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Thread: 12v component in 24v truck

  1. #1
    Join Date
    Dec 2006
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    Default 12v component in 24v truck

    what is the correct way to run a 12v component in a 24v truck. Do you just run a connection off a single battery? Will this continually draw one battery down and cause a problem? I am talking about a radio, invertor, etc.

  2. #2

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    Well the best way to do it would be to build or purchase if available a voltage dropping device. Either something that just has a big resistor in it to drop the voltage from 24 to 12 or a voltage regulator that will drop it from 24 to 12. The regulator would be better because the output voltage would be constant were as the resistor would go up and down as the trucks voltage goes up and down. I would think a web search would either find a manufactured item or schematics for rolling your own. That would be the best way to run 12V in a 24V system.
    Zone holster maker

  3. #3

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    24 VOLT TO 12 VOLT POWER CONVERTER
    ECONOMY 10-AMP REGULATED POWER CONVERTER Ideal for 2-way radios cellular phones fax machines lights gauges and other 12-volt accessories Reliable even in toughest off-road construction and material-handling environments Operates sensitive 12-volt

    $42.99 J.C. Whitney.

    I found this after a web search for 24 volt to 12 volt converter. Might be just what you need.
    Zone holster maker

  4. #4
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    There are a couple ways to do this...it comes down to price, complexity and how many amps you need.

    Tapping off one of the batteries will work in the short term but presents the charging system with a problem...it will either overcharge one battery in order to bring the more drawn down battery to full or it will charge the one to full and leave the other less than full all the time. Either way is a problem and will lead to at least one battery failing. It is a cheap and dirty way to accomplish the sought end.

    If you need 20 amps or less, you can get a reasonably priced converter to step down from 24 to 12 volt. Forget the JC Whitney ones, they are very inefficient and throw away a lot of juice as heat...if you need a spare cab heater, they work ok...to get a good one:
    Go to www.Samlexamerica.com
    Mouse over Products in the left hand menu and go to refurbished. They make 3 different ones, up to 23 amps peak, 20 amps continuous and they are highly efficient. I have had one of them for several years now with no problems. They only sell the refurbished to the general public, the rest has to go in bulk to business.

    When you go more than 20 amps or so, the prices really jump up, so if you need more than that, it would be better, though more costly and complex, to put in a 2nd alternator with its own 12 volt battery and run both a 24 and 12 volt systems on the truck...complete with dual fuse boxes and wire harnesses. As long as the 2 systems are properly grounded, there is no danger of crossfeeding voltage...unless one hooks a 24 volt wire to a 12 volt device or vice-versa. This is the most reliable method of doing what you asked...though, as I said, it is the most complex and costly.

  5. #5

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    I used to use the resistor type setup to drop voltage but started having problems with the fluctuating so I tried this voltage reducer http://www.ase-supply.com. I have been very happy with it so far. It is alot more expensive but leaves me room for the TBI, radio, CB, and more to be hooked to it. Only problems I've found besides cost is dimensions and you can't get it wet. i had to downsize a 120mm ammo can to mount it inand bolted it behind passenger seat to keep it dry.
    Last edited by brute4c; May 17th, 2007 at 01:04 PM. Reason: corrected link

  6. #6
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    My 20 amp Samlex unit is roughly that size, costs half the price, and outputs 4 times as much. The Samlex are the best efficiency, output and price units I can find anywhere. I have a box in the bed that I moved the batteries into...and the converter is mounted in there...

    Heres the specs on mine:

    SDC-23 24VDC-12VDC Converter, 20 Amp




    20 Amp 24V-12V Switchmode DC Converter. Designed for heavy-duty applications.


    Specifications
    Model# SDC-23
    Input Voltage 24 VDC
    Output Voltage 13.8 VDC +/- 8%
    Dimensions 5" x 8" x 2.5"
    Output 20 Amps
    Shipping Weight Lbs. 2.5

    Applications
    Earth moving equipment
    Heavy trucks
    Buses
    Marine vehicles
    CB radios
    12 Volt lighting systems
    AM/FM sound systems


    Design Features
    Advanced switchmode design
    Mount in almost any location
    Compact and light weight
    Reverse polarity protection
    High efficiency
    Current limiting circuit
    Overvoltage crowbar circuit
    Non-Isolated for negative ground system

  7. #7
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    long island new york
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    Default

    Thanks for the information guys.

  8. #8

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    As I said the JC whitney one was after just a quick search and in no way was meant to be an indorsement of the product. Personally being into radios I'd would roll my own, but that's just me...

    The basic answer is the same. If you want to run 12V items in your 24V MV get a converter.
    Zone holster maker

  9. #9
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    Or if your draw is high enough, install the 2nd alternator/3rd battery...

  10. #10
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    Port Orchard, Wash.
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    Quote Originally Posted by brute4c View Post
    If you need 20 amps or less, you can get a reasonably priced converter to step down from 24 to 12 volt....
    Go to www.Samlexamerica.com
    Mouse over Products in the left hand menu and go to refurbished. They make 3 different ones, up to 23 amps peak, 20 amps continuous and they are highly efficient. I have had one of them for several years now with no problems. They only sell the refurbished to the general public, the rest has to go in bulk to business.
    I couldn't find the "refurbished" units, but made an inquiry with the local distributor.
    -- Tim Taylor


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