Very low voltage

Portable standby generator troubleshooting and repair questions. (Gasoline, diesel, propane, natural gas)
Mboyce
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Sun Mar 03, 2019 6:59 pm

What I have is about 12 year old GP17500e portable standby generator, has always been under cover (never out in the elements). It fires up and runs fine although there is only 25 volts output at the top of the 50 amp breaker. The red light on the voltage reg is lit, I’ve checked the brushes and they appear in good shape (still springy and long). Any help would be greatly appreciated
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Chris
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Sun Mar 03, 2019 7:09 pm

It sounds like maybe the voltage regulator is bad if the voltage is so low, yet the LED is lit. Does the light appear fairly dim? I'm assuming yes from the low DPE voltage I'd guess it has.

Probably the easiest test is to manually flash the 4 wire with 12V from the battery and see what the output is. If it's much higher (won't be normal still) you can almost count on a bad AVR. You should also test the voltage coming back to the AVR on the DPE circuit (wires 2 and 6 at the bottom of the AVR). It's power to the AVR and if that's abnormally low, you could have a bad DPE winding, or possibly a DPE breaker with high resistance.

If the LED wasn't lit, I'd suggest some other tests, but let's start there...

If you need any parts along the way just let me know! The store is almost up and ready to go, but still doing some tweaking on the back side.
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nwfb32
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Mon May 20, 2019 10:33 am

Could you define low voltage from the DPE?

I'm in a similar situation with a GP6500. I am only receiving .5v AC into the AVR at wires 2&6. And residual AC voltage at the outlets (~2v AC). However, if I apply 12v DC directly to the brushes I receive 6v AC to the AVR at wires 2 & 6 and 30v AC at the outlets. When I apply 60v DC directly to the brushes I get 110v AC at the outlets, but I did not check voltage to the AVR from the DPeE. With 60v DC applied directly to the brushes the generator powered a small load (box fan) but the alternator began to smoke after several seconds.

DPE windings checked OK. 1.0-1.1 ohms betweeen wires 2 & 6, and both open to ground.

Am I missing something? Could it be just the AVR?
Chris
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Mon May 20, 2019 10:57 am

nwfb32 wrote:
Mon May 20, 2019 10:33 am
Could you define low voltage from the DPE?

I'm in a similar situation with a GP6500. I am only receiving .5v AC into the AVR at wires 2&6. And residual AC voltage at the outlets (~2v AC). However, if I apply 12v DC directly to the brushes I receive 6v AC to the AVR at wires 2 & 6 and 30v AC at the outlets. When I apply 60v DC directly to the brushes I get 110v AC at the outlets, but I did not check voltage to the AVR from the DPeE. With 60v DC applied directly to the brushes the generator powered a small load (box fan) but the alternator began to smoke after several seconds.

DPE windings checked OK. 1.0-1.1 ohms betweeen wires 2 & 6, and both open to ground.

Am I missing something? Could it be just the AVR?
I'm thinking the smoke was probably not a good thing.... :cry:
60V seems like WAY more than needed, even at full load. What is the rotor resistance at the AVR? I'm thinking that sounds more like badly worn brushes or a rotor going bad.
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nwfb32
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Mon May 20, 2019 11:10 am

Yeah, if you let the smoke out of pretty much anything it's damn near impossible to get it back in.

Where do I check rotor resistance at the AVR? The only thing I checked there was resistance between wires 2 & 6 from the DPE. Service manual that I found online stated .97-1.13 Ohms. I am reading 1.0-1.1 there and infinity to ground
Chris
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Mon May 20, 2019 11:29 am

Yep, start at the AVR and work your way back to the slip rings. If it's high at the AVR, it's most likely dirty slip rings or a bad brush. Although, the smoke may be leading down a dark road of doom...
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nwfb32
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Mon May 20, 2019 9:00 pm

So... Lots checked and here is where I am
-Dead short through brush assembly to slip rings (less than 1 ohm)
-60-63ohms between slip rings

With wiring disconnected between stator and outlets
-Stator windings show open to ground from on all wires
-L1 & L2 =0.7ohms
-L1 & R1, L1 & R2, L2 & R1, L2 & R2 all = open
-R1&R2 = 0.8 ohms
-Wires 2 & 6 (exciter winding) = 1.0ohms (acceptable range per manual .97 to 1.13)

Ran again with 12v supply directly to brushes and AVR removed for about 20 minutes. Outlets and Wiring directly from stator produced 33v AC. When 12v DC source was removed from brushes, output was again 2.5ish v AC. AC voltage from exciter winding going to the AVR was still about 0.5 v with NO 12v DC supply to the brushes and about 6v AC with the 12v DC supply connected to the brushes.

Manual doesn't state proper resistance between L1/L2 and R1/R2, only that all should be open to ground. It does state resistance between wires 2 and 6, the exciter windings, should be between .97 and 1.13 ohms.
Chris
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Mon May 20, 2019 9:18 pm

There's something preventing a field from being established it sounds like... I'd be looking at the rotor still. Have you checked both slip rings to the rotor shaft for resistance?

It might be time to get a megger involved and see if there is insulation failure somewhere... :sad:
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nwfb32
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Mon May 20, 2019 9:26 pm

Do you mean between the slip rings and the "core" of the shaft itself, to the end of the windings at the soldered terminals, or something else?
Last edited by nwfb32 on Mon May 20, 2019 9:28 pm, edited 1 time in total.
nwfb32
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Mon May 20, 2019 9:28 pm

Also - didn't mean to hijack someone else's post here... Sorry about that.
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