100% capacity which gradually diminishes. Lithium batteries also experience capacity loss, although that doesn't seem to become significant (below 80%) until about 400- 500 cycles. I'm sure there are installers who have better data based upon dozens or hundreds of installations. On the other hand, they might not want to provide data that kills the golden goose.


Wednesday, February 8, 2017

Coach Battery Replacement


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My Roadtrek which I could name "Tried and true" or "Rock steady" continues to perform. But there is maintenance to do. Some of this is preventative.

It became apparent that I needed to replace the coach batteries when one of them dropped to 0 volts. It had shorted, I guess, because the bank was at 6.5 volts, which was the voltage across one of the batteries and also the voltage across both. One battery seemed to be doing okay and the other was a tag-along. Just like America, 50% are doing the work and the other 50% is contributing nothing. beyond lip service.

I was aware that the batteries were not able to deliver the designed capacity. Capacity is the ability of a battery to provide the required power (watts) or ampere-hours for the required amount of time. My coach battery capacity prior to the 0 volt failure was below 50%, even though they measured suitable voltage on the indicator in the Roadtrek.

My batteries achieved a life of 4 years. Well maintained AGM batteries can go for 6 years, or more. I use a 50 watt solar panel with de-sulfating controller to maintain the batteries when off of the grid. My measurements indicate this is sufficient when storing the Roadtrek. On a sunny day the batteries will reach peak voltage. After a couple of cloudy days the voltage might decrease to about 80% as an indicator of "state of charge." I take my measurements early in the morning, prior to sunrise and after sufficient time to dissipate any "surface charge."


I'd done a lot of research including opening a discussion via the FMCA Roadtrek International "cyberrally" email.

I'd also designed a LiFePO4 system, should I want to upgrade to a lithium battery system. However, I decided at this time that going with AGM battery replacement was the prudent thing to do. More on that decision in a future post.

I was spending some time in the Tucson AZ area, so I found a distributor who carried the 220Ah 6-volt AGMs I was interested in and would install them for an additional $30. The total price was irresistible.



One thing we observed was the ends of the crimp connectors showed some oxidation. Is that a problem? The oxidation is higher resistance than bright copper, and over time that oxidation will creep up the wire. Resistance is a voltage loss and a source of heat. After cleaning, the ends were again shiny copper.



The installer then applied liquid plastic via a glue gun to seal the end of the connector. This should prevent further oxidation.



The new batteries included lifting means. One of the reasons I didn't do this was the fact that the old batteries didn't have such a means. I was faced with either purchasing a strap, or wrestling with 63 pound batteries. I've stored the lifting means in the compartment with the batteries.



Here's the completed installation:




After several weeks of monitoring the battery voltage, and with the solar panel connected, it seems the new batteries are doing well, achieving maximum terminal voltage and sustaining it into darkness.

My Roadtrek which I could name "Tried and true" or "Rock steady" continues to perform.

Sunday, October 25, 2015

Lithium Batteries and Solar Power, Revisited




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Winter approaches and we are near the end of our first two years with a camper van. It is time to winterize and to review my "to do" list. One item has been improving the coach battery system. We did store the camper for two winters with the batteries on a solar panel.

This worked fairly well. But, I wasn't happy with the amount of power provided by these 220Ah batteries, and began exploring alternatives in late 2013, immediately on purchase. I'd done the numbers and knew we would be on the edge based upon our intended use of the vehicle. Why do I say "on the edge?" It is because of the available capacity of these batteries, which is not 220Ah if one wants them to have a reasonable life expectancy of 5 or more years.

