In article ,
denton wrote:

Hi all...
I have purchased a Extreme Cycle Duty Orbital 12-volt Sealed Battery as a
replacement for an aging standard deep cycle lead acid battery that floats
across the output of my 35 amp homebrew power supply with blocking diode (50
amp jobbie on heat sink).
I typically use 13.8 vdc on the outboard of the blocking diode to charge the
old deep cycle battery to keep it up to snuff, but am wonding if I should
change the charging voltage for the new battery.
Comments anyone?? Thanks in advance...

This appears to be an AGM (Absorbed-electrolye Glass Mat) battery, one
of the newer generation of deep-cycle lead/acid batteries.

I've done a bunch of reading on AGMs, and I've heard of some people
who've done months of reading and study... and the conclusion seems to
be that there's a lot of disagreement about the ideal charging regime
for an AGM battery.

Some people feel that using a standard fast-charger is fine, with
fast-charge voltages up to 14.5 or so. Other people feel that this is
a Really Bad Idea, and that AGM batteries should not be charged at
above 14.0 volts. Float voltages of 13.4 - 13.8 seem to be what's
usually recommended.

One of the nice things about AGM batteries is that they'll accept a
lot of current (recharging quickly) even when fed a relatively low
recharge voltage. Given the controversy about the maximum safe
recharge voltage, and given how quickly they recharge even at
relatively low voltages, I prefer to be conservative and keep the
voltage under 14 volts.

It sounds to me as if you've got a workable setup for this battery
right now. You'd be floating it at around 13.8, and recharging it at
(13.8 minus whatever voltage drop occurs).

Exide seems to rate their AGM batteries for a 25-ampere recharge rate.
My hunch (which you might want to verify with an ammeter) is that the
battery you have won't try to draw more than that from a 13.8-volt
supply, and that you'll be within a safe recharging regime.

You *might* want to consider trimming down the output voltage of your
supply to 13.6 or so, which would cause a trivial decrease in transmit
power but might give you some safety margin to keep the battery from
starting to electrolyze during float charging.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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