New LiFePO4 battery, new solar, battery compartment heaters

 

Work station in Arizona

The modifications are substantially complete.  Earlier posts go into the pros and cons of LiFePO4 batteries, and the issues encountered when attempting to charge them in below freezing conditions.  I decided to install small heaters in the outside battery compartment.  I also upgraded the solar system I had installed in 2014. 

I'm of the opinion that components should be sized and selected carefully so as to extract the best benefits from the system.  In other words, the components should be selected to perform as a system.  It is desireable to get the best performance for a specific cost. System component selection includes the type and wattage of solar panels, the solar controller type and capacity, the Ah of the battery, the wattage of the inverter and other components, and even the size and ampacity of the wiring.   To do otherwise means overspending on some components while being performance limited by the weakest links in the chain.

In my experience, too many of us RVers are inclined to spend our money to get what we think we might need, rather than spending it on what we will use.  Experience may be the best teacher. 

When I decided to replace the coach batteries, I concluded this was an opportune time to evaluate the performance of my existing solar-battery charging system and make any alterations. In doing so I unconcealed  the weak link in the chain and decided to so something about it. Of course, this is an iterative process; once the weakest link is eliminated, there is the next one on this particular chain to deal with. 

I suggest some self-control and restraint may be in order. Otherwise, one might build a Roadtrek with a "warp-drive" Lithium-ion battery pack.  Oops, G just reminded me that this has already been done.  LOL.

This is the list of tasks:

1. Remove AGM coach batteries, install Lithium-ion LiFePO4 battery.
2. Mount shunt on the new battery (for the existing remote volt-ammeter display).
3. Remove existing de-sulfating solar controller used with AGM batteries.
4. Install (2) 12VDC battery compartment heaters and controllers.
5. Install (1) 120VAC battery compartment heater and controller. This heater has adjustable wattage.
6. Install MPPT solar controller. I chose a controller which accepts "user" settings which precisely match the recommendations of the battery manufacturer.
7. Install Blue-tooth communications module for MPPT.
8. Install low battery voltage automatic cutoff switch. 
9. Install fuses and wiring for the above.
10. Connect existing solar panel. Convert this to a remote portable solar panel.
11. Prep for a new rooftop solar panel. (2 total panels). This is anticipated to be a 100W solar panel on roof (to do). Wattage limited by the rooftop real estate available. 
12. Retain 120VAC power in battery compartment (installed 2014).
13. Install connector for portable Li-ion battery charger in the battery compartment. This is optional, but permits charging the battery without solar or the use of the Tripp-lite charger/inverter installed by the Roadtrek factory.

Remaining, to do:

1. Complete the solar panel wiring.  Add new rooftop 100W flexible solar panel. The goal is to have one mounted on the roof and one portable.  The existing panel is wired as the portable. This will allow parking in shade while simultaneously acquiring some solar energy via the portable panel.  I expect parking in the shade will be preferred to parking in full sun when the outside temperature is above 100F.  This is based upon our experience. LOL. 

Wiring:

All wiring is properly sized for the amperes which will be carried.  Fuses were added to protect the DC wiring. I did install a fuse for the portable solar panel. 

1. Battery wiring modifications are 4AWG.
2. The main Solar Panel wiring is 10AWG. Portable solar panel wiring is 12/14 AWG.  All solar wiring is new.
3. The 12VDC MPPT output is 10AWG and fused for 20A. 
4. The 120VAC compartment heater is sourced by the Roadtrek installed GFCI outlet under the side door passenger seat.  A power strip with circuit breaker was added. The power strip has an Off-On switch. This heater is controlled by a temperature controller and an adjustable watt control was added to vary the heat.
5. The 12VDC from the battery to power the 12VDC heaters is wired with a SAE connector cable, 16AWG and fused at 10A.  After the fuse each controller and each compartment heater is wired using 18AWG. Each controller/heater combination has an Off-On switch and a fuse. Actual connected amperes per controller = 2.0A (24W), but 18AWG can accommodate a significantly higher wattage heater, up to 200W and the controllers can each manage up to 120W.  None of the components should be stressed as sized.
6. DC power connectors are rated 65A.
7. Shunt for remote volt-ammeter was connected to the new battery.
8. Tripp-lite charger-inverter was retained. 
9. A plug-in connector is wired to the battery for a portable Li-ion charger, if that is desired to charge the battery. 
10. Each controller has a temperature sensor.  These are located in the battery compartment. Two are connected with 18AWG and one uses the factory provided cable, about 1/8 inch OD (AWG unknown).
11. The MPPT solar controller is wired with connectors for quick and easy removal, if that should be required.
12. The MPPT solar controller includes a temperature sensor. This is located in the battery compartment.  This is not necessary for the functioning of the MPPT controller with LiFePO4 battery, but it is a convenient method of monitoring the compartment temperature.  The controller and battery parameters including compartment temperature are displayed on a LCD display as well as via a smart-phone blue-tooth app. 

