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Komatsu D31 Battery Relay

Discussion in 'Dozers' started by Jerry58, Sep 22, 2022 at 7:36 PM.

  1. Jerry58

    Jerry58 New Member

    Joined:
    Mar 20, 2021
    Messages:
    2
    Location:
    West Virginia
    Hello,
    I have been having problems keeping batteries charged on my D31. It seems that the alternator is working ok so I assume they were draining while it was setting. Yesterday while running the machine I suddenly found myself engulfed in dense smoke. I shut dozer down immediately and started searching for the source of the smoke. I was able to determine the two small wires running from the battery relay were melted and very hot. Could the battery relay failing be the source of the drain and then failed entirely causing the melt down? From what I can figure the two small wires on top of the relay are marked R and BR. The R wire runs to the alternator while the BR wire goes to the switch. The two bottom large lugs on the relay are for ground to the machine the other to the negative post on battery. I don't have any schematics so I have had to do lots of searching for what info I have. Hoping someone here can help.

    Thank you,
    jerry
     
  2. John C.

    John C. Senior Member

    Joined:
    Jun 11, 2007
    Messages:
    11,709
    Occupation:
    Machinery & Equipment Appraiser
    Location:
    Northwest
    Here is a video that shows how the battery disconnect switches work. There are two types which is explained in the video.

     
  3. Jerry58

    Jerry58 New Member

    Joined:
    Mar 20, 2021
    Messages:
    2
    Location:
    West Virginia
    Thank you for the video, my switch is the negative disconnect type. I was not able to really understand what he was doing while testing the negative switch as his hands and the switch it self was blocking the view of the placement of the leads while checking for continuity. I was able to track down the origin of the smoke today. The BR wire from battery relay was melted all the way back to the ignition switch, I could find no other wires that were affected.
     
  4. heymccall

    heymccall Senior Member

    Joined:
    Feb 19, 2007
    Messages:
    3,920
    Location:
    White Oak, Pa
    With a multimeter, measure resistance across the two small poles of the battery disconnect. If it's 0, or near zero, the coil is shorted. And, that wire/ disconnect coil should've been fused. Did someone bypass any of the ignition switch wiring or fuses, or put way too big of a fuse in? It should be a 10 ampere.
     
    DB2 likes this.
  5. John C.

    John C. Senior Member

    Joined:
    Jun 11, 2007
    Messages:
    11,709
    Occupation:
    Machinery & Equipment Appraiser
    Location:
    Northwest
    When you turn the key switch to the on position, you should hear the battery disconnect snap closed. You should also hear it open when you when you turn the key off.

    Use the ohm meter and check either of the small terminals resistance to ground. If there is no resistance, the coil inside is shorted. Disconnect the wires from the terminals and then check both wires for continuity to ground. Your machine does not have a computer so turning on the key switch just grounds the circuit allowing amperage to flow through the coil and close the switch when it is working correctly. The power to the switch comes from the battery through the key switch when the engine is not running and through the alternator when the engine is running. Most dozers could shut off either on the key or the throttle control lever.
     
    Coaldust likes this.