Low Profile Solar Installation

 

Profile of Solar Panel

Here's a few details about the installation of a 200W semi-rigid solar panel.  This is mounted on T-Track and polycarbonate.  Using aluminum T-Track allows the sliding of bolts onto the track.  These are in-turn used to fasten the panel.

End view of T-Track

I cut the T-Track to the length of the panel and fastened with bolts.  VHB tape was then applied to the track. 

VHB applied to the right track, which is bolted to the solar panel

 After cleaning the fiberglass roof of the Roadtrek with soapy water and alcohol I lifted the assembly to the roof.  The panel was positioned, then the film removed from the VHB tape.  I applied pressure to get a good seal.  I then unbolted the solar panel, and using a rubber mallet I lightly hammered the entire length of the T-Tracks.

I also installed pieces of Eterna-bond tape, overlapping the T-Track.  This is a backup for the VHB tape.

I installed a 24 inch x 48 inch polycarbonate ventilated sheet between the T-Tracks.  This provides a center support for the solar panel.  It is about 1/4 inch thick. 

I then applied sections of polycarbonate panel atop the T-Tracks.  This will further suspend the solar panel above the roof and provide for some ventilation.  Slots were cut in the sheets at the location of the bolts.  Eight sets of bolts, washers, lock washers and nuts fasten the solar panel to the T-Track. I may eliminate the "crush" at the bolts by installing shims.

Side view of solar panel mounting

Here's a view of the Eternabond mounting approach. This was taken prior to dropping the panel onto the T-Track and aligning the bolts. I used Eternabond white, 2 inch.  This is UV resistant:

As can be seen in the photo at the beginning of this post, the panel and mounting is barely visible.  I'm going to give it a few months to "age" in the sun and see how the mounting does, before taking a long trek.

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Note: No AI tools were used to produce this blog. Most photos are unretouched.

(c) 2025 N. Retzke 

 

Solar System Upgrade - Update

My solar system for the Roadtrek has changed. I first installed a solar charger and portable panel in 2014. This was for the AGM lead acid batteries. 

200W Panel on Roof
Wiring incomplete

Then a second panel was added so I could charge both the coach and chassis batteries.  I later replaced the AGM batteries with LiFePO4.  The chronology is included in this post.

Why Solar and LiFePO4 battery combination?

I think this is the ideal approach to keeping the coach battery charged and in best condition.  Lithium batteries include a Battery Management System (BMS) which is electronics that monitors and controls the charging and the balancing of the cells.   The BMS protects from overcharging the batteries and prevents charging in temperatures below 32F.  

A battery has several cells, each of which when fully charged provide 3.65V of output.  Four cells combined in the battery provide 14.6V at full charge, or a nominal 12.8 VDC. Each of these cells will charge at slightly different rates, and one of the duties of the BMS is to control this so that eventually all of the cells will be fully and equally charged, or "balanced".  

Solar provides the energy to accomplish this, unattended.  An alternate approach is to use a 120VAC charger, but that requires a power cord and access to a power outlet.  My system does accommodate AC charging or charging via the alternator.

My Circumstances

My goals have changed since 2014. I have a 3-way refrigerator which can use propane but the controls are 12VDC. Some battery power is necessary for it, as well as lighting, etc. 

Running the refrigerator on 12VDC and conserving propane is a primary goal.  A secondary objective is running battery heaters on 12VDC when the vehicle is disconnected from shore power and in cold weather.

If 12VDC is selected for the refrigerator, the specifications indicate that 175watts or more are required, intermittently.  That's 13.7A at 12.8VDC.  I prefer to use 12VDC while in motion so that I can conserve propane.  Of course I could connect the alternator to the coach, but the solar panel provides DC during stationary periods. 

Before heading out on a trek we turn on the refrigerator and pre-chill it.  I can use 120VAC, but 12VDC is easier.  The solar supports this.

I have no intention of living off the grid, but I might be off of it for a day or two.  I had done some research and it requires about 300W to keep the Roadtrek battery charged when plugged into AC.  Part of this is losses in the Tripplite charger. However, I did add a NOCO 10A charger with LiFePO4 mode.  This more closely matched the battery manufacturer charge specifications.  I can use either the NOCO or the Tripplite.

The battery manufacturer recommends charging at up to 20A. I'd prefer to charge entirely off of solar power at any time the Roadtrek is stationary and unused.

Procedure

This is an entirely "home built" and designed system. I've been using a 100Ah battery, but using newer, smaller LiFePO4 batteries I could install two 100Ah  batteries in the original space.   Real estate in a Class B is precious and I prefer not to use it for batteries. 

My earlier posts delve into the pros and cons of LiFePO4 batteries and compare specifications to lead-acid AGM batteries.  I won't repeat that in this post.

Solar panel output and life decrease under higher temperature conditions.  For that reason, mounting of the solar panel is important.  My 210P has a fiberglass roof and it was tempting to "glue" the panel directly to the roof, as some do.  However, that may increase the panel temperature.  It is better to mount the panel slightly above the roof, but that may increase wind resistance. 

I decided upon a semi-flexible 200W panel, which was the largest that the Roadtrek roof could accommodate. I did not want to drill holes in the fiberglass roof, and that would have necessitated adding reinforcement.  I instead mounted T-track to the roof using 3M VHB tape. The solar panel was mounted atop this.  I also installed polycarbonate plastic panels under the solar panel. This provides a "sandwich" which slightly elevates the panel above the roof, supports the panel and promotes airflow beneath the panel.  The wind resistance is slight.

I routed the solar wiring through the heat pump area, at the rear of the Roadtrek and avoided drilling holes for this in the roof. 

I want to avoid roof leaks too.  I want the operation to be as maintenance free as possible. The Roadtrek 210P has had no leaks and I want that to continue.

The system installed accommodates using the rooftop panel or a portable panel. I installed a jack for a portable panel in one of the rear exterior bays. I can use a portable panel or I can plug-in 12VDC devices and charge them or use them. 

