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Old 03-16-2014, 03:12 PM   #1
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Gen set power slumping below 110v

For the past couple months power from my Onan 7500 gen has been choking about once per minute. The inverter shuts off and comes back on, lights flicker etc.

It happens at the generator input on the transfer switch and not shore power so I know it's coming from the gen.

Is this something that could be fixed with a regular gen tune up at Cummins? Perhaps spark plugs, filters etc. ?
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Old 03-16-2014, 03:24 PM   #2
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Quote:
Originally Posted by RufussSewell View Post
For the past couple months power from my Onan 7500 gen has been choking about once per minute. The inverter shuts off and comes back on, lights flicker etc.

It happens at the generator input on the transfer switch and not shore power so I know it's coming from the gen.

Is this something that could be fixed with a regular gen tune up at Cummins? Perhaps spark plugs, filters etc. ?
Hmm is your 7500 gen a gaser? You mention spark plugs.

What is the gen load when this is happening?

Have you checked your fuel supply and filters?

More info would help but it sounds to me that having it looked at by a pro or someone with gen savvy would be worthwhile but there are a lot of Gen savvy folks here that can help. Answers to the above questions might help,
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Old 03-16-2014, 03:30 PM   #3
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It's diesel... so no spark plugs haha? I dunno.

Could it be the fuel filter?

Perhaps a loose wire?

As far as load, it happens regularly no matter the load. Just a single low power LED light bulb or the full A/C, coffee maker etc. About once per minute.

It just dips for a split second. Enough to make the lights flicker and A/C make a thump sound. I've only run the A/C for a few minutes to see if it affected the power. It didn't seem to change anything so I just keep it off to protect it against any power issues.
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Old 03-16-2014, 03:40 PM   #4
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It could be your fuel supply; I,E.: Bad filter, bad fuel, or bad fuel pump etc, but your transfer switch could also be acting up check that out. Is the transfer switch clattering? And yes check all connections,

You mentioned the AC was cycling on and off : hmmm I would shut the AC down until the problem is sorted out, which I believe you did, good.

And indeed, a diesel does not have spark plugs.

Good luck.
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Old 03-16-2014, 03:59 PM   #5
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It appears to be happening at the generator. There's no clacking at the transfer switch.

I removed the wire cover at the front left of the gen and checked the voltage. It slumps down to 106v and the lights flicker, then it jumps right back up.
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Old 03-16-2014, 04:17 PM   #6
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You said it was "choking", this made me think of fuel supply interruptions, such as bad fuel, bad filter or bad fuel pump.

There is electronic circuitry that controls voltage and frequency also and you may have some electronics acting up, but my initial thoughts are still fuel related if it is "choking".

Is there any fault code being flashed to your panel?

Do you have a gen book with a fault cause vs symptom relationship?

Any real experts out there who can jump in?
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Old 03-16-2014, 04:27 PM   #7
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The engine seems to be running fine. It's just losing voltage for a split second.

There is no fault code. Just solid red light.
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Old 03-16-2014, 04:46 PM   #8
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Could be the bushings of the genhead going out.
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Old 03-16-2014, 04:50 PM   #9
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If the gen sounds OK, no choking or undulations, then the problem must be electrical or electronic, for which I am at the end of my remote help capabilities without doing further circuit analysis with appropriate test equipment, perhaps others who have experienced this problem can help, an oscilloscope would be of assistance to look at the waveform and frequency to see what is going on,

Good luck,
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Old 03-16-2014, 05:05 PM   #10
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I suppose a trip to the Cummins service center is in order.
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Old 03-16-2014, 05:07 PM   #11
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This is a good idea IMHO
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Old 03-16-2014, 05:09 PM   #12
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Can you post your model number?

Depending upon your model number yours may be an inverter or conventional generator configuration. The 7500 quiet diesel series would instantly shut down if the Hertz dropped below 55 or over 70. Switch off your main breaker(s) in the electrical panel inside the coach. As mentioned above you will need to read the Hertz along with the voltage - it needs to be read right there at the corner of the genset where the wiring connects. I'd be interested to know if the voltage is sagging along with the frequency (HZ) - especially if there is no change in RPM. It is especially rare for an inverter/controller to go bad in the quiet diesels.

If the engine is not surging then I would look in more detail at the genset side of your transfer switch - specifically for burnt or worn contact points, loose, burnt or corroded wiring. There are two solenoid contactors in the transfer switch, 1 for shore, 1 for genset. I would also pull and prod on the conduit (liquatite) with the wiring connecting the genset to the transfer switch in an attempt to find some wiring loose perhaps in a J-box along the line.
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Old 03-16-2014, 05:20 PM   #13
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The gen does rev up when the A/C, microwave, coffee maker is running.

It's an Onan Quiet Diesel 7500
Model: 7.5HDKAJ11451C
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Old 03-16-2014, 05:22 PM   #14
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What type of meter do I need to check the Hz?
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