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Float issues

Sanjuan34

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Joined
Nov 20, 2021
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I just installed a Chins 400ah LiFePO4 on my boat. I have a Xantrex 2000XC inverter/charger.
Chins recommends absorption 14.6 and float 13.8v.
I have been playing with settings and researching for a few days now.
My issue is this:
When the charger gets to about 14.1v, it's builds to 14.2 quickly and then shoots to 14.5-15v instantly. The BMS cuts off and it drops back to 14.1. It keeps repeating this cycle endlessly. I watch the amps build and then go to zero.
Maybe the charger builds the amps to quickly?
Any thoughts?
 
I recommend a charge of 13.8 and a float of 13.4. That is a charge of 3.45 volts per cell, which will get you to abov 90%. See if this keeps the battery from spiking to 15.

14.6 charges to 3.65 per cell and if any cell reaches 3.65 before the others the single cell max voltage would cut the BMS off. Seems like this is happening to you.

For my lithium batteries, I charge to 3.45 per cell. YOu are not losing that much capacity.
 
When the charger gets to about 14.1v, it's builds to 14.2 quickly and then shoots to 14.5-15v instantly.
That is normal.
@Off-Grid-Garage made this nice graph which shows the charge curve for an LFP battery.
The BMS cuts off and it drops back to 14.1.
You don't want the BMS tripping on a high cell during normal operation.
I agree with @chrisski, suggest you lower the charge voltage and the float voltage.
It keeps repeating this cycle endlessly. I watch the amps build and then go to zero.
Maybe the charger builds the amps to quickly?
The battery and charger are doing what they are supposed to do with the charge profile specified.
 
I recommend a charge of 13.8 and a float of 13.4. That is a charge of 3.45 volts per cell, which will get you to abov 90%. See if this keeps the battery from spiking to 15.

14.6 charges to 3.65 per cell and if any cell reaches 3.65 before the others the single cell max voltage would cut the BMS off. Seems like this is happening to you.

For my lithium batteries, I charge to 3.45 per cell. YOu are not losing that much capacity.
Good advice.
Seems I might have been a little impatient. I kept watching the voltage, as time passed the voltage that it returned too when BMS cut out climbed, 14.11 14.12 14.13.......
After enough time it equalized and then held a constant voltage and completed absorption.
My guess is the cells needed balancing.
Anyway, my future plan it to operate at 80% and bring to 100% only when I reconnect to shore power.
 
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