I chose a better quality battery that does not include internal heaters.  LiFePO4 batteries cannot be charged at below 32F.  So, they must be heated in cold weather.  I decided upon using external 120VAC and 12VDC heaters, independently controlled with thermostats.  When it is cold and the coach is on AC power I use 120VAC to heat the battery.  At other times I use 12VDC. When in movement I can supplement the solar and use the alternator to heat the battery.  

The heaters were installed in 2022 and have worked well. 

The battery BMS assures that the battery does not overcharge of over discharge.  I also installed a "Battery Protection" device.  This monitors the battery voltage and automatically disconnects the battery if the voltage decreases to a preset low limit.  The purpose is to disconnect the battery while there remains some useful energy. I can remotely reconnect and provide power if necessary.  It is controlled using my Android phone. 

The solar system charge settings are matched to the battery manufacturers requirements.

The installed system can provide 20A for 5 hours when off of solar (overnight) or about 8A for 12 hours.  On solar it can provide 10 to 15A continuously without draining the battery. This is determined by the solar energy available. The battery can function down to 10.4V, which is the voltage at which the BMS will disconnect the battery. 

Why only one 100Ah battery?

The Lithium battery I installed can be discharged down to 10.4 volts.  However, it better to avoid this so discharging to 11.2 to 11.8 volts is preferred to achieve the design life of the battery.  That's in the range of 5-10% SOC or State of Charge. 

For comparison, an AGM battery shouldn't be discharged below 50% SOC to achieve rated life.

This implies that a 200Ah AGM battery can routinely provide 100Ah of capacity, but more at the sacrifice of battery life. A single 100Ah LiFePO4 battery can provide 90-95Ah with little degradation. So, a single 100Ah lithium battery can nearly replace a 200Ah AGM battery. 

What I could gain using two 100Ah of lithium is about 180-190Ah of useable capacity, which exceeds that of 200Ah AGM batteries. 

In 2022 I surmised that one would work.  I also concluded that improvements in manufacturing and battery technology would allow me to add a second battery, or replace both for less than $400 at some time in the future.  That is where we are, today.

For more on my transition to Lithium see the links to solar on the right.  Here is one such link: 

https://roadtrek210.blogspot.com/2022/04/transitioning-to-lifepo-batteries.html

Chronology

2014:  That first panel was a portable 30W solar panel to keep the engine battery charged. I stored the Roadtrek outdoors and there was no AC outlet available.  Then I added a de-sulfating solar controller with portable 50W solar panel for the coach AGM batteries. My goal was simple:  keep the batteries charged when stored outdoors.

2022:  I made a major change in April & May 2022.  I installed a better solar charging system for a larger 200W solar panel, replaced the AGM batteries with LiFePO4, and added both 120VAC and 12VDC heaters for the battery.  Lithium batteries can't be charged at below 32F, so some type of heat is necessary for winter use; my coach battery is located outside the coach interior and is exposed to freezing weather.  I continued to use portable solar panels. 

I also installed a device to protect the battery from low voltage discharge.   I used a setting of 11.80V as an automated cutoff.  This is adjustable and lithium can tolerate deep discharges better than AGM batteries. 

2025: I installed a 200W solar panel on the roof.  Circumstances delayed this, and I decided to delay further until we completed our 2025 mult-month, 7,200 mile trek. 

I created several blog posts about this. 

My goals have changed. I have a 3-way refrigerator which can use propane but the controls are 12VDC. Some battery power is necessary for it, as well as lighting, etc. If 12VDC is selected for the refrigerator, the specifications indicate that 175watts or more are required.  That's  13.5A at 13VDC.  If I use 12VDC while travelling I can conserve propane.  Of course I could connect the alternator to the coach, but the solar panel provides DC during stationary periods. 

Before heading out on a trek we turn on the refrigerator.  I can use 120VAC, but 12VDC is easier.  The solar supports this.

I have no intention of living off the grid, but I might be off of it for a day or two.  I had done some research and it requires about 300W to keep the Roadtrek battery charged when plugged into AC.  Part of this is losses in the Tripplite charger. However, I did switch to a NOCO 10A charger with LiFePO4 mode.  I'd prefer to charge entirely off of solar power at any time the Roadtrek is stationary and unused.

In 2022 I added a Renogy solar charge controller. At the time I was using it with a portable solar panel.  This was an entirely "home built" system of my design.  

When I installed, I intended to put a solar panel on the roof in the future.  It took a while to find the appropriate panel.  Dimensions were the problem. I found a suitable 200W semi-rigid panel.  I also purchased materials to fasten it to the roof, but I wanted it to "stand off".  One issue with solar panels is heat.  This can reduce power output and the life of the panel. On the other hand, I also want to minimize wind resistance.  

I chose metal T-track to fasten to the Roadtrek roof.  The roof of the 210P is fiberglass, and I didn't want to puncture it, or glue the panel directly to it.  Instead, I purchased polycarbonate greenhouse panels, aluminum T-Track, 3M VHB tape and bolts.

The track is attached to the roof using the VHB tape. A polycarbonate panel can be set between the tracks to provide airflow and support the panel if one should lean on it.  The panel is attached at eight points to the track using bolts, nuts, washers and lock washers.

Alternately, the polycarbonate can be installed above the T-Track. This raises the panel about 1/4 inch and aids airflow. 

Circumstances delayed the project.  The earliest I could have done this in Spring 2025, but decided to do it in the fall.  So, here we are!

Solar Panel wiring will be routed through the air conditioner enclosure into the interior of the Roadtrek. I'll add a slot to the cover of the AC, but there will be no penetrations of the roof.   

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Note: No AI tools were used to produce this blog. Most photos are unretouched.

(c) 2025 N. Retzke 

Solar charging of chassis battery

 

Charging chassis battery using 30W solar

We had to leave the Roadtrek at the campground for a few days.  I wanted to keep the chassis (engine starting) battery charged. On July 4 I connected the 30W solar panel.  This has a self-contained solar charger and so I simply plug it into the dash 12VDC accessory jack.  These jacks were originally intended for cigarette lighters.

The chart above shows the daily charging, which I can check with my Android phone via the internet. 

The chart indicates daytime charging and nighttime discharge.   

