Eclipse August 21, 2017

It was very overcast this morning, a little sun and that quickly went away as more clouds blew into the area.

However, at 1:23pm there was a small break, not total, but we were able to catch a glimpse of the eclipse.

Steel Crazy - Steel Band

Yesterday we attended an evening "Concert in the Park" at the veranda of the Wheaton, IL public library. Wheaton is the 32nd safest city in America, according to NeighborhoodScout’s 2017 list of the 100 safest cities.

The featured entertainment was "Steel Crazy" a musician/steel band from nearby Aurora, Illinois.

Comparing AGM and Lithium RV Battery Systems

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.

New Voltmeter-Ammeter-Wattmeter for AGM batteries - Part 2

New Ammeter-Voltmeter-Wattmeter

September 15, 2017: Added short video clip

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Short video:

New Ammeter-Voltmeter-Wattmeter

See Part 1 for the background information about the AGM batteries in my roadtrek 210P:

http://roadtrek210.blogspot.com/2017/08/new-voltmeter-ammeter-wattmeter-for-agm.html

Why add a digital voltmeter-ammeter?
The decision to add a digital meter was easy. Then I proceeded to decide upon the type of meter. I had seen a FMCA Roadtrek Chapter Cyberrally post about how someone added a digital meter and I wanted to do the same.

Finding a meter wasn't all that difficult. A meter which stored "Ampere Hours" would have been ideal, but I opted for a digital voltmeter-ammeter-wattmeter. The selected meter also included adjustable alarm points for high and low voltage. That would be useful for monitoring low battery voltage, or a point at which I wanted to pay closer attention to battery draw.

I ordered the meter ($15.99 at the time) with DC shunt. I wanted to connect it directly to the battery so I could monitor battery voltage even with the battery disconnect "off". A switch and protective fuse was necessary. The parts list included:

1. Meter with 100A shunt
2. Off-On switch
3. Case for meter and switch (Case dimensions: 5-1/2" x 3-1/8" x 1-1/2")
4. 25 ft. 4-conductor cable
5. Automotive fuse holder (I used a fuse from my kit)
6. Miscellaneous connectors.
7. Note: for details, see the parts list at end of this post. 

The most difficult part for me was determining where to mount the meter. I had decided that I wanted a surface mount case, so I could remove the meter in the future and leave no trace. Determining how to run the 4/C cable was also a bit of a challenge. I decided to route it behind the fiberglass side panel, into the coach along side the door, then behind the side panel and exiting just below the 120VAC/12VDC power distribution center. This required the temporary removal of the rear passenger seat. Lots of screws.

Passenger seat removed, propane furnace exposed

With the passenger seat removed, it was possible to remove the side panel, and pull the cable behind the panel. I pulled the cable from the battery compartment to the passenger seat area, and re-assembled the interior panel. I left a foot lomg "pigtail" for connecting the meter.

Cable at Passenger Seat

I then mounted the rear of the meter case to the wall. I used 3M Dual Lock™ General Purpose Reclosable Fasteners. Note the female electrical connectors on the cable from the battery compartment:

Base of Meter Case

I assembled the meter in the case. Marked the case and cut the opening with a Dremel tool and cutting wheel. I used connectors so I can remove this if necessary. The "female" end goes on the cable from the battery compartment. The "male" end is in the meter case. This is so there should not be any exposed live parts if I pull the meter, even if the fuse at the shunt is intact.

Meter and Off-On switch in case

This is the front of the meter and switch, assembled in the case:

Front of meter case with Off-On switch

I mounted the meter to the case mounted on the wall:

Meter case mounted to the wall

This is the shunt, which was supplied with the meter. For the meter I purchased the shunt is connected between the negative battery post and the negative conductor. The shunt is rated 100A/75mV. The shunt is actually a precision resistor and the higher the current flowing through it, the higher the voltage drop across it. The voltage drop is 75 millivolts at 100 amperes.

Shunt

The shunt was installed in accordance with the manufacturer's instructions. A right angle screwdriver is helpful for installing the wiring to the shunt (I used a phillips).

CAUTION - Installing the shunt requires removing the negative battery lead. Exercise great care not to short a tool from negative to the nearby positive terminal. DEATH OR INJURY CAN RESULT. Be sure there is no battery load when doing this procedure.

