24v solar for Adventure Trailer

#1
Hi all,

I am planning a 4 to 5 month cross country trip next Spring. We have a Jeep JKU and will be hauling a trailer with RTT. I will be working during the trip and have some fairly considerable loads for the required electronics. I have been focused on keeping our set-up as light as possible. I have decided on Lithium batteries and figure I need at least 400 AH to keep me powered up conservatively.

I have access to a used low miles Tesla model S battery module for next to nothing. I have started to plan for this as the baseline of my system. I am reaching out for some input on this system in hopes that I may avoid some costly errors or dangerous situations. I understand the potential dangers of the Tesla modules related to incorrect charging profiles / settings etc. With my intended use and a few safety considerations, I felt comfortable.

I just installed a Genesis Dual battery kit in the Jeep with 2 Odessey batteries. I would like to install PV panels on the Jeep rack that are quickly deployable & removable for sites that require alternate orientation or when the wife takes off while I work. My initial thoughts / goals:

  • I am thinking of going with (2) 24v 300 watt Monocrystaline panels.
  • I have a 3500 watt inverter Generator as backup, to handle charging when PV input is limited, and to handle daytime AC needs.
  • Charge controller - I understand the ability to input some very specific profiles, specific to the Tesla Module is key to avoid a dangerous overcharging situation. Looking for recommendations here.
  • inverter - I feel a good 2000a pure sinewave inverter will handle my needs.
  • Victron battery protect - configured to ensure i do not discharge below 20%.
  • 40A 24\12v step down transformer / converter for 12v accessories and LED lighting
  • Shore power charger - I'm looking for suggestions here. I understand you can throw a ton of Amps at the Tesla modules. Want something fairly robust here.
Comments? Recommendations? I've got time, so looking forward to the discussions.
 
#2
I would completely avoid using the Tesla batts in a mobile context, maybe as a science experiment in the back shed.

The EV forums have some hobbyist types working on reverse-engineering the BMS / Charging controls.

But it's yanking them out of their very sophisticated Temp Management systems would really concern me, living right on top of them in an enclosed space.
 
#4
I build my own lithiun battery packs, so getting a tesla module thats already buildup and ready to go, that will be easy to incorporate into your system. The power on those modules is tremendous for there weight and if you can them cheap, why not.

For me the most important thing on a lithium battery pack is to be able to monitor the voltage on each cell for the tesla module (6s74p) that would be 6 cells to monitor. This is very important during charging, the voltage should be very close to each other for proper balancing. You might have to make your own 6s balance connector that can be connected to tesla modules own proprierty connectors. 6s balance connectors you can find on ebay inexpensively, they are a standard JST size and fit most lithium balance monitors/alarms even balance chargers.

Tesla modules are charged to less then full everytime, maybe 4.1 volts per cell, for a 6s battery pack that comes to 24.6 volts. (max 25.2 volts)

Something I definitely recommend with lithium batteries is an overvoltage relay to monitor battery voltage and disconnect the charge source when the battery voltage reaches the max voltage you set for it. On the tesla module when the voltage reaches 24.6 volts, the relay will disconnect the solar panel, or whatever power source you are using. This is a diagram of how I have my 4s lifepo4 battery pack hooked up to the solar system. With the overvoltage relay the system can be left unattended 24/7. The solar controller is set to stop bulk charging and switch to float at a certain voltage, but if it doesnt the relay won't let battery go over its max voltage. If the controller and relay fail, then the battery BMS will stop the charging. Thats 3 levels of control. Without the overvoltage relay, the battery would need constant supervision, its like a deadman switch, if your paranoid about safety you can add multiple overvoltage relays (they only cost 5 dollars).

overvoltage relay
diagram a.jpg
3in1 balance tester, use to check battery balance condition
active balancers.jpg
 

dwh

Tail-End Charlie
#5
Two 300w PV modules...on a Jeep...

I have one 300w module on my van's roof and no room for anything else. The bloody thing is 77" x 40" and weighs 50lbs.
 
