Interesting Generator Issue

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Interesting Generator Issue

December 26, 2011, 09:55:32 am

We drove the coach over to the kids' house on Christmas day and parked it in the driveway. About 5 hours later I started the generator; mostly because I had actually only started the generator once since we bought the RV and thought it was time to see if it worked longer than a couple minutes. I was watching the coach battery voltage and it got my attention when the voltage went to 15vdc and kept climbing slowly. After 5 minutes it was at 17vdc and I shut the generator off and started the engine... the voltage dropped back down to 14.5vdc.

Back in its spot behind the shop with 50-amp shore power the coach voltage showed 14.5vdc still.

This seems somewhat confusing since I thought that the generator merely replaced shore-power and the converter provided the DC power tot he coach (and batteries) so there should have been no difference between shore-power and generator power.

I'm going to test this again today and see what happens.

Craig

Re: Interesting Generator Issue

Reply #1 – December 26, 2011, 10:03:16 am

Yes, that does sound particular. Depending on converter, charger or inverter charger, I guess some of the older less complex ones could vary output voltage based on input voltage, so I would start by using a voltmeter to check 120 VAC at any outlet in the coach. If OK, you have a converter (or charger or inverter/charger) issue.

I guess it is also possible that you have a loose or corroded connection between charging unit and battery and it is not properly sensing battery voltage.

Re: Interesting Generator Issue

Reply #2 – December 26, 2011, 10:35:54 am

It certainly sounds like a converter issue. Most 93, U225's did not have an inverter. The converter is located in the compartment accessed from the drivers side that goes under the steps to the rear of the generator compartment. Some of the older converters were affected by higher input voltage so my guess is that is what is going on.

As Brett suggested, run the generator and check the voltage at an electrical outlet. Don't rely on the 110V meter on the cabinet above the table inside the coach door, they can be very inaccurate. You can adjust the voltage output from the generator by setting the generator motor speed. If you have an Onan Emerald III, there is an idle speed screw head near the top of the engine just to the left of the carburetor that reaches back under the cowling. It may be very hard to turn but by turning it counter clockwise it should reduce the rpm's of the generator and reduce the voltage output. I kept mine set a 117V with no load. With both air conditioners on is should not go below 110V.

My guess is that at some point you will need to replace the converter. I didn't want to spend the money for an inverter conversion so I purchased an Iota 90 amp converter/smart charger from Best Converters online. The 90 amp charger recharged the house batteries in just a few hours, much faster than the OEM charger.

Let us know the outcome when you figure things out.

Re: Interesting Generator Issue

Reply #3 – December 26, 2011, 10:47:00 am

Kent,

On my PowerTech diesel generator, adjusting the rpm adjusts the cycles per second or Hertz, 60 being the target setting.

Adjusting the voltage regulator adjusts the A/C voltage output. My voltage regulator is in the metal box containing the outside start/stop switches and breakers.

Wouldn't it be the same for the propane generators?

Re: Interesting Generator Issue

Reply #4 – December 26, 2011, 10:47:47 am

Kent,

I would NOT recommend adjusting generator output voltage by fiddling with the engine adjustment screw(s).

RPM determines frequency (HZ). The voltage regulator determines voltage. Yes, lowering RPM will lower voltage, but will mess up frequency.

If you are going to pursue this route, start by adjusting HZ to 60. If, with HZ set, voltage is incorrect start looking at the voltage regulator.

Re: Interesting Generator Issue

Reply #5 – December 26, 2011, 10:55:25 am

I had a Progressive Dynamics 80 amp model w/Charge Wizard in my '93 U280 as the replacement for the original. Great charger, no drama.

Re: Interesting Generator Issue

Reply #6 – December 26, 2011, 11:51:54 am

Craig,
There is a possibility of a second charging source that might be causing the problem. I don't know if the propane generators have one but I know on my diesel unit there is an automotive style alternator on the engine. If this alternator is going over voltage you would only see it with the generator running which matches your symptoms. It could be the "voltage sense" wire has a bad connection causing the output to go high. Just an idea.

Re: Interesting Generator Issue

Reply #7 – December 26, 2011, 11:52:00 am

Assure that the voltage meter you are using is accurate!
Last year I had an inexpensive digital voltmeter monitoring start battery voltage while the engine was running. Voltage climbed to 18v before I stopped and check voltage at start batteries with a Fluke, voltage was 14.25v. I disposed of the faulty voltmeter.

Re: Interesting Generator Issue

Reply #8 – December 26, 2011, 12:11:28 pm

Quote from: P. Wyatt Sabourin – December 26, 2011, 11:52:00 am

Assure that the voltage meter you are using is accurate!
Last year I had an inexpensive digital voltmeter monitoring start battery voltage while the engine was running. Voltage climbed to 18v before I stopped and check voltage at start batteries with a Fluke, voltage was 14.25v. I disposed of the faulty voltmeter.

