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Onan Generators

Onan 6.5 NHD-FB/1M Repair or Sell?

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Old 11-10-2017, 11:17:13 AM
Pete Spaco Pete Spaco is offline
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Default Re: Onan 6.5 NHD-FB/1M repair or sell?

"Currently the generator has frequent Hz spikes. It runs about 62 Hz, but will momentarily spike to 90 - 120 Hz. It will run fine for 10 minutes or so, then go through a couple of minutes of spikes every 2 seconds to 15 seconds, then calm down again. When this happens there are no significant changes to the load (the furnace or refrigerator hasn't turned on or off), nor is there an audible change in the speed or workload on the genset engine. It seems to behave better under heavier load, but even then the spikes still occur, just less often. I'm assuming the problem is the voltage regulator, but if someone knows better, I'm all ears."

As previously mentioned, this generator CAN NOT create increase frequency unless the engine speed increases.
Do you know whether this is happening when the spikes occur, or not?

Tell us how you measure those "frequency spikes".

"I have much of my equipment on battery backups. The observed Hz spikes exactly correspond to the battery backups shifting to battery power. The Hz spikes are real. The battery backups are doing their job - shifting to battery when the line power goes out of spec."
Are you certain that the frequency spikes are coming from the generator and not from the "battery power" equipment? You could be suffering from a power DROP OUT from the generator.
If you disable the battery backup, do the "frequency spikes" still occur?

Pete Stanaitis
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Old 11-10-2017, 08:32:00 PM
RadicalDad RadicalDad is offline
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Default Re: Onan 6.5 NHD-FB/1M repair or sell?

As previously mentioned, this generator CAN NOT create increase frequency unless the engine speed increases.
Do you know whether this is happening when the spikes occur, or not?
The Hz spikes are too fast and too frequent to be correlated with changes in engine speed. And I don't hear anything different in the genset when these occur.

Are you certain that the frequency spikes are coming from the generator and not from the "battery power" equipment? You could be suffering from a power DROP OUT from the generator.
If you disable the battery backup, do the "frequency spikes" still occur?
I am measuring direct from the wall socket, not the battery backup outlets. True, I'm using cheap multitesting meters, but two of them are reporting the same thing. Again, for clarity, when the battery backup relays click, that is when I see momentary Hz spikes. Setting one cheap meter to look at voltage, and the other to look at Hz, I don't see voltage spikes, only Hz spikes. And also to repeat, both meters show Hz spikes. Hard to imagine that two different meter brands of completely different design would show the same problem. And the problem doesn't occur on utility power, only on generator power.

Other folks in this thread have suggested possible faults in the wiring at various places in the house, the electrical panel, and out to the generator. Many thanks for those suggestions. Unfortunately, I had an electrician in last spring to investigate those possibilities. He went through the entire electrical box and the runs from it looking for loose connections and other faults. Found a few problems, but nothing that would account for what we're seeing. He even put in a new circuit that has just one outlet next to the box that we used for testing. It shows the same problems, even when that circuit is the only one connected to the generator.

As for my learning to do the maintenance - well maybe. I'm currently earning my third graduate degree and I work as clergy. Which is to say, I have to be careful about what I take on - there is only so much time in a day. Despite the fact that my first career was in software engineering, it seems I ought to be able to pay to have this maintenance done and stick to doing the things I'm good at that no one else can do. My poor experience with Cummins NW and inability to find someone else who isn't flakey to service this generator is why I'm considering selling it to someone who can love it while I get something that will support my needs.

Speaking of being clergy, there is a big life-cycle event happening this weekend. I've been prepping with the family and fellow clergy all day and I've got visiting clergy house guests tonight through the weekend. Which is to say, thanks for everyone's ideas, please keep them coming, apologies for my delay in replying today, and I won't be able to look at the forum again until late Sunday. Everyone here have a sweet weekend!
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Old 11-10-2017, 09:04:24 PM
len k len k is offline
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Default Re: Onan 6.5 NHD-FB/1M repair or sell?

I wouldn't sell it, I think if you do you'll be longing to get it back. Think you'll be even more disappointed with what they are selling new these days.

