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.

My original setting used heating pads and another thermostat to turn them on, but you usually end up with a net loss as you need a few larger heating pads to warm up the batteries.

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

[booster]

We assume you also found out that if the batteries see below -4*F they can be permanently damaged, even without being on charge?

For the solar, you can get damage when the controller is not attached to batteries but the panels are still connected to the controller. Sun comes up and the voltage can go high without the reference from the batteries. You would really need to have a double disconnect for the solar to take the panels off the controller first, and then the controller off the batteries next. You would go the other way when turning back on, controller to batteries first and then panels to controller second.

It is way overkill for capacity, but Blue Sea makes a timed manual disconnect switch that does that automatically when you switch it on or off.

[Boxster1971]

Originally Posted by booster

We assume you also found out that if the batteries see below -4*F they can be permanently damaged, even without being on charge?

For the solar, you can get damage when the controller is not attached to batteries but the panels are still connected to the controller. Sun comes up and the voltage can go high without the reference from the batteries. You would really need to have a double disconnect for the solar to take the panels off the controller first, and then the controller off the batteries next. You would go the other way when turning back on, controller to batteries first and then panels to controller second.

It is way overkill for capacity, but Blue Sea makes a timed manual disconnect switch that does that automatically when you switch it on or off.

I don't see a need for double disconnect. Just place disconnect between panels and controller and leave the controller connected to the batteries. Not sure what OP intended.

- - Mike
2012 Sprinter 3500 Extended converted B-Van by Airstream

[booster]

Originally Posted by Boxster1971

I don't see a need for double disconnect. Just place disconnect between panels and controller and leave the controller connected to the batteries. Not sure what OP intended.

- - Mike
2012 Sprinter 3500 Extended converted B-Van by Airstream

I am assuming, based on what he said initially that he also wanted the batteries disconnected from the controller, which many of us do if the van is going to be sitting a long time, as there is some draw to the controller from the batteries.

[avanti]

Originally Posted by booster

I am assuming, based on what he said initially that he also wanted the batteries disconnected from the controller, which many of us do if the van is going to be sitting a long time, as there is some draw to the controller from the batteries.

Of course, in the proposed setup, there is some draw from the batteries to the temperature controller thingie.

As much as I like those cheap little devices, in this particular case, I would be tempted to use a battery-powered residential thermostat.

[nebulight]

I want the panels disconnected from the controller, but the controller to remained powered on as that is also my battery monitor as it's got the connection to the shunt. So a single disconnect should work fine and must work fine as I don't want to disconnect the batteries from the controller or else I will lose my SOC status.

As for the cheap thermostat, I've got a second one in case this fails. Worse case if the device dies is it will not power on and the external relay will be open with no charge at all.

If I run into a lot of issues with them failing, I may see if I could find a better thermostat that can be powered by 12v.

[avanti]

Originally Posted by nebulight

As for the cheap thermostat, I've got a second one in case this fails. Worse case if the device dies is it will not power on and the external relay will be open with no charge at all.

If I run into a lot of issues with them failing, I may see if I could find a better thermostat that can be powered by 12v.

Just to be clear, I was not criticizing the quality of those devices. I use stuff like that all the time, and although I have infant mortality issues with a few of them, once they work, they seem to work forever.

What I was suggesting was you use a plain old ordinary home electronic thermostat. Random example:

https://www.amazon.com/Honeywell-RTH...tal+thermostat

The advantage is that these are powered by internal dry-cell batteries and so have no load on your coach batteries. But, if you are keeping other stuff powered up anyway, I guess it doesn't matter much.

[nebulight]

Originally Posted by avanti

The advantage is that these are powered by internal dry-cell batteries and so have no load on your coach batteries. But, if you are keeping other stuff powered up anyway, I guess it doesn't matter much.

That is nice that they run on battery, but these have such little draw that it's almost undetectable with my shunt/battery monitor.

[nebulight]

Follow up. I finally got everything installed. I had to extend the wiring coming from the solar panels and needed to make a custom cable with a terminal lug on one end for the relay and a spade/fork connector on the other end for the charge controller:



I used heat shrink to cover the end of the new cables. Final install mounted the thermostat to the underside of the bed frame and mounted the relay to the right next to my other relay and shutoff switches.