FireFly Battery Charging Amps

[sailorboy1]

So I have had my FireFly batteries 2 years now. I have never done the recovery charge and for the most part they are being charged by solar. Even the last 4 months while I have had shore power the the batteries and solar running the DC loads as normal.

I have been thinking maybe I should run the batteries down to do the recharge to try to get the high rate recharge that old US distributor says "they know is good for the batteries". I have tried this in the past once when the batteries got into the 50% state of charge range and all they would accept is 0.28C, which is nowhere near the 0.4C the manual talks about.

This morning I was lower than normal at 78% SOC and am running the engine and that was putting in 62a. Then I turned on the 70a charger and was putting in only 82a (I know the charger can do the 70a at the current voltage). So I was supply charging that could have done at least 130a and the batteries were acceptance limited to 82a, which is 0.17C.

The question is: who has been able to recharge their FireFly batteries at a high acceptance and what was it.

[dfelsent]

I’ve certainly charged my firefly bank at .25C when at a low SOC. That was the limit of my alternator and solar together. The voltage was considerably less than the absorption voltage, somewhere around 13V if I recall correctly. This implies that higher current would have been accepted if the sources had been capable of delivering it.

[smac999]

Any good condition agm battery will accept over .4c if low and you provide it.

Try one battery at a time. The 2 chargers may have been fighting. One could have dropped to float when the 2nd came on.

What was the battery voltage with both chargers on?

[ItDepends]

I have a two year old 24 V/464 A-hr Firefly bank (8 G-31) that has been in continuous cruising service since its installation. I do a recovery charge about once a quarter. Besides a recommended procedure for maintaining the batteries, it is a good way to monitor their capacity. The batteries still deliver almost exactly the nameplate capacity from fully charged, to dead flat.

When I have shore power available I do the restoration charge, and I fill them back up with BOTH the generator running AND shore power charger. The total charge rate is 200 Amps at 25.5V when they first come back up. That's 0.43C The charger rate tapers off a bit as the voltage rises so they are at 180 A (0.39C) when the system reaches absorption voltage. That happens at this charge rate at about 75% SOC.

From there:

150 A @ 77% SOC
125 A @ 82% SOC
100 A @ 85 %SOC
80 A @ 88% SOC
50 A @ 92%SOC
25A @ 96% SOC
20A @ 97% SOC

All this is at a temperature compensated absorption voltage of 28.6V

You mention a limitation on charging Amps. When the batteries are accepting fewer Amps than you think they should are they at the full absorption voltage? If they are below absorption voltage, the issue is with your charging system, NOT the batteries.

If that is all the charge rate they will accept at full absorption voltage, then something is quite wrong with them.

[RickG]

ItDepends' numbers look reasonable. Our bank of 7 G31s show nearly 100% capacity after four years of full-time cruising. I see multiple chargers battling and our alternator goes to float if the solar or shore charger via Honda 2000 is putting out more than 20 amps.

Cheers, RickG

[sailorboy1]

I don't feel my charge sources are "battling" during the highest rate I have seen go into my batteries as the voltage is still down in upper 13s and all the charges sources of charger/alternator/solar are all trying to put out as much as they can to get to 14.4