The shunt is connected directly to the negative battery post. The black (Negative) cable is connected to the other side of the shunt; the yellow arrow points to that connection. Three of the leads of the 4-conductor cable is connected to the shunt. The fourth conductor goes to the red (Positive) battery terminal.  I installed an automotive fuse between the positive battery terminal and the lead going to the meter. That is to protect the wire in the event of a short circuit

CAUTION - A properly sized fuse is necessary to protect the wire in the event of equipment failure or short circuit. Fire, damage,  injury or death can result from an unprotected circuit.

Shunt installation and automotive fuse on positive battery terminal

With the installation complete I threw the "Off-On" switch to the "On" position.

I checked the display using a precision digital VOM. I measured the mV at the shunt and calculated the meter reading. The meter agreed.

Meter Setup
The meter has alarm points and some options:

1. Set backlight off or on. The default is "on".
2. Set voltage alarm threshold. The meter includes both "high" and "low" voltage alarms. These are set independently. The presence of an alarm flashes the backlight alternating "off" and "on". I set the low voltage alarm at the 50% DoD level for my coach batteries.
3. Set the measuring range. This meter will work with a 50A/75mV shunt or a 100A/75mV shunt. I set this to match the installed shunt, which is 100A/75mV.
4. Energy reset. The meter will accumulate and store kilo-watt hours (kWh). This value can be reset to zero.  

Meter Limitations
The meter is a DC meter. This means that the ammeter measurement is polarity sensitive. The meter as connected can only measure discharge current from the battery across the shunt. When charging the meter displays 0.00 amperes. However, by reversing the connections it is possible to measure charging current. I tried this and it works.

It was interesting to watch the Tripplite inverter/charger step through the charging levels. I may add a DPDT switch for this purpose, but it is completely optional. I've monitored the Tripplite by watching the AC current; as the Tripplite throttles back the AC current decreases. However, other 120VAC loads will mask that.  It is also possible to pull the compartment cover over the Tripplite and observe the charge state LEDs:

Green = Full Charge

Detailed Parts list, my cost $36.45 plus tax and any shipping:

1. MICTUNING DC 6.5-100V 0-100A LCD Digital Display Ammeter Voltmeter Multimeter Volt Watt Power Energy Meter Blue with 100A/75mV Shunt, Part No. MIC-DVG-015.
2. Serpac black plastic case, model 151i, BK.
3. Rocker switch, Philmore No. 30-882.
4. 4-conductor shielded cable, 24 AWG. (Use #22-24 AWG; smaller AWG is easier to pull).
5. Insulated terminal disconnects, male and female (from toolbox, not included in price total).
6. Fuse and fuseholder to protect the wire from the meter to the (+) positive battery terminal. Size of the fuse is determined by the size of the wire. 

New Voltmeter-Ammeter-Wattmeter for AGM batteries - Part 1

Earlier this year I replaced the AGM batteries in the Roadtrek with new AGMs. I decided against lithium (LiFePO4) batteries for the time being. For one thing, I hadn't decided which real estate I would give up. I wasn't sure I'd put them in the battery compartment as it is outside the rig and uninsulated.

I've posted on social media (G+ and FB) that I wasn't happy with the 4-point L-F-G-C "idiot light" arrangement in the Roadtrek, in particular because I discovered that the "G" or "Good" indicator was illuminated even when the batteries were below 50% depth of discharge (DoD).

What was my issue? It was about battery life and capacity. To get optimal life from AGM batteries most experts recommend not allowing the battery to regularly fall below 50% state of charge (SoC). The "G" or "Good" LED extinguishes below that level. The "F" or "Fair" light on the Roadtrek is below that. A simple plug-in digital meter was an option and one can be purchased for between $5 and $15. Here's one:

12V Plug-in digital Voltmeter

Our rental rig had such a simple meter, and I could plug one into the rear cabinet above the entertainment center in our 210P, which had a cigarette lighter for the 12V amplified antenna. I added a "Y" connector for this purpose. However, I also wanted an ammeter and a wattmeter, but I didn't want to spend the amount necessary for a Trimetric and I wanted something easy to install.

Here's the 12V connector I used to install a "Y" cable. That allowed me to connect a meter in addition to the 12V TV antenna amplifier. But viewing the meter in this location isn't very convenient.

Location of simple plug-in digital meter connector:

12V Connector in rear compartment

Installed and functional digital meter:

New Digital Meter

Battery Life Issues
All of this is really about getting full value and maximum capacity from the batteries. As AGM batteries age, they will lose capacity. Such batteries have specifications based on specific conditions, such as an ideal temperature of 77F. AGM batteries operate on chemical principles, and chemistry is influenced by temperature.

