BigBattery 170Ah PowerBlock low temp cutoff does something for charging, but not sure at what temp or what happens with discharging

Ulmo

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Test results video at end of post with description.

Regarding Will Prowse's review of these nice batteries:

Then Will commented on that video with this update:

"Correction to this video: Unfortunately, I was correct about questioning the low temp charging protection on the powerblock 170Ah. The cells in the video CANNOT charge down to -20C. I have the data sheet and it clearly states that these cells can only be charged down to 0C. I was told by the head engineer that these cells in particular can be charged down to -20C. I figured it would be a fun test video to freeze the pack and charge it at high rates to see what would happen, but now we know. They would be destroyed. Lithium plating would cause dendrite formation that would cause a short through the separator of the cell. Which would ruin the pack. Bigbattery is offering a refund to anyone not satisfied with this. They were on backorder with this item, so they did not ship them out yet. I would go with the SOK battery. Video table of contents: 3:58 Setup for capacity test for SOK battery 4:41 Capacity test results for 206Ah SOK battery 5:09 Setup for capacity test for Power Block 6:51 Capacity test results for 170Ah PowerBlock Battery Teardowns: SOK Battery: 7:12 Powerblock: 10:23 SOK VS Powerblock Conclusion: 16:24 Verus Budget DIY: 17:02"

I just received one, so responded like this: Regarding the battery at https://bigbattery.com/product/12v-lifepo4-power-block/?ref=8

"I received my BigBattery 170Ah PowerBlock today. In email they claimed they would lower the cutoff to -4ºC, and I said I'd prefer 0ºC cutoff but just to send it to me since I'll be installing my own low temp cutoff anyway. They emailed back saying okay, and that they'll set my low temp cutoff to 0ºC. Now that it's here, I got curious, and I just tested the low temperature cutoff by holding the thermometer in ice, but it never shut off. Are you using salt icecubes? Where can I get liquid nitrogen or dry ice? So many questions. If I can figure out where to buy that stuff today, I'll try again, while holding my temperature infrared gun on it. Update: no place I can find in my county sells dry ice, but I checked on the two way radio, and someone knows of a place in the next county that does, so I'm off to get some there. UPDATE! It is doing low-temp cutoff with dry ice for charging, but not discharging. I have a video here:"


I had my power supply on, so I think what was happening was when the volts of the volt meter at the battery went to 14.0, that was raw power supply voltage with no drop due to the energy being used to charge the batteries, and when the volts at the volt meter at the battery went to 13.something, that was because of the voltage drop due to charging up the batteries.

(For the curious, yes, I had to drive to the next county to buy dry ice. They barely had it, the container being moved during remodel, and the store staff wasn't even sure they were going to keep the insulated box. I recommended they keep it.)

So, my conclusions:

1. I do not know at what temperature charging cuts off. I want it to cut off at 0ºC, but since the dry ice is below -20ºC (minus twenty degrees centigrade) -- I measured the dry ice at around -24ºC with my infrared gun), it may be that the low temp charge cutoff is still too low. I don't know if the cutoff is at -20ºC, -4ºC, or 0ºC, or my preference, +1ºC.
2. I would like to know what the low temp discharge cutoff is. From my testing, the dry ice does not turn off discharge. It seems to me that discharge may or may not experience the same issues to the LiFePO4 chemistry as charge, but I'm not sure.

Obviously charging at or below freezing is very very very bad. If the low temp charge cutoff cuts off in such a manner it never charges while freezing, then that would be good. I do not know.
 
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Ulmo

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Update:

I turned off the power supply, and only had a fan and a few USB devices running off the battery. This is a discharge test.

It showed 13.2 volts.

I put the temp sensor in the dry ice.

It dropped to 12.7 volts. The devices (fan, USB devices) all continued running.

I took the temp sensor out of the dry ice.

The volts raised back to 13.2.

There is some sort of discharge change with the temp sensor, but I'm not sure what it is. Is it a removal of charging circuitry? Is it attempting to shut off the battery, but it doesn't do it all the way?

Note: I have a capacitor bank attached to the fan and USB supply that's connected to the 12V bus I'm powering. I'm not sure what effect that might have. The capacitors run out pretty quickly, so I think would not do much, but I'm not sure.

I could run the test without the capacitors plugged in.
 

Ulmo

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New discharge test with capacitors unplugged:

13.2 volts in use room temp.
12.7 volts in use when temp sensor is placed in dry ice. Devices still running fine.

Returns back to 13.2 volts when temp sensor removed from dry ice. Devices never shut down.
 

Ulmo

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I don't have am amp meter. Could it be that it was still charging a little, or not at all? What kind of hall effect sensor works on circuits like this? Does Ideal sell one or something?
 

Will Prowse

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The latest model has a proper temp sensor threshold. They messed up when programming the BMS. The latest model actually works.

Your pack voltage should drop to practically zero during a low temp charging disconnect.
 
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