#6
Two 300w PV modules...on a Jeep...

I have one 300w module on my van's roof and no room for anything else. The bloody thing is 77" x 40" and weighs 50lbs.
Yeah I see your concern, I'm aware of the size. I have handled them a bit for an off grid home install. The panels i'm looking at are 65" x 40" and closer to 40# each. I'm 6 '-5" tall and 300# so they are easy enough to handle.

I have been thinking of a system which allows me to stack them. Top panel is stationary, attached to my 76" x 54" Rhino rack pioneer platform. The panel below, on rollers in a channel under the rack, can be deployed and tilted when deployed or simply removed and placed on the ground.

I am also considering keeping one panel mounted to Jeep rack with a quick release system and second panel sliding into a channel under the RTT, being deployed when we are set up.
 
#7
I build my own lithiun battery packs, so getting a tesla module thats already buildup and ready to go, that will be easy to incorporate into your system. The power on those modules is tremendous for there weight and if you can them cheap, why not.
Yeah, I have been following Jehu Garcia for a while on his YouTube channel and had originally planned to build my own packs. I felt comfortable with the process, but was concerned with the time and expense of procuring some decent cells. Since a friend ended up having some spare Model S modules i figured they are much more well engineered than anything I would come up with

I used to mess with lipo's and balance charging them when I raced RC cars a few years back. Those batteries were always charged to hear 100% and had such high rates of discharge, that they often needed to be balanced during charging. I understood the S Modules are so well matched at assembly and so well managed during their life in the vehicle with their BMS, that it is difficult to get them out of balance in this application. I'm planning to charge to 90% (24.4v) and discharge to no less than 19.0v. I have heard from others using the modules in this application that with such a low rate of discharge (compared to intended design) they just simply don't get out of balance. While others with experience have been quite laxed in their monitoring, I prefer to be able to easily monitor this and plan to do so. Thank you for the info on the connectors and balancing monitors. I plan to incorporate.

I was comfortable with the Victron battery protect to keep from over discharge to avoid killing the battery. I was less comfortable relying on charge control parameters alone for the obvious safety concern for over charging. Thank you for the info on the overcharge relay. This is exactly the kind of info i was looking for to add some redundancy to the overcharge protection.

I plan to have a physical voltage monitor that is configured to lithium parameters, but would like to find a charge controller that allows for remote monitoring via an application on my cell phone.

Looking forward to additional input to help me hone in on appropriate components. Any thoughts on a shore power / charger unit appropriate for the Tesla module? I understand they like a fast charge and can handle quite a significant rate. Are you aware of a traditional AC charger that works with the Lithium charge parameters?
 
#8
I would completely avoid using the Tesla batts in a mobile context, maybe as a science experiment in the back shed.

The EV forums have some hobbyist types working on reverse-engineering the BMS / Charging controls.

But it's yanking them out of their very sophisticated Temp Management systems would really concern me, living right on top of them in an enclosed space.
I certainly understand your response and expected to hear this.

There are a number of these units being used in RV's. In this application they are being used at a fraction of their designed charge / discharge capabilities and unlikely to be a fire concern. I would be interested in hearing about any you are aware of.

We will not be in the tent during the day while charging. We are pretty comfortable sleeping over an enclosed battery in a tent considering the quick egress from all sides.
 

luthj

Adventurer
#9
So my thoughts on this type of Lithium pack.

MUST HAVES
cell level monitoring voltage and temperature
the BMS must disconnect upon high, low voltage and temp, both for the pack and individual cells. If a cell goes high temp and voltage, it can and will breach. The thermal runaway speed of the Lithium Cobalt batteries is quite fast.

Do not rely on the BMS for daily needs, such as overcharge/undercharge. The charge controllers must be programmed to handle this. So a charge controller than has active current (shunt) feedback for example. That way you can terminate charging when the voltage and current are met. You could go with a timer based terminations. Say 24.XV for 5 minutes or so.