I had noticed that, after 4 years the batteries in the Roadtrek didn't seem to be able of providing the desired voltage for the time I wanted to use them "off the power grid". That indicated a loss of capacity.

The entire point of adding a digital voltmeter-ammeter is to get a better idea of the condition of the coach batteries. Even better than battery voltage is specific gravity, but that can't be readily determined. Below is a table for my current batteries which provides some idea of the life of the batteries when discharged repeatedly to certain levels of DoD (depth of discharge). As can be seen, the 50% DoD provides about 1200 charge-discharge cycles. Decreasing to 80% DoD provides a life of about 700 cycles. Avoiding DoD below 50% provides a good compromise between battery life (cycles) while providing adequate capacity.

The problem we face is that to extend battery life we either use them less (fewer cycles per year means more years of service before reaching end of life). Or, we can reduce the DoD. As noted in the table below, if the DoD is only 20% it is possible for a battery to provide 3600 charge-discharge cycles. Of course, to achieve only 20% DoD requires much less use of the available battery capacity.

Why Measure Battery Volts and Amperes?
How long can we run things in the coach on batteries and avoid discharging the batteries below 50% DoD? The ammeter and voltmeter with the tables for our batteries can be an aid to this.

For example, my batteries can provide 18.33AH for 12 hours. However, that is to 100% discharge, which is what I want to avoid. 50% DoD will allow a draw for only about half that time, or about 18.33AH for 6 hours.  Or, I could reduce the load and extend the time. If I really need to run solely on batteries for 12 hours, my batteries can provide about 9 amperes per hour:

                                           220AH/12H = 18.33A
                                           18.33A x 50% = 9.165A

The times are approximate. If we have an ammeter we can determine what the actual current draw on the batteries are. If we have a voltmeter. we can determine the state of charge of the batteries.

Battery Life and Charge-Discharge Cycles

Depth of Discharge - New AGMs

Using the Voltmeter
The digital voltmeter will provide an indicator of the state of charge (SoC) of the batteries. "OCV" is open circuit voltage, or the state when the batteries are not connected to a load:

Relative State of Charge @ 77F - New AGMs

Note that SoC tables may vary. Here is a "typical" AGM table, which differs from the chart above.

Typical AGM battery SoC table

Battery Life 
Taking care of batteries and extending their life will obviously reduce costs. They are expensive. 220AH of AGM batteries is about $450 to $600. However, the other desireable thing is capacity. I want to be assured that the battery is capable of providing the amperes I need for as long as I need them. A battery with reduced capacity may not be able to do that.

Capacity is the ability of a battery to deliver the amount of power it was designed to do. Over time, battery capacity will decrease. As the battery nears end of life, it's capacity will diminish significantly. The batteries I have are designed to provide 25A @ 460 minutes  (7.7 hours) when new. As the batteries lose capacity, they will provide 25A but for shorter periods of time. And as the battery discharges, the voltage will decrease. A battery with diminished capacity will experience more rapid voltage fall-off. DC power is volts x amperes. As the voltage diminishes, so does the power if the amperes are constant.

While extending battery life does reduce operating costs, I am more interested in having the desired capacity available to me.  My batteries are rated 220AH. That means that they can continuously provide about 18 amperes for 12 hours, if they can provide full capacity (see notes):

220AH/12H = 18.33A.

Real World Capacity
The capacity achieved is based on battery condition, ambient temperature and other factors.

As noted above, the 12 hour rating for my AGM batteries is 18.33A.

In the real worlds AGM battery capacity does gradually decline, and by 700 cycles capacity decrease to 50-60% is usual. That means that the above number will gradually decrease:

• New AGM battery (80-100% capacity) = 18.33A for 12 hours
• Battery after 400 cycles (80% capacity) =  14.7A for 12 hours.
• Battery after 700 cycles 50-60% capacity = 9.2A for 12 hours

Lithium batteries also have a gradual reduction in capacity, but generally a 220AH battery:

• Lithium battery after 400-500 cycles (80% capacity) = 14.7A for 12 hours. 

Note: The above numbers are based on battery manufacturer published data and this information does vary from manufacturer to manufacturer. It is important to realize that battery data is usually under ideal conditions such as 77F temperature. AGM battery capacity decreases as battery temperature decreases and can perform (charge and discharge) over temperature ranges of (-)4F to 104F. Lithium batteries generally can operate with charging temperature of 32F-113F and discharge temperatures of (-)4F to 140F. Electric vehicle and experimental data indicates that high environment temperature could accelerate the aging of LiFePO4 batteries, while low temperature could reduce output power capability. Data suggests normal life can be achieve if operated in the range 50F to 104F.
However, it is important to check with each manufacturer for their specifications.

