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Miller Bobcat 225 NT

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  • Miller Bobcat 225 NT

    Hey all.I'm a shop teacher in Denison, TX.We are working on a Bobcat NT 225 welder.Ser# KJ114712 Stock # 90350016hp Onan Twin Engine we just rebuilt in our shop. It had a bad valve seat and ruined the block.If you need a portable welder, you have a reason to teach mechanics, welding, and machine troubleshooting. We LIKE to fix things.Ok here's the problems. Starts runs and welds fine now but the 12v battery charge circuit won't work now and the slow idle won't work. Two separate issues. --------No 12v charge -First - I checked the 3 wires that run to the voltage regulator/rectifier. The Batt voltage wire has 12v.The other two from the alternator under the flywheel give of 34 Volts AC. My guess is the voltage regulator is fried.I tried switching wires. Another guess is those two AC wires are interchangeable anyway.The battery wire went to the center contact on the regulator and switched the two ac wires, neither worked. --------Is the AC output of the alternator enough/ is it good? -------------SLOW idle/FAST run------- When I turn the starter switch on fast/idle I get 14v to the two wires that energize the solenoid.When I turn the starter switch on fast/run the power goes off to those wires.When I hotwire the solenoid with 12v from a battery, the solenoid will only hold the plunger if you push the plunger in deep, when it almost bottoms out, you feel a little pull and it holds it there. I think it should pull harder longer because it surely has to pull the throttle shut for slow idle.Seems like the solenoid is just weak.------------Any advice you can give that would keep me from buying extra parts would help.----ThanksMike GreenDenison High SchoolDenison, TX
    Last edited by fireballv82003; 09-19-2015, 05:18 PM.

  • #2
    The battery charging stator output varies with engine rpm but your 34V is within spec so I agree it's likely a bad regulator. Be advised that the Onan charging system requires a good battery to be connected in order for it to function. With no battery the voltage regulator "turns off".

    On the idler, it sounds as if the solenoid position adjustment is off. When the engine is at no-load high idle, the throttle position is very close to that of low idle so the idler solenoid position needs to be adjusted so that the plunger is bottomed out in the solenoid at the low idle speed of 2200rpm.

    If you don't already have it, go to the Resources tab above and click on Owners Manuals & Parts Lists, enter the machine's SN from the faceplate to download the correct manual that describes the adjustment procedure.
    http://www.millerwelds.com/om/o405d_mil.pdf
    MM200 w/spot controller and Spoolmatic 1
    Syncrowave 180 SD
    Bobcat 225G Plus LPG/NG w/14-pin*
    *Homemade Suitcase Wire Feeder
    *HF-251D-1
    *WC-1S & Spoolmatic 1
    PakMaster 100XL
    Marquette "Star Jet" 21-110
    http://www.millerwelds.com/images/sm...rolleyes.png?2

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    • #3
      Not familiar with the idle solenoid, but if it is common to most all I have dealt with, the linkage should be adjusted so that when actuated the plunger can bottom out in the solenoid body. If it doesn't, the pull in windings will burn out in short order---- then bad solenoid. Also the plunger needs to be set so it is far enough into the solenoid body when not actuated so that the pull in windings can pull it in.

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      • #4
        The Bobcat idler solenoid isn't a dual winding (pull-in/hold) type and the linkage isn't adjustable but rather the solenoid mounting is.
        MM200 w/spot controller and Spoolmatic 1
        Syncrowave 180 SD
        Bobcat 225G Plus LPG/NG w/14-pin*
        *Homemade Suitcase Wire Feeder
        *HF-251D-1
        *WC-1S & Spoolmatic 1
        PakMaster 100XL
        Marquette "Star Jet" 21-110
        http://www.millerwelds.com/images/sm...rolleyes.png?2

        Comment

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