Generator power issue, even though it runs fine.

[gvjackson]

AC appliances with a motor have an issue when running with power from our generator (Onan QD 7500), but are OK with shore power. I have used a Kill-a-Watt meter to check the quality of the power from the generator, and it shows 119.5 Volts and 59.9 Hertz, which seems A-OK (Of course the Kill-a-Watt does not provide info on the waveform: sine/square/other).

With generator power, electric motors run at some small fraction of their normal speed, while they run at normal speed with external AC power (shore or a portable generator). Resistive loads, like a soldering iron, work fine, and the Converter/Charger provides DC power and charges the batteries, although battery recharge times seem longer. The Norcold 1200 fridge has obviously been running fine on this faulty power, but then, it is a resistive load as well.

The fact that I had a generator problem came to light when I was using two forced air heaters to load the generator for the monthly exercise and noticed that I could barely hear them running, then noticed the fans were slowly turning. Since the generator starts easily, runs fine, even responds normally to changing loads, I foolishly thought both heaters were malfunctioning, until I plugged one directly into shore power and it spun up and ran normally. It was then that I realized that the loss of two microwaves on a prior trip happened on generator power at rest stops, having run fine at the prior camp sites on shore power!

The Onan troubleshooting guide in the manual and online is all about not starting, or starting but getting no power. No mention of bad power!

I have checked the ATS (auto transfer switch) and it is operating normally and the internal components are free of char. The Powerline Energy Management System also seems to operate normally. Have reset the breaker on the generator, and the house breakers as well.

Was about to schedule a generator service visit, but that could be a waste if the generator is fine and I am missing something obvious to others, so I am checking with the forum. I found nothing similar to this issue with a forum search, though the parameters are pretty broad.

Thoughts on some component check I have missed? Some test(s) to run? Similar experience/solution? Or, Thoughts on what might be wrong?

Thanks for any guidance!

[twinboat]

Load the generator up with the Kil A Watt connected.

I believe the 7500 is a variable speed unit. If it doesn't increase the RPMs enough, the output power will drop off.

It may be as simple as a fuel filter change to get it running properly.

[xrated]

It is definitely a generator problem. There are only two ways to change the speed of an AC Motor.
1. Change the number of poles inside the motor (not practical to this discussion and of course excluding two speed wound motors)
2. Change the frequency (Hertz/cycles) of the applied voltage. This can be done pretty easily by using a Variable Frequency Drive (VFD) which is made specifically for that purpose.....but the Onan generator isn't a VFD, so there is something going on with the generator, because you said that things work normally on shore power.

Twinboat may be on to something with his reply....I don't know, as I'm not familiar with that generator.....but his comment makes perfect sense. If the generator is slowing down under a load, that will decrease the frequency (Hertz/cycles) of the applied voltage and cause the exact issue that you've described.

[pbpaul]

Don’t know if this will help you but it is possible to have what appears to be good voltage yet when you throw on a load, find that your power source is not capable of delivering sufficient
current. As an example, that is often the case with a car battery that has a lousy connection at a good battery. Your dome light, which requires little current is getting enough to be bright but when you hit the starter, the poor connection just doesn’t allow enough current to flow to turn the starter motor and turn the engine over. I know we’re talking two different systems but the principle is the same. Either the generator is not providing sufficient current in the first place or else there is a bad connection or switch or breaker or something along those lines between the generator and the load. Like you, I would want to eliminate anything like that before calling the generator people even though it could be the generator itself in the end.

[kcmusa]

https://www.flightsystems.com/pdf/on...ting-guide.pdf

[xrated]

Originally Posted by pbpaul

Don’t know if this will help you but it is possible to have what appears to be good voltage yet when you throw on a load, find that your power source is not capable of delivering sufficient
current. As an example, that is often the case with a car battery that has a lousy connection at a good battery. Your dome light, which requires little current is getting enough to be bright but when you hit the starter, the poor connection just doesn’t allow enough current to flow to turn the starter motor and turn the engine over. I know we’re talking two different systems but the principle is the same. Either the generator is not providing sufficient current in the first place or else there is a bad connection or switch or breaker or something along those lines between the generator and the load. Like you, I would want to eliminate anything like that before calling the generator people even though it could be the generator itself in the end.