The solar panel is placed on the windshield and is facing west.  It doesn't get sun until afternoon, but that is adequate.   I placed the solar panel outside the windshield, although it works well on the inside, too.  I tie it down because of storms in the area; I don't trust the suction cup mounting. 

I've used this larger panel for several years and it has performed well.  

30W solar panel charging the chassis (engine) battery

(c) Norman Retzke 2022

Solar and Potential Savings in a Class B RV

 

Financial benefits of solar on a 210P

Is there a financial incentive? At the AZ resort, electricity is $13.00 basic service charge monthly + $0.07612 for the first 500kWh, then $0.09337 for each kWh in the range 501-1000. To this are added Arizona assessments, environmental compliance charges, a utility ‘power supply’ charge, a PPFAC charge and taxes.  Typical energy charges adding all of these is about $0.1495 per kWh.

I’ve monitored the AC power used to simply power the coach, keep the AGM batteries charged and a vent fan running. The cost for that amount of electricity is about $51.67 each month.  Using solar and a good battery may reduce my 120VAC power bill by about $310 each season in AZ. If the batteries run well for 7 years, that’s a possible $2,170 in electric bills I won’t pay. 

The other six months of the year, at our “lily pad” in MI the cost per kWh is currently $0.14. That’s a cost of $290.30 to charge batteries, power the 12VDC coach, etc. for six months.  

Add the possible AZ and MI savings, and I may save $600.30 each year, or $4,202 over the projected life span of the coach battery. 

These are approximate numbers taken with intermittent readings prior to replacing the AGM batteries with LiFePO4.

Of course, to this add any 120VAC consumed.  I don't have a "full-solar" installation. At present the Tripp-lite charger/inverter is "Off" and I use AC for the Cool-Cat air conditioner/heat pump, the refrigerator 120V heater and microwave/convection oven. 

If more solar were available, I could probably run the refrigerator off 12VDC during daylight hours, increasing the savings from solar. However, "full solar" existence isn't practical in my opinion.  The Cool-Cat heat pump requires 1,227 watts when the compressor is running and cooling.  To that add electricity for the refrigerator, etc. as well as battery charging current to be stored for overnight use.  I'd need a lot of batteries and a lot of solar panels.  The roof of the 210P has space for at most 200W of panels.  I can add portable panels to the capacity of the controller and more batteries but living off the grid is not my goal.

Why? I won't park a Roadtrek in full sun in Arizona when the ambient reaches 100F in the shade. That's a recipe for a human BBQ.  

This season a couple moved into the resort after a trial at boondocking in nearby Quartzite.  Their several months-long experiment occurred with peak temperatures only about 80F.  They related their experienced and told us that they made the decision to get a site in the resort. They decided the resort fees were worth it as this provided unlimited running water, sufficient power for air conditioning, easy tank dump, etc.  Oh, and a bar & grill, swimming pools and internet access, too. 

Measuring AC Power consumed

I have two methods. One is the Power Protection Device at the 30A connector.  It includes an ammeter display. It is useful for roughly monitoring the amperes being consumed @ 120VAC.

AC Amperes with Cool-Cat AC running, Tripp-lite charging, refrigerator on AC

The other device I use is a Kill-a-Watt meter.  This can be used to determine the amperes and watts consumed on 120VAC circuits, or for individual appliances.  It is accurate and precise. It allows a variety of measurements and price calculations at any entered cost per kW. It will calculate the power consumed at any entered price per KWh and it will totalize this cost.  Here's an example of an instantaneous ammeter reading:

Kill-a-Watt indicates Coach 120VAC at 10.23A. Measurement 
with Cool-Cat air conditioner running, Tripp-lite not charging and
minimal appliances powered up

Measuring the Solar Power Available

The MPPT controller has calculations and historical data available. Data is accumulated and stored monthly. Some of the statistics available:

• Power generated
• Charge Ah same day
• Max charge power
• Max battery volt
• Running days total
• Battery full charge times
• Battery charge Ah total
• Generation amount kWh

Initial Observation

How is the LiFePO4 battery and charger doing?  So far, very well. I keep the coach powered up on solar with the vent fan running. The Tripp-Lite charger/inverter not being used. This is an experiment.  Every day the coach battery is fully recharged after a few hours in the morning sun.  Of course, this is AZ with a lot of sun.  On the other hand, this is a small 50W solar panel which is showing its age. Power output has decreased and peaks at about 85% of rated. 

It is premature to call this a success, or the LiFePO4 battery superior to the AGM batteries. For one thing, this trial has been a little over a month in duration and we are stationary. For another, I did install the coach battery in the outside compartment. It is a well-known fact that the battery management system (BMS) of a LiFePO4 battery will not allow it to be charged if the battery temperature falls below 32F. G and I have trekked and camped overnight in temperatures as low as 5F. As a consequence I did install low-wattage 12VDC and 120VAC compartment heaters.  We’ll see how that works. 

There are some LiFePO4 batteries which incorporate 12VDC heaters in the battery.  I could have chosen this type.  However, I am concerned about how much energy those heaters may use when off the grid or while the Roadtrek is stored in cold weather and not plugged into shore power. I decided two 12VDC and a 120VAC heater and solar power were a better solution, in my circumstances.  I also installed an automatic low-voltage disconnect for the battery.  The BMS will disconnect and prevent the battery from completely discharging, but LiFePO4 batteries are best disconnected at a higher voltage threshold if maximum cycles and life are to be achieved. Ergo the automatic disconnect. 

Increasing the solar Available

My plans will increase the amount of solar for the Roadtrek.  There are limitations because of the available roof space.  I have no such limitations in AZ under the shelter, so I can add even more kW on my shelter roof. 

Background Information

It was time to replace the coach batteries in my 2013 210P.  I attended the FMCA Convention in Tucson in March, and I used that opportunity to visit with battery suppliers and manufacturers in the exhibit hall. There was a battery seminar scheduled, but an issue prevented the presenter from being there so that seminar was cancelled.

I had to choose:  AGMs or LiFePO4. To assist in making that choice I wanted to review the latest technology and I didn’t want to overspend on Lithium-ion if I went that route.

