Forum Discussion

MattR's avatar
MattR
Explorer
Jul 28, 2018

Onan Generator Issue - 12v Voltage Drop When Starting

My 4k BGE spec H Onan generator has stopped working. It will attempt to start (crank) but refuses to start up. I thought it was a loose connection as the voltage at the +12v terminal drops from 12v to 4-5v when I hold down the start button. I traced the positive wire to the battery, cleaned the terminals well, and re-crimped the ends. Same issue. So it must be a problem on the ground side, right? The manual specifies a ground connection on the right side of the generator but mine didn't have a wire there... so I added one. A good connection to the chassis. Same problem. I held down the start button for a minute or so and a ground wire on an unrelated appliance (furnace) melted. Any ideas? Where would it be grounded if there weren't a wire connected to the grounding spot? There hadn't been one for decades and it presumably worked fine until now. The voltage across the starter solenoid when cranking is 0.1v. Is it normal for the S terminal to be connected to ground when the start button isn't held down?

Thanks! I've been working on this issue off and on for days but my next trip is coming up on the 1st and I need to get this issue resolved.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jul 31, 2018
    Out of the (?) of soldered battery lugs I have made, the number 0 Zero pops up when it comes to cable conductor to lug degradation. This goes way back to when JFK was in office.

    Too bad genuinedealz does not offer soldering at a premium price.

    A few companies offer LEAD (not tin) plated battery lugs. Takes a painter's mask and goggles to solder lead coated terminals, but that is exactly how I thwarted terminal failures because of group 65 batteries in Ford diesel rigs. The lugs came from Quickcable.

    I made a set of nasty-jawed leads for my voltmeter. Steel with crocodile teeth. It's easier to gnaw through crud and grime on a frame rail.
  • MattR's avatar
    MattR
    Explorer
    Jul 30, 2018
    I have two wires hooked to the negative terminal of the battery but one is a tiny little wire. I actually replaced both ends of main wire from the battery to the chassis.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Jul 30, 2018
    On your batteries do you have ONE or more wires hooked to the NEGATIVE terminal?

    Sounds like the wire you added was Generator to Chassis.
    The furnace is also chassis grounded (All propane stuff is).
    But the battery-chassis ground is..... not up to spec. Could be the OTHER end of the cable.

    This would only apply however if MORE THAN ONE wire is connected to the battery negative.. But I'd check the other end of the battery negative cable 1st. Or run the generator ground lead (4ga) all the way back to the battery.
  • MattR's avatar
    MattR
    Explorer
    Jul 28, 2018
    MattR wrote:
    I was reasoning that if it was the connection between the battery negative terminal and the chassis which was poor then the voltage drop would be much higher (similar to the voltage drop as measured between the chassis and the 12v terminal at the generator).


    My reasoning must have been faulty... I went ahead and cleaned the chassis connection and re-crimped the negative battery lead. It started right up. I'll have to get everything back together and test it out but it looks like I found the poor connection. It's odd... the connection looked to be in much better shape than any of the other battery connections/crimps.

    Thank you everyone for your help! I'll let you know how things go once I get everything back together and the melted wire replaced.
  • Artum_Snowbird's avatar
    Artum_Snowbird
    Explorer
    Jul 28, 2018
    I would suggest that you have a point of excessive resistance, thus the voltage drop trying to drive the current through the resistance. In my case, the nut on the positive lead right on the starter had worked itself loose.

    After I removed the generator from the motorhome and took the cover off, the lead was just flopping on the bolt and the nut had backed off quite a ways.

    Tightened it up and all was well.

    It's not easy to take the generator out, but not really difficult either. I borrowed a motorcycle jack and that made it really easy. Hardest part was pulling out the generator output wires from their junction point.
  • midnightsadie's avatar
    midnightsadie
    Explorer II
    Jul 28, 2018
    IF it never done this before? start with a different battery just for fun, might even put a jump from a car on it.
  • MattR's avatar
    MattR
    Explorer
    Jul 28, 2018
    The battery rests around 12.8v right now. Draws down to 11-ish when attempting to start the generator (as measured at the battery). Battery is around 18 months old.

    2 gauge wire from battery to either generator (+) or chassis (-). You are correct, I did not replace the chassis side of the negative battery wire. I measured the voltage from the chassis to the battery positive terminal while cranking and it was identical to the voltage across the battery terminals even while cranking... I was reasoning that if it was the connection between the battery negative terminal and the chassis which was poor then the voltage drop would be much higher (similar to the voltage drop as measured between the chassis and the 12v terminal at the generator). Is that not correct? Should I focus on the battery cable/chassis connection?

    Thank you everyone!
  • dougrainer's avatar
    dougrainer
    Nomad
    Jul 28, 2018
    You did not state that you replaced or repaired the Cable from the BATTERY Neg post to a good solid clean unpainted surface ground. What is the gauge wires from the Battery to ground and the pos to the Genset? Your clue to bad/inadequate battery supply ground was the melted wire. The path of resistance attempted to go thru the furnace circuit, resulting in the melted wire. Doug

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