Generator Realities: Troubleshooting

For the guy who doesn’t want to learn anything about a generator or who simply doesn’t have time to learn, the following happens more than you would think. One of my friends bought a new diesel pusher motor home with a nice complicated name brand generator that burnt up two expensive control boards in the first year and a half of ownership (see footnote).
The following is what happened to one guy who wrote me 5/2010.  I can tell he is a smart guy, and had he made time to get a manual for this generator set I think he could have made a few simple checks on his own and determined the trouble. He just wasn’t aware of what a lot of repair shops will do to you if you let them.  Here are snippets from the emails during our conversation.
What I am looking for is an economical replacement for the 7.8KW Power Tech brand generator head on my RV.  I just got the unit back after spending way too much money to be told that the Kubota diesel is fine but the rotor and stator are bad and I need a new generator head to the tune of $1800 to $2300 plus labor.  At that point, I decided to get smart and do it myself plus, I like the KISS principle.
I was curious how he was treated by the repair shop, and Jay was kind enough to share the following with me when I asked for more detail.
LOL.  They first threw a new regulator at it to the tune of nearly $400 including overnight shipping and then when that didn’t work, they determined that they had to pull the whole generator unit out from under the coach.  That took about 3 hours. After ohming it out and talking to the manufacturer in Florida, they ended up charging me for a total of 6.5 hours of labor (included installing the regulator, pulling it out, and “diagnosing” it) @ $110/hour plus the regulator for a total of about $1150.  All that got me was a non-working generator sitting in the back of my pickup and a new regulator.  To top it off, they told me that this was an older brush-style generator and when took it apart, it turned out to be an exciter type so I’m not necessarily taking their word as to what is wrong with it either.  They’ve quoted me about $2300 for a new 10KW generator head plus $1100 labor to get it back in and running and that doesn’t include servicing the engine end.  I’ve found an electric motor rewinding shop that said they’d diagnose the rotor and stator for $30 once I have it apart so I may do that just to see what’s really wrong.

That’ll teach me to have an RV shop do generator work.  This is my first motor home (just got it in February) and I should have done it myself instead of having someone else do it for me but it was new to me and I was too hesitant.
It’s very typical for these RV shops to hire less than a good generator tech. Here’s some advice if you are stuck with an expensive and complicated generator set.
Call the generator manufacturer and ask them who is qualified to work on your generator set! Ask them if they sell a manual for the unit. After you’ve read Jay’s story you can see the value of paying money for a good manual and doing a little arm chair reading about it. An average tech should have proved the gen stator and rotor good or bad in 15 minutes. Looks to me like they had a less-skilled guy do the work and they charged $110 an hour while they attempted to learn the gen set.  Jay said they even had the wrong wiring diagram for his generator!

Update: 6/11/2010 I heard from Jay.  He took both rotor and stator into the rewind shop and they could find no fault with either part! Jay put the generator back together and mounted it up to the engine, he called the generator manufacturer and they were most attentive to his problem and guided him through some tests that proved the exciter, rotor, stator and more were good! Later they guided him through a voltage regulator adjustment and he has a proper output at no load.. more testing to be done, but I bet he is fine.

One thing to note here when and IF you are buying a new or used motor home, there were a lot of companies that built motor homes with near zero concern or consideration as to how an owner or repairman would gain access for repairs. If we analyze what went on here, the customer paid the RV repairmen a good chunk of money to gain access to the unit. Had the Coach Builder designed it even half way right, there would be access to test points to prove the gen head good or bad, and access to replace a bad VR, generator starter and solenoid etc. Certainly their diagnosis was bad.. but a large portion of the labor was spent in gaining access. Hats off to the generator head manufacturer for supporting the owner! If you buy a motor coach slapped together with little access, Murphy guarantees you’ll need access soon!

Update 7/2/2010:
I received a nice email from Jay today.