My Roadtrek is relatively new, but the first set of AGM batteries were ruined when the Roadtrek control panel “Inverter OFF-ON” switch failed to open when I put it in the “OFF” position.  Sitting in storage in that condition for a couple of weeks completely depleted the AGM batteries, ruining them. After that experience I turned off the inverter function when I store the Roadtrek.  I did this by changing the Tripp-lite mode switch to “Charge Only”.

When the first set of AGM batteries failed I replaced them with similar batteries and installed a 50W solar panel and 180W desulfating solar controller to keep them charged.

LiFePO4 Today

LiFePO4 technology continues to evolve. I’m currently aware of two different cell construction techniques. I investigated different constructions and manufacturers.

Prices for a 100Ah battery range from about $350 to $950 each, plus shipping and tax.  Why is that?  There are differing cell qualities.  There may also be large mark-ups by some sellers.  I determined that there is no standard for determining cell quality in China, where many or most of the “internals” in these batteries are manufactured.  As a consequence, it is important to purchase from a reputable manufacturer. It is possible to overpay, if one assumes the higher the price the better the quality.  On the other hand, there is a lower price threshold below which it would be better to avoid.

A Decision in favor of LiFePO4

I continued my research and decided upon a  LiFePO4 battery from a quality manufacturer.  Delivered and with state sales tax the price was   $624.93.  It arrived on April 1, 2022.

I'll run some of the solar numbers later in this post. However, I concluded the LiFePO4 would be more reliable and therefore more likely to achieve the solar performance I wanted.  Solar panels are only a  portion of the system.  Energy storage is also very important.

The was shipped 30% charged, which is normal for this manufacturer.  I promptly charged it using a 10A charger which was compatible with the specifications for this Lithium-ion battery.

A new MPPT solar controller

I had determined that my solar controller with a de-sulfating mode was not ideal for the Lithium-Ion battery. It was ideal for AGM batteries.  I replaced the solar controller with an MPPT type; it had a user mode with custom settings which were ideal per the battery manufacturer’s specification.  I installed that, entered the proper settings and have since allowed it to charge the coach battery and run basic appliances off the grid (lights, fan, etc.).  I’m satisfied with the initial performance.

I’m currently in southwest Arizona with the Roadtrek on my winter site. It is parked under a shelter, which is why I used a portable solar panel. The panel is currently on the shelter roof. The ambient may be 60F at night but can reach 90F during the day. We do get some morning sun loading in the front of the Roadtrek. I run the vent fan most of the day unless I am using the Cool-Cat heat pump/AC.

(c) N. Retzke 2022

Solar Installation

 

Solar Panels don't work when the Roadtrek is under cover.

Solar system upgrade

Shortly after I purchased the Roadtrek I installed a portable solar panel and controller.  I decided to use a portable panel because when camping in the summer I prefer a shady location.  Solar panels don't work well in full shade, but the Roadtrek is far more comfortable when parked that way. 

I installed the panel to keep the coach batteries charged when off the grid and in particular when storing the Roadtrek.  Our boondocking experiences are short, so I don't need a lot of solar energy, preferring the Onan generator to run the AC appliances and Cool Cat heat pump.

Our winter "lily pad" is in Arizona and it can get quite warm, even in winter.  Particularly if we are parked in full sun.  When at the site in the photo above, the solar panel is on the roof overhead and so it is providing electricity most of the day, while the Roadtrek is in the shade.

When we are camping and park in the shade, the interior of the Roadtrek is generally whatever the ambient temperature is.  If it is 78F, then the interior is 78F because we ventilate it. Of course, when trekking full shade is not always available.  So, we are sometimes in partial shade and at other times in full sun.  The benefits of rooftop solar is reduced because of the shade. Ergo the portable solar panel.

An opportunity for change

In recent years the quality of flexible Monocrystalline solar panels, their price and warranties have improved. We also have the benefit of the experiences of early adaptors who have experimented with a variety of mounting approaches and panels.

When I decided to replace the AGM coach batteries with Lithium-ion LiFePO4, I also had the opportunity for other improvements which included expanding the solar systems.

Of course, one of the challenges of a Class B is living with the space limitations of the interior and exterior compartments.  I wasn't willing to use a lot of interior real estate to house batteries, the solar controller, wiring and etc. 

Ultimately, I decided to mount the LiFePO4 battery in the outside compartment, install 12VDC and 120VAC heaters to warm the battery when the compartment temperature falls below 40F.  I mounted the components and routed the wiring via a variety of nooks and crannies. 

I've posted recently about the selection process and heaters, so I won't repeat that here.  This post will focus on some of the other installation details.

Currently, the Roadtrek is under a shelter with limited space above. Furthermore, it was 96F yesterday, and today it is a balmy 91F in the shade.  In this weather I won't be mounting the rooftop solar until we get to our lily pad in Michigan.

Instead, I concentrated on installing everything to support the portable solar panel, with some preparation for the rooftop solar.

Solar wiring and controller

Solar MPPT Controller, battery voltage 13.3V

I reviewed the available locations, the paths for the wiring of the heaters, the availability of 120VAC and so on.  I decided to install the MPPT solar charge controller on available wall space adjacent to the TV in the rear of the coach. I installed a bulkhead fitting beneath the controller for plugging-in the portable solar panel. A second connector will be installed for the rooftop panel. There is also a 65A connector for the controller 12VDC output.  I want to easily disconnect the controller if necessary for maintenance purposes.

Bulkhead connector for solar panel wiring

A matching connector was installed in the exterior compartment. This is where I plug-in the portable solar panel. I included a MC4 adapter. What remained to do was to route the solar cables to connect these bulkheads. I did come up with an approach to simultaneously use both rooftop and portable panels, if that is desired to collect more solar energy.

Connector for portable solar panel

The solar cable was routed from the exterior compartment, into the coach electrical compartment at the rear of the Roadtrek, and from there into the compartment adjacent to the interior fresh water tank. It was terminated on a fuse and terminal block and from there it was routed behind the fabric panel to the armoire and to the interior electrical bulkhead.   I wanted to install a fuse and terminal blocks to provide access for future maintenance. 

