Any generator experts?

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  #1  
Old 02-13-08, 12:03 AM
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Any generator experts?

Hi folks,

I'm asking for help rather than offering it this time .

I've got a vanguard-powered devilbiss generator (model GBV7000) with an electrical problem. I replaced the engine on it and started it. It was running a bit fast, but the first thing I did was plug in a saw to see if it would run it. It did. I began adjusting the RPM and after doing so, I tried the saw again and nothing. There is no power at the receptacle.

Ok...I pulled the back cover off the generator and looked at the wiring and capacitor. Nothing obvious. I pulled the stator and inspected...no burned windings or funny smells. I tested all the windings in the stator and they are good. I tested the windings in the rotor and they are good. I tested the diode and it is good. I checked continuity from the stator wires all the way through the switches to the receptacle and the connections and wires are all fine.

The only thing I can think of is possibly the capacitor being bad, but it checks OK with the ohmmeter (charges and discharges, and is not open or shorted to the case).

Any ideas? Thanks in advance.
 
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Old 02-13-08, 01:47 AM
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Have you tested continuity through the 12 pin molex connector? Looks to have 7 wires attached through it.

There also appears to be 3 circuit breakers all connected on the red wires. One is on the red lead from the 12 pin connector then goes to a junction. From there one feeds the cap and the other goes to the outlet(s). The final line from the junction goes to the "full power" switch.

Try a smaller load (100 watt bulb) and see if you get anything. If it does, then the cap may be weak.

You can checkout the wiring diagram here:
http://www.devap.com/repair_pdfs/at_search.asp?id=G

Cheers!
John
 
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Old 02-13-08, 10:06 AM
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I'm not an expert but merely sharing my thought. Is the engine running at the proper RPM (stupid question, I know.. but 100rpm can throw the frequency off enough to cause it to not work) I'm assuming everything is right and I'm off-base but I had to ask..
 
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Old 02-13-08, 12:18 PM
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This is a tip I copied from another site. It often restores power with conditions you describe. As an alternative to flashing a rotor winding with a battery applied to the brushes, an electric drill may be used.

Follow these steps to flash the generator:
  • Plug the electric drill into the generator receptacle. (Cordless drills do not work)
  • If the drill is reversible, move the direction switch to the forward position.
  • Start the generator
CAUTION
Do not get your hand or other materials caught in the chuck. As soon as the field is excited, the generator will produce power and the drill will turn on.
  • While depressing the trigger on the drill, spin the drill chuck in reverse direction. This will excite the field and the generator will now produce electricity. If spinning the chuck one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.
The reason this works is because the electric motor in the drill will act as a small generator when spun backwards. The magnets in the drill's motor induce a voltage into the motor windings, which is fed back through the trigger, cord and into the generators receptacle. From there it goes into the power winding of the stator. The voltage going through the power winding creates a magnetic field, which is intensified due to the iron core of the stator laminations. The rotor intersects this magnetic field as it is spun past the power winding, thus inducing a voltage in the rotor winding. Once current flow is present in the rotor winding the rotor has been flashed.

If flashing the field does not make the generator work, you may have additional problems, besides a lack of magnetism in the rotor. Further testing will be needed.
 
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Old 02-13-08, 12:44 PM
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He did state that when he first got the engine running, it was running too fast but the generator was making electricity but when making throttle adjustments the electricity quit.
 
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Old 02-13-08, 01:00 PM
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is there a fuse. if it was running too fast it might have produced too much amps and blew the fuse.
 
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Old 02-13-08, 05:09 PM
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cheese,

I'm no expert on these things either. If everything tested with-in the resistance specs. set forth by the OEM and you see nothing obvious it's possible it did drop residual magnetism.

Some OEM's state to loosen the rotor thru bolt then smack the laminates with a dead blow hammer to remove it from the engine, A shock such as this could knock the magnetism out of one.

You may try Airman's posted procedure for flashing if you don't have a field flasher, I have one Homelite sold years ago that I put in first before tearing it all down and going through testing procedures.

Good Luck
 
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Old 02-13-08, 07:27 PM
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If the generator was running your saw at too high of an engine rpm, you should not have lost the magnetism by just adjusting the rpms down to 3600 or slightly above. I have seen wires come loose in the panel to the outlets and breakers. About the only thing I can think of is the testing of continuity back to the brushes or the fields from the outlets. I have had a stator open up and loose continuity when the engine is running but test good when shut down. I beleive there is a test for that in the manuals. I quit working on generators last summer due to the manufacturers were not paying their warranty claims but only allowing credit towards parts.
 
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Old 02-14-08, 01:16 AM
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Thanks for the ideas.

LegalV8...I don't have the engine running at the specified 3600 rpms yet, because I got off track when I lost power to the saw. The engine was running too fast, so I adjusted the thumbwheel back to lower the rpm, with no results. This was when I noticed that someone had the idle screw on the carb screwed in way too far, so a backed it way out, but then the speed was too low. I brought it back up some, but I haven't set it exactly. It's probably close to 3200rpm right now. I sped it up manually to see if I gained a response from the saw without result. I'll try a light bulb like John suggested. That wouldn't be dependent on the frequency.

31YTech, I had power after reassembling it, so the polarity of magnetism was still present, and fully recharged as soon as it powered the saw. I thought about flashing it anyway, but I've never heard of one just dropping the field in an instant, while running...have you? Maybe it did?

