Re: Firefly Battery Update.

Bill Kinney


I agree that the inability to fit a full complement of batteries would be a major problem.  But I am curious why you consider a difference of 0.2 volts a major issue? And it seems you consider 24 Volts an absolute minimum acceptable?  Everything onboard still works perfectly well down to voltages of 23 or so.

The voltage curve you present from Firefly is NOT a zero load curve, but is voltage at the C10 discharge rate, or pulling 50 Amps out of a 480 Amp hour battery bank.  That's a pretty extreme load, and is the one we see only during our deep discharges when we duplicate that curve pretty much exactly. 

We also never discharge below about 60% SOC in normal use.  (About 190 Amps-hrs discharged).  If you need more than that, and on a 54 you likely do, I'd certainly agree that 8 Firefly are not the right choice.

This is our SOC, voltage and current draw graphs from a couple days at anchor. Some sunny, some not :)  Lowest seen voltage is 24.4v on the early morning of the 20th at a SOC of 57% while pulling about 5 Amps. Our generator autostarts at 0630 if the SOC is below 70%, runs to about 93% SOC, and then we let the solar panels take over.

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