Lifepo4 charge voltage dropping?

[Blackhat]

Hey everyone, just got my first Lifepo4 battery tonight and put it on a charger to get ready to run a capacity test. I was checking the voltage and in the process toggled the charger a few times... and the battery read 13.6 volts with the charger disconnected and DROPPED to 13.5 when the charger kicked on. Tried it several different ways because I thought I was crazy, and every time it showed higher when not charging. I reconfirmed it 15 minutes later, with 13.54 v during steady state charge, 13.65 v immediately after disconnecting the charger, then 13.55 v when the charger was restarted.

Charger was providing 16.4 amps, which is the max it can do. Battery is a Zooms 100AH. Charger is an Everstart 15 amp charger for car batteries. Measured with a multimeter directly on the studs, not touching the charging clips.

Is this known Lifepo4 behavior? What causes it? Is it related to BMS design? I would suspect the LA charger somehow, but don't see how it could be supplying current while lowering voltage. Am I wrong to think this is extremely weird?

I don't see reason to believe the battery is defective or anything, but I don't understand how the terminal voltage would drop when energy is being actively added to the system.

 

[Jred]

Many car chargers limit voltage to +/-13.5 volts. Not enough to top off Lifepo battery.

 

[Blackhat]

Many car chargers limit voltage to +/-13.5 volts. Not enough to top off Lifepo battery.

But how is it providing current?

 

[Jred]

I am assuming you are using an amp clamp meter. Having just gone thru this with a Schumacher charger - the current circulates thru the battery and is released as heat from the charger.

Volatge seeks equilibrium…once the battery reaches the chargers peak voltage, that’s it. No more increase no matter what the current is.

 

[Blackhat]

I'm using the amperage readout on the charger, not a separate clamp meter for current.

As the charger applied current, the battery voltage rose over time. So it's not like the charger hit it's max voltage and was just pretending to push current. Charging was progressing as one would expect.

What was your recent experience with the Schumacher?

 

[Jred]

I'm using the amperage readout on the charger, not a separate clamp meter for current.

As the charger applied current, the battery voltage rose over time. So it's not like the charger hit it's max voltage and was just pretending to push current. Charging was progressing as one would expect.

What was your recent experience with the Schumacher?

The Battery (Battleborn 100ah) hit 13.6 and never rose above that charge. Amp clamp would show 12-20 amps regardless.