Off grid cabin— frozen 48v battery in low voltage and BMS won’t start up

[Messier11]

Hi everyone,

I have the ‘build’ described in the below thread, in short 48v 280ah battery, Victron MPII 5000/48 and a JK BMS — in my Off grid cabin.

My 6k$ budget DIY Scaleable Off-Grid 15 kwh 48v LiFePo4 hybrid build with remote control and supervision function

v2. Introduction Hi everyone! I have always spent the summers and part of the winter out in the archipelago it the most northern part of the Bothnian Bay in Sweden (Finland is only a slap shot to the East). During summer time, we get sun 24 hours a day and, conversely, during parts of December...

diysolarforum.com

Shortly after I left the cabin in the summer, I could see through the remote monitoring that I started having issues with the charging from the MPPT. I have no idea why. Anyway, the battery fairly fast shut down itself, and I got to the cabin for the first time in 6 months yesterday.

Even despite heavy insulation, the batteries were really cold when I got there. Probably around minus 4-10. The voltage of the battery was first 11.6v, and they have not kept up to 11.86v after getting warmer (app 0.6-1v per cell). Not sure if they still are frozen in the core, should have started to get warmer at this point. But let’s see.

The JK BMS won’t start. When I connect a 9v battery to it, I can hear a buzzing sound from the Charger/Converter (MP2 5000/48 Victron), but I get no life from the BMS. The buzzing sounds a bit like conductors are charging up, or something like that.

I have a gas generator which I can charge the battery with, but to do that I must of course get the BMS to work.

Any tips on how to proceed? Should I try getting the BMS to start with a 12v battery? Let me know if I should post more info or any pictures.

 

[HRTKD]

Pull the balance wire connector out of the BMS and plug it back in. On my Overkill Solar/JBD BMS that does a reset. While the battery should still be able to be discharged at such low temperatures, charging should not be done until the batteries are above 0°C. In your case, I would give them plenty of time above that temperature reading to ensure they are thoroughly warm.

 

[Yurtdweller]

I concur. It is not advisable to charge frozen LiFePo4. I rarely see freezing temps, but I have noticed my own 16 cells (lf280ks) have serious thermal mass. When the temps dip below freezing overnight, the cells are still at +10°C in the morning. This indicates to me that your cells need to be in a warm room for quite a few hours before they are safe to charge.

 

[timselectric]

And when you deem it safe to start charging. Start slowly, this will help warm the batteries, also.

 

[Messier11]

Thanks guys, I tried to pull the balancer cords out, but it doesn’t help.

Think it’s a bit odd, even if there is only 11.96v in the battery, the BMS should start right?

You think I could damage it if I tried with 12v?

 

[timselectric]

Can you access the BMS information?
This could tell you why it's off.

 

[Messier11]

Can you access the BMS information?
This could tell you why it's off.

Nope, doesn’t show up.

But the voltage is of course extremely low, just 0.6-1v per cell…

 

[HRTKD]

Maybe the BMS died? I thought at first that you had a 12 volt system, but that's obviously not correct. I think that BMS is going to want to see closer to 48 volts before it starts.

 

[Messier11]

Should I bypass the BMS when I start charging?

 

[upnorthandpersonal]

This is weird. LiFePO4 electrolyte does not contain water, and needs very low temperatures to actually freeze. I had my cells frozen at least once (-20C) but never had them drop in voltage the way you're seeing. I even have a video where I tried charging a -17C frozen cell. That cell was outside for several days before doing that test.

The JK will also power itself off when the cell voltages drop very low to prevent over-discharge.

 

[HRTKD]

Should I bypass the BMS when I start charging?

That would not be my first step. Leave the BMS connected. Once you have brought all cells above 0°C, apply a gentle charge (i.e. low amps). The BMS may see the voltage and start up. If that doesn't work, then a gentle charge directly to the battery would be a next step.

 

[Messier11]

This is weird. LiFePO4 electrolyte does not contain water, and needs very low temperatures to actually freeze. I had my cells frozen at least once (-20C) but never had them drop in voltage the way you're seeing. I even have a video where I tried charging a -17C frozen cell. That cell was outside for several days before doing that test.

The JK will also power itself off when the cell voltages drop very low to prevent over-discharge.

This is what I have been thinking, could I have something stealing current even if the JK BMS shut down? But the only possible circuits that can be created must go through the balancing cables, otherwise it’s of course not possible…

Should I try starting the BMS with 12v if the 9v isn’t enough?

 

[Messier11]

That would not be my first step. Leave the BMS connected. Once you have brought all cells above 0°C, apply a gentle charge (i.e. low amps). The BMS may see the voltage and start up. If that doesn't work, then a gentle charge directly to the battery would be a next step.

