Question regarding solar and lithium batteries.

[DaveMatthewsBand]

Just an FYI... the amount your battery charger puts out is divided equally across all of your batteries.
Even with lithium, the charge amperage is limited to 50 amps (for Battle Born as an example).
My inverter charges at 125 amps, however each of my 4 batteries is only getting 31.25 amps.
Let’s say I had 2 Battle Born lithiums, then each battery would be charged at 50 amps, because the BMS on each battery limits the charge rate.
So spending the extra money on a battery charger with a high output is only worth it if you run multiple batteries.


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[srobins]

Steve

I'm not sure what the difference could be.
I did shorten my wire runs from the converter and batteries by putting them in the passthru.
I have about 6' Red & Black 4 Awg from the converter to the DC Bus and about 2' of 2/0 Red & Black each from the batteries(including the parallel jumpers) to the DC Bus.
My BMV-712 still has to be installed, so no info on that.
Also I haven't run the batteries down much as of yet.

I am beginning to believe the issue I am seeing with lower charge rates in a result of the longer wire run from the converter to the batteries. Although the converter is putting out 14.6 volts (measured at the converter terminals), I am seeing about a 1 volt drop in the wiring going to the batteries during charging. Coupling this with the higher voltage of the Lithium batteries results in a smaller delta between the battery voltage and charge voltage. When my batteries were at 92 percent charge (according the the BMV-712) my charge current was 34.9 amps and the voltage was 13.52 volts. Apparently I am seeing about a 1.08 volt drop in the wiring at that current.

I believe it was TucsonJim that posted a chart of the Voltage vs. Capacity of the Lithium batteries. The chart indicates that at a 90 percent charge the lithium are at 13.3 volts. If this is accurate than I am only providing 0.22 volts over the batteries voltage to charge them. When the batteries do reach 100 percent charge, the voltage at the batteries is at 14.63 volts and zero current. At that point I believe the battery BMS has shut the charging down.

It would appear that the lithium batteries do require a voltage closes to the 14.6 volts to charge them at the 0.5C (50 amp) rate and that any voltage loss between the converter and batteries can significantly reduce the actual charge rate.

[gbkims]

When my batteries were at 92 percent charge (according the the BMV-712) my charge current was 34.9 amps and the voltage was 13.52 volts

And the charge current is dividing between the paralleled batteries, so ~17A per battery?

[srobins]

And the charge current is dividing between the paralleled batteries, so ~17A per battery?

Yes - approximately 17 amps to each of the two batteries.