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Old 04-26-2009, 07:55 PM
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Reducing 24v DC to 12v DC

A buddy of mine purchased a 10 wheel diesel army truck that runs on 24v DC. We were considereing putting a radio in but arent sure how to step down the voltage to 12v. Whats the easiest and safest way?

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Old 04-26-2009, 08:02 PM
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Check the volts at any outside light socket, I'll bet it reads 12 volts. The 24 volts is only used for cranking the engine over, through a starter relay.
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Old 04-26-2009, 08:52 PM
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lol, it's also got a 110v outlet in the bed. Hypothetically speaking then, how would you step down the voltage if you needed too?
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Old 04-26-2009, 09:11 PM
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Quote:
Originally Posted by DaSouthWon
lol, it's also got a 110v outlet in the bed. Hypothetically speaking then, how would you step down the voltage if you needed too?
You should find a inverter to 110 Volts on the truck somewhere. This will be from a 12 volt source also. Check the output at the alternator for it's voltage, it will be 12 volts also.

LOL

Last edited by carsavvycook; 04-26-2009 at 09:22 PM. Reason: Wrong Word used
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Old 04-26-2009, 10:42 PM
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Quote:
Originally Posted by carsavvycook
Check the volts at any outside light socket, I'll bet it reads 12 volts. The 24 volts is only used for cranking the engine over, through a starter relay.
My dad and I had an old army 6X6 years ago, and it had 24 volt bulbs everywhere. I know, because they weren't cheap.
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Old 04-26-2009, 11:33 PM
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http://www.okoffroad.com/stuff-voltage-reducer.htm
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Old 04-26-2009, 11:37 PM
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Quote:
Originally Posted by WDCreech
My dad and I had an old army 6X6 years ago, and it had 24 volt bulbs everywhere. I know, because they weren't cheap.

I will give you the benefit of dought on this. I am only 52 right now.
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Old 04-27-2009, 07:17 AM
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Interesting. I guess that explains the lack of auxillary equipment in the truck. I wonder if the military radios and other mobile equipment are designed to run on 24v or if there is a converter hidden somewhere in the truck. It's likely been stripped out even if it had one since the vehicle last saw military use in the late 90's.
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Old 04-27-2009, 08:49 AM
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You can go to Radio Shack and get a voltage regulator. You will need to buy a small pc board, some other components and solder it all together.
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Old 04-27-2009, 07:39 PM
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Standard military radios and other accessories are designed to run from 24 volts, so they run directly off the main power on the old 6x6 trucks like the M35A2. I don't know if the newer 5 ton M923 trucks are the same, but they must still have 24 volt power somewhere.

The older 1 1/4 ton CUCV (Commercial Utility Cargo Vehicle) GMC truck had a split power system with two alternators, and it used 12 volts for the truck and 24 volts for the accessories. I assume that the HMMWV uses something similar.

I don't think you will find a 110 volt inverter on a 6x6 truck. We had AC inverters on smaller vehicles to run Radio-Teletype equipment when moving, but large vehicles towed 120/240 volt generators on a trailer.

Bruce
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Old 04-28-2009, 07:18 AM
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This truck is a Kaiser M35-A2, and it's got lots of surprises. Anyone know what the recoilable spool of ground cable on the side of the bed is for?

The 110v looking receptacle appears to have been installed by the factory but who knows for sure. We haven't traced where it goes.

Does anyone know the best place to pull a 24v source from to convert to 12 volts. Additionally, if I had an ignition switched power supply would I need an additional converter or is there someway to use a relay inline with the switched source to get buy with just one? I'm thinking this could be done with a simple 4 pole relay switch.
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Old 04-28-2009, 06:19 PM
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We used many M35A2's with a S280 shelter mounted on the back. The S280 refers to the size, and there were several variations of equipment inside the shelters. One of the most spacious was the mobile operations center (MSC-31), which had map boards, two radios, a switchboard, telephone, intercom and both heat and A/C. This manual shows a picture of the "roadside" (left side) of that van.
http://www.tpub.com/content/operator...223-150054.htm

All of the vans had ground cables and six foot ground rods. The vans had to be grounded when used because they were powered by gasoline 5kw or 10kw generator sets (a set is two generators on a trailer), or sometimes by a common-use diesel 60kw generator. If they weren't grounded right, you found out very quickly if you stepped on the ground while holding on to the van body. One generator set could power multiple vans by using the power cables to interconnect several vans.

Bruce
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Old 12-10-2010, 12:27 AM
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currently in iraq right now. but even with these new rigs we have they are all 24v. one thing ive noticed on all military vehicles is that all the batteries are 12v and doubled up to make a 24v system. Ive had success in the past running the wiring to just one battery.
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Old 12-10-2010, 09:08 AM
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If you look at the batteries, they are 12V, if you take a multi meter and check the pos terminals you will find that they should read, 12v on one battery and 24v on the other (leaving the ground on the 1st battery neg terminal, we used to pull 12v off these all the time to do just what you want..... run a non-military radio while driving down the road. If your's is like this you can get a regulator as suggested above.
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Old 12-13-2010, 04:35 PM
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all of our road building equipment at work is 24 volt, to install 12 volt accessories we just wire in a box that steps the 24 down to 12. can buy at any equipment dealership. For the life of me, I cant remember what it is called though...
Tried wiring off of one battery once, and in the process fried a brand new 2 way. much cheaper to do it properly.
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