Announcement

Collapse
No announcement yet.

Big40 no power generation until warm - runs on pto hydraulic system - now no power

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Big40 no power generation until warm - runs on pto hydraulic system - now no power

    I have a Miller Big40 that used to be a diesel powered unit. I purchased it cheap with a hole in the engine block. I have since converted it to run off of my F550 pto hydraulic system. The conversion was the easy part.

    The generator has been working sporadically but normally comes to power after it has run for 2-20 minutes but never when the pto first kicks up the rpms. Lately, with the cold weather, it was taking longer to produce power. I only keep an extension cord with tattletale LED light to let me know when power has started before I plug in my air compressor so there is no load while I am waiting for it to power up. Now, with warming weather, I can not get the generator to fire up at all and I require the compressor and other tools on my job sites.

    I have pulled the brushes and they are fine. I will be polishing the slip rings today but they look good too. The hour meter shows 1850 hours so no excessive usage when it was diesel powered.

    I've studied the schematic. Is there some reason that the generator should have 12v battery power applied to a line in order to work properly? I don't have any power wired to the welder as the engine and engine components are completely removed.

    It's been a while since I tried the welder portion of this unit but when I did, it was worse than terrible. I'm not sure if the generator was making power when I tried it for welding but it acted as if there was not enough amperage and it did not want to hold a steady arc. Pidgeon poop welds were the best it could do at the time and nothing was deep enough to be a trusted weld.

    Ideas on where and what I should start testing to get this figured out? I can always throw my Lincoln back into the truck but the whole concept was to get away from another cooling system, oil system, battery and other related maintenance issues that cost me lost time.

  • #2
    The two main options that come to mind are a lack of initial startup magnetism, or a failed component that's open-circuit until it warms up enough to make contact. The original unit probably supplied 12V to the field (brushes) through a diode. What voltage do you have at the brushes while it's not working? That'll help diagnose either case.

    Comment


    • #3
      Originally posted by Bushytails View Post
      The two main options that come to mind are a lack of initial startup magnetism, or a failed component that's open-circuit until it warms up enough to make contact. The original unit probably supplied 12V to the field (brushes) through a diode. What voltage do you have at the brushes while it's not working? That'll help diagnose either case.
      That's what I was reading on the schematic that the center brush was getting 12v+ when the unit is operational. Any idea on how much amperage is required for that lead? I can run a switched line that comes on via relay from the pto control if required. I am assuming that that power is required for proper welding production from today's repair work.

      I pulled the unit apart today and got further into inspection and diagnosis. I checked the brushes which are in great condition, cleaned the slip rings and found 2 wires that were not bolted down to an insulated block at the bottom of the frame below the brushes. There was a red painted dot on this section of frame (positive) and a black dot on the frame portion 180 degrees above. One of the wires was about 1/0 copper and the other was about 14 gauge leading to a capacitor on that frame. I bolted these back down and after testing, the generator portion was working great, So the generator portion is repaired to the best of my knowledge. It started my air compressor easily and was providing power within 2-3 second after the pto came up to full speed.

      When I tested the welder portion, that is still not working correctly. I could not even run a decent bead with a 7018 1/8" rod at nearly 200 amps although the welder was really pulling hard on the hydraulic circuit.
      Last edited by TreeMuncher; 04-04-2021, 06:23 PM.

      Comment


      • #4
        If the generator portion is working, you have field current, so that's not the problem. You might get rid of the 2-3 second delay with a 12v source, but I wouldn't worry about it now. If it's putting a lot of load on your power source, I'd check for a bad output rectifier diode next. Most other failures that cause low output also cause low engine load, not high engine load.

        Comment

        Working...
        X