LiFePo4 Battery pack max Voltage

[k-harvey]

My latest purchase of a LiFePo4 charger disappoints me as the voltage for 12v near new pack( 8 cells -4 lots of 2 in parallel )gets to only 13.7 volts where i expected it to reach 14.6 giving greater AH needed for the job. I was previously using my automatic LA car charger(naughty I'm told) & even got a slightly higher voltage.
Could this be that in purchasing the charger from Greenbike i was asked what voltage charger was needed for the 12 volt charger ( I thought they'd know) any way I said the battery packs as 12 volt are supposed to be a max. of 14.6 volt . So chargers usually have a higher voltage than the battery & in this case the charger ,charges at 14.6V.
Is this usual for a 12v pack to have this maxi-min of 13.7 Volts.??(with BMS) Did i dictate what Max.voltage the charger produced.
I'm dis appointed as the car charger seems just as good & got to a higher voltage.

 

[dogman dan]

13.7v is undercharged. 14v is fully charged, 3.5v per cell. But your bms may require 14.6v to fully balance the pack.

I suppose it's a fairly cheap charger, one with no voltage adjusting pot inside? The plastic ones rarely have it.

Re reading, your charger is set to 14.6v, and is putting that out? You may just need to leave the pack plugged into the charger for a long time after the green light turns on, to allow the bms to fully charge the pack. It's stopping to allow an overcharged cell to discharge, then the charger will go red for just a few seconds. This will happen over and over for many hours, even days.

 

[wesnewell]

There's a difference in fully charged and max charge rate, Lifepo4 is fully charged at 3.6V per cell, so 14.4V for a 12V pack. Charge rates are higher just like they are with any battery. The condition of the cells will determine what voltage they actually hold after the charger is removed. 3.5V per cell and above is considered good.

 

[Wishes]

There's a difference in fully charged and max charge rate, Lifepo4 is fully charged at 3.6V per cell, so 14.4V for a 12V pack. Charge rates are higher just like they are with any battery. The condition of the cells will determine what voltage they actually hold after the charger is removed. 3.5V per cell and above is considered good.

From experience, lifepo4 does not hold its maximum voltage of 3.65 after fully charged for very long. Once you take it off the charger, it will drop to 3.4 to 3.5 volts just by sitting there. And not long after you start discharging it, it will settle at its nominal voltage of 3.3.

So 3.4 per cell, 13.6 for 4 cells, I'd say your 13.7 is not to low if the pack has rested a bit between the charge and when you take the measurement.

Wishes

 

[dogman dan]

Yes, even new lifepo4 cells may not hold the surface charge, that above 3.5v per cell. Really good new cells will hold above 3.65v per cell for a time, but that .15v vanishes in an instant when any discharge is done. There close to zero capacity above 3.5v.

Then from 3.5v down, there is a very steep initial voltage drop before hitting the flat part of the discharge curve graph. That's in the 3.3v ballpark.

Lastly, it's entirely possible that the pack is connected to a bms with it's discharge circuits set to a voltage below 3.5v. It should not be so, but it could be.


What I think is happening, is he's not leaving it on the charger long enough to let the bms fully balance a badly unbalanced pack.