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What is the best way to prevent charging Tesla battery when too cold?

Before the Question, relevant system details.

1 Tesla 6s "24v" Battery Module, your standard model S module

Victron Multiplus 24/3000/70

BMV-712 w/Temp sensor

Victron Cerbo GX

2x Victron 100/20 MPPT charge controllers

4x 200w 12v Solar panels

Heating pad for battery, which I intend to trigger with a relay function


I've been fiddling around in VE Configure 3, and I'm not yet able to find the temperature reading on the battery. I have plugged in the temp sensor, but I don't see a reading anywhere, or any way to make sure the charger doesn't activate if the battery is too cold.

So my question is, with the given devices, what's my best option for ensuring the charger doesn't activate if the battery is too cold? IE, say I arrive to a frozen RV, the heating pad needs time to warm the battery before it's safe to charge, and I'm connected with shore or generator power, which would, assuming the voltage is low enough, start charging the battery.

If I've read correctly, I should be able to communicate with the MPPT controllers with the BMV-712 via bluetooth, though that seems a bit sketchy. I'd feel a lot better with a hard wired connection. I'm not sure how the internal temperature sensor for the MPPT controllers would work. is that somehow measuring the battery temp, or just ambient temp? The docs aren't entirely clear there. Is there a way to wire it directly from the Cerbo GX which I assume, can read the temperature from the MultiPlus?

So I suppose to summarize my question(s), given the above components, what's the best way to disengage the MPPT controllers and the charger when the battery is too cold?

MultiPlus Quattro Inverter Charger
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4 Answers
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easy-rooster answered ·

Well, I've managed to answer most of my own questions after fiddling around with the battery and the inverter all day yesterday.

1) The temperature reading on the battery is visible in Victron Connect. software. Also, after upgrading to the latest firmware, I have the ability to flip the "Lithium batteries" toggle from Victron Connect, and in the description of what that mode does, it will prevent the battery from charging if it's below 5C, and it will decrease charge voltage if the battery goes above 40C. So that solves the issue of cold charging from the standpoint of the Inverter. The inverter will also prevent cooking the battery as well. I guess once I connect my solar MPPT controllers, I can figure out if they're reading ambient or battery temp, or if I can control it manually with the Cerbo GX or something. I have more testing to do still. I've been waiting around for a sunny day so I can do voltage, impedance and various other testing with my panels to make sure I've sized my breakers and fuses for that leg of the system properly, but the smoke from the California wildfires are keeping the sky in a state of nuclear winter.

2) After taking a closer look at my Cerbo GX, and the charge controllers, I noticed they had a similar interface. After looking through the docs, I found that these are the hard-wire connections I was looking for, so I can connect the Cerbo GX to the charge controllers with VE direct cables, so I ordered some of those. I'll also hard wire up the BMV-712 to the Cerbo, then the Cerbo can be connected via Ethernet to the Inverter, and my computer in the RV.

I'm quite please with how nicely the Victron Connect software works for setting up the Inverter, it seems to have most of the functionality of VE Configure 3, but with a nice interface, and helpful information, like shown here. While it does state that there is no voltage temperature compensation WITHIN normal temperature ranges, I'd like to know exactly what changes when it goes above 40C, that information I didn't find. I assume it gradually decreases current until the temp comes back in line? Can anyone confirm that?

For future use, I'd also like to see the ability to customize the cold temperature range. The docs for the NCR18650B Panasonic cells used in the Tesla batteries say charge current should be halved if the charge temperature drops below 10C, so as it stands now, I'll have to make sure I set my maximum charge current to not exceed that half capacity voltage for the entire charging range, considering there would basically be no protection between 5C and 10C.


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scullerguy avatar image
scullerguy answered ·

057 Technology recommends using electric car coolant instead of plain water, due to corrosion issues. A simple closed system with a pump, reservoir, CPU radiator, and fish tank heater will do the job.

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stxshadow answered ·

Just try SimpBMS. It can do all that stuff and is "ready to use" with tesla (model S pack ) and victon. I use it in my 48 Volts (12s4p) solution and it is working quite nice.

Simpbms is also able to read the pack temp sensor and display it via VRM / Console.

Jens

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thezeroth answered ·

I would put a separate independent protection system right after the battery, because in addition to preventing it from charging when below freezing and too hot, u should prevent it from going under or over certain voltage, you should also be able to disconnect it automatically if the pack overheat. thermal rundown (say if you overcharge the pack) can easily cause a fire that is too hot to put out and will destroy your RV.

I saw they already reverse engineered the BMS board that comes in each Tesla module, that means if you have the skills, you can easily program a raspberry pi to read the voltage and temperature of cells of module and control a heavy duty 500 Amp relay to disconnect it in an emergency. raspberry pi also can be used to instruct the BMS board that comes in each Tesla module to balance the cells; as keeping cells balanced is another concern.

Also Consider using the builtin liquid cooling/heating of Tesla battery, its not that difficult to implement, u need a little pump, tube, etc. u can use the RV water heater as heat exchange heat source and fresh water tank as cooling source.

I haven't seen a ready solution for Tesla battery module in the market yet, battery protect solutions that already exist, don't support the Tesla battery module voltage range and can not handle 500 Amp, maybe we should create an opensource solution and publish a step by step guide on the internet.


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