Don,
I think the relay is more trouble than it is worth. Its primary
function is to prevent the battery from destructively discharging back
into the power supply if the crowbar circuit fires.
A better solution, in my opinion, is a heavy-duty Schottky diode on the
positive output terminal of the power supply. I use an International
Rectifier #122NQ030R Schottky diode rated at 120 amperes and 30 volts.
The diode case (anode) is bolted to a copper bar that is mounted on the
positive output terminal, and both the battery and the radio are
connected to the diode's cathode terminal. You must be sure to order
the "R" (reverse) version of the diode, so that polarity is correct.
This diode is available from Digi-Key and other suppliers for less than
$20. The point of using a Schottky diode is that the forward voltage
drop under load is very small. Nevertheless, the power supply output
voltage should be raised a bit to compensate for the diode voltage drop,
and it should be set so that the float voltage is within the range
specified by the battery manufacturer.
73, Eric Lemmon WB6FLY
Don wrote:
>
> Just Picked up a Astron RM-60 with Battery Backup Option to use on my UHF
> Micor, also a Yellow Top Deep cycle Optima Battery. The Astron calls for a
> 50 amp Relay in the B Plus line...
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