Camino....are you saying that I may have lost the magnetism by running it at much less than 3600 rpms (which it did do)? If so, then maybe this is the case. I did check continuity from the receptacle on the front panel all the way to the connector behind the end cover at the field windings. The wiring, receptacles, circuit breakers, diode, stator, rotor, and connectors all test to be good. This one doesn't have brushes.

What happens when the capacitor goes bad or leaks? That's the only thing I can't rule out. I can test it with my meter, but that doesn't test it as it is intended to work. It just tells me it isn't shorted or open, and still has some capacitant ability.

Thanks again. It will be interesting to see what the problem ends up being. I don't often get tangled up with the electrical part of a generator.
 
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Old 02-14-08, 08:18 AM
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It is difficult to say all that needs to be said in a posting and easy not to convey a point. You stated the generator stopped generating, i.e. no voltage. My point was to flash the field using the drill since it could have lost magnetic field. This is the easiest thing to do other than checking circuit breakers and fuses which I assume was done. Start with the easy and proceed to the more difficult. The capacitor is your voltage regulator and if bad can result in low voltage or total loss of voltage.
 
  #11  
Old 02-18-08, 05:45 PM
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Hope you have figured this out, if not:

If you are quite sure that all the auxiliary electric and electronic components are in good order, then that leaves the mechanical portion.

An alternator (AC generator) needs three things to induce an EMF.

1. Residual magnetism (flashing the field has already been discussed)

2. Proper air-gap ( the clearance between the rotor and stator) I have know idea what your genset calls for but just be sure the rotor is concentric within the stator laminations. Is the outboard bearing OK? Don't forget the bearing housing.

3. Proper direction and speed of rotation. That capacitor you mentioned is probably there to compensate for sudden load changes (speed droop) and slight variations in speed, but the generator needs a specific rotational speed.

A couple of basic questions (since you have recently had the driver to driven coupling apart)

1.Could a winding have gotten cut in the repair process? Have you megged the coils - checked for continuity? I assume that this is a single phase machine, so it should be straight-forward.

2. Are you sure that the generator rotating element is really at the proper speed? It must be at (or very near 3600 RPM). I doubt that there is a tach on your unit so I wonder how you check this. I ask because I see that there have been some adjustments to the governor settings.

3. If it is rotating at the correct rate while idling, are you sure that this RPM is maintained when a load is applied. How is the engine coupled to the generator shaft? A broken key will often transmit power adequetely with no load - but slip under load. You will not notice anything, but the generator will fall out of phase and fail to induce a current.

Just some food for thought.

Good Luck.
 
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Old 02-18-08, 07:54 PM
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Thank you Chengny, and the rest.

I could have saved you some typing time if I could have posted last night, but the weather was bad and I had no internet.

After double checking everything, I decided to put it all back together and plug in a light bulb. No-go, but the speed was a bit low still. I sped it up and still nothing. I reached down and manually opened the throttle on the carb and all of a sudden the light came on. I let go of the throttle and the light stayed on. I ran it for a long time and it still works fine. I turned it off and cranked it back up several times and it is now working fine. Who knows...I guess it was just not turning fast enough?

I was under the impression that the slower the unit ran, the less the voltage would be, and lower the hertz would be. In this case, apparently there was nothing at all at around 3200 rpm. Suddenly power appeared at a higher rpm. Was I wrong to expect some sign of power at lower rpms?

Maybe that's a difference between generators with brushes, and those without? Most of my limited experience with generators has been with 5000 watt and less units with brushes. I'm not a pro on those either.

Again, thanks to all who responded!
 
  #13  
Old 02-19-08, 05:33 AM
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The Frequency is crucial - thats why the RPMS have to be set right. Even though it probably was making electricity, most devices are designed to run on 110v and 60Hz. If its at 35 or 40Hz, it won't work because its not alternating fast enough but a light bulb will usually work anytime since its not a motor. Every other generator I've seen has said that the throttle is set at the factory and to not mess with it as this will (for lack of a better statement) mess it all up. 3600rpm is what they need to run at to operate as intended.
 
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Old 02-20-08, 06:59 PM
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Originally Posted by Legal v8 View Post
The Frequency is crucial - thats why the RPMS have to be set right. Even though it probably was making electricity, most devices are designed to run on 110v and 60Hz. If its at 35 or 40Hz, it won't work because its not alternating fast enough but a light bulb will usually work anytime since its not a motor. Every other generator I've seen has said that the throttle is set at the factory and to not mess with it as this will (for lack of a better statement) mess it all up. 3600rpm is what they need to run at to operate as intended.
Your theory is find but does not hold up when you have an idlematic control. The idlematic brings the engine down to about 1800 rpms when there is no demand and will resume to 3600 when there is demand. The generator is still making voltage when at 1800 rpms and you can see it with a volt meter. At gen school we were told to set the cycles above 60 so that when at max load 25 amp on 110 volt side, the unit would still be putting no less than 58 cycles. Some of these engines did not respond to the load as well as others or did not have enough ponies in reserve to take the load. We service several hundred of these for the fiber optic network stations for when there is a power failure. What really gets me is that when there is a power failure in the winter months these units do not have a method for providing warm air to the carbs and the guy that handles the network can not figure why the carbs ice up. They are too tight to buy the equipment to work in winter weather.
 
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Old 02-20-08, 07:20 PM
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I was under the impression this particular machine has a fixed throttle. I have two 16hp vanguards and one 20hp honda at work (9kw, 10kw, and 13kw respectively) and they are all fixed throttles as well. nonetheless...
 
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Old 02-20-08, 08:53 PM
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This one is a fixed throttle. It wouldn't even burn the light bulb until the rpms were close to normal operating range.
 
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