Lithium battery questions

[Rjpetr65]

Hi all

I just upgraded to (2) Lithium batteries (LiFEpo4) with built in bms. I also upgraded the converter to a Boondocker 1260 CL 60A converter charger.

I am concerned about charging current. The BMS shows that the batteries are pulling 20A constantly. Even after several hours of charging and reaching a voltage of 13.4 Volts, the bms shows 93% charged and is still pulling 20A from the charger.

I thought that the charger (and/or battery bms system) was supposed to go from CC to CV when the battery charge reaches 90%? I.e., it’s supposed to go 20A Constant Current down to a lesser current and Constant voltage.

Here are the specs of each device

Converter charger set to 14.2 volts constant voltage (not multiphase). .

12 volt deep cycle Lifepo4 batteries are brand new.

All cables as short as possible

Most cables are 4 gauge. Some are 2 gauge for short runs.

Voltage at converter output is 14.2 but across batteries is 13.4 (90% charged reading on BMS).

What am I missing? Should I keep charging to 100% and see if it switches to low current mode?

Why, after several hours of charging and reaching 93% charged at 13.4 volts, is this thing still pulling 20 amps?

[ependydad]

With lithium, you don’t need the drop-off at 90%. I’d say let it run and see what happens. The batteries’ internal BMS will self-protect.

[babock]

Originally Posted by Rjpetr65

Voltage at converter output is 14.2 but across batteries is 13.4 (90% charged reading on BMS).

You definitely need to upgrade the size of your cables between your charger and your batteries if you want to charge as efficiently as possible. My bet is there are cables in there that are smaller than you are saying. What are the size of the ground wires? That is a HUGE percent drop! I try to keep my voltage drop to less than 2%. You are over 5%.


I use a 60A PD lithium converter. It pumps out 60A until the battery is charged and it goes immediately to zero. That's going to happen once the battery gets to 14.2V depending on the brand of battery.