I have recently rebuilt a battery back-up system for my home station. I figured
I would describe the system in case anyone is thinking about doing something similar. First a couple of disclaimers:
1. I am aware that it is best practice not to store the lead-acid battery inside. However, in
my case there is no easy way to accomplish outside storage without wiring runs that are far too long. I do not have a garage,
just a carport and it is at the opposite end of the house from the radio room. I have had a battery back-up under my desk
for about 10 years without any problems, so I will continue to do it this way. If you have a convenient place like a garage
or a shed that is close to your operating position, then I woul;d certainly recommend placing the battery (or batteries) there.
2. My system uses manual control of the switch-over from line power to battery power. If you
wish to make that operation automatic, there are plenty of devices available to do that.
My system is built into a home-made enclosure built of ABS plastic panels held together with
wood corner braces. The panels are secured to wooden blocks in the four corners with deck screws and finish washers. If you
have, or can obtain a suitable commercially available enclosure, by all means go for it. I needed a relatively low, wide and
deep enclosure because two of my radios and their associated mic selectors sit on top of the power distribution module.
The wiring schematic is relatively simple. There are power-pole connectors on the back of the
enclosure for three feeds. One is the feed from the Astron power supply, another is the feed from the deep-cycle battery under
the desk. The third is the feed from the module to the power busses that feed the radios and other 12 volt (nominal) accessories
aroud the operating position.
The feed from the line power supply is fed through a 30 amp circuit breaker to one side of a
DPDT(Center OFF) switch that is also rated at 30 amps. The positive leg goes to one pole on one side of the switch, the negative
leg goes to the other pole on the same side of the switch. Because I wanted to keep the fusing on the battery very close to
the battery, I used two 30 amp automotive blade fuses (in holders) right at the battery itself and did not use a circuit breaker
in the module. Again the positive leg from the battery goes to one pole on the other side of the switch and the negative leg
goes to the other pole on the same side of the switch. The feed to the power busses is then fed from the center poles of the
switch with the positive and negative legs matching the inputs from the battery and the power supply. This is the basic system
and can be used in that form. However, I wanted to have a little more information than that.
Into the feed from the switch to the power busses I inserted a shunt to drive an ammeter readout.
I also wired a voltmeter across the positive and negative legs so that no matter which source is feeding the radios, I know
how many amps are being used and what the voltage is. The meters and shunt were purchased from a reliable on-line retailer
of such devices and have worked perfectly from day one. They are nice big 2.5" wide meters clearly marked as Amps and Volts.
The ammeter has a range up to 30 amps and the voltmeter range is 15 volts. Both are ideal for this use.
In addition to the toggle switch in the center of the front panel between the two meters, there
are the two circuit breakers mounted on either side of the toggle switch. I placed all of the controls, breakers, and readouts
on the front of the enclosure since there is obviously no way to read or use them at the back. THe back side has the three
power-pole connectors ganged together in a single block and secured to the back wall of the enclosure.
Next, because I operate frequently at night, I wanted the meters to be illuminated. I could
have used LEDs for this purpose, but I chose to use grain of wheat bulbs simply because I had them on hand. The two bulbs
were wired in parallel and fed from the feed to the power busses so that they light up whether on line power or the battery.
The current draw of the two bulbs is negligible for my purposes.
After all else was built, tested, and operational, I created small labels for each of the circuit
breakers and the switch out of cardstock printed on my PC and attached them to the front panel with double sided adhesive
Apart from it's primary function the power module also elevates the radios and their associated
mic selectors about 3 and 1/2 inches above the surface of the desk. This makes the mic selectors easier to operate and places
the radios closer to eye level.
This addition once again brings the station into full operational status with regard to emergency
communications. I figure that with the current battery, I have about 24-36 hours of operation available provided I keep my
transmissions short and only have one radio on at a time. I am planning to add solar panels in the future which will extend
the opeational time further.