Solar cable exiting exterior compartment and upward into coach electrical compartment

Portable solar panel cable in electrical compartment

I routed the solar panel wiring from the electrical compartment to the terminal blocks installed adjacent to the interior fresh water tank.  I removed the 12VDC wiring cover in the armoire. and pushed a solid 14AWG behind the fabric side panel, from the armoire to the fresh water tank compartment.  I then used that to fish very flexible 18AWG.   The 18AWG would be used to pull the solar cable through.

I soldered and taped the solar cables to the 18AWG so they could be pulled. Solder is a superior strength connection and smaller in diameter than a butt slice connector.  This approach was necessary because the wiring was a tight fit.

Solar cable prepared for pulling

To give myself sufficient space to grab the wires in the wall I temporarily removed the fresh water tank fill line and pulled the solar wire through.

  

Solar cable at fresh water tank

To do the pull I removed the wiring cover inside the armoire and disconnected the cable for the power seat, at the UP-DOWN switch. This permitted me to move that cable out of the way.

  

Power seat switch electrical connector in armoire

I then pulled the solar cable into the armoire and connected it to the bulkhead connector.

 

Solar cable into armoire.

    

Bulkhead cable connected to solar cable

   

Front of solar bulkhead connector on armoire below MPPT controller

The mid-point of the solar cables were terminated in the compartment adjacent to the interior fresh water tank. This for maintenance purposes, and I did install a fuse on the solar panel positive.

Solar terminated adjacent to interior fresh water tank

I then put the armoire interior wiring cover back in place. 

      

Interior of armoire

I terminated the12VDC power at the MPPT controller and powered it up. I then entered the necessary battery parameters.  Prior to connecting the MPPT controller to the bulkhead solar connector I plugged-in the solar panel and checked the polarity at the bulkhead connector. Satisfied it was proper I plugged in the solar cable at the controller.

Operational MPPT controller, 12VDC power and solar panel connected

     

Portable solar panel

  (c) 2022 N. Retzke

Notes:

1. This is not a how-to-do-it post.  I'm providing it as-is and it is not a recommendation or a procedure manual.
2. I'll be installing a rooftop panel when I'm at my summer lily pad location.

  

Transitioning to LiFePO batteries

LiFePO4 Battery on shelf, during installation

 

After doing my most recent research, I decided to replace the faltering AGM coach batteries with a LiFePO4 battery.  The decision was the easy part. Next came selecting a battery, installing it and integrating it into the existing Roadtrek 12VDC system.  I also have a solar system and de-sulfating controller.  Such a controller is not recommended with the LiFePO4.

The battery can be mounted in any position, and the space available provided two options.  I decided to go with terminals up. I did elevate the battery slightly by resting it on plywood.  It has a metal case and I don't want it sitting in water.  I've never had an issue with water in the battery pan but I don't ford streams or drive through flooded underpasses. There is always a first time.

The new battery will use the existing shunt and power wiring in the compartment.  The integration of other components did require some additional work on my part. I didn't want to make alterations to the existing wiring of the coach: no shortening or removal.  I wanted the wiring to be recognizable to a technician familiar with the Roadtrek or a future owner.  I also wanted to provide the ability to transition back to AGM batteries at some future time, although I don't expect to do that.

Maintenance Free LiFePO4 batteries?

There are limitations with any coach battery and LiFePO4 batteries have their own.  I decided to address these in my installation. 

It is true the LiFePO4 batteries are "maintenance free".  One significant advantage over other battery types is the internal, electronic battery management system (BMS) which is there to protect the battery.  (See Note 1).

However, to achieve optimal battery life (4000+ cycles) it must be operated within the design parameters.  That may require some external hardware.  I concluded that in my Roadtrek, replacing AGM batteries with LiFePO4 is not quite "plug and play" or "drop in and forget". 

Integrating the various 12VDC Components - a List

The LiFePO4 batteries aren't simply a "drop in" proposition. Here are the things I considered:

1. Tripp-Lite charger/inverter is to remain in place.
2. Retain Tripp-Lite 750W inverter function (~59A at 12.8V).
3. Make the provision for a future LiFePO4 charger. 
4. Solar charging system - update to compatible LiFePO4 controller.
5. Upgrade the battery manual disconnect.
6. Retain existing volt-ammeter and shunt.
7. Add a low voltage automatic disconnect to enhance the BMS cutoff (to preserve the battery).
8. Add battery compartment supplemental AC/DC heat to extend charging time.

Low Temperature Battery Considerations

One of the issues with the LiFePO4 batteries is their intolerance to cold.  The BMS will not allow charging if it determines that the battery internal temperature is at 32F or below.  Power output will vary with ambient temperature, but not as much as with the AGMs I'm replacing.   

High ambient temperature may accelerate the aging of the battery while low temperature may reduce output power capability. In general LiFePO4 batteries perform better at low temperatures than do the AGMs I'm replacing. 

I decided to install the battery in the unheated compartment where the AGM batteries were installed.  Minimal 12VDC power wiring changes would be required.  In that location the battery will be exposed to freezing temperatures at any time the outside ambient is below freezing.  Of course, I do have the option of relocating it to the interior of the coach at some time in the future.

Keep in mind that if stored outdoors all Class B's will have their interior temperature decrease to below 32F in fall and winter if the vehicle is north the freeze line. In cold weather the coach interior will be at cold until it is warmed by running the engine.  So too will any batteries stored within.  If the coach is parked in the sun the interior may be warmer than outside. The Roadtrek coach battery can be discharged when cold, but the LiFePO4 battery can't be charged until the battery internal temperature rises above 32F.

I concluded that to store the Roadtrek in winter, if that is necessary below freezing conditions that I'll simply remove the batteries.  If I use it at below freezing temperatures some supplemental heat to warm the batteries would be desireable. That will extend the charging of the LiFePO4 battery as weather cools.  

I do realize that at some point the ambient temperature will be so low as to nullify the supplemental heat and the BMS will prevent charging the battery. I don't expect to encounter that situation. LOL.

Some batteries are available with internal 12V heaters but that draws down the battery in cold weather if the vehicle is not running and not connected to shore power.  Furthermore, if this is an internal battery function and can't be controlled by the user it simply runs the battery down faster if off the grid.  In my opinion that's undesirable in a RV.

