How to Increase Generator Voltage

[tkbowers]

I have an Onan Marquis 6500LP generator, Model 6.5NHMFA26115C, S/N A953989409 (electronic ignition) in my motorhome with just under 1,000 logged hours. What is involved in bumping up the output voltage?

While dry camping this month, I was charging my batteries, and the automatic transfer switch dropped out for about a minute not long after starting the generator. It re-engaged on its own at which time charging appeared to proceed normally.

The output voltage on my generator generally runs a bit low (110 to 112 VAC), and I'm thinking that a momentary dip below this output may have caused the interruption. I replaced the transfer switch (Esco ES50M-65N) in June of 2014 and assume that this equipment is still functioning properly.

Thank you.

Tom

1994 Foretravel U-240

[wolfe10]

Tom,

Is that 110-112 VAC reading on a good digital voltmeter or on your OE analog gauge (known to become quite inaccurate)?

And, on our model, the VAC is electronically controlled.

I am assuming that the generator is running just fine (not "hunting" or changing RPM). If it is, then we can discuss a tune-up/clean propane regulator.

[kaypsmith]

The brushes may be having an issue, this unit appears to be several years old.

I wasn't able to find a manual for that model # online. I have in the past seen an issue where they have become worn and the spring is slightly weak causing a similar issue just after startup.

[wolfe10]

That would be an inexpensive and fairly easy thing to check/replace.

And, with the old brushes out, you can look and see if you need to polish the surface they ride on. Again, not a big job.

[tkbowers]

I'm responding to posts from a number of individuals.

Yes, I used a hand-held digital voltmeter. If the voltage is electronically controlled, I assume that means that it is not adjustable. The generator engine appears to run fine.

New brushes were installed this past February, but no mention on the invoice of polishing the commutator. How do you polish this component?

[kaypsmith]

Tom, I checked your ATS specs "The ESCO ES50m-65N automatic transfer switch offers a 30 second time delay to allow the generator to get up and running. The unit monitors for low voltage on the generator side with a cut off voltage of 90 VAC" This being the case, if it is working properly, 90 volts would have to have been achieved for the dropout, voltage this low can be devastating to your household equipment. I would highly recommend that the generator be monitored

with a voltage monitor from startup for a while. I would only have a 1500 watt element style heater attached and turned on highest setting for the monitoring session, also insure the ATS is not in line for testing. Is this a 3600 or 1800 rpm

unit?

[tkbowers]

Thank you for the information on my ATS.

My generator runs at 1,800 rpm.

Please explain your statement "...,also insure the ATS is not in line for testing."

[kaypsmith]

1800 rpm is very good, this means that the generator uses four windings 3600 only uses two, these numbers mean that the generator is heavy duty versus lightly built. 1800 rpm will outlast 3600 at least three to one or more, ie., 1000 hours on 1800 is like 3000 or more on 3600.

The reason for testing before the automatic transfer switch (ATS), is to insure that the generator itself is the failing point. An ATS is an raw form electronic device, even though it is relatively new, doesn't mean it is failsafe. An electric surge of any kind,
such as bad grounding, or an overvoltage spike can weaken or take that device out, or could even be faulty from the beginning.

By removing that from the equation, you are getting an honest reading about the condition of the generator. If bad ATS possibly a reason to go back on the seller for replacement, of if it is the culprit, much cheaper than major generator repairs.

Also to polish the commentator, with brushes out, use a very fine abrasive, such as 800 grit sand paper or emery cloth, spinning the stator slowly, apply enough pressure against the abrasive against the area that the brushes ride on. Also observe that there is no burned looking places across the dielectric (separators) between the copper pieces in the commentator, just one such place will allow the generator to be at less than 60 cycles, which will impede the voltage output. 110 to 112 voltage is an acceptable voltage, you just don't want any brownouts.

Good luck with your project and happy holidays, Kay

[RoryTug]

Could it have been altitude?

[tkbowers]

Kay, Now I understand, measure voltage upstream of the ATS. I'll be dry camping at Quartzite next month and will have many opportunities to do this. Thank you!

[kaypsmith]

One thing that I didn't make clear, but thought with the info on the ATS, if the voltage drops below 90 volts for any reason, the ATS relay will drop, then it does have a 30 second delay before it will engage the relay again on the generator side. That's one reason for checking the generator output before it gets to the ATS, also it takes the ATS out of the equation for testing purposes. Also this dropout if happening often could be signs of other things going wrong. If the dropout keeps happening, by other indications this is not the first time that it has happened, something as simple as a near break in the wire or loose connection in the generator, or even between the generator and

the ATS. Don't forget the neutral wire and connections are as important as the hot wires. Again, good luck, Kay

[tkbowers]

Kay, The ATS relay drop has happened only once since I had my generator repaired almost a year ago.

Prior to this repair, I was having a similar problem, but with much more frequency. However, when the generator ran properly, voltages hovered around 120 VAC. This low voltage condition was a known issue with my particular model, and was caused by operating it in high humidity conditions. I attached a copy of the Onan support bulletin for reference.

The repair was successful, but I noticed that normal voltages were now in the range of 110 to 112 VAC. I was told not to worry about it and anything above 108 VAC was acceptable.

You've given me a lot of good information. I use my motorhome every month, will observe and keep an eye on things, and perhaps update this thread.

Thanks again. Tom

Onan Product Support Bulletin 637.pdf

[kaypsmith]

Tom, I'm glad that all is well, and the service bulletin is available, thanks for sharing this, I will add it to my notes as well.