Good Evening George,

After several weeks of work and travel related delays, I’m pleased to let you know that I was able to test run the generator tonight and I ran the entire motor home off of it as a load test.  By chance, my Kill A Watt P4400 arrived in the mail today ($19.99 off so I was able to use it to check my voltage and with both air conditioners, the microwave, and the refrigerator running, the generator held at 116.5 volts.  No-load voltage is right at 122 volts.  Needless to say, I’m as pleased that it’s working as I am aggravated at the RV tech that wired the regulator incorrectly.

I did take your advice and made myself a hinged front panel for access into that electrical box in case I ever need to get into it again.  I also changed the connections from having the coach hardwired into the generator to putting a 50A receptacle on the generator so that if I ever do need to use that generator for powering the house during a power outage, I can do it without running through the coach breaker box and receptacles.  Now to get it put back into the coach.

Thanks for all your help and encouragement.  I hope that someday I can still buy a PMG from you but for now, it’s nice to know that I can now troubleshoot what I have.

Hope you have a happy Independence Day,


His comment about the PMG? Jay had originally asked about a replacement for his generator head that was pronounced dead by a RV Shop Repairman. I knew there was a fair chance his gen head was just fine, and it would have been unethical to sell him anything without encouraging him to get a competent generator guy to look at the stator and rotor. I believe Jay’s story is far more typical than we would like to think. The more you know about your own equipment, the better off you are.

One last note….if you don’t own a Kill-A-Watt meter, why not? I remember trying to run a pellet stove years ago with a small generator during a power outage. It wasn’t long before the combustion chamber scooted up and the stove just didn’t run right. Later I checked the frequency with an old reed type instrument and found it to be running at 55hz, and low voltage of course. The control board was expecting 60hz, I think the sine wave was the basis for timing as per other functions the board controlled as well. The combustion fan was powered by an induction motor, and of course it was running off 55hz and NOT providing the combustion air the stove needed. Had I had a $20 Kill-A-Watt I would have whipped out a screw driver and adjusted the governor. On this particular unit, I ended up drilling a hole in the plastic side cover to insert a screw driver into the governor adjustment.

As a final note: Jay is a DIYer, we can see from his last email message he is a busy man and decided to rely on others to do the basic trouble shooting.  The more complex the generator is, the more likely you are to involve others in the repair process. Jay has problem solving skills. Just imagine how much more he would have paid if he didn’t have the DIYer background. We are now the minority, most thirtyish men that I know barely know where the oil fill is under the hood of their own cars. No matter how challenged you are, the Kill-A-Watt and an access point between the PMG and breaker would have given you all the information you needed. The engine either runs or it doesn’t, the generator either spins or it doesn’t.



Gen Parts are often made in lots under contract. The best price is normally obtained when circuit boards are made for the production line, the company decides what the failure rate might be and asks for a certain amount of spares to be made at that time as well. When spares leave the shelves faster than expected, there are times when the price is raised quite high to slow the trend. The options the company might consider:  Claim the unit is now ‘manufacturer discontinued’, or spend a lot more money per part to make another (often smaller lot). Sometimes the quote the company gets to have a short run made is reflected in the price of current spares on the shelf.

I once was gifted a really nice (like new looking) Makita generator, the repair shop told the owner there was no spark at the plug and the electronic igniter module was manufacturer discontinued, the company did not have any kind of replacement part to fit. In other brands, I have seen that the price of these little modules were so high, people would naturally ask themselves.. “If I buy that piece, what will fail next and how much will the next part be?”

Again, if it isn’t part of the design, it can’t fail. Some will continue to tell you that all this sophistication is necessary. I suggest all you need to do is meet the standards for Electric power as expressed by the ANSI standard, and you need enough generator to start your loads. Outside of Electronic modules in engines, most generator failures are the result of a gen head failure. If you break failures down into categories, you’ll find most problems= engine OK generator head makes no power  just as in Jay’s situation above. The reason they threw the voltage regulator at the problem was it has a high probability of failure based on their experience. Of course they were wrong in Jay’s case, but Jay was paying for the new part and labor, so why not throw parts at it? After the VR, we see failures like the diode being bad on the rotor in brushless designs, lack of excitation voltage because the rectifier is bad brush types and more. PMGs have none of these parts in their design, but it is more expensive to make a high performance PMG.

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