A Short Review
What is the true available 12VDC power? 220Ah of AGM batteries can only provide 110Ah while keeping them above a "safe" discharge level of 50%.  What does that mean? If one wants to run some appliances and an inverter, the batteries can provide the following power:

  • 5 amperes (60 watts @ 12 volts) for 22 hours, or 
  • 6.5 amperes (78 watts @ 12 volts) for 16 hours, or 
  • 8.5 amperes (102 watts @ 12 volts) for 12 hours, or 
  • 12 amperes (144 watts @ 12 volts) for 8 hours. 
The real issue is having sufficient battery capacity to run necessities through the night while off shore power and without a generator. At a minimum this would be the refrigerator and a vent fan or the furnace plus some lighting. The loads of your rig might be different than mine. To run any 120V appliances including a PC would require the inverter which has losses as part of the process of converting 12VDC to 120VAC. It would be best to use 12VDC appliances and a PC which can run from 12VDC. We've got a propane range top and so we can use that for cooking. If the weather is mild, it is possible to use the propane BBQ or if allowed, a wood burning campfire. These things reduce the electrical requirements for the batteries. Of course, we can simply fire up the generator. However it is my desire to make it through a typical night in mild (40F to 85F) weather without shore power or running the generator. That is not necessarily a daily requirement. In fact, based on our actual experience. we only need overnight battery capacity on an occasional basis. That translates into the cost-benefit analysis of the battery and solar system.

The existing AGM batteries, if in excellent condition could provide about 6.5 amperes for 16 hours. I do need to emphasize that I am assuming the batteries are in good condition and fully charged. If not, then less power would be available. Why 16 hours? That's maximum for winter with darkness and operating on batteries from 5pm to 9am. I'm assuming cool temperatures in which there would be no need for supplemental coach heat beyond use of the furnace. However, I've done some analysis of our electric blanket and that is a viable alternative.

If my refrigerator operates on propane I do need some 12VDC for the controls. The furnace electronics and fan also require 12VDC. Lighting loads vary. I've got fluorescent and LEDs. In a pinch we could use hockey puck LED lights which run of AA batteries. But we don't want our "tiny home on wheels" to morph into "our tiny cave on wheels."

How Much DC Power is Used?

  • Suburban Furnace = 2.8A (intermittent)
  • Max-Air Fan @ Medium Speed = 1.5A
  • Refrigerator 12V electronics = estimated 1A
  • Propane/CO Alarm = 0.1A
  • Smoke Alarm = 0A (9V battery)

These  items consume 5.4 amperes. That is approaching the maximum 16 hour capacity of the batteries, and based upon experience that's a realistic maximum for daily hours with less than perfect batteries. It would seem that Roadtrek did a good job sizing this system. Remember that the furnace runs intermittently. That's why I didn't include the lighting load. However, if one uses the inverter, then the requirements increase by about 1.5 amperes or more. That's because of the inefficiency and losses in the inverter.

Do I Need Lithium Batteries?
Based upon our actual experience since December 2013, I would say that we do not. It is true that our current battery system is marginal. However, based upon actual needs, we don't need to do an upgrade at this time.

That said, it is possible I will replace the AGMs with LiFePO4 batteries when that time comes. Here is my reality: It is all about cost-benefit analysis. I do have a design and it will be easy to adjust the design as time goes on. With each design modification I'll get current prices and current technology.  Trigger events to upgrade would include battery failure, inverter/charger failure, a desire for more solar than I currently have, and so on.

It is also possible that some day I may take this on as a "hobby" project. But I am under no pressure to make the modifications at this time.

Here are some links to earlier posts on this subject:

http://roadtrek210.blogspot.com/2015/02/agm-battery-alternatives.html

http://roadtrek210.blogspot.com/2015/02/are-lithium-coach-batteries-expensive.html

Here is a handy calculator to help you determine how long your coach batteries can handle a specific load in amperes:

http://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html

Note: Edited amps used to add CO/Propane detector, misc.

Tuesday, February 24, 2015

Are Lithium RV Coach Batteries Expensive?


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Here's a bottom line for a small RV system, using off the shelf lithium battery components. I'm editing this post to add the following which I think is a very important consideration:

AGM batteries 220Ah = 110Ah useable,
Lithium (LiFePO4) 200Ah = 160Ah useable,

In other words, a similarly rated lithium battery system will probably deliver about 45% more power than a similarly rated AGM battery system, and it will probably do so for at least 6-7 years. Now do I have your attention?