Battery Life based on Depth of Discharge
A well maintained AGM (absorbent glass mat) battery has a life of 6-8 years. Average life has been stated to be 3-5 years. If not maintained, that will diminish to 2-4 years. Note that it really is charge-discharge cycles that are the limit. Battery manufacturers assume a certain number of such cycles in a year. That assumes optimal temperatures of 77F and that the batteries are immediately charged to 100% immediately upon the end of the discharge cycle.

For example, with 50% DoD my batteries are designed to provide 1200 charge-discharge cycles:

1. If used every day, a battery will experience 365 cycles per year.  Under such use, the batteries have a service life of 3.2 years. 
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 6.7 years. 
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries could provide a service life of 10.0 years. 

 For example, with 80% DoD my batteries are designed to provide 700 charge-discharge cycles:

1. If used every day, a battery will experience 365 cycles per year.   Under such use, the batteries have a service life of 1.9 years.  
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 3.9 years. 
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries could provide a service life of 5.8 years. 

How does one "maintain" a maintenance free battery?

1. Recharge as soon as possible after use - preferably within 24 hours.
2. Recharge the battery properly.
3. Use a "smart" charger.
4. Battery should not be charged if the core temperature reaches 120F (49°C).
5. Avoid discharging below 50% SoC (state of charge).
6. When recharging, recharge to at least 80% SoC before beginning another discharge cycle. 
7. Charge to 100% as often as possible. 
8. Avoid heat; heat shortens battery life. Each 15°F (8C) rise in temperature reduces the life of the battery in half.
9. Know the correct state of charge (SoC). Knowing this will help to extend overall cycle life. A battery monitor is worthwhile and use one that is accurate.  

Battery Cost 
There is a cost to overtaxing batteries, as noted above. Best case is a battery with 50% DoD, and that yields 1200 cycles under best conditions. As noted above:

1. If used every day, or 365 cycles per year or a service life of 3.2 years.  The cost is $140 per year ($450/3.2)
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 6.7 years. The cost is $67 per year ($450/6.7).
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries  could provide a service life of 10.0 years. The cost is $45 per year ($450/10).

 For example, with 80% DoD, which provided more AH, but sacrifices battery life:

1. If used every day, a battery will have 365 cycles per year.  At 80% DoD, my batteries are designed to provide 700 cycles.  Under such use, the batteries have a service life of 1.9 years.  (Cost is $236 per year)
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries with a life of 700 cycles could provide a service life of 3.9 years. (Cost is $115 per year).
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries with a life of 700 cycles could provide a service life of 5.8 years. (Cost is $78 per year).

Notes: 
Ampere-Hours. An amp hour (AH) rating is a rating usually used on deep cycle batteries. It is an ampere rating taken for 20 hours. For a 100 AH rated battery a load may draw 100AH from the battery for 20 hours.For such a battery, that's about 5 amperes an hour. 100AH/20H  = 5A).

1. The total time of discharge and load applied is not a linear relationship. As the battery load increases the actual capacity decreases. For example, a 100 AH battery with a 100 amp load should provide one hour of runtime. But it won't. The capacity of the battery will be severely reduced.
2. Each battery manufacturer provides AH data under various loads. For example, here is the table for my batteries, with a final voltage of 1.75V per cell (3 x 1.75 = 5.25V, or a dead battery):
1. 20 hours = 220 AH
2. 10 hours = 210 AH
3. 5 hours = 190 AH
4. 3 hours = 175AH
5. 2 hours = 155 AH
6. 1 hour = 130 AH

Using the AH from the battery table, a rough guide for capacity can be determined. For example, 10 hours = 210AH. To achieve a 50% DoD, 210 x 0.5 = 105AH realized capacity. To achieve a 80% DoD, 210 x 0.8 = 168 AH realized capacity.  However, these figures are approximate and are based upon a new battery and 77F. The approximate condition (state of charge, SoC) can be determined with a voltmeter.

Using the above, the 10 hour ability of the batteries is actually about:

10 hours, 50% DoD = 105AH/10H = 10.5A.
10 hours, 80% DoD = 168AH/10H = 16.8A.

Note that the above information is in accordance with the battery data provided by the manufacturer of my batteries. The actual data will vary by manufacturer.

August 10, 2017 added and expanded "real world" battery life data.