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RVing message boards => General Discussion => Topic started by: CapnDirk on November 05, 2017, 05:55:34 PM

Title: Smoked the generator?
Post by: CapnDirk on November 05, 2017, 05:55:34 PM
Well, disaster has struck apparently.  I've had it running many times sorting things out in the carb, ignition, fuel, and 12V systems and have been making steady progress and engine is running and starting fine.  However, while running it trying to figure out the AC voltage issue, the generator body itself started spewing white smoke with that electrical smell.  Nothing has changed, and given the numerous times I've run it I can't fathom why the generator windings or whatever would toast.

Anyone have any ideas?  Output on the two AC wires was 153V

Onan 6.5 3cr/16004p 120/240

Thanks
Title: Re: Smoked the generator?
Post by: Gary RV_Wizard on November 06, 2017, 06:38:37 AM
Moisture is the #1 enemy of the windings on the stator and armature and leads to eventual deterioration of the insulation coating on the wire and a short circuit. Regular operation under load is the prevention - the internal heat build-up drives out the moisture. A failure now could be a result of problems that originated years ago.
Title: Re: Smoked the generator?
Post by: CapnDirk on November 06, 2017, 09:22:08 AM
Thank you Gary.  That makes sense.  It has been damp and rainy with the generator outside in my driveway, and can explain why I was able to run it so many times without a problem.  I covered the carb and air filter area do keep that area dry, but the winding area would have been open to water. 

Can we say that given that the unit had been started for 1-2 minutes several times in the past that I can rule out some other component failure/short?  Don't know if it can be repaired but certainly would not want to do it again.

Best regards.
Title: Re: Smoked the generator?
Post by: Gary RV_Wizard on November 06, 2017, 01:43:28 PM
Hard to know whether some rain is a problem or not. It may be the wire coatings have been deteriorating for years and the latest bath was enough to cause the immediate problem.

The housings aren't designed to be waterproof, but they probably don't expect floods either. Dampness and humidity is sufficient to cause problems over the long term, so running the genset periodically to dehydrate is wise preventive maintenance.
Title: Re: Smoked the generator?
Post by: Larry N. on November 06, 2017, 02:18:46 PM
Quote
the unit had been started for 1-2 minutes several times in the past

That type of usage can cause problems. It's not long enough to warm up anything, including the engine, nor to charge batteries (it'll drain them a bit), but it is long enough to generate some additional moisture, so may exacerbate the problem, especially if you're in a humid area. Remember, too, that each time you start anything electrical, there is some sort of current surge (may be minimal or not, depending). That shock alone may not be enough to cause problems, but might add to other things.

Understand that I don't mean that starting and then running for a couple of minutes is a problem for one time, just that repeatedly doing that, especially without getting things warm soon after, can give long term headaches.
Title: Re: Smoked the generator?
Post by: CapnDirk on November 06, 2017, 02:57:42 PM
Thanks Larry.  Starting it for short periods of time was to work out running, and other electrical problems.  My mention of it was to indirectly point out that I likely did not have a hard short at that time.  Humidity is 75% currently and rains offten.

So, is there anything I can do, or do I scrap something I recently bought and put money into?

Thanks for the help.  Would not have thought that something that lives outdoors would smoke due to moisture.
Title: Re: Smoked the generator?
Post by: grashley on November 06, 2017, 05:11:44 PM
I have no idea of the cost, but it sounds like you have a good motor, chassis, and electrical components.  You just have a bad generator portion of the unit.  Can the generator be replaced or repaired?
Title: Re: Smoked the generator?
Post by: Bob T on November 06, 2017, 05:44:41 PM
I would suspect that the generation part of your unit could be rewound or have the windings replaced.
Would be worth looking into as may be cheaper than purchasing entire new diesel Genset
On the other hand, with new unit you would get warranty, zero hours to start.
Having no idea what the cost of entire new unit is, it may be difficult decision.
Title: Re: Smoked the generator?
Post by: Willandgiselarv on November 06, 2017, 06:10:21 PM
I had the same thing happened to my 13kw generator on my boat, the engine was fine but because after service a panel was not put back on water dripped onto the "generation " portion ...had a rebuild "generation part replaced cost was 6k for parts and labor . It was a 13kw Westerbeke now owned by Cummins, same w Onan. If you are in Northern California there is an excellent shop that just deals w generators.
The engine was not touched.
Title: Re: Smoked the generator?
Post by: CapnDirk on November 07, 2017, 09:54:01 AM
Grashley:  You are correct in that the engine is now running fine, and I put a new fuel pump on it.  It has 120 pounds of compression and even on both cylinders.  If the engine was a problem to, I would not consider saving it.  At this point I've been looking for the cause (several here seem to agree) and possible solutions.

