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HJ61 Onboard air

Discussion in 'Diesel Tech / 24 volts' started by BjarniThor, Mar 18, 2017.

  1. BjarniThor

    BjarniThor

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    Hello

    I am thinking about installing an ARB air compressor in my HJ61. It is a 24 V
    truck. The compressor is an ARB, model CKMTA24. According to the specifications, the
    compressor draws 25 A at max load. The alternator in the truck is rated as 40 A.

    The plan is to use the compressor to air up big tires (38”). This means that the
    compressor is expected tow run at full load continuously for up to maby 10 -15 min,
    with the engine preferably running at idle.

    I hope the alternator will be up to the task ???
    What would be the minimum engine speed for the alternator to charge full 40 A ?
    Similar, how many ampers is the alternator likely to charge, with the engine running at idle (800 rpm) ?

    Hope you can share your view on this.
    Thanks
    Bjarni
     
  2. DancesWithMutts

    DancesWithMutts

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    With the engine at idle your alternator probably won't put out enough amps to keep up with the compressor. However your battery will have plenty of juice. The compressor will discharge your battery a bit, but you will charge back up in no time once you hit the highway.
     
  3. Jentuh

    Jentuh

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    The compressor will only draw max current at max pressure. that will be 25 Amp at around 8 bar. You need 3 bar at max?
    This means that with the engine running idle, the alternator should easily keep up as you only use 10 amp or so?

    Slightly off topic, but what I did was installing a buffer tank. This way you can fill your tank upto 8 bar while driving, and quickly pump tires / clean air filter when needed.
    I'm in the process of hooking the PTO onto it, hugely complicated solution, but a lot of fun :)

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  4. roscoFJ73

    roscoFJ73

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    Why would you want to run it at idle? This is what the hand throttle is for, I always turn mine up to at least 1100 rpm when I connect something to the battery terminals.
     
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  5. BjarniThor

    BjarniThor

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    Hello

    Thanks all.
    I would also install a Tank with the compressor.
    And yes, as jentuh point out, when pumping up tires, the pressure will be less than 3 bar.
    According to the ARB specifications for the CKMTA24 compressor, it will draw 14 A under "no load" conditions.
    So when filling tires, the current draw according to this is expected to be somwhere between 14 A and 25 A (?)

    Additionally, as roscoFJ73 points out , it is also no problem to bump up the engine speed a little with the hand throttle while pumping.

    All this seems to suggest I would be just fine with this installation, at least regading the current use.
    I will probably go ahead with this project.
     
  6. AirheadNut

    AirheadNut

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    You shouldn't have any problems. I have an Oasis onboard air system in my G Wagen. The specs on their website says that it is a 180 amp max unit (can pump up all four 37 inch tires in well under 10 minutes) and the electrical system doesn't seem to have any problem with it.