Onan 7.5 KV Diesel Generator, Model HDKAJ

[Bill Schneider]

Tried running the generator, but transfer switch would not switch over to generator input. Measured generator output at transfer switch input. No voltage measured between L1 and L2. No voltage measured between  L1 and Neutral or L2 and Neutral. However, if I measure between L1 or L2 and chassis ground I measure 120 VAC. Problem seems to be in the Generator, not the transfer switch. I try running the generator once every month or so and have not had any problems until now so I haven't educated myself on the generator outside of normal maintenance. Thanks for any help or advice, Bill

[Paul Schwalen]

Bill,

On our 7.5 Onan there is a black toggle switch on the front panel of the gen.  If that switch gets flipped to off the output of the gen  will not  be sent to the transfer switch.  I found this out when your symptom happened to us sometime ago.  Somehow I had tripped this switch while I was checking the gen oil.

Good luck.

Paul

[Edward Buker]

Just to clarify that switch is actually the circuit breaker for the generator. It looks and acts like a switch but it can be tripped by current flow,

Later Ed

[Bill Schneider]

UPDATE. The circuit breaker was the first thing I checked. it wasn't tripped. In my original message I stated the voltage measurements were taken at the transfer switch. If the circuit breaker was tripped, I don't see how I could have measured 120 VAC to chassis ground on the generator leads at that point. The Neutral appears to be floating and not tied to ground in the generator. I don't see how I could measure 120VAC to chassis ground, but basically nothing from L1 or L2 to Neutral. I also checked the fuses under the cover on the generator panel and the terminals for tightness at the output of the generator under the other front cover. I may have a regulator board problem. I put this on the FORUM hoping someone might have had a similar problem or there was a generator tech among us. I was trying to avoid going to cummins SW in Florida if I had overlooked something, but I would have probably had to go to them for parts anyway. I'am on my way to Key west (Navy RV Park at Sigbey) so will have to Boondock when in overflow. Consequently, I have to get this resolved before I get down there.

[Tom and Pam Brown]

Bill, inside the transfer switch there is a relay that has a magnet that engages ti transfer the power.  Mine went bad and I had to replace it and it cured the problem.  Everything worked fine on shore power but the switch would not go to the generator side.  It is about a 50 dollar part and can be found at an electrical supply store mine was made by GE.

Tom

[Edward Buker]

Bill,

I believe that the neutral and ground are not tied together in the generator and your results would also indicate that. The ground at the generator is tied to the frame of the RV so you can measure 120V between the frame/ground and the L1 and L2. The neutral line is floating, and for some reason, is not seeing the 120V that it should between itself and the L1 and L2 Lines. Because you are seeing 120V to ground, I believe that the regulator board is working to control the generator RPM/60 cycles. I do not have a schematic for your generator. If you have one, you should follow the neutral wire back to its source, and see what could be open and not allowing the neutral to be connected. I suspect a brush contact or perhaps a relay contact if there is one involved. Neither of these items would be very easy to service on the road. Your symptom should make it pretty easy for Cummins to sort out the root cause.

The transfer switch is probably fine given it will not switch over without seeing 120V between the neutral and L!/L2.

Hope this helps.

later Ed

[Bill Schneider]

UPDATE/SOLUTION  Thanks to all who responded, especially Ed. Ed, I was looking for your input as you usually answer the electrical issues. You reinforced my diagnosis. I finally found an RV Park that would let me pull the front cover off the generator. I knew I had a problem with the neutral lead and I was able to get a better view of the wiring with the cover off. As it turned out, the terminal board ( 5 conductor, L1, L2, 2 Neutrals and ground)on the upper left front corner off the generator was the problem. There is a small inspection cover over it, but not big enough to really see what was wrong without removing the front cover.  The output side of the terminal where the neutral wire going to the transfer switch attaches and the neutral leads coming from the generator on the input side had cracked and seperated slightly. I was able to move the neutral lead to the transfer switch to the other neutral lug ( the 2 neutral lugs are tied together on the generator side) as a temporary fix. I plan to replace the terminal board at first opportunity. This was a strange problem and thanks again to the Forum.  Bill

[Edward Buker]

Good for you Bill.

 Every time you can fix or understand a problem with your coach you gain confidence and piece of mind. Shariing the solution may help someone else with a similar case.

It sounds to me like the wire tension and vibration stressed the terminals and caused a fracture fail. If you can, either by adding a little wire with a crimp connector, or by pulling some extra wire, put a one or two turn coil in the wire before the terminal it would be a big help. This removes the stress and is a customary good wiring practice when there is adequate space and vibration is involved.

Later Ed