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Thread: FMTV - 24/12 Converter instead of the Niehoff dual-voltage alternator?

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    Colonel Wile E. Coyote's Avatar
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    Default FMTV - 24/12 Converter instead of the Niehoff dual-voltage alternator?

    Bought some lightly cannibalized FMTV A0 trucks a couple of years ago and finally getting around to putting them back together. Two have the alternators robbed off of them (Niehoff N1506-1), and since trying to buy a replacement from our supplier friends is almost what was paid for the trucks - I was thinking of going with the straight 24V alternator which seem to be around more reasonably priced - and wiring a 24V to 12V converter to run the 12V end. Anyone try that yet? Does anyone know the all-up current draw on the FMTV A0 12V side of things with all the 12V accessories on?

    I can't immediately come up with any reason why that setup wouldn't work, other than maybe potential trouble trying to find a converter of the appropriate current rating.

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    4 Star General Steel Soldiers Vendor Suprman's Avatar
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    It will work fine. I have 100a surepowers in the classifieds that will do the trick. You would need to install a contactor relay to disconnect the 12v converter output when the truck is off.

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    It should work, but you need a converter with a very low cutout voltage so it doesn't drop off line when you crank the engine.

    They make these for commercial vehicles to provide a standalone 12V or to float the 12V center of a 24V battery string like the 24/12 alternator does.

    Was working on getting accurate 12V and 24V loads but my current probe is broken. I calculated the lighting loads based on the bulb specs which should be the majority of the 12V loads. At night stepping on the brakes with turn signals on about 25A peak lighting load...

    signal lights: 2.1A X 7 or 4.2A brakes, 4.2A signals(8.4A hazard) 2.1A Rev

    Marker Lights: .56A X 13 or 7.28A

    Headlights: 4.7A X 2 or 9.4A

    Gauges/switches: .1A X 17 on a basic A0 truck?

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    4 Star General Steel Soldiers Vendor Suprman's Avatar
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    The surepowers divide. Your output will be half your input. I believe you can run it equalizing. Keep your 12v off the battery location and switch the converter 12v out to the batteries.

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    Been looking at those 12v converters/ battery equalizers too. Havenít looked at the electrical diagrams to see where all the voltages go.

    Seems how the alternator and voltage regulator are pricey and near non existent on the regulator side of things.


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    That is what I am going to switch to when my alt packs it in...

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    Had my alternator go out last week and rebuild shop is quoting 2150$ to rebuild so looking for options found this.
    http://double-alt.com/military.html
    Didn't know what everyone thought of this or other options?
    1995 M1084 A0
    2009 M989A1 Trailer

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    The double alt will work on first gen trucks. May be issues with an a1 though.

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    I would get a straight 24 and one of Supermans 100A surepowers... There was quite a discussion on the quality of the double-alt not all that long ago.

    In the end pulling 12V out of the middle of a 24V string and trying to charge 12 and 24 simultaneously is a problem prone way of doing a dual voltage setup. The best way is a pure 24V bank and a 24-12 converter. You also have a fallback if the converter fails. You can still tap 12V out of the middle of the 24V bank short term to get you home...

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    Are there any of the 24 volt only models that would bolt up to existing bracketry?
    1995 M1084 A0
    2009 M989A1 Trailer

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