I posted the other message before reading all the posts. The gentleman who
said that an isolation diode is required is absolutely correct. If there
is not one built into the supply, it must be added externally. You can use
a small RV or marine battery isolater for convenience. Sears used to sell
one at a reasonable price. Meter the battery voltage directly at the battery.
Gel cells charge at high rates. The 10% limitation stated elsewhere is not
correct. My own Prevailer gel cells (two 4Ds in parallel) have lasted at
least seven years (one I got used and don't know its exact age) and
routinely accept up to a 50 amp rate (the limit of the charger) if deeply
discharged. These are on my boat.
The charging rate of a battery is dependent upon the terminal voltage (what
the charger is capable of) and the battery's internal resistance. Given a
constant terminal voltage, the charging rate will taper as the battery
becomes charged and its internal resistance rises.
To my knowledge, current limited charging is not an issue in lead acid
batteries.
So called three stage smart battery chargers put out as much current as
they are capable of until the battery's terminal voltage rises to its
specified finish value (i.e., 14.1 volts for my gel cells) and hold that
voltage until charging current drops to near zero, maintain that voltage
for a short period of time, and finally drop to the float value (i.e., 13.8
volts).
I just looked around and found http://www.trojan-battery.com. Looks like
it has lots of good information.
73, Malcolm WX4YZ
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