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Cold Temp LiFePO4 Charging Test

Will Prowse

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What do you guys think?

I am guessing that the pack needs heat to be pumped out of the cell while charging. Or the rate needs to be higher. Pretty interesting results.

I was pretty quick to start charging after I took the battery out of the freezer too. It was less than a minute.

How would you modify this test?
 
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Hi Will, cycle inside the freezer. Try various charge regimes to simulate a solar start morning.......
 
I've been looking forward to this test with interest because I've been considering how to design a solar shed for Midwest winters. Lag in cooling of the thermal mass of the batteries along with the speed of heating during low temperature charging are important for determining how cold I can allow the shed to get overnight.

One suggestion I would have is to get an electronic temperature probe inserted inside the battery between the cells. You're kind of flying blind in these test as to how the cell temperatures are changing throughout the cooling and charging cycles. Since degradation at temperature is what you're testing for, this is worth throwing a few bucks at to be able to verify the internal test conditions. I had to buy a couple of temperature loggers for work, and they're pretty inexpensive (less than 12 grand anyway :rolleyes:)

I appreciate the time and effort invested so far.
 
Nice work, and surprising results. Finding the true internal temperature of dense objects like these larger cells is problematic, and that density may protect them from reaching ambient temp as soon as we think they would.

My layman's example is that when I "cold-crash" my fermented home-brew beer in my already below freezing garage (20 F) the 5 gallons of liquid drops from 65 F to 48 F in 24 hours. It takes another 24 hours to drop another ten degrees to ~38 F which coincides with what I've read about how liquids need low temperatures for a longer time to reach ambient the lower that ambient temp is. So perhaps removing the cells and freezing them separately for a longer period (a week?), then testing them would give results more like what we've read about.

Also, order the cycling machine, dammit! We need that data!
 
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What do you guys think?

I am guessing that the pack needs heat to be pumped out of the cell while charging. Or the rate needs to be higher. Pretty interesting results.

I was pretty quick to start charging after I took the battery out of the freezer too. It was less than a minute.

How would you modify this test?
Video is pulled? Private linkey...
 

What do you guys think?

I am guessing that the pack needs heat to be pumped out of the cell while charging. Or the rate needs to be higher. Pretty interesting results.

I was pretty quick to start charging after I took the battery out of the freezer too. It was less than a minute.

How would you modify this test?
Why won't the video load? Says its "private"
 
Cycling in a -20C freezer right now. Should be interesting
I am curious if the amps or such go down when cold.
My mobility scooter goes a lot slower when it gets cold.
About 5 Celsius or lower it gets affected.
So I am very interested in the outcome here.
 
So the question in my mind is how much of the loss from 176 Ah to 155 Ah is just the reduced capacity of using the batteries at a low temperature and how much is permanent degradation from the damaging effects of charging at low temperature.

This will be interesting.
 
So the question in my mind is how much of the loss from 176 Ah to 155 Ah is just the reduced capacity of using the batteries at a low temperature and how much is permanent degradation from the damaging effects of charging at low temperature.

This will be interesting.
That is on my mind as well.
As I use mine when outside on my mobility scooter.
 
So the question in my mind is how much of the loss from 176 Ah to 155 Ah is just the reduced capacity of using the batteries at a low temperature and how much is permanent degradation from the damaging effects of charging at low temperature.

This will be interesting.
Yes exactly. I need temp probe and capacity test at room temperature to know. Will repeat test with new cells.
 
Best price for loop tester was 12k$ so I'm doing it manually. I have inverter and charger in parallel so it takes seconds to switch over, but I need something better
 
Can I see that video? I would like to know the genesis of this thread, since I don't understand the discussion without the context. I cannot view the video. I posted another thread about something that might be similar:

 
Ok, so I did a first test charging at -17C. I had the battery hooked up (after it being outside for a few hours) for about an hour, but could only get 2 to 3A of current into the battery. In other words, the internal resistance got so high it was impossible to get power into the battery. After about an hour, I let the battery warm up for a few hours and then charged it fully at 0.5C. I did a 0.2C capacity test an hour after the battery was full and managed full capacity. My guess is that the time I kept the battery on the charger combined with the low power I was able to put in at this temperature prevented any significant damage.

My next step would be to leave the charger on the battery for a longer period of time, however the power supply does not like -17C either and starts acting up. Which brings up an important point: even if you could charge at -17C, would you trust the charge controller, BMS, etc. at those temperatures?
 
Keep the charger inside, and run slightly longer wires to the battery outside?
 
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