Rigid 3600 rpm 8kw generator

[Carlb]

I purchased a used rigid generator with a 14hp electric start Subaru engine and 8kw /10kw surge head that did not make electricity.  Since the rest of the generator was clean and the engine only had 96 hours on it I figured i would take a shot.


I am good with engines but not so good with generators so any help would be greatly appreciated.   If there are any other things i need to add please let me know as i only took readings i thought were relevant, but, again i don't know a whole lot about gen heads.   

When i applied 12vdc to the brushes i got 46vac out of the generator.  Suspecting a bad AVR I ordered a new one and replaced the old one.  To my dismay it was still not producing power.


I took a volt reading across the brushes with the engine running and got 15vac (brushes looked good and the slip rings were clean.

When i ohm the rotor i got 61.5 to 62 ohms of resistance (dont know if that is good or bad)


There are 4 heavy gauge wires coming from the stator 2 black and two white.

When i ohm these wires i got

L1 to R1 0.2 ohms
L2 to R2 0.2 ohms

R1 to R2 0 ohms
L1 to L2 0ohns
L2 to R1 0 ohms
L1 to R2 0ohms

There are 4 smaller wires coming from the stator  white, green and two blue wires.
I only get resistance between the white and green no other combination results in any reading.

Is there a way to check the smaller wires which i believe are the harmonic winding but i am not sure. do i need to do this with the engine running.

Thanks for the help in advance


Carl

[ArcticCogen]

...
When i applied 12vdc to the brushes i got 46vac out of the generator.  Suspecting a bad AVR I ordered a new one and replaced the old one.  To my dismay it was still not producing power.


I took a volt reading across the brushes with the engine running and got 15vac (brushes looked good and the slip rings were clean.

When i ohm the rotor i got 61.5 to 62 ohms of resistance (dont know if that is good or bad)
...

I think you were on the right track initially.  That AVR should be putting a DC voltage into the slip rings.  Where does the AVR get its power from?

[Carlb]

Artic,

there is a plug coming from the stator with four wires two blue one green and one white that plugs into the AVR.  There are two wires red and white that come from the AVR to the brushes.  I am not sure what readings i should be getting at this plug so it is difficult for me to test if i am getting the appropriate voltages at the plug to the AVR.  I am unable to find any specifications for this gen head so i don't know what the readings should be.

Thanks 

carl

[BruceM]

Hi Carl, I was hoping someone familiar with your unit would be able to help you.
It's a two pole head, so the two sets of windings (resistance) would most likely be connected in parallel if 120VAC, and series if 240VAC.  Which is this one?  How are the windings wired to the AC outlet? 

I'd test the bridge diode on this first, since your 12V test did get some output.  You can confirm bridge function with an ohm meter or batter and volt meter. Cheap enough to just replace, if in doubt.

My favorite test would be to use a Variac to drive a known good bridge diode.  You could either spin the head and then switch on your utility AC connected Variac and dial up the variac voltage until your output is at 120/240VAC.  A few hundred watt or more Variac will suffice.  If the Variac is then connected to the AC output of the head, you must start with the variac set to maximum voltage out, and quickly dial it back as the AC voltage comes up. 

Best Wishes,
Bruce

[Carlb]

Bruce,

It does have two windings and the outlets are wired for 120 and there is a 240 30amp twist lock.  At the gen the neutrals are combined together and bonded to the frame.  The two hot leads go to each of the two 120vac outlets and both go to the 240 vac outlet.

This does not have a simple bridge rectifier it has a AVR with 4 wires coming from the stator and two that go to the brushes.  With the engine running there is only about 2vac coming out of the stator on two of the 4 wires going to avr.  I replaced the AVR but may have gotten a bad one since i cant find any other fault, but,  I am not generator guy.  if i apply 12 vdc to the brushes i get about 30 vac to the AVR. 

I do have an old school Variac and some 30amp bridge rectifiers that i can test with bypassing the AVR.  If i connect the bridge rectifier to the output of the harmonic winding i may get enough voltage to the brushes to get it going but I don't know if the voltage will go too high with just the bridge rectifier. 

I will try the varaic with a bridge connected to utility power and dial it up until i get 120 from the outlets.  If that works ok i will take a vac reading on the plug that goes to the AVR.  If the voltage is similar to the voltage i am sending to the brushes via the varaic I may try hooking up the bridge to the output of the harmonic winding or do you think that is a bad idea.


Do you know if the AVR can simply be replaced by a Bridge diode?


Thanks

Carl.

[BruceM]

Your particular AVR has the bridge diode integrated into it, and seems to be fed directly from the stator AC?  That is the norm for AVR designed units as the AVR will limit the power being fed to the rotor brushes by chopping off some of the AC waveform much like a light dimmer. The AVR monitors it's own input (the stator AC output) and adjusts the DC voltage/power to the rotor too keep the stator voltage at 240/120 VAC.  The rotor has huge inductance so as long as the input is rectified (always the same polarity) it will smooth out lumps and spikes completely.

You can easily change this generator to 120 only, full power (no balancing of legs), if need be.  

If all is well with the variac on utility power (do NOT switch it on until the generator cooling fan is spinning), you either needed to flash the rotor on 12v or the AVR was bad.  Running it on the variac on utility power will remagnetize the rotor so it should subsequently work fine to connect the variac to the stator AC outputs, as long as you start with the variac on the highest voltage and then quickly turn it down as the voltage comes up.

[mike90045]

I flashed my generator with a automotive tail light and a jumpstart pack.   I hooked the power pack to the AC leads on the bridge (with the light bulb in series with the jump pack) and relied on the taillight to limit amps.   At stand still.  no whirling parts.  Worked after that

hints, steps, measurements: (From ST  head)
http://www.utterpower.com/Trouble.htm

[Carlb]

Thanks guys for the help.  I will try the varaic today and check to make sure i am getting ac from both L1 and L2 as well as the winding that powers the AVR which i believe is bad.  As stated earlier I believed it to have a bad AVR from the beginning so i purchased a replacement but I may have gotten a bad replacement since everything else seems to check out ok.   I have another AVR on its way and if everything checks out today I will wait for the new AVR and put it in when it gets here.

Thanks again


Carl