Bob:  That was my thought to, I don't think I'm going to find another stator to buy.

To all:  Do you think the armature survived?  and just the stator smoked?   And does anyone have any test procedures to make curtain there was not another cause (beside moisture) to make sure I don't burn a replacement.

Thanks to all.
Title: Re: Smoked the generator?
Post by: Roy M on November 07, 2017, 10:54:28 AM
You need to remove the generator and with the manufacturer's spec sheet and wiring diagram in hand check rotor, main winding and exciter resistance. I do suggest taking it to an experienced generator tech, you don't want to start throwing very expensive parts at it without thoroughly troubleshooting first.
Title: Re: Smoked the generator?
Post by: Bob T on November 07, 2017, 03:21:22 PM
If you have the manufacturers schematics you could ring out the windings on the generator but a regular meter may not tell the full tale.
You may need to use a meggar which will put higher voltage through windings but no amperage.
Then you should be able to tell if windings shot or varnish burned off.
That should let you know if windings faulted.
Here is a link to an insulation testing document you can have a look at https://www.instrumart.com/assets/Megger-insulationtester.pdf
Roy M made a very good recommendation if you arent experienced in this type of troubleshooting, take the unit to a GOOD experienced generator shop.
Title: Re: Smoked the generator?
Post by: sadixon49 on November 07, 2017, 03:35:48 PM
Or as we used to say in the electric shop at work, "once you let the magic smoke out, ( all things electric run on magic smoke), you have to send the unit out and have the smoke put back in."
Title: Re: Smoked the generator?
Post by: CapnDirk on November 11, 2017, 10:19:21 AM
Thanks guys.  I do know my way around electricity and a meter from other disciplines.  From what I'm hearing my plan is to get it appart, test the armature myself, and take the stator to the shop.  Anything else I should check?  Someone mentioned the exciter?
Title: Re: Smoked the generator?
Post by: Charlie 5320 on November 11, 2017, 11:05:09 AM
The exciter voltage comes from the regulator, and varies on an onan.  Exciter  voltage is applied to the slip rings applied by the brush set. Smoke from the generator = big bucks to fix even if you do it yourself. Good luck trying to find a company to rewind either stator or the rotor. One thing you can fix is where the winding is coupled to the split rings, if it burnt there. My buddy had a 7000 watt onan that had a bad connection where they crimped the winding wires to the slip rings. We cleaned and soldered them, don't know why they don't solder them from the factory. I also bought a generac 6600 a few years ago that didn't work, got it for $200.00. After investigating why it didn't work, it appeared as though it had never been ran. Oil, air filter, plugs looked brand new. It also had a problem where the windings were attached to the rotor.  I have it set up for backup power for my house, and have used it a few times. It will even run my house AC if needed.
Title: Re: Smoked the generator?
Post by: CapnDirk on November 11, 2017, 11:09:49 AM
Thanks Charlie.  In my research it seems that finding another stator is going to be next to impossible.  I still find it odd that moisture would have done it in, but uthers know better than I.
Title: Re: Smoked the generator?
Post by: Charlie 5320 on November 11, 2017, 11:40:08 AM
Thanks Charlie.  In my research it seems that finding another stator is going to be next to impossible.  I still find it odd that moisture would have done it in, but uthers know better than I.
Well trying to run power through some wet windings will cause a short for sure. Some people that only run a generator for a short time finds this out sometimes. Even running one when it is very cold out will cause moisture to form in the windings when it cools, so I don't do it. I'd rather fight the carb issues than shorted windings. I don't run my generators during winter, but when I do run them, I do so for a couple hours at a time.
Title: Re: Smoked the generator?
Post by: CapnDirk on November 11, 2017, 12:10:43 PM
There seems to be two camps on this.  Exercise the generator in winter, and don't due to moisture.  I wonder if those that advocate exercising are in warmer/less humid areas.  Here in the Pacific Northwet we get 1-7 inches a week for months, and right now even though not raining, the humidity is 90%
Title: Re: Smoked the generator?
Post by: Charlie 5320 on November 11, 2017, 01:20:38 PM
I look at it as the fight between two evils. If you don't run it the carb gets crap in it from the moisture. If you run it to keep the carb clean, and run it long enough to get the moisture out of the windings, when you shut it down the moisture will again form on the hot surfaces. I run mine monthly till Oct. then don't run it again till March, but I live where it gets pretty cold. The generator is the last thing I think about when it is 0 or below outside. I'm more worried if I can get the tractor started so I can use the snowblower.  ;D  I do keep it in the garage but NO heat. High yesterday was 36 degrees.