HZ are DIRECTLY porpotional to engine RPM, so bottom line if engine RPM is not increasing by 50 % then 50% increase of 60 hz to 90HZ is NOT real ( not really occurring). I seriously doubt gen is suddenly turning at 90hz.

Tell me about these breif 90 hz times. Do they instantly occur or ramp up over several to 10 or more seconds. When they occur does the carb throttle suddenly increase?

I wouldn't use your charger/inverter tripping out as evidence that hz are high, use a hz meter. Charger/inverters have a history of trip points being set too tight, and even tripping out on an Onan 7.5JB gen with a massive flywheel ( it can't change rpm that fast). Most people here use a $25 kill-a-watt meter ( home depot or ebay) with good results to measure HZ.

If brushes or AC voltage reg are intermittent that might create an interrupted sine wave that some cheap hz meters might interpret as a higher than 60 hz output, even though gen is still turning at equivalent of 60 hz (1800 rpm). ( meters use differentl methods to measure hz, some methods are more susceptible to errors)

I suspect your hz meter is being fooled and 90 hz is not real.

This is not a big project. As I already said I'ld check that brushes are not sticking, broke , or worn. Service manual tells you where they are and how to measure them. Down load the service manual (965-0500) I listed in post 3, and look at paper page 51 for how to measure brush wear. They are easy to get at.

Last edited by len k; 11-10-2017 at 09:37:46 PM.
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Old 11-30-2017, 01:54:42 PM
Drangd1 Drangd1 is offline
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Default Re: Onan 6.5 NHD-FB/1M repair or sell?

Jumping in as an retired troubleshooter.

I always measure HZ and voltage at the same time, two meters of the same make and model. For me that is two Fluke 87's. You want to see what is happening at a moment in time.

One thing that has not been mentioned is the grounding of the generator. Worth a check to see if it is tight. As mentioned before a loose connection could cause this issue.

Are your meters peak sensing or RMS. Big difference in readings, if peak the spikes could be real/measured. Root mean square meters in simple terms average the readings. Do you have anyone that will loan you an Oscilloscope? I would love to see the trace when the HZ jumped.

I lean towards the loose/corroded connection theory some where near the voltage regulator. That is an easy but possibly dirty check.

You mentioned that an electrician tested/inspected your electrical system. Did he measure your grounding electrode? With two sources of power this area can get complicated quickly. It takes a special meter and you drive stakes in the ground for readings. Or spend more money than I have and get a direct read meter, ~$2000. The generator and the electrical service should share the same ground. I missed it if you have a transfer switch, 3pole? 4pole?

Side note anything with electronics should have a surge arrestor ahead of it.
The point of use plug strips work well. I bought one from Amazon when I put in my new furnace. Even my garage door opener/microwave has one. Mother board for it is $160 and a new opener is $139. To do surge/spike correctly you need to install two units, one at the source/panel/meter/generator and the other one at the point of use. Your UPS's will serve this function. Do not get caught up in the "We pay 1 million dollars for damaged equipment." It is almost impossible to prove to collect. Even with all my test equipment I could not prove it, as you need active real time monitoring down to the sub cycle range. I have done it in a lab, but that does not count.
Pick the the one with the highest joules and hope it is enough. If lightning strikes less than a half mile away. Probably not. Grandmother used to unplug stuff during lightning storms, so do I way cheaper in the long run.

Sure would like to know the solution when you find it.
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Old 11-30-2017, 02:15:26 PM
Jim Marcozzi Jim Marcozzi is offline
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Default Re: Onan 6.5 NHD-FB/1M repair or sell?

With a 90-120 HZ increase, you'd hear this engine sound like it was attempting to take off to the moon when it did it...if it really were speeding up 50-100%. In fact most VRs could not even back off the field enough to keep the voltage steady at those RPMs

The first place I'd start looking is the VR, field wiring, brushes and AC feedback into the VR. If the field is getting intermittent current and quickly interrupts the AC power output or "rattles" it, many frequency meters will count the extra spikes as a waveform peak and factor those in on their freq calculation, giving you a false HZ reading.
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