I just can't understand the new battery pack I purchased from bigbattery. Its a 2.4kw a123 (8series5p) battery pack like Wiil tested. I've charged and discharged it several times. It was charged to 28.8v and it is now discharging. The current voltage reading is 25.6v which by the curve it's at 17% yet i've only used 41.1 ah. Any ideas on what's going on.
I just can't understand the new battery pack I purchased from bigbattery. Its a 2.4kw a123 (8series5p) battery pack like Wiil tested. I've charged
- Thread starter CDell
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I have the Wolf battery from Bigbattery.com. my battery will go down to 23.0 becuz that's what I had set on the MPP LV2424. Bigbattery.com said the Wolf range is from 20.0 to 28.8 so 23.0 works for me. My problem is it never charges higher than 26.6.
Ok, it is a LiFePO4 pack, full is 29.2V empty is 20V
So, a full test would be from full to empty.
Most won’t charge beyond 28.8 or discharge below 24 to ge longer life cycles out of the packs.
According to bigbattery specs the bms over voltage is set at 28.8 which is what I charge it to. So your saying the batteries are never charged to the 100 ah level since I only go to 28.8v? Low voltage shutoff is at 20v. With this in ind how many ah should I expect to see?
Bob B
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Oh ... sorry, didn't look close ... I thought you were the OP.
I'd like to be careful that we don't sidetrack the thread for the OP ... maybe you could start another thread with your questions?
OK, Lets say the batteries are fully charged. It almost immediately drops to 26.6v. It slowly discharges at about 2.4 amps in a day because of vampire load. It reaches 25.6 volts even though I've only used 41 ah. If I look at the curve the batteries are at 17% which indicates I've used 80 ah of power but I haven't. What am I missing. I would think they're fully charged because of the 26.6v reading. Do you think I will show another 60ah if I go to the cutoff of 20v?
Bob B
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You are not going to get an accurate estimate of the SOC based on voltage at the mid range of charge .... the only way to know for sure is to do a full charge and then discharge while tracking amps.
I take it you are going by the voltage displayed on the battery. You need to use a DMM to check the voltage. It's very possible the voltage displayed on the battery could be a bit low and the voltage on a DMM will display a higher voltage or visa versa. The voltage indicator on the battery is measuring in tenths. That alone is not going to be accurate enough because of the flat part of the curve and the voltage displayed on the battery might not be the most accurate.
From what you have said the battery is fully charged. 28.8 volts is equal to 3.60 volts per cell. Consider that fully charged.
You need to measure the ah's used to capacity test your battery from 28.8 volts down to 20 volts. And as Bob said, voltage is not a good indicator of SOC.
Terrapin
New Member
This worked very well, and I confirmed it's test results with a Hall Effect monitor. The results shown were spot on. I did hear from others after my test that they can burn out if used at full discharge for long terms. But I got lucky I guess. I let it run full bore for 28 hours to test my first 4S 280ah build. Search Will's Channel on YT for more info. They are pretty cool units.
