Question on float voltage

techntrek

System recap - (16) 12 volt FLA in series, 115 amps 20-hour rating, attached to a double-conversion UPS. Emergency duty, carries most 120 volt loads until my big genset starts up, and for long outages it was the primary power source up to 18 hours per day (rare). Batts are about 3 1/2 years old.

My old UPS floated at 226 volts, or about 14.1 volts per battery. High but I didn't have much choice since it wasn't adjustable. Watering was critical before the 6-month point, I was pushing my luck if I went beyond that. The upside was I had a few more amps available during a long outage. Downside other than heavy water useage is it probably took some life off of the batts.

New UPS is fully adjustable. I've already moved the float point from 13.6 to 13.8. I'm starting to rethink that since some sources say long-term/emergency float should be 13-13.2. Now that I have the Prius available as a power source for the UPS my strategy has changed - the batts are only needed until genset startup, or for shorter outages if I don't need the big genset. For long-term outages the Prius will be in use up to 20 hours per day.

So now the goal for the batts isn't more amps available, but long life. What is your recommendation for the float voltage? I assume I should go down to 13.2... (@ room temperature) No manufacturer specs available, if someone was going to ask.

niel

Re: Question on float voltage

techntrek,
this is really determined by the battery manufacturer as to the best float voltage. it is a minor charge meant to offset self discharge. having it a bit higher probably won't hurt it, but will create more maintenance. it won't be more charged than the normal float setting as when a battery is fully charged it just doesn't accept more and will dissipate the excess as heat.

techntrek

Re: Question on float voltage

Well, I've now read a dozen or so articles and FAQs which quote numbers from 13.0 to 13.8. I might bump it back down a notch or two.

niel

Re: Question on float voltage

i don't think it would be below 13.2v and my feel is it is most likely around 13.4v to 13.8v, but as i said it's depending on who makes them.