On 02/14/2011 05:58 PM, Percival P. Cassidy wrote:
On 02/13/11 03:36 pm, philo wrote:

I'm looking for charger/maintainer -- either an off-the-shelf unit
or a
schematic so I can build my own -- suitable for a flooded deep-cycle
battery, either a pair of 6V "golf cart" batteries in series or a
Group
31.

snip

You do not need anything too fancy...
to "float" the batteries all you need to do is keep them at approx 2.25
volts / cell...so it's possible that your 13.8 v charger will do the
job...

You can test it by checking the total voltage after a 24 hour period...

ideally, a 12v battery should float at about 13.5 volts.

If the float voltage is a little higher or lower it won't be too
critical...but make sure it's well below the 14.2 v gassing point.

I've been in the lead-acid battery business for 36 years...
so have quite a bit of long term empirical data

The West Mountain Radio people told me that their "Super PwrGate"'s
13.5V float setting voltage (not adjustable) might be too high for a
flooded deep-cycle battery. Their user manual refers users to

www.windsun.com/batteries/battery_FAQ.htm

which recommends per-cell float voltages flooded deep-cycle batteries
that translate to 13.02V to 13.20V for a 6-cell battery.

"Perce"



That link did not work...but really, the exact float voltage is not that
critical...the free gassing point of a lead acid battery is 2.37 volts
/cell or 14.2 v for a 6 cell battery...

to float the battery you must stay reasonably below the gassing point or
there will be considerable water consumption...hydrogen and oxygen
production and heating.


OTOH: the nominal open circuit voltage of a fully charged lead acid
battery is 2.12 volts / cell or 12.7v for a 6 cell battery....

so anywhere from 13.1 - 13.8 volts would work for "floating".

Back in the old days when I started in the industry,
the settings on the chargers could drift a bit...so we'd try to keep
everything in the middle of the accepted range or about 13.5 volts


If the battery is going to be on float for an extended period of time...
though the water consumption is minimal...it still needs to be checked
periodically and topped off as needed (never fill a battery up into the
"neck" area...the water level should be a bit below it)

Finally...a few times a year the battery should be equalize charged to
avoid the possibility of sulfation. Usually 6 hours will suffice.
The battery should be brought up to 14.2 volts and allowed to rise to
approx 15 volts depending on the type of charger