A friend of mine and I designed a very simple circuit to modify the
Astron 20A Power supplies to do this job. Obviously this could be done on
any power supply but the Astron 20A is common and inexpensive and they leave
enough room to put this all inside easily. The first thing you will need is
an A.C. operated relay. Radio shack has one that we chose simply because
they are cheap, $8.00 and the contacts are rated high enough to handle the
20 Amps. It is RS P/N 275-0217. The contacts are rated for 10 Amps but
since this is a double throw type, both "throws" can be tied together. I
drilled another hole in the rear of the Astron to mount another binding post
for the battery connection. The relay coil is connected directly to AC
power coming in, the contacts are wired to the 13.8 VDC output wire so that
when the relay is energized, the power is routed though the relay from the
power supply to the output binding post, the output binding post being wired
to the "throws" of the relay. When AC power is lost the relay deenergizes
and these contacts of the relay are wired to the backup battery. That takes
care of isolating the battery from the power supply, the only thing left is
a simple charging circuit. To accomplish this, an 8 Ohm, 25 Watt resistor
from the relay "throws" to the battery contacts was added. This only allows
for trickle charging, but as the battery voltage approaches the supply
voltage, the current "self regulates" to almost nothing. Also, since AC
power is present 99.9% of the time trickle charging in this way is not a
problem. This does the job nicely.
We have done this mod to 2 different repeater systems with excellent
results, and no failures of the backup system. Not as easy as buying a
power supply ready for the task, but still easy to do and I would bet,
usually less expensive.
Hope that helps
73, Wade- KR7K
----- Original Message -----
From: "Al Wolfe" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, January 21, 2005 10:16 PM
Subject: [Repeater-Builder] Re: Powering the Repeater With Marine Batteries
>
> Mathew,
> There has been some good advice on here about different method to
> accomplish what you want to do. I have used both the relay idea and the
> diode isolator with success. As others have mentioned, using a "smart
> charger" is your best insurance for reasonable battery life.
>
> FWIW, the Feb. QST (pg 78) reviews a "PWRgate PG40" by West Mountain
> Radio. Basically it contains two 80 amp Schottky diodes on a heat sink and
> three Anderson Powerpole connectors. The diodes drop about 0.4 volts under
> load. It's designed for forty amps. It sends whichever input voltage is
> higher to the output and will isolate your power supply from the battery.
> That is, if the AC fails to the power suppy, the battery won't back up
into
> the power supply. It apparently also has a diode and resistor that can be
> used to charge the battery from the power supply at a rate of up to one
amp.
> (Would take days to charge your marine batteries!) I think it may be a
bit
> over priced at $69.95 but it or something like it may be an answer to your
> situation.
>
> 73,
> Al K9SI
>
>
>
> Date: Fri, 21 Jan 2005 17:11:37 -0000
> From: "w9mwq" <[EMAIL PROTECTED]>
> Subject: Powering the Repeater With Marine Batteries
>
>
> Last night my power supply took a dump! Good thing for backups.
> Anyways, what I am wanting to do is put 3 marine batteries together
> to run the power for the repeater with a charger to charge the
> batteries. If I use a 12 Volt Car charger, do I risk the chance of
> noise, or would the batteries filter that. What would be a good
> source to charge these batteries? The power supply that will be
> taking the place of the worthless Pyramid supply will be an Astron
> 52 Amp Rack Mount Supply. I have heard in the past that batteries
> have been charged with these power supplies, but not sure if this if
> true or not. Any ideas? Thanks.
>
> Mathew
>
>
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
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