One source of (almost) free diode pairs is any alternator shop. The
common configuration of diodes in an alternator has three on a
plate, and two plates. One plate is common anode, the other plate
is common cathode.
The common failure mode is that one diode opens or shorts and the
technician replaces the entire plate. This means that two perfectly
20 to 75 amp premounted diodes (depending on the alternator
current rating) goes in the trash. Some shops press out the
good diodes and reuse them, many don't.
At one site I've seen an alternator diode plate with two diodes (it was
obvious that the bad diode was on the end that was hacksawed off)
mounted to an insulator block and that on a rack panel.
Mike WA6ILQ
At 09:25 AM 01/09/07, you wrote:
I have to agree with Dave. Using the proper charger or power supply
for keeping the batts up. I have my batteries housed in a stainless
steel enclosure that is anchored into concrete outside my ham shack.
I learned the hard way about using the proper charger... I just
tapped into my repeaters 25amp power supply to keep the batteries
charged till I could make a charging circuit ... ahhhh, big mistake.
That charging circuit - oops, I forgot... about a month of
operation, I was working around the tower and smelled what smelled
like battery acid. Sure enough, I cooked both flooded lead acid
batteries and they were fuming acid vapor. Lucky the box is a
comercial built ss box.
Now, after that incident, I have been using a marine (boat) "smart
charger" which automatically determines wether to charge or float.
Since battery chargers are, ummm, quite noisy and not all that nice
on batteries due to most of them only using a half wave recifier (
AC is not nice on batteries ). I added a 25A bridge rectifier and
added extra filtering which is just a big Motorola mobile power
filter block from the Micor dayz. It is also isolated using some BIG
diodes - like Dave's, the threaded case type diodes which is bolted
to a heatsink.
The system is running well in this configuration. If using flooded
type batteries, do a monthly check on acid levels ! I recomend AGM
batteries ( Absorbed Glass Mat ) or if that is a little pricy, get
marine deep cycle batteries - do not use automotive batteries unless
you just absolutely half to.
Dave / N9NLU
<http://www.kmcg.org>www.kmcg.org
On 1/9/07, ve7ltd <<mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED]> wrote:
I have had good luck using a pair of diodes to isolate a power supply
from a charging circuit. I essentially have a Statpower 10amp battery
charger (specifically designed for the flooded cells I am using). The
batteries float on the charger voltage when the AC power is available.
The battery positive lead then feeds through a diode and joins
the "positive power bus" of my repeaters. Using a proper charger is the
most important part so you dont boil off the electrolyte in your
batteries.
The positive power bus is fed from a large GE power supply. The
positive lead from the power supply feeds through a diode to feed the
power bus.
The idea of using a diodes is to keep the higher voltage of the power
supply from passing current into the batteries when AC is available,
and vice versa when AC is off.
However, if you are using a high power PA or your repeater draws more
than about 20 AMPs on TX, you have to be careful of your choices of
diode. I use large feedthrough diodes, mounted on large heatsinks, but
on lower current draw you could get away with using a smaller bridge
rectifier mounted to an unpainted metal piece in your repeater cabinet
with some heatsink compound.
Dave Cameron
VE7LTD
--- In
<mailto:Repeater-Builder%40yahoogroups.com>[email protected],
"wm5c" <[EMAIL PROTECTED]>
wrote:
>
> Hi,
>
> New member here. Thanks for allowing me to join.
> Our club has acquired some large lead-acid 12v batteries we would
like
> to use to back up our repeater in emergency situations. Does anyone
> know of a good (but simple and inexpensive [we are a very small group
> in a very small town]) circuit to accomplish this? Any input would
be
> appreciated.
>
> Danny WM5C
> Heart Of Texas Ham Operators Group (HOTHOG)
> Brady, TX
> <http://www.hothog.org/>www.hothog.org
>
