T-Pain Is On A Boat: Re: [Electric Boats] AGM Battery: To Float Or Not To Float

Thursday, December 31, 2009

Re: [Electric Boats] AGM Battery: To Float Or Not To Float

"For battery LONGEVITY, is it preferable to have the battery absorb every last bit of energy and sit there fully charged with an external float charger (set to, e.g., 13.2v at 70degF), or is simply turning off everything when float current gets below a certain point preferable?"

Joe:

There are no bad or old questions here just new opportunities to learn something. New people are joining the list with new ideas and expertise all the time. Your question is something I have been wondering about too. I've charged my 48 volt 200 amp AGM battery bank up to full charge and then shutdown the charger because my boatyard will not allow any AC lines going to boats over the winter. So I am relying on the wind generator and solar panel to keep things charged up until I next check on the boat and plug in the AC charger. I have been wondering if this is the best way to store and charge my AGM's over the winter too. So far the batteries have been holding up using this system but, I'm not sure if it is the best way to store the AGM batteries over the winter. Since I'd rather not think about taking them off the boat every year.

Capt. Mike

http://biankablog.blogspot.com

--- On Thu, 12/31/09, joemultihuller <siudzinski@telis.org> wrote:

From: joemultihuller <siudzinski@telis.org>
Subject: [Electric Boats] AGM Battery: To Float Or Not To Float
To: electricboats@yahoogroups.com
Date: Thursday, December 31, 2009, 5:53 PM

BACKGROUND

I am running a string of Optima Yellow Tops, each one with its own dedicated isolated charger. My present daily non-marine use typically discharges the bank less than 30% of full capacity (i.e., I rarely go below 70% of full charge), with charging immediately after use. I have no parasitic loads after I turn everything off, and these batteries can maintain their fully-charged state for months.

Some chargers, e.g., West Marine's programmable 30A unit, consider charging complete when the battery draws less than about 0.85A at their float voltage of 13.4v (65degF), at which point the charger turns off. The charger then cycles on for a few seconds at lengthy intervals (minutes to hours), and then shuts back off when that lower current limit is again reached.

Other chargers simply maintain a constant float voltage (13.2v - 13.4v at 70degF), and the battery itself determines how much current it wants - over a day or two, the current draw decreases until it finally stabilizes in the low milliamp range for a healthy battery.

Contrasting these two techniques simply tells me that the former charges the battery to maybe 98% whereas the latter stuffs that additional 2% of energy into the battery. The difference is inconsequential to me as I never approach a full drawdown of the batteries.

The QUESTION on the table:

For battery LONGEVITY, is it preferable to have the battery absorb every last bit of energy and sit there fully charged with an external float charger (set to, e.g., 13.2v at 70degF), or is simply turning off everything when float current gets below a certain point preferable?

My reason for asking is that I have a whole bunch of different chargers and can program just about any scenario (including 'desulphation' pulsing), and am looking to optimize my final installation which I plan to migrate to the boat.

Thanks in advance for your advice, and sorry to belabor what is probably an old topic but one which I could not find an answer to.

JoeS.