I'll be installing both 120VAC and 12VDC supplemental heaters, which I can control.  I'll be monitoring the compartment temperature to get some data about the effectiveness. 

Avoid Over Charging and Over-discharging

Another issue is the possibility the internal battery cells can be damaged if they're discharged below a certain threshold. That low point is approximately 5 percent of total capacity. If the cells are discharged below this threshold their capacity can be permanently reduced.  The BMS will protect the battery, but at too low a threshold to preserve optimum life. 

The solution is an external, automatic cutoff or a low voltage alarm (or both).  

I have installed a low-voltage automatic cutoff. 

Three methods of Charging

I have three methods for charging the batteries in my Roadtrek. Ideally, each method would provide the appropriate charging voltage and current for LiFePO4 batteries, but they don't:

1. Tripp-Lite charger inverter using 120VAC power (3-stage voltage and current control).
2. Solar using solar panels and a controller (voltage and current control).   
3. Engine alternator (simple voltage regulation, no control).

The first two methods can be adjusted to adhere to the battery charging specifications.  The alternator has no such adjustments.  To avoid over-charging the coach batteries I can use the battery separator to disconnect from the alternator and rely upon solar charging.  Alternately, a DC-to-DC charging system could be installed.  There are practical limits to how much I'm willing to spend on this.

External low voltage disconnect - Details

The battery manufacturer recommends that an external low voltage disconnect be used.  The manufacturer suggests 11.2V as the disconnect point.  

• Battery low voltage disconnect < 11.2V

Such a voltage represents about 5% battery capacity remaining.

There are a couple of methods to achieve this:

1. Manual switch.
2. Automatic switch or relay.

It is true that the battery management system will protect the battery from complete discharge. However, 10.4V is about 2% battery capacity.

• BMS Low-Voltage disconnect <10.4V

In general, a battery constructed of Grade A cells can probably achieve the specified cycles if the battery is operated within the manufacturer's parameters.  Discharge to very low voltage is to be avoided. 

A battery low voltage alarm is a possibility, too.  For example:

• Battery low voltage alarm < 11.8V

Such an alarm would occur when the battery capacity has decreased to about 8%. 

Adjusting to a new reality.  As I use the LiFePO4 battery I'll have to adjust.  For one thing, the output voltage versus State of Charge is different than the AGMs.  The new battery is more stable than the AGMs.  After charging, and intermittent use for a week, the battery voltage has decreased by 0.06V.  This battery seems to be much "stiffer" than the AGMs.  This may change as the battery ages and capacity decreases to about 80%. 

State of Charge - SoC - Details

I provide a typical chart later in this post.  State of Charge (SoC) is a very useful battery measurement. It states the present, actual capacity of the battery compared to its total capacity. 

State of Charge is a percentage: 

• 100% SoC means the battery is fully charged, new and undamaged.
•  0% means fully discharged. 

 SoC is calculated this way: 

• State of charge (%) = Remaining Capacity (Ah) / Total Capacity (Ah).

LiFePO4 batteries are chemical devices and so they operate similarly to the AGM lead acid batteries we are familiar with. There are several SoC values to keep in mind.  These are the absolute minimum SoC, the preferred SoC and the actual SoC.  

Absolute minimum SoC is the most discharged state with the lowest possible terminal voltage that doesn't destroy the battery.  For my battery this is 10.4V.  However, discharging to such a low voltage will diminish the capacity and useful cycles of the battery. 

For maximum battery life, only discharge it down to the Preferred level, but no lower. Hmmm, that seems reminiscent of the recommendations for AGM lead-acid batteries, doesn't it?  Here are the three values:

• Alarm and recharge at <11.8V (the Preferred minimum state of charge, 8-10%). To maintain reasonable battery longevity and performance do not discharge below this value.
• External battery cutoff <11.2V (Actual minimum state of charge, 5%). This is the realistic minimum.  The battery can be discharged to this state, but some battery degradation and performance will occur is the battery is operated this way.  This discharge level is a trade-off between available power and battery life.
• Battery BMS low voltage cutoff <10.4V (Absolute minimum state of charge, 0%). This is approaching the point of battery destruction.  The BMS will stop battery discharge when this state is reached. 

LiFePO4 Terminal Voltage and SoC

A typical 12V LiFePO4 battery is constructed of four cells called a 4S battery pack. The battery output voltage decreases as the batteries discharge and remaining capacity decreases.  A typical 12.8V battery output will vary from 13.8V to as low as 10.0V (completely discharged).  

The nominal output voltage is 12.8V.  There are differences among manufacturers, but here are typical voltages:

• Absorption Voltage (charging) 14.4-14.6V  (3.6-3.65V per cell).
• Float (fully charged) 13.6-13.8V (3.4-3.45V per cell).
• Full discharge 10.0V (2.50V per cell).
• Nominal voltage 12.8V (3V per cell)

The terminal voltage will decrease as the battery discharges and the capacity diminishes.  To get an accurate reading of SoC the battery must be rested.   Here's a typical chart. You will note that the battery output voltage is reasonably flat throughout the useable discharge cycle, from about 100% down to 10%:

• 13.6 V = 100% SoC (Fully charged)
• 12.1V  = 10% SoC (Preferred minimum)
• 1.5 V output decrease from Fully charged to minimum SoC.

LiFePO4 Capacity versus Battery Voltage 

Note:

1. There are different battery constructions out there.  Some have as many as 8 internal cells. This is an evolving and improving technology. Low temperature automatic protection by the BMS and internal 12V heaters are relatively new.  Some batteries are well constructed internally, and some are not. Some have steel cases, while most have plastic. Prices range from about $325 to $900 for a 12V, 100Ah battery.

(c) N Retzke 2022

Practical Solar

 

Making coffee in the morning in the "Solar powered" Class B
Must turn off the hot water heater before using the burner!
Outside ambient: 20F,  Inside: chilly!

Realistic expectations  

We trek and we have spent up to 100+ continuous days in our Roadtrek.  But first, we rented a "100% electric" solar powered Sprinter coach and took it to the National Parks in Utah.  It was mid-October 2013. Nighttime temperatures were about 20F.  It was a good test of how well a solar powered, electric coach would perform.  That was our purpose in choosing it, and I wanted to see how the BlueTec engine performed, etc. 

