Good question! I have an Astron RS35m modified to VS-35m and a
couple of different group 27 batteries. One is a SLA and the other
is an Interstate Deep Cycle flooded. I know you aren't supposed to
parallel unlike batteries. I brought the other in out of the trailer
to charge and it's been there ever since. I had it set to 13.8 for
the radios, and after about a year, checked the Interstate and found
it about a GALLON low in the cells. I filled it back up and it seems
to work fine. That's when I modified the Supply to Variable (screw
adjust with locking shafts) and dropped it down to 13.2v. The
batteries never got warm to my knowledge though. Rather than a
rectifier (I was afraid of an exposed diode) I added a 30 ATC fuse
in line from the pass xstrs to output terminal and a heavier crowbar
circuit. If the fuse blows, the output meter drops. A larger
resistor was added to the wiper of the internal Voltage Reference
adjust to limit current back from the battery. A Silicon rectifier
has .6v drop.

Now to the Orbitals. You don't say what color. Yellow top are said
to be deep cycle. Blue top are said to be dual purpose. You might
want to check the specifications on their web page or whatever. I
hear they are more rugged and can charge harder. I don't see any
need to. It is hard for me to believe that electrolyte trapped in a
glass mat with thin plates is "better". If you are just floating, I
would think you could set to 13.8 v (with .6 drop in rectifier) and
forget it. In a car they hang from a bunch of hi draw and start and
charge at 13.8-14.4v. They say not to equalize more than 4 times a
year!

Do a Google on them and there are mixed opinions of them. I've never
bought one because they are twice as expensive as a flooded deep
cycle.

"Dave Platt" wrote in message
...
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:
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