[Milsurplus] 12v -- 24v Vehicle Power

[Tom Dawson]

Back about 1981, I had a requirement to power some 24V equipment in  a Ford 
Van.  They had managed to wedge another 12 Volt battery under the hood but 
there was no hope for a second alternator.

What I did was acquire a big DPDT 12 Volt relay and switched the alternator 
output so as to be able to charge both batteries in series on command.  This 
was possible because the feedback to the regulator could remain on the 
single 12 volt battery, so the alternator output just went up enough to 
(with the drop across the second battery, keep 13.8 across the main battery. 
It was enough to start the motor generator that powered the 400Hz equipment 
(APS-10 Radar) and, with the engine running, we could keep the gear going 
for the duration of the test.  We manually switched back to 12 volt charging 
while driving.

Since we only ran the gear when stationary, there wasn't much 12 Volt drain 
on the 12 Volt system so the current through the batteries was nearly the 
same.

Krude, but effective, and not possible with internal regulators on the 
modern alternators.  Got the idea from those old "run your 110Volt power 
tools and lights off your car" (as long as they're DC compatible) ads.


73

Tom
WB3AKD
----- Original Message ----- 
From: "Ray Fantini" <RAFANTINI at salisbury.edu>
To: <milsurplus at mailman.qth.net>
Sent: Thursday, October 08, 2009 1:30 PM
Subject: Re: [Milsurplus] 12v -- 24v Vehicle Power


>
> There are almost a endless supply of Chevy M-1009 CUCV and M-1008 Pickups 
> on Government Liquidators web site, and always several on EBay. I have 
> seen them for sale at Gilbert and Aberdeen for as low as $2,000.00 and 
> good condition drivable and titled for $4,500.00 and up and would have to 
> say that if you want a truck for you radios that would be a good choice 
> instead of trying to retrofit a civilian vehicle. They already have 24 
> volt systems, many have the radio mounts and holes for external antenna 
> mounts. Interesting note about the M-1009 is that they have two 
> alternators in series along with the two batteries in series but the 
> engine control system is 12 volts so there is a big resistor on the fire 
> wall that provides 12 volts from the 24 volt bus so they did not use the 
> output of one battery. On the subject of parallel batteries I had a 1985 
> Chevy Box van that I bought from DRMO that used the same 6.2L diesel in a 
> 12 volt system and it used two batteries in parallel with t
> wo cables between them, no diodes or nothing. Other Chevy diesels I have 
> seen are the same way.
> Ray Fantini
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