Top view - Heater Controls installed beneath rear-side entry passenger seat.
These are accessed by flipping up the seat bottom which is on a hinge.
When not in use or not required heater power is OFF using the switches.

Under side wiring - Heater Controls Shelf

Initial Heater settings (adjustable, using battery compartment temperature). System design can accommodate higher wattage heaters if this is determined to be necessary.)

. 

Battery Installation - Heater wiring and temperature sensors exposed,
prior to being covered.

Silicone heat pad cover and 12VDC heater controls fuse

Top view - 12VDC from MPPT Solar controller-
Mounted adjacent to interior water tank - Not yet installed:
portable solar panel fuse blocks

Battery Monitor DC Voltmeter-Ammeter mounted adjacent to RT power center. Voltmeter added in 2014. This is connected to the coach battery via a shunt and the circuit is fused. Connections are before any disconnect, so the battery voltage can be read even with the Roadtrek DC disconnect in the "off" position. 
I repeat, the circuit is independently fused!
An Off-On switch turns off power to the meter when not in use.

MPPT Solar Controller smart-phone App. 
Other screens provide more detail, control of load and history

Issues, Observations & Procedures:

1. I installed the MPPT solar controller, but two days later the LCD screen went blank.  I thought it might be some sort of "screen saver" but pushing the front buttons got no response.  The Blue-tooth (r) smart phone application worked fine and indicated the controller was functioning normally.  I contacted the factory and they suggested a hard reset (disconnect solar panels and power down the controller).  After 30 minutes I powered it back up. No change.  Renogy had me take some voltmeter readings to confirm all was properly connected. I sent photos to them and even several smart-phone screens at their request.  They agreed that the controller was performing normally but the LCD screen was inexplicably blank. They concluded it was a failure and the controller was replaced at no cost to me by the supplier.  
2. Making certain wiring changes in a class B can be challenging.  It took a bit of thinking and disassembly to determine how to do this; where to mount components, route the wiring, etc.  I determined a course of action prior to purchase of the various components.  Purchasing the battery was the easy part, after I had decided upon 1) Manufacturer, 2) AH, and 3) Where to mount it.
3. I didn't want to remove the side fabric panel in the inside rear of the Roadtrek.  To do this would have required more deconstruction than I wanted to do.  As it is, I had to temporarily remove some of the freshwater plumbing to gain access.  It took a bit of effort, but I was able to fish a stiff wire behind the fabric panel and pulled the new wiring for the portable solar panel into the space between the liner and the exterior fiberglass coach shell.  A new plug-in connector for the portable panel will be installed inside the passenger side rear exterior compartment. 
4. The solar panel system will be designed to accommodate using one or two panels, one fixed and one portable. The reason to have a portable panel is this will allow adding solar when the vehicle is stationary.  It also permits parking the Roadtrek with the rooftop panel in the shade while the portable panel is placed in full sun. However, if one panel is in full sun and the other in partial/full shade, series wiring is not optimal.  The design addresses this.
5. I built and wired the battery heater controls and tested them with the heaters on a bench.  This proved the wiring and functionality.  I wanted to bench test so that if any issues occurred after installation in the Roadtrek it would be attributed to the coach wiring and more easily isolated and corrected. 
6. I used ring terminals throughout which is prudent in an installation subject to vibration and jolts.  I used heat-shrink tubing to protect, insulate and support smaller wires at the connectors. I installed the heat-shrink tubing where appropriate. 
7. The 12VDC for the heaters is wired directly from the batteries with an ATC fuse. The fuse is within a foot of the battery + connector. In this manner the 12V heater system is protected and can operate independently of the Roadtrek power disconnect. I used an automotive SAE connector dis-connect cable.  There is no acceptable way to install a terminal block and I won't use a butt-splice for power. I joined the coach battery cable to the SAE cable using ring terminals bolted and insulated with shrink-tubing. 
8. The solar controller for the AGM batteries was installed by me inside the battery compartment in 2014.  This was disconnected when I installed the LiFePO4 battery. The replacement controller is larger, and I wanted it installed inside the coach. This required a change in DC wiring.
9. I decided upon a more costly MPPT solar controller so as to extract as much out of the solar panel(s) as possible.  I don't plan on living off the grid with solar.  But I do want to have sufficient solar to keep the battery charged and sufficient 12VDC for the basics of the coach (refrigerator controls, hot water heater controls, overhead fan, propane alarm, lights, PC, phone charging, etc.  But not all at once, LOL.).  
10. I oversized most of the heater circuit electrical components. Temperature controllers are rated 10A or more, wiring for the heaters has greater ampacity than required. Cabling for longer runs is 16AWG multi-conductor with jacket. This did increase the cost, but should provide trouble-free operation. Wiring outside the coach is protected and is installed in wire-loom split tubing which is properly supported.
11. I used 65A protected connectors for the battery connection to the MPPT solar controller.  This is an independently fused circuit, but I wanted a means to easily and safely disconnect battery power at the controller.
12. Solar panels are connected with MC4 connecters. 
13. I made several simple wiring sketches of how to add the low-voltage battery disconnect and placement relative to the existing 50A circuit breaker and the inverter.  I was able to mount the disconnect adjacent to the Tripp-lite inverter/charger.  I was able to re-arrange the 12VDC+ wiring for the disconnect and was able to add 12VDC wiring from the solar controller using available space.
14. The heater wiring was designed in my head, no sketches made.  I made a mental list of what was required, compared this to my inventory in Arizona and purchased what was needed.
15. I marked various power conductors and other wiring clearly.  I'll make a drawing for posterity and future maintenance.
16. I have a bit of clean-up to do in the battery compartment, but the project is essentially complete.
17. I'll add the second solar panel when convenient.  I'd like to see how this performs before I do that.
18. When not is use all heater controls are turned off using the switches I installed for this purpose. 
19. With adequate solar, the battery separator can be in the OFF state when travelling.  