It's always possible that the meter (which was the monitor on the dsahboard) was in error. Maybe even likely. I'll know more today. I think checking for 120vac at the outlets is the first order of business. I've had some reservations about the "converter" because it doesn't have a "smart" charger and could boil the batteries (which are lead-acid). I'm not comfortable with 24/7/356 14.5vdc on the batteries so something will have to be changed.

I'll know more once I get to the coach and start troubleshooting. I would have done more yesterday but family things were going on... and then it got dark.

Thanks for all the great advice and suggestions.

Craig

Re: Interesting Generator Issue

Reply #9 – December 26, 2011, 12:44:26 pm

Quote from: Rudy – December 26, 2011, 10:47:00 am

Kent,

On my PowerTech diesel generator, adjusting the rpm adjusts the cycles per second or Hertz, 60 being the target setting.

Adjusting the voltage regulator adjusts the A/C voltage output. My voltage regulator is in the metal box containing the outside start/stop switches and breakers.

Wouldn't it be the same for the propane generators?

Rudy and Brett, the information I posted is according to the Onan Tech at Cummins/Onan in OKC. He showed me how to adjust the voltage for my porpane Emerald III when I had it in for service in 2010. I am going by what he said and that it worked on my 93, U225. I don't believe the Voltage Regulator on the Onan is adjustable.

Now that I think about it, if he wasn't a whole lot better than their Cummins mechanics, I probably don't trust his advice as much as I do yours. Although he seemed pretty sharp, he was an old timer, I didn't have great experience with the Cummins guys at that shop. I think I trust you guys more than I do them so Craig you may rethink the advice on my post.

Where's Dave when you need him?

Re: Interesting Generator Issue

Reply #10 – December 26, 2011, 01:37:15 pm

You never want your freq over 63 Hz nor lower than 57 Hz, this is the 5%+/- that UL prescribes, for voltage 10%+/- 108-132 volt. Now with that said, you never want your generator to run above 125 VAC, some models will have a wire wound resister to burn up/out/open. Not good. There are so many models but you never adjust voltage by the throttle stop screw, if you have a mechanical governor, you can adjust it by the tension on the spring. If there is no voltage adjustment, just remember the DO NOT EXCEEDE 125 VAC, if the freq is 60 Hz and your over 125 VAC, get it fixed. Of course, having a dependable VOM that also reads hertz is a requirement.
Again, having the service manual for your model and spec number is highly recommended, most are listed on this forum, I suggest go have a read.
Any tech that recommends adjusting voltage by the throttle stop screw, could not be trusted to feed your pet dog.
FWIW

Re: Interesting Generator Issue

Reply #11 – December 26, 2011, 03:18:43 pm

The problem seems to be over-voltage from the generator. Measured at 127VAC. The manual says that there are transformer taps for changing the voltage but that it wants 127VAC no-load. I put a 1500watt resistive load on it and it went to 126VAC. So I'm going to have to investigate changing the output voltage. I really should also check frequency since they are so closely linked. I have a frequency meter but it's RF; but I might be able to set up an inductive pickup around a wire to a heater element that would give me frequency.

Either that or take it to someone who has stood a little close to the clue train.

Craig

Re: Interesting Generator Issue

Reply #12 – December 26, 2011, 03:23:30 pm

Craig, What is the frequency / hertz when your reading the 128 v ?

Re: Interesting Generator Issue

Reply #13 – December 26, 2011, 03:29:02 pm

Quote from: Dave M – December 26, 2011, 03:23:30 pm

Craig, What is the frequency / hertz when your reading the 128 v ?

I don't have a frequency meter for the AC system. Or, if one is on U225, I haven't seen one; certainly not the typical frequency meter (with the moving pins).

Craig

Re: Interesting Generator Issue

Reply #14 – December 26, 2011, 03:47:19 pm

Without a frequency meter either digital, analog or reed type, you are guessing. Guessing will not work.

Re: Interesting Generator Issue

Reply #15 – December 26, 2011, 03:56:29 pm

Quote from: Dave M – December 26, 2011, 03:47:19 pm

Without a frequency meter either digital, analog or reed type, you are guessing. Guessing will not work.

Yup. I have an RF frequency meter that might work if I make an inductive coupler on a power cord. Otherwise I'll have to wait until I can either get something suitable or find someone suitable.

Craig

Re: Interesting Generator Issue

Reply #16 – December 26, 2011, 06:18:27 pm

Quote from: wa_desert_rat – December 26, 2011, 03:56:29 pm

Yup. I have an RF frequency meter that might work if I make an inductive coupler on a power cord. Otherwise I'll have to wait until I can either get something suitable or find someone suitable.

Craig

I have used a Kill-A-Watt meter to get a quick, easy look at frequency and voltage. I have also used it to check how much specific appliances draw. It is available at big box home improvement stores.