It's not a current (amperage) issue....it's a frequency issue! Huge difference between varying speeds in a DC motor AND varying speeds in an AC Motor. Read my post #3 on the only two ways to change the speed of an AC Motor......which is what is happening when he is running on generator power. For some unknown reason, at this point in time, his generator is supplying a voltage at some number LESS than 60 cycle AC.

[gvjackson]

Thanks all for the replies!

Yes, frequency should be king in this issue. I will repeat the Kill-a-Watt testing with various loads. However, if memory serves me correctly (which is a dangerous thing these days) prior to the testing with the meter, I do not recall a difference in the speed of the heater as I cycled it from fan-only (very little load), up through the 500W, 1KW, and 1.5KW settings. So, using both heaters, I will do the same with the meter in the system, collect the observations, and report back.

By the way, as I cycled through the heater's settings, I could hear the generator ramp up exactly as it normally does when I have exercised it, which is why I hadn't suspected it.

Kindest Regards!

[xrated]

Originally Posted by gvjackson

Thanks all for the replies!

Yes, frequency should be king in this issue. I will repeat the Kill-a-Watt testing with various loads. However, if memory serves me correctly (which is a dangerous thing these days) prior to the testing with the meter, I do not recall a difference in the speed of the heater as I cycled it from fan-only (very little load), up through the 500W, 1KW, and 1.5KW settings. So, using both heaters, I will do the same with the meter in the system, collect the observations, and report back.

By the way, as I cycled through the heater's settings, I could hear the generator ramp up exactly as it normally does when I have exercised it, which is why I hadn't suspected it.

Kindest Regards!

In your first post, you stated that electric motors ran at some reduced speed when operating from the generator supply.....I assume that you were talking about the fan motors on the heaters also...Yes???

[gvjackson]

Originally Posted by xrated

In your first post, you stated that electric motors ran at some reduced speed when operating from the generator supply.....I assume that you were talking about the fan motors on the heaters also...Yes???

Yes, that is correct.

Here are the numbers from the variable load test using the Kill-a-Watt and two heaters for the load. Not what was expected! Read them and weep (with/for me). Hopefully this formats OK, but might not be good on a small screen.

Condition --- Volts ----- Hz --- Amps (via Powerline Display)
Start -------- 120.4 --- 59.7 --- 2
+3 mins ---- 120.6 --- 59.7 --- 2
Fan Only ---- 120.6 --- 59.7 --- 2 (Fan @ Slow Speed)
500W ------- 119.6 --- 59.7 --- 6 "
1000W ------ 119.3 --- 59.7 --- 8 "
1500W ------ 118.7 --- 59.7 --- 13 "
2000W ------ 118.2 --- 59.7 --- 15 "
2500W ------ 116.9 --- 59.7 --- 19 "
3000W ------ 116.6 --- 59.7 --- 23 "
All Off ------- 120.4 --- 59.7 --- 1

Voltage readings varied +/-0.2V, never saw the Hz vary. Checked Kill-a-Watt @ house before leaving. It read 117.7 @ 60.0 Hz. Will check with my portable generator. Could 0.3 Hz make that much of a difference for electric motor speed? Can't imagine it, but, I don't know.

Concerned and confused in NEOhio.

[twinboat]

How did the fans run during the test ?
Did they slow down or run normal ?

[gvjackson]

Originally Posted by gvjackson

Could 0.3 Hz make that much of a difference for electric motor speed? Can't imagine it, but, I don't know.

Answered that question with the portable generator test, which averaged 115 volts @ 59.0 Hz, and it powers the motors fine. So, still lost in space, or is that electrons.

[gvjackson]

Originally Posted by twinboat

How did the fans run during the test ?
Did they slow down or run normal ?

Same slow speed from fan-only mode to 3KW load. Did not detect any variation in speed as the load incremented. I do have an rpm counter for my RC helicopters, but, I don't think that would add anything at this point.

[bfisher003]

I wonder if there is a problem with the actual inverter part of the generator?? It kind of sounds that way to me.

[twinboat]

Originally Posted by gvjackson

Same slow speed from fan-only mode to 3KW load. Did not detect any variation in speed as the load incremented. I do have an rpm counter for my RC helicopters, but, I don't think that would add anything at this point

.

Did you use the same outlet as the Kill A Watt ?

Could the heaters be running off your inverter ? Could have a tripped input breaker.