From: whs70@dancer.cc.bellcore.com (sohl,william h)
Subject: Re: Computer power supplies and radios.
Organization: Bellcore, Livingston, NJ
Date: Wed, 27 Jan 93 16:41:37 GMT

In article <26JAN93.23285391@nauvax.ucc.nau.edu> cvm@nauvax.ucc.nau.edu writes:
>I have seen several posts saying that it is easy to use a computer power supply
>to power a radio.  I remember an old post talking about using the computer
>supply to charge a deep cycle battery and power the radio, but I can't find it. 
>Right now I am running my radio off a deep cycle battery and charging it with
>an automotive charger as needed.  I would like to use the power supply to
>charge the battery/power the radio.  How can I do this?
>
>I have a 150 watt power supply, a group 27 deep cycle battery and a mobile two
>meter radio (Alinco DR-110T).  I know the radio does not draw more that 15 amps
>(the fuses are 15 amps) on high power, but don't know exactly how much it does
>draw.  The power supply does not have any amperage ratings on it, but I am
>afraid it would not supply enough current for high power transmitting.  The
>power supply provides 5, 7 and 12 volts (approx) on the various connectors.  12
>volts would probably be enough to run the radio but not charge the battery. 
>Do I have to modify the power supply to get a high enough voltage to charge the
>battery?  Also I need some overcharging protection.  Any help would be greatly
>appreciated.

You can probably use everything just the way you have it without using
the automobile battery charger:

The power supply output current at 12 volts (150 watts) has a theoretical
output current of 12.5 amps (I=W/E).  The high power rating of the 
Alinco DR-110T is probably 50 watts or so and that current draw
at 12 volts would, therefore, be at least 4 amps.  Even if we
double that current rating to account for inefficiencies, etc, you
still only have 8 amps draw leaving a "safety" margin of an additional
4.5 amps.  If the Alinco high power rating is less than 50 watts, the
numbers are even more favorable.  

One thing that could alter this assessment is if the 150 watt rating
is a combined rating for all the outputs (the 5, 7 and 12 volts
combined.)   For example, the 150 watts could be indicative of
the 12 volt tap supplying 2 amps (44 watts), the 7 vot tap
supplying 2 amps (14 watts) and the 5 volt tap supplying about
17 amps (85 watts) which brings the total power coinsumption
to the 150 watt rating.
If that's the case, the 12 volts tap would not have enough
output current to run the Alinco totally by itself when transmitting,
but with the battery in the circuit as described, you shouldn't
have a problem with current supply.  What this arrangement would
possibly require is a current limiting resistor in series with the
12 volt power supply tap to avoid placing too high a current
demand on the 12 volt output when you transmit.

The 12 volt output should be adequate to charge the battery, even if
the voltage is exactly 12.0.  Theoretically, the voltage should be
equal to 12.6 volts or greater, but you won't ruin or otherwise
destroy the battery if the power supply is exactly 12.0 volts.
If you actually measure the output voltage of the power supply you may
find the no load voltage to be something greater than 12.0 volts
(probably around 13) which would be fine to keep the battery fully
charged.  As to overcharging protection, unless the no load voltage
of the 12 volts in considerably greater than 12.6 volts (if it is
over 14 volts or so) you shouldn't need any "overcharge protection."
Remember, if you use the setup you describe, the maximum current
(charging current) you can have going through the battery would be
the 150 watt maximum rating of 12.5 amps.  That's considerably less
than the charging current and voltages the battery is presented
with in an automobile.  Output voltages and charging currents from an
automobile alternator range as high as 15-16 volts and as much as
60 amps or more, especially for "heavy duty" alternators in 
vehicles with air conditioning, etc.

Automobile batteries are pretty robust things and take an amazing
amount of punishment n normal use.  The "setup" you propose
should be far less demanding of the battery than normal use would
otherwise be.

Standard Disclaimer- Any opinions, etc. are mine and NOT my employer's.
-----------------------------------------------------------------------
Bill Sohl (K2UNK) BELLCORE (Bell Communications Research, Inc.)
Morristown, NJ             email via UUCP      bcr!cc!whs70
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Newsgroups: rec.radio.amateur.misc