What I am planning is not a "build it in your basement" system comprised of battery packs assembled at home from hundreds of batteries. There are some serious considerations when using lithium batteries, which can be safe and environmentally superior to lead acid batteries. Those batteries do require monitoring and controls so that a cell failure can be managed. My concept system which will probably be built is comprised of pre-assembled batteries packs and off the shelf controllers and solar panels. This system is similar in design to current AGM coach battery systems:

Battery watts: 1200 (or 2400) (1.2-2.6 kWhr, replace 2-6V 220Ah AGM batteries)
Solar Panel = 140 Watts
Cycles: 2000 to 3000 at 70-80% discharge (DoD). Up to 5000 cycles possible. (See notes).
Self discharge = less than 3% per month.
Battery weight = 25 to 33 lbs.
Battery storage temperature limits = -20 to 114F
Battery operational temperature limits = 32 to 114F (some batteries are rated 5F to 115F).
Includes MPTT Solar Controller and 140 watt solar panel.
Includes 120V charger for lithium batteries.
Cost of entire system components: $1,690 - $2,600

Why the cost differences above? There are different technologies available. The most reliable are the most expensive. I think the lower number is realistic. After all, I won't be sailing my RV around Cape Horn. Note: Read the notes at the conclusion of this post for some important info that impact the specifications above.

Can I Get More Power?
The above can be "scaled up" with more batteries, larger solar panels, etc.  A 2400 watt (whr) system could cost about $3,000. The batteries would weigh about 60-65 lbs, which is about half of a similar AGM battery. The costs are for components, but excludes installation and tax.

A 4800 watt system could cost about $5,600.  As you can see, at the higher wattage the cost is approaching about $1 per watt. However, it is possible to get batteries for as low as $0.55 per watt.

Quick Comparison - AGM Limitations versus Lithium
It's useful to keep in mind that the list price of an additional 2400 watts of AGM batteries in a Roadtrek 210P is currently $871. The battery cost difference is why lithium is not currently standard. In recent years there have been some real price drops in lithium and today, 2400 watts of AGM batteries cost about $500-600 while similar lithium batteries begin at about $1,800.

However, AGM batteries are temperamental. They have longer charge times, can and do sulfate, weigh twice what lithium batteries do. AGM batteries perform longest with a 50% discharge (50% DoD, or Depth of Discharge). In other words, a lithium battery with an 80% DoD limit can provide 30% more power each and every day as compared to an AGM battery. Such a lithium battery is designed for at least 2000 cycles, which is about 7 times the life of an AGM battery. Achieving 5000 cycles would result in a system which could have a life measured in decades.

Of course, any RV manufacturer's pricing includes mounting and wiring systems as well as installation labor, etc. I am convinced I could install an entire system, including improved solar and MPTT charging system with at least 2400 watts (whr) of lithium power for a cost of about $3,000. If I want to get wild, I could go for 4800 watts at about $6,000.  The 2400 watt system would be almost a "drop in" solution. 3600 or more watts would require a closer look at the available battery space.

Other Battery Considerations
One more thing to consider is cycles. That's the number of times a battery can be charged and discharged. A Deep Cycle AGM battery, if discharged to not less than 60% the cycle life will be 300 plus cycles. (That's per reputable battery sources). An AGM battery might achieve 500 cycles. A lithium battery is good for 2000 to 3000 cycles at 80% DoD and ideal temperatures (see the notes). In other words, a lithium battery system is rated for a lifespan 6 to  10 times longer than that of an AGM battery system.  That is one of the reasons manufacturers are beginning to look seriously at replacing AGM battery systems with lithium battery systems.

What's the Limit?
Most costly component is the batteries. To get to 20,000 watts as Roadtrek is experimenting could require about $10,000-$12,000 in batteries (at wholesale). I would guess those batteries weigh about 500 lbs. However, to put this into perspective a Roadtrek 210P comes "stock" with two AGM batteries rated a total of 2400 watts. 4800 watts with AGM batteries weighs in at about 280 lbs.

What does 20,000 watts of AGM batteries weigh?
I'd guess that 20kW (kWh) of AGM batteries would weigh in at about 1,200 lbs plus the weight of the system to contain them. Similar capacity lithium batteries would weigh about 500 lbs. However, there are differing lithium battery technologies available, and that influences both volume taken by the batteries and weight. (See note 10).