Packaging and connecting the bank is just as important as all the fancy BMS stuff. So preventing vibration damage from weight on terminals, or cells moving about. This is every more applicable to trailers, which get the crap beaten out of them, even on okay roads. Does your trailer have shocks? If not, add some...

As mentioned, with an adequate BMS, and fractional C usage, you should be okay.


Also, if you will be driving a lot, you may consider a DC-DC charger. You can pull 50-100A from most OEM alternators. The DC-DC will be boosting the voltage anyways, so just keep the charger on the trailer, and keep wire run drops within the chargers input spec. An anderson connector or similar with large wire would be needed.
 
#10
So my thoughts on this type of Lithium pack.

MUST HAVES
cell level monitoring voltage and temperature
the BMS must disconnect upon high, low voltage and temp, both for the pack and individual cells. If a cell goes high temp and voltage, it can and will breach. The thermal runaway speed of the Lithium Cobalt batteries is quite fast.

Do not rely on the BMS for daily needs, such as overcharge/undercharge. The charge controllers must be programmed to handle this. So a charge controller than has active current (shunt) feedback for example. That way you can terminate charging when the voltage and current are met. You could go with a timer based terminations. Say 24.XV for 5 minutes or so.

Packaging and connecting the bank is just as important as all the fancy BMS stuff. So preventing vibration damage from weight on terminals, or cells moving about. This is every more applicable to trailers, which get the crap beaten out of them, even on okay roads. Does your trailer have shocks? If not, add some...

As mentioned, with an adequate BMS, and fractional C usage, you should be okay.


Also, if you will be driving a lot, you may consider a DC-DC charger. You can pull 50-100A from most OEM alternators. The DC-DC will be boosting the voltage anyways, so just keep the charger on the trailer, and keep wire run drops within the chargers input spec. An anderson connector or similar with large wire would be needed.
Thanks for the feedback, exactly what I am looking for so that I can narrow down a search for the remaining components. I am sure I will be back in touch as I research components for this system. I have several months to sort it out before committing to purchases.

I had not considered monitoring temps at a cell level based on the information I have seen for the Tesla Model S modules for this use. I understand the charging and discharging that we would apply are significantly lower than what it was designed for that it would be very unlikely to have an issue. I had also read that each cell was individually fused at 10A and would essentially isolate itself for safety. I would prefer to be able to monitor the temps however, so if there is a way to tie into the modules wiring to do so, I will certainly explore that.

I have been considering a BCDC and running some heavy cable and Anderson plug for Trailer charging. I am not up to speed on the effect of this on Lithium, but planned to get into that. I'm not sure what the stock alternator will push, but I installed a 200A smart isolater upgrade with the Genesis kit. I will upgrade the alternator and carry original as a spare if it makes sense.

It is a 12,000 mike trip, so plenty of driving. yes the trailer has trailing arm suspension with dual shocks per wheel. The plan for most areas is to set up basecamp with the trailer for a week or two and then head out for day trips or short overnight camping trips in the jeep. There may be some rough passes while hauling the trailer, so I will look into ways to isolate or mitigate shocks / vibrations.

Thanks for the additional information
 
#12
With a DC-DC like sterling etc, you can set whatever current and voltage rules you want. Is your vehicle 24v?
Ha, NO! Good point there! I remember now that when I was thinking about that in the past, I had abandoned the thought of charging from the alternator. I plan to have 1 panel on the roof of the Jeep which I can keep connected while traveling and solar / Generator charging capability in camp (when Shore power is not an option).
 
#14
Sterling makes DC-DC chargers that are 12v to 24V. They are a good option.
Reeeeeallllllyyy..... Thanks. I was going to ask if there was some sort of converter / transformer, but thought I should look around first. I will take a look at what they offer.

This is an item I will likely need to weigh cost vs expected use. I need to consider that maybe this would be an add-on down the road if it looks like it would be a benefit.

Thanks again
 

dreadlocks

Active member
#15
I will be working during the trip and have some fairly considerable loads for the required electronics. I have been focused on keeping our set-up as light as possible.
IMHO A generator is going to be lighter, cheaper and take up less space at the end of the day..
 
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