We are currently on shore power. Kill-A-Watt shows 59.9 Hz and 122.5 VAC. Klein DVM shows 123.3 VAC. Extech DVM shows 59.97 Hz and 122.8 VAC. It appears the Kill-A-Watt I have provides a reasonable measurement of frequency and voltage. It might be a tool to add to your collection.

Re: Interesting Generator Issue

Reply #17 – December 27, 2011, 11:15:49 am

Quote from: J. D. Stevens – December 26, 2011, 06:18:27 pm

We are currently on shore power. Kill-A-Watt shows 59.9 Hz and 122.5 VAC. Klein DVM shows 123.3 VAC. Extech DVM shows 59.97 Hz and 122.8 VAC. It appears the Kill-A-Watt I have provides a reasonable measurement of frequency and voltage. It might be a tool to add to your collection.

I think it does look promising as a tool that can do more than just check power usage. And they're not all that expensive either. I'll go get one today.

Thanks.

Craig

Re: Interesting Generator Issue

Reply #18 – December 27, 2011, 09:03:42 pm

With one thing and another I frittered (and napped) away the day but got the Kill-A-Watt unit and used it to check the frequency of the generator at our U225. It's 70Hz!!! And 126VAC. So tomorrow I'll back off on the speed of the generator. Should be interesting but at least we're in a warm spell (42F) after weeks of 20-something.

Not sure why the generator is running so fast... I'm wondering if someone increased its speed for some other reason without thinking about what that does to the frequency. I do have the manual. Glad we were not off on a 4-day cross-country ski trip (which begins Thursday).

Thanks again for all the invaluable ideas. You folks rock!!!

Craig

Re: Interesting Generator Issue

Reply #19 – December 27, 2011, 09:28:31 pm

Craig, The normal issue for setting speed, is to adjust to where it sounds about right, that is never near where it should be, then people wonder why the generator always seems to have issues, one reason I laugh so much.

Re: Interesting Generator Issue

Reply #20 – December 27, 2011, 09:38:28 pm

Quote from: Dave M – December 27, 2011, 09:28:31 pm

Craig, The normal issue for setting speed, is to adjust to where it sounds about right, that is never near where it should be, then people wonder why the generator always seems to have issues, one reason I laugh so much.

The previous owner was an electrician... I would have thought he'd notice 16.5vdc (which is where the voltage settled after about 5 minutes). 70Hz is not good for running lots of things, either. At any rate it should be a fairly easy fix unless there was some issue with the generator's engine that caused someone to increase the RPM. I suppose I'll find out tomorrow. Hope it doesn't rain.

Craig

Re: Interesting Generator Issue

Reply #21 – December 27, 2011, 09:46:32 pm

In the generator business, electricians generally make more money for me than god with lightening strikes, for some reason they seem to have the idea they are the bright bulbs, all others are dim bulbs, so again I laugh cleaning up their mess.
Gotta love em.

Re: Interesting Generator Issue

Reply #22 – December 27, 2011, 09:48:39 pm

Quote from: wa_desert_rat – December 27, 2011, 09:38:28 pm

The previous owner was an electrician... I would have thought he'd notice 16.5vdc (which is where the voltage settled after about 5 minutes). 70Hz is not good for running lots of things, either. At any rate it should be a fairly easy fix unless there was some issue with the generator's engine that caused someone to increase the RPM. I suppose I'll find out tomorrow. Hope it doesn't rain.

Craig

My guess it will turn out just right. Foretravels seem to work that way somehow.

Re: Interesting Generator Issue

Reply #23 – December 28, 2011, 07:16:43 pm

Well, I know a whole lot more about our generator now and the frequency is set at 63Hz. I think that the generator will go longer on fuel, too.

Basically, the manual for the generator was less than useful and had paragraphs on adjusting the governor which were totally unrelated to the device installed on our coach. So I had to figure out how it works first, then find out what adjustments make the frequency go from 70Hz down to the 60Hz I want. After trying several methods I discovered a screw that, when turned, adjusted the governed speed of the unit. It's way back inside and hard to see. Nevertheless, after two hours of messing around I spent 15 minutes adjusting the screw and, "Viola!" (as they say in orchestra circles) I got the frequency down to 63Hz. It seemed reluctant to go down further and that's within spec for an unloaded unit. So we're good to go.

I'm going to have to spend some time scaling the rust off the unit and stabilizing and painting it this summer. That should be fun.

Thanks again for all the tips and hints. Foreforum people are the best.

Craig

Re: Interesting Generator Issue

Reply #24 – December 28, 2011, 09:35:16 pm

Craig, Nowhere have you mentioned the Make, Model & Spec numbers on what ever generator you are playing with. There are various governors used even on Onan generators over the years. There are the normal flyweight types and later they went to a electronic governor. During all your tweaking with the governor, don't forget the UL Spec is +/- 5% max, no load to full load.
Just a thought

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