Why would I do this? 
Well, I think I'll be replacing my AGM batteries next year, less than 36 months after vehicle purchase. Replacement with similar batteries will cost me about $600. In other words, the battery cost has been about $300 per year. Add to that the following possibilities achievable with an upgrade:
  • zero maintenance with solar (I do have solar on the AGM batteries)
  • no lead
  • 10 year life (okay, let's assume 6 years at 75% real, available power).
  • 80% depth of discharge
  • A real 1920 watt-hour available rather than pretend 2400 which is at best 1200.
  • I'd like to get more electrical power when off the grid than I do currently, and I'd like to achieve this without running the engine, or starting the generator. I'd also like to have more power available for cooking when off the grid and conserve propane. I have no intention of living on solar power.  The existing system is rated about 1.3kWh and I think I can double that with the lithium batteries. 
  • No need to charge below freezing during vehicle storage. It's my understanding that lithium (LiFePO4) batteries should not be charged if they are below freezing. However, they can be stored for long periods under freezing conditions and can discharge okay in cold weather. (Note 11).

Notes:
  1.  I have the advantage of being able to prototype and test such systems. I think a "drop-in" upgrade package for RVs would be useful.
  2. I'm currently most interested in LiFePO4/LiFeMnPO4 battery technology. I want batteries which are safe.
  3. Costs are determined by battery technology.
  4. Battery prices are all over the map. Lowest cost is about $0.55 per watt (whr).
  5. Battery life for AGM lead-acid and lithium (LiFePO4) batteries are determined under somewhat ideal conditions. Those conditions include ideal DoD as well as ideal ambient temperatures. Battery life is reduced under higher temperatures. What's ideal? Depending upon the battery, 74-77F is ideal.
  6. In the real world some RVers are attempting to live off solar systems with lots of solar panels and large battery systems. This requires sunshine.  Unfortunately, many such sunny areas also get higher ambient temperatures and that's not good for batteries. Over in Tucson they talk about five annual seasons, of which one is named "fire." Elevated temperatures reduce battery life. So what's reasonable? I'm going to assume a 25% reduction in battery capacity within 5 years. However, for a  lithium (LiFePO4) battery that would be far superior to my AGM batteries.
  7. A lot of what we know, and what we are doing, is based upon lead acid battery technology. For example, with AGM batteries it is preferred to keep them fully charged. So this approach was also applied to lithium batteries. However, there is now a concern that maintaining lithium batteries at full charge may actually reduce their usable life. In other words, there may be a trade-off and that has fueled some argument about what is the best way to maintain lithium batteries while achieving the longest possible life.
  8. I am concerned about the above. A lot of what we currently know is based upon old lead-acid theory and requires years to validate in the "real world." When one is spending $thousands on batteries, that should be a concern. Roadtrek currently has a prototype with 20kW (kwhr?) of lithium batteries. Will they get it right?
  9. Why do this? I'll post on that later, but I've provided a brief explanation in the text of this post.
  10. You may wonder about that 20kW number. That's what a Roadtrek blog has stated a prototype lithium system has. I assume they meant a capacity of 20kWh (20 kilowatt hours). Not beyond the realm of possibility. I've seen a similar battery pack and it measures about 25 inches x 24 inches x 15 inches and weighs in at about 425 lbs.
  11. It's my understanding that it's okay to discharge these batteries if the temperature is below freezing and they can be stored for long periods below freezing. However, they should not be charged if the temperature is below freezing. This will require some additional research on my part. 

Oops, I am so used to working in higher power systems I typed "kW" in several places when I should have typed "W." I have corrected this and now indicate "watts" where that is so. I also omitted the 120V charger for the lithium batteries on my list. It was included in the costs. It may not be clear from this post, but I could achieve an increase in available kW with the lithium batteries. My current 6V batteries are rated 220Ah under "ideal conditions."


Saturday, February 21, 2015

AGM Battery Alternatives


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It's again that time of year when attention goes toward the coach batteries in the RV. When the RV is in frequent use, this is never an issue. Running the engine will charge those batteries, as will plugging into shore power.

