Protecting the charge controller with low temp charging cutoff LiFePO4 battery

[steveluannj]

I thought I was being safe when I spent the money for a Lithium battery with low temp charging protection. I now have a concern about the charge controller. Manuals for all charge controllers say that the battery must be connected first, then the solar panels. I was planning on leaving the panels connected, and letting the battery's BMS disconnect when the temperature is low to protect the battery. I now realize that the charge controller is not protected in this case. I have not seen a fix for this issue- so is it an issue? None of the system designs I have seen have a component to protect the charge controller. I am not sure what the behavior of the BMS is when the low temp protect is active- but is it different than the behavior when the battery is full? In either case, the output from the charge controller has nowhere to go.

[howson]

I thought I was being safe when I spent the money for a Lithium battery with low temp charging protection. I now have a concern about the charge controller. Manuals for all charge controllers say that the battery must be connected first, then the solar panels. I was planning on leaving the panels connected, and letting the battery's BMS disconnect when the temperature is low to protect the battery. I now realize that the charge controller is not protected in this case. I have not seen a fix for this issue- so is it an issue? None of the system designs I have seen have a component to protect the charge controller. I am not sure what the behavior of the BMS is when the low temp protect is active- but is it different than the behavior when the battery is full? In either case, the output from the charge controller has nowhere to go.

Perhaps a relay powered by the battery? When the battery shuts off in a low temp (or any other) scenario, the path from the solar panels to the MPPT is disconnected.

[StephenO]

I thought I was being safe when I spent the money for a Lithium battery with low temp charging protection. I now have a concern about the charge controller. Manuals for all charge controllers say that the battery must be connected first, then the solar panels. I was planning on leaving the panels connected, and letting the battery's BMS disconnect when the temperature is low to protect the battery. I now realize that the charge controller is not protected in this case. I have not seen a fix for this issue- so is it an issue? None of the system designs I have seen have a component to protect the charge controller. I am not sure what the behavior of the BMS is when the low temp protect is active- but is it different than the behavior when the battery is full? In either case, the output from the charge controller has nowhere to go.

I am in the process of upgrading to lithium including new solar, so my experience is very limited. But, I have read that Victron's battery monitors can connect an external temperature sensor. From there, using the VE Network, your MPPT controller should be able to use that temperature reading for cutoff protection.

From the manual of the Victron controller I am getting....

• Temperature sensing - the measured battery temperature is used by the chargers in the network for temperature compensated charging and in case of lithium battery for the low temperature cut off.

Maybe this is something to consider? Although this assumes you are using Victron gear

[ajg617]

I contacted FSI about the same question - basically is the solar charge controller going to suffer if the BMS cuts off (or I physically remove) the batteries (two LiFePO4s). I was curious because the only place to remove current flowing to the batteries is a fuse between the controller and the batteries, not between the panel and the batteries. It was suggested I install a solar CB between the panel and the controller which I have since done. Purchased this and installed it between the panel and the controller.

This was really a safety measure should the temps dip so low that I would want to remove the batteries (not too frequent but we did hit -13F last year) even though I have battery heaters (which means very unlikely that I'll need to pull them). It's a manual CB but sufficient for my needs.
https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

[rtrainer]

I think the bigger question is, what happens if you are in a cold weather location and the BMS disconnects the battery? A manual disconnect won't help because it might be the middle of the night when this happens.

[BobinICT]

I am using the Victron controller and their temperature sensor, the sensor is mounted on top of the batteries on the A-Frame in a duel battery box. We got down to -40 and the BMS's shut down where I had no power to the rig. I emailed Lion Energy and they stated the BMS had shut down the batteries because of the cold, they do not have low temp shutdown, and once warned up they would wakeup, which they did. I only had the solar connected and just waited. Eventually everything came back online when it warmed up. I have my controller set to shutdown, not supply a charge at 34. So apparently it's nothing or I dodged a bullet. I just don't know. I just put my faith in Victron and all went well. Perhaps the batteries woke up around 32 and therefore in a sense, it was like the batteries being hooked up and then the controller came online at 34.

[ajg617]

I think the bigger question is, what happens if you are in a cold weather location and the BMS disconnects the battery? A manual disconnect won't help because it might be the middle of the night when this happens.

That's why my LiFePO4s have battery heat pads with thermostats. They turn on when ambient temp is 35F before the BMS shuts off at 32F (and that's internal battery temp). They turn off when ambient temp is 45F. I've measured the battery temps with a gun after a night in single digits and the temps were about 37-38F on an area of the battery (side) not covered by the heat pads I installed. Unless you have a method of keeping the batteries above 32F, the BMS should disconnect.

[ajg617]

I have my controller set to shutdown, not supply a charge at 34. So apparently it's nothing or I dodged a bullet. I just don't know. I just put my faith in Victron and all went well. Perhaps the batteries woke up around 32 and therefore in a sense, it was like the batteries being hooked up and then the controller came online at 34.

You may have dodged a bullet. My understanding is that LiFePO4 cells can be permanently damaged in temps below approx -13F - at least that's what Battelborn has stated.

[steveluannj]

Howson: The relay would still get power from either the converter or the charge controller, so that would not work. Perhaps a thermostatically controlled relay in the PV line. I already have a circuit breaker, so I can keep that open until I find a permanent solution.
I can't see the cold temp cutoff in the Victron information in the selling web page. Would all models do this? Seems like there should be a good, safe way to protect lithium batteries and the charge controller. Now I am wishing I bought a different battery and spent the savings on a new charge controller. :-(

[BobinICT]

You may have dodged a bullet. My understanding is that LiFePO4 cells can be permanently damaged in temps below approx -13F - at least that's what Battelborn has stated.

I apologize for my incorrect post. It was -40 wind chill. Sometimes things get fixated in my mind and I just remember it, was, cold. The lowest it got was -12 and that's when the batteries shutdown sometime between when I checked last, like the night before. The reply stated once the batteries warm up to over 32 and a charge is applied they would come back which they did.

[ajg617]

I apologize for my incorrect post. It was -40 wind chill. Sometimes things get fixated in my mind and I just remember it, was, cold. The lowest it got was -12 and that's when the batteries shutdown sometime between when I checked last, like the night before. The reply stated once the batteries warm up to over 32 and a charge is applied they would come back which they did.

Personally, I would still query Lion about lowest temps before the cells can be damaged.

[steveluannj]

I checked the Renogy web site, and their information does say that the controller does handle the BMS shutting down the battery for overcurrent or undercharge conditions. I chatted with technical support, and they said that the controller should handle a low temperature cutoff as well, so I am not going to add anything to my system to disconnect the solar panels automatically. I will still probably pull the battery inside in winter, if only to secure it against theft. I won't do anything special while camping, for those occasional times when nighttime temps drop below freezing. That can happen any day of the year in the mountains.

[acoleman43]

I may be wrong about this so please verify....I believe some of the Victron Smartsolar MPPT controllers have a programmable relay that can be programmed to shut off if temp is below -4 Fahrenheit.

[rtrainer]

Per the Victron Smart Solar MPPT manual

[steveluannj]

Per the Victron Smart Solar MPPT manual

If I were starting from scratch, this would be a feature I would require in a charge controller. Even if I needed to buy the Victron, I could have saved enough on the battery to make up for it. If my charge controller does go out, this is what I will replace it with.