Disconnecting solar when below freezing for LIFEPO4 batteries

[nebulight]

Disclaimer, I'm not a pro, but did some internet research on how to throw this setup together. Use info at your own risk

Charging lithium batteries below freezing temps can cause irreversible damage. With my installation of 400ah of lifepo4 batteries inside the van, I've been looking for an automated way of disconnecting charging when approaching freezing temps. I ended up using an ITC-1000F 12V model with an external relay. Since I couldn't run my solar through the internal relays of the thermostat (didn't want to risk burning them out as they only support up to 10 amps), I'm using it to trigger an external relay. I went with an EV200 for a few reasons. One it's rated for high amps so I don't think I'll risk burning it out or having it stick, and two I got a REALLY good deal on it. I put together a little video showing how I wired it up as when I was starting out as a newbie, I was looking for help on this topic and couldn't find much.

https://www.youtube.com/watch?v=YlrP-CwFnlg

 

[autostaretx]

Couldn't you rig up a battery heater that kicks in (a) when there's solar power (b) AND the temperature is approaching/below freezing?

--dick

 

[Midwestdrifter]

Similar to autostaretx idea, I figure you could do something like this.

A 10-20w heater pad. An adjustable voltage sensitive relay (12-14v should work) two thermal disk switches. Both close on temp drop. One for around 50F, and the other for 80F? That way a single switch failure wont cause a pack overheat.

Adjust the VSR to close when voltages are high enough for charging to be present.

 

[nebulight]

The problem with heating the batteries in order to charge usually ends up a net loss of power, so disconnecting is the preferred method (for my setup anyway). The previous setup did use heating pads. You could see the inkbird setup sitting on top of the inverter in the video that was hooked up to two heating pads between the batteries. The problem with small heating pads is they don't produce enough heat to really do much over the long run. You'd need bigger pads. I had two pads between the cell groups but they drew around 17-19amps (two pads) and were AC so the inverter had to be on all the time. This would end up being a net loss of power as even on a good day, 300w of solar couldn't keep up. Just easier to disconnect the charge load as this would be for when the van in sitting. If I'm out and about in the van, the heater would most likely stay running and keep the batteries warm enough for a charge.

 

[fourgonbound]

Nebulight,
That's a cool setup and pretty easy to implement.
I have a Victron BMV 712 and there's an option to buy a temp sensor for the battery. Once that's done, you can program the battery monitor to open/close a relay depending on the temp (there're more options too like low/high voltage cutoff, etc.). So I might use that for my LiFePO4 battery.
I also asked Victron if they can update their software to have the solar charge controller stop charging if the ambient temp is below freezing. Their MPPT controllers have a built-in temp sensor to compensate voltage during charging (which we don't need for LiFePO4) and it would be cool if their software could implement this feature.

 

[quiverkiller]

Battleborn batteries, for instance, have an internal battery monitoring system that automatically controls this (if it gets too cold they won't allow them to charge) and all other aspects of their operation.

 

[calbiker]

Nice video! The only thing I take exception to is the big relay. It uses lots of power 24/7. I would get a different relay, one which makes contact when the coil isn't energized. Once temperature goes below 35F the contacts open and charging stops. In this case the relay consumes power only when charging is shutdown. Use the temperature sensor heater function to activate the relay.

 

[fourgonbound]

Nice video! The only thing I take exception to is the big relay. It uses lots of power 24/7. I would get a different relay, one which makes contact when the coil isn't energized. Once temperature goes below 35F the contacts open and charging stops. In this case the relay consumes power only when charging is shutdown. Use the temperature sensor heater function to activate the relay.

I was just thinking about this too. According to spec, the relay uses 0.13A@12VDC when holding. That starts to add up, especially in the winter when solar sucks anyway.

 

[rollerbearing]

Victron has some other products worth looking at for this application.

They have the Victron Battery Protect which is essentially a MOSFET solid state relay capable of handling up to 200 Amps depending on model.

It is programmable for battery voltage protection, but also has a "remote" input that can act like the coil input to a relay. The advantage is ultra low ON remote/"coil" current input (1.5 ma)

One could very easily wire it with any number of thermostat devices.

Also worth checking out are Victron's MOSFET battery isolators.