From a comfort perspective, it was not ideal, and G had to ask "How is it that one would spend $100K to buy this?" Adequate if the ambient temperature was in the range 50F to 80F and if one wasn't parked in the full sun during the daylight hours.  Otherwise uncomfortable. The Sprinter had sufficient batteries and solar, and a large inverter, but it did have power limitations. For example, we couldn't use the electric cooktop and simultaneously make hot water for bathing or cleaning. For comfort heat it had a 1500 W electric heater, which was not adequate at below freezing, nighttime temperatures. There was no propane. It was a Mercedes camping experience as we slept in sleeping bags.

However, that experience allowed us to make a more realistic list of "must haves" and after reviewing these and discussing the Sprinter and our experience, we purchased a Roadtrek 210P which uses multiple fuels for coach amenities.  After the Roadtrek financial bankruptcy, the 210P is no longer made, which is a shame. 

I'm not going to repeat my earlier posts, in particular the one about our experience and decision to purchase the 210P. I do have earlier posts on solar, batteries, etc. 

Solar Power and Batteries

We purchased a new Roadtrek a bit sooner than would have been ideal at the time. We were both working and had very limited time for trekking. On the other hand, the price in December 2013 was really good, with a steep discount.  So, we purchased it. Because we live in a HOA and our garage cannot accommodate the Roadtrek we had to store it, and the largest issue was keeping the chassis and coach batteries fully charged. I did run the generator monthly.  The 210P did not have solar.

To keep the chassis battery fully charged, I purchased a 50W solar panel and controller. That's documented in a earlier post. I selected a de-sulfating controller. That was in Spring of 2014. 

I mounted the solar controller adjacent to the coach batteries, and I decided I wanted a "portable" panel, because when it is hot it is preferable to park in the shade. My approach allowed us to charge the batteries during the day while we were comfy. The cable connecting the solar panel to the controller is about 20 ft long and is coiled and placed under the passenger seat when we are in movement.

The Coach Solar

The 24"  x 24" 50 watt panel is stored behind the drivers seat when we are travelling. Why only 50 watts?

I had evaluated our DC electrical power needs. Our Roadtrek 210P has a 2.8kW Onan gasoline generator. It also had multiple energy sources. For example, propane is the source for the furnace, hot water and a range top, as well as the third source for the 3-way refrigerator. All of the controls are 12VDC.

We have no interest in living "off the grid" for weeks while running the refrigerator and Air Conditioning or space heat using 3000 watts of batteries and solar panels. In fact, our 210P simply doesn't have enough roof space for all of those solar panels. 200W would be pushing the maximum roof space available. Our interest is charging the coach and chassis batteries, reducing but not replacing the amount of grid electricity we need and so on.  This is because of practical considerations. Those considerations include roof area available or size of portable panels, battery considerations and cost.

What can we get if we maximize the roof panel? For example, 100W solar panels can produce about 5.6A. Depending on the orientation of the panel, the intensity of sunlight and the hours of direct sunlight received in a day, a 100W panel can generate 20- to 30-amp hours (Ah) daily. In fact, the amount of energy may be only half of this because of clouds, panel orientation and hours of daylight. 200W could provide a maximum of about 60-amp hours each day. 

To charge the coach batteries using 120VAC and the Triplite charger-inverter requires anywhere from about 3.6A to 9.3A at 120VAC.  To fully charge 50% depleted batteries can take 12 hours.  At the lower charging rate using the Triplite 120VAC inverter-charger, 3.6A is a minimum used, or about 430 watts. I've measured the AC at the pole with everything off in the coach except charging via the Triplite.  At a typical seasonal campground where we pay $0.14 per kWh; that's $1.45 per day to keep the coach batteries fully charged. 

If the batteries are at 50% the AC required for charging can increase to 9.3A (1,116 Watts).   The 50 watt panel can't do that. It can provide about 4.2A at 12 VDC. 

The 50 watt solar panel is sufficient for my needs to keep the coach batteries fully charged under low load.   If we need more charging current I can run the Onan generator, or run the vehicle.  Running the vehicle will charge the chassis battery and, if the battery separator is closed the coach batteries will also charge. 

If we need more 120VAC than the 750 watt inverter and batteries can provide while off the grid, we run the Onan generator. The generator uses 0.3 gallons of gasoline at half load.  That's acceptable and in this manner we can recharge the coach batteries and run appliances. The Onan can provide sufficient AC for the heat pump/air conditioner. 

Why a Portable (detached) solar panel?

I preferred a portable solar panel because we can park the Roadtrek in the shade and put the solar in the sun, and I can orient the panel for maximum DC energy.  The de-sulfating solar controller I purchased is rated for 180W maximum panels.  I can always upgrade to more solar.  However, if I really want more solar, I'll probably mount a flexible panel on the roof and carry another 100W portable panel.  In that way I could get up to 200W if parked in the sun or, at a minimum 100W if parked in the shade with the portable panel in the sun.

I've written about batteries in earlier posts. I don't like the low temperature charging limitations of Lithium-Ion batteries.  Combined with the high cost, I don't see an overwhelming advantage for us. In my earlier posts I do go into greater detail about this.

50 Watt panel in full sun

Charging at MI campground

Coach battery voltage while charging in MI on 50W solar panel
Current (amperes) is not accurately displayed when charging;
the meter displays current draw (discharge) on the battery. 
While charging the current flow is in the other direction

50 Watt behind the windshield
The glass does reduce the efficiency, however, if facing the sun for half of the day the panel does keep the coach batteries fully charged. 

At the AZ "lily pad" the Roadtrek is under the roof.
  I place the portable solar panel on the roof.

The Roadtrek is in the shade, while the solar panel is directly above,
 on the the roof, in full sun.

Charging the Chassis Battery

The chassis battery also needs to be maintained.  My theft prevention device does increase the 12V DC power needs when the vehicle is stored. With the arrival of thin solar, or flexible solar panels I purchased a 30Watt for that purpose. The 30 watt panel can provide 2.5A at 12VDC.