I am not 100%, but they shouldn’t be under 0 Celsius now, they have been in a plus 0 zero room for 24 hours, and now it’s like 25 degrees in that room. Will be interesting to see what happens.

 

[upnorthandpersonal]

Should I try starting the BMS with 12v if the 9v isn’t enough?

No, don't - it just needs a 5V delta - 9V is plenty!

but they shouldn’t be under 0 Celsius now, they have been in a plus 0 zero room for 24 hours, and now it’s like 25 degrees in that room.

Give them time to warm up. It's a pretty big thermal mass.

 

[HRTKD]

Give them time to warm up. It's a pretty big thermal mass.

Agreed. Passively warming the cells could take a long time. My actively warmed cells take a good 45 minutes to come up from ~30°F to 45°F.

The closer you are to 0°C, the slower you should charge (low amps). The higher the temperature, the faster you can charge. There's a graph around here somewhere that shows that the closer you get to 0°C the lower the amps should be. I don't recall if it's a linear graph or a curve.

 

[timselectric]

After the BMS shuts down discharging. The BMS itself is still drawing from the battery. Over an extended period of time it could have drained the battery very very low. And then shut itself down from lack of enough voltage to run. I would charge directly to the battery as a last resort. But at some point you will have to take the risk. It would be better if you had a way to bring each cell up slowly, individually. If you have the means to do so. Just to get each one above 2.5v .
Another option is if you happen to have a 36v battery charger. You could charge the whole battery to get the cells above 2.5v . This will hopefully revive the BMS and allow regular charging to take place. (Slowly at first, of course)

 

[Messier11]

After the BMS shuts down discharging. The BMS itself is still drawing from the battery. Over an extended period of time it could have drained the battery very very low. And then shut itself down from lack of enough voltage to run. I would charge directly to the battery as a last resort. But at some point you will have to take the risk. It would be better if you had a way to bring each cell up slowly, individually. If you have the means to do so. Just to get each one above 2.5v .
Another option is if you happen to have a 36v battery charger. You could charge the whole battery to get the cells above 2.5v . This will hopefully revive the BMS and allow regular charging to take place. (Slowly at first, of course)

Yeah, problem is that besides the gasoline generator and a 12v car battery system I have no power out here.

I will see what happen when the temperature gets up, but I don’t expect any massive change. I am going back to the civilization on Saturday and won’t be back until late June when I’ll be here for two months. I am thinking of getting another 16 cells and a proper charger, then I could create a new battery and charge these cells up carefully and use them as a back-up battery.

Who is the go to vendor these days? I bought from Jenny Wu the last time and was happy.

 

[HRTKD]

It seems you have a bit of a Catch 22 here. The Multiplus isn't on because your battery/BMS is dead. To charge the battery you need the Multiplus on. If you fire up the generator and the Multiplus comes online, it will use the existing settings to charge the battery which may be more amps than you want.

If you can get the Multiplus to come online with the generator, set the Multiplus switch to invert only so that it doesn't charge. Then change the charge settings to a lower amperage and you might get the battery charged.

A BMS that has turned off discharge due to low voltage should draw very little power. The Overkill Solar BMS has been documented as being able to run for months. I know that's the the BMS in question here, but...

 

[yabert]

But the voltage is of course extremely low, just 0.6-1v per cell…

The good new is you will be able to save your cells after charging them slowly (low amps, let say less than 28A for your 280Ah cells or 0.1C).
I have recover LFP cells drop as low than 0.1V with success many years ago.
In your case, to save your battery the simpler way is to have power (generator?) and and adjustable 48V power supply. Remove BMS, simply connect the power supply to the battery and monitor cells voltage during charge. When most cells are around 3V or more, reconnect the BMS.

 

[Messier11]

It seems you have a bit of a Catch 22 here. The Multiplus isn't on because your battery/BMS is dead. To charge the battery you need the Multiplus on. If you fire up the generator and the Multiplus comes online, it will use the existing settings to charge the battery which may be more amps than you want.

If you can get the Multiplus to come online with the generator, set the Multiplus switch to invert only so that it doesn't charge. Then change the charge settings to a lower amperage and you might get the battery charged.

A BMS that has turned off discharge due to low voltage should draw very little power. The Overkill Solar BMS has been documented as being able to run for months. I know that's the the BMS in question here, but...

The funny thing is, I can actually fire up the MultiPlus with my 12v system. A RPI runs on the 12v system and through a USB cable is connected to the MultiPlus with what is it called, V.Bus at the other end? When I turned on the 12v system the MultiPlus started…

I would need to by-pass the BMS right?

Is it very bad to charge it with too much current instantly? I am not sure I can access the charge settings without a laptop…