However, in winter, some of us put our RV into storage. Those AGM coach batteries then self-discharge. Sulfation may occur and if the batteries are sufficiently discharged they may freeze and undergo permanent damage. In winter, our attention turns to the coach batteries. When spring arrives some of us may be unhappy to find that our batteries have only 75-85% of rated capacity, or less.

Is There a Better Way?
In my case, I installed a 50 watt solar panel and charging system to help those AGM batteries. I also installed a smaller solar panel to offset parasitic drain for the engine battery. Both of these have seemed to help. I went to the storage facility for my RT and the coach battery monitor indicated my coach batteries were in "fair" condition. That has been typical; I suspect my RV which was purchased one year after manufacture had damaged AGM batteries. My current interest is in getting the maximum benefit from whatever coach battery system I have.

On my most recent RV inspection the engine started fine and I charged the coach batteries for a half-hour. Not a lot, but intended to augment the solar charging system.

But is there really a better way? I think lithium batteries are the way to go. I've begun exploring this.
  1. Smaller lithium battery systems have been proven in sailboats.
  2. Faster recharge times. 
  3. Lithium batteries have half the weight of the AGM batteries on a weight versus output basis; that's another 70 lbs. of gear, or improved fuel economy, in my case. Or more battery capacity at the same weight!
  4. Lithium batteries, while more costly initially do have a higher number of charge-discharge cycles and can tolerate deeper discharges. In simple terms, they will last far longer than the AGM batteries. 
  5. There is some evidence that lithium batteries cost less over the life of the battery than do AGM batteries. For anyone who intends to use a RV for 10 years or so, this is significant. 
  6. Lithium batteries don't freeze at low temperatures and have the winter problems of AGM lead-acid/water batteries. In other words, fewer winter maintenance issues. Roadtrek states in their 2014 210P manual "AGM Battery Warranty....... is voided if AGM batteries are tampered with, topped off with distilled water or allowed to sulfate or freeze due to lack of charge."
  7. Lithium batteries have lower self-discharge rates. In other words, they can be stored for extended periods at full charge and don't self deplete. 
  8. Lithium batteries can tolerate deeper discharge than can AGM batteries.
  9. AGM batteries have high ambient temperature restrictions.  AGM batteries are designed for an average annual temperature of 77F (25C). If the average annual temperature is 95F (35C) then the battery life will be reduced by about 50 percent. 
Improving Solar Response
I've also been researching improved solar panels and I've decided it would be pointless to put them on an AGM battery system.  Improved solar panels would benefit with an improved electrical storage system. In other words, the system is limited by the weakest link in the chain.

I'll continue my research and will post the upgrades as I make them.

Why Do Manufacturers Use AGM Coach Batteries?
That's a question you might ask. The reasons are straightforward.
  1. AGM technology is well established and existing system designs are in place.
  2. Alternative battery technologies, such as lithium, are at a higher initial cost. This increases the purchase price of the RV.
  3. New designs will require engineering manhours which is an additional cost to the RV manufacturer.
  4. Other technologies are new and are not well understood. In other words, while technically superior, some technologies have not yet been widely offered because the sales, marketing, management and engineering departments at RV manufacturers have not yet come to grips with the benefits.
  5. It's a competitive world. Most users (RV buyers) compare total cost to overall performance. It's only after purchase that the limitations become apparent.
  6. Leadership entails risks. However, most western companies are risk-averse. My company recognized this. We were leaders in our field and as president I would remind our employees that "There is the leading edge, and then there is the bleeding edge." I can say that we did find ourselves from time to time on the "bleeding edge." Good engineering, attention to detail and serious prototyping kept us and our clients from going over the edge. I would say that lithium batteries, which are well proven in smaller systems such as sail boats are not at all like what I was facing with hardware and software which didn't perform as expected. This isn't 2008, nor was the microprocessor invented only four years ago. This is 2015 and there are a lot of Tesla motor vehicle on the road, and lithium batteries are not uncommon on sailing vessels. Lithium batteries are entering the mainstream.