[Milsurplus] 24 volt power supply in 12 volt vehicles

[Bruce Gentry]

The discussion about the solid state vibrator modules reminded me of a 
very sucessful project I did almost twenty years ago. I wanted 24 volts 
in a pickup truck to run radios. There are all sorts of power supplies 
possible, but I happened upon an inexpensive one that can be built 
easily.  The first requirement is an older solid state power inverter 
for making 120 volts AC from 12 volts.  The one I used was built by 
Tripp-Lite, but I am sure there are others as well. It is the older, 
conventional type with a large transformer, not the ones of today.  The 
12 volts went into the center tap of the transformer primary, the 
switching transistors grounded the ends of the primary alternately. When 
one bank of transistors is grounding one end of the primary, the other 
end is at twice the input voltage. I used a pair of large diodes to 
rectify the 24 volts.  Athough I had a filter condensor for the 24 volt 
output, it was smoothed and stabilized further by two 12 volt 
batteries.  The truck has a 120 amp alternator, so making 20 or so amps 
at 24 volts isn't a strain. RFI from the power supply is quite low, you 
have to hold a pocket radio tuned to the bottom of the AM band near it 
to hear anything. The truck has a ordinary  mechanical injection diesel 
engine, so there is no RFI from vehicle systems either.

       Bruce Gentry, KA2IVY