Parts and Costs:

I used off- the -shelf components.  To reduce the cost of the battery compartment heaters, I used 12VDC temperature controllers which display in degrees Celsius.  The 120VAC control does display degrees F.  This list is not necessarily all-inclusive; see Note 1 at the end of this post.

Temperature control and compartment heater components:

120VAC temperature controller: $19.00.

12VDC temperature controllers: $7.00 each. (Total $14.00)

120VAC heater: $13.00.

4-outlet AC power strip with circuit breaker: $9.00.

12VDC heaters: $9.00 each (Total $18.00).

Heat Resistant Thin Silicone Grade Rubber Gasket Sheet $9.00.

Off-On toggle switches: $2.00 each (Total $4.00).

5-pair 65A connectors: $7.50 (one used).

SAE Quick connect bulkhead fittings 2-used, $5.00 each (Total $10.00)

MC-4 to SAE portable solar panel connector, 35A, 10AWG: $15.00.

Five 4-point terminal blocks: $2.40 each  (Total $12.00).

Two ATC/ATO inline fuse holders $6.00 ($3.00 each, one shunted for 12VDC negative). 

Solar and battery related components:

Automatic Low-voltage battery disconnect: $83.00.

MPPT solar controller:  $111.00.

Li-Ion LeFePO4 battery, 100 Ah: $575.00.

6-terminal buss bar (battery negative to MPPT): $13.00.

60 ft. 10 AWG wire for solar: $40.00

Two ATC/ATO inline fuse holders $6.00 ($3.00 each). 

4 AWG cables with lugs for automatic low-voltage battery disconnect: $13.00.

Battery manual disconnect switch: $15.00.

MC-4 connectors for solar cables w/ tool.  10 pairs $16.00.

Hardware, misc. wire and terminations (some from my inventory):

2/C 18AWG, 65 ft: $13.00.

2/C 16AWG, 33 ft. $23.00.

#16-14 butt splice connectors.

#22-16 butt splice connectors.

Thermal adhesive tape, about 5 ft. used.

20 ft. 1/2" wire loom split tubing: $13.00.

M8 bolt, nut, washer.

M4 screws, nuts, washers.

8-32 pan head machine screws, nuts, washers.

Heat shrink tubing, various diameters.

Nylon screw mounting cable clips, various sizes.

Zip wire ties and adhesive mounts, various sizes.

3/14" wide double coated foam tape.

Ring type wire connectors, various sizes #18-#10AWG.

#8 x 3/4" self-drilling pan head screws.

#8 x 1-1/4" wood screws. 

1-1/2 x 1-1/2 aluminum angle.

3/4 x 3-1/2 wood slat, length as required.

3/4 x 7 wood shelving. 

Gorilla glue.

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. When not in use all heater circuits are turned off using the switches I installed for this purpose. The 12V heaters are fused and controlled independent of the Roadtrek battery disconnect switch.
3. My solar panels for test purposes are (1) 30A and (1) 50A.
4. I'll be installing a rooftop panel and have wired for a portable panel. 
5. Every trekker has goals and expectations.  It is useful to outfit the Roadtrek so that their personal goals can be realized.  This included comfort expectations, the available heat, 12VDC and 120VAC power, cooling and water. 

(c) N. Retzke 2022