The 30W panel can also be put inside, on the dashboard and facing outward.  This will charge the chassis battery when the vehicle is stationary and stored. 

Monitoring the batteries. 

I have two DC voltage indicators. One plugs into the accessory socket on the dashboard and it displays the chassis battery voltage. The other I added and is mounted inside. It provides coach battery voltage reading and current draw, when the battery is discharging. I added a power "Off-On" switch for the interior meter so as to conserve DC. I've included photos here. I have an earlier post on the coach battery monitor.

30 Watt solar panel

Chassis battery charging voltage on Solar, 13.1 VDC

(c) 2021 Roadtrek210.blogspot.com.

Solar and 12V Refrigerator

 

Partly Cloudy - Rain Expected

We are preparing for a trip and I'm checking the systems of the Roadtrek.  One of the things I test is the 3-way refrigerator (AC-DC-Propane) model RM2554. For the test the refrigerator and freezer are empty. I then place a sensor in the freezer.  

Why empty? I wanted to see the performance of the refrigerator. Had I put frozen stuff in the freezer, the temperature of the freezer would have decreased or increased because of the temperature of the contents. 

I plugged the 210P into shore power and set the refrigerator to AC with a cooling setting of "5". I began this test at 4:30pm.  The freezer gradually reached a low of -15F with the outside temperature at 8am of 56F.

I then switched to DC to see how well the refrigerator can function on that power source. This would be the method used when traveling in the vehicle. According to Dometic "The DC mode is a holding mode not a full cooling mode. DC should be used once the unit is cooled down on gas or AC and driving (constant supply of DC) down the road." 

Refrigerator selected for 12V DC, maximum cooling

I'm curious about the apparent difference when on DC cooling as opposed to AC cooling.  According to Dometic the energy sources, both AC and DC are identical. The DC cartridge heater  supposedly provides the same energy for cooling as the 120VAC cartridge heater provides:

• 12 VDC cartridge: 175W (30A Fuse)
  

• 120VAC cartridge: 175W

12VDC Issue

With the Roadrek running on coach battery power and the refrigerator "OFF" the power meter indicated only 0.11A of DC battery power being consumed. At the time the roof vent fan and interior lights were off.

Battery System Status while on Solar and Overcast

I allowed the refrigerator to chill overnight on 120VAC power.  The freezer temperature gradually reduced to minus 15F.  At 8am I disconnected the Roadtrek from shore power. 

I then switched the refrigerator to 12VDC.  The power meter indicated a problem.  The RT was consuming only 0.41A.  That implies the cartridge heater of the Dometic was not getting 12VDC power. By noon the freezer had warmed to about 33F.

12VDC Battery running the refrigerator

Troubleshooting the Problem

The 12VDC power to the cartridge heater is controlled by a relay. I readily determined that the 12VDC cartridge heater was not hot. Using a DC Voltmeter I checked the 30A fuse.  It was okay. I then determined that the relay coil was getting power. I surmised that the relay had failed.

Existing relay, unscrewed from aluminum mounting

I went online and began looking for a replacement relay. The relay is a standard automotive DC relay, similar to a horn relay.  I didn't have much luck with online Dometic suppliers, who seemed to want to sell me a new circuit board and relay.  I did more research and found a generic supplier. I purchased two relays for about $4 each; I'll keep one as a spare.

I installed the relay and put the refrigerator on DC mode.  I checked the power at the heater and it was getting 12VDC. Success!

Rerunning the Test by chilling on AC Mode and then switching to 12VDC Mode

I followed the Dometic manual and chilled the refrigerator on AC mode. Normally I'd then fill the refrigerator with cold food and then switch to DC while travelling. For this test the refrigerator was empty.

A little morning haze turned to bright sun

On this day we had bright sun. The Roadtrek was parked mostly in the shade. At 4pm with the ambient temperature at 87F and the freezer interior about 80F I  plugged the Roadtrek into 120VAC shore power. I allowed the refrigerator to run overnight on AC and a cooling setting of "5".   It took 2 hours for the freezer to cool to 32F. At 6:00pm the freezer had cooled to 32F. At 7:00pm it had cooled to 20F and at 8:00pm it had cooled to 11F.  At that time the ambient temperature was about 76F.

Nighttime ambient dropped to a low of about 67F at 6am.  

The freezer temperature continued to decrease throughout the night. By 8am the freezer was about minus 10F.  I then selected DC mode on the refrigerator with maximum cooling setting of "5".  I let the refrigerator run on 12VDC from 8am to until 4pm.  At 4pm the freezer temperature was about minus 2F.  I assume the gradual rise in temperature was because of the increasing exterior temperature.  The interior of the Roadtrek was 94F at 4pm. It had been in mostly shade during the day. 

Refrigerator on AC and later on DC power

The Refrigerator was consuming about 3A DC according to the power meter. I have an in-line Ammeter I could use to confirm this.  However, if this is the DC consumption running on my solar system should not be an issue.

The temperature in the vicinity of the 12V cartridge heater was 145F:

General Refrigerator Information

According to the service manual, the refrigerator consumes:

• 12V Controls: 3 A.(That's the fuse size, too!).
  

• 12V Heater: 15A (175W).
  

Based on my power meter it seems the DC mode requires less Amperes than the manual indicates. That is a possibility. It would explain why Dometic describes the DC mode as a "holding mode".  If the DC cartridge heater was the same watts as the AC cartridge, I would expect the refrigerator to cool identically on DC and AC mode.

According to Dometic the refrigerator will function down to 9.6 VDC.  However, I am curious to see if decreasing battery voltage at night when there is no solar will impact the DC cartridge heater and if there is a lower voltage limit. It is also possible that the DC relay won't function properly at such a low voltage.  Relays of this type have a minimum "pick-up" voltage and also have a "drop-out" voltage. If the DC holding the relay "in" falls below the "drop-out" voltage the relay will de-energize. If this occurs the relay will disconnect the cartridge and the heater will no longer have 12VDC power.

Here's the circuit board in my refrigerator.  The photo indicates the part number. Yours may be different. Both the relay and the 30A DC fuse are mounted externally to the circuit board.

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