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Author Topic: Rigid RD90800s 8kw 3600rpm generator  (Read 9798 times)

carlb23

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Rigid RD90800s 8kw 3600rpm generator
« on: September 18, 2015, 05:22:00 PM »
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 5vac (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



« Last Edit: September 20, 2015, 12:24:13 PM by carlb23 »

tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #1 on: September 19, 2015, 02:35:55 AM »
most 3600 2pole generators have a capacitor across  the harmonic winding, encapsalated in plastic and prone to failure shaped 1/4 round 2 to 3" long hooked to stator. the rotor has a diode bridge mounted around the shaft, these four diodes must be unsoldered tested and resoldered and reincapsolated unless you have a shop to test rotor as assembled. The cap fails with holes burned in it if not can be checked with a Sencore Z meter or equal, It applies the working voltage to the cap under test and much more real than the typical digital volt ohm meter. Check You Tube- some English guy flashed the field with 2 electric drills one plugged into the generator the other driving the shaft of the first, the first a universal ac dc version trigger locked on, the second chucked up to drive the first. It is common for some one to run engine out of fuel with load on generator this can suck the residual magnatisim out of the generator and lead to your symtoms
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tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #2 on: September 19, 2015, 02:41:37 AM »
As for the other leads, most of the electric start engines supply their own battery charge system, and the generator windings for the purpose are not used.
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M61hops

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #3 on: September 20, 2015, 07:03:25 AM »
Hi carlb23.  Check for DC voltage on the field winding, AC in the field won't make the generator put out power.  The field needs to make a North and South pole magnet that stays North and South.  Maybe a bad bridge.    Leland 
I pray everyday giving thanks that I have one of the "fun" mental disorders!

tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #4 on: September 22, 2015, 04:41:31 AM »
If you have the end cap/shroud off, you should be able to see the diodes mounted on the rotor. The rotor is the field. the brushes transmit the AC harmonic voltage in conjunction with the above mentioned capacitor through the brushes to the rotor generating the DC voltage to produce the magnetic field mentioned above. being as how the rotor is spinning I do not know how to measure directly. The cap on my unit was rated at 400 volts, albeit a different brand. I would expect  around 70 volts AC on the brushes to feed the diode bridge on the rotor. the diodes should be 1/4 inch diameter 3/8ths long mounted close to the rotor shaft 2 on each side for balance, in my case but in any case 4 each for a full wave bridge. If you had a Variac one could apply AC to the brush leads  in increasing amounts till the voltage out was right. At that point the residual magnetism should be restored. I would run it under a load for a bit to be sure, then shut down and see If it comes up on it's own. Another way is to parallel some 110 lite bulbs 100 watt hooked to a separate supply  individualy switched to series connect to the brushes, the more bulbs on equal a higher voltage to the bridge. As I remember my tests your readings seem OK. I'm about to refresh the fuel for the winter and will supply voltage readings and maybe a pic or 2
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carlb23

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #5 on: September 22, 2015, 12:49:11 PM »
there are no diodes on the rotor and no separate cap on this generator.   It appears the Bridge rectifier and the cap are part of the AVR and it feeds DC directly to the brushes.

I think i had a bad AVR to start with and the replacement may have been defective.

I have another AVR on the way and it should be here in a few days


I do have a Varaic and a 50amp Bridge rectifier.   I will use it to send enough dc power through the brushes to see if i get 12 on each leg

Thanks

Carl

tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #6 on: September 23, 2015, 03:00:34 AM »
Well that is good to hear as I have totally blown the above post. I checked mine early this morning and low and behold no brushes, a senior moment no doubt. the rotor/field has no wires or brushes and rectifies the induced voltage from the residual magnetism to self regulate, another Chinese marvel. When I read Ridged 3600rpm 8kw I assumed the big box store $660.00 knock off specials of which I've worked on several and own one. I apologize for the  miss information.
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tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #7 on: September 24, 2015, 04:46:44 AM »
Be sure to protect the Variac! put an inline fuse for the rated amps, mine is 10 amps but only that at 1/4 from low voltage end. I would start at 30volts AC fed through the bridge to the brushes put in 2 trouble lites on the 2- 120 volt legs and see what happens. If have a Kill A Watt meter,  you can set rpm for correct frequency, voltage. once those are correct put a load on it. I did something similar once turned around to grab meter and watched the magic smoke come out. upon complete disassembly, found fine silt and 3 dried up worms in the windings. Turned out it was from the Washington I-5 floods in Centralia a few years ago.
have fun!
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carlb23

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #8 on: September 24, 2015, 12:14:24 PM »
applying voltage through the varaic with a bridge to the winding produces 120vac on both legs but it looks like the harmonic winding may be bad.  I am still waiting for the replacement avr but it looks like the head may be toast.  It's probably not worth trying to have the stator rewound even if i could find a shop that rewinds stator anymore.  A new OEM replacement head is only 265 dollars.

BruceM

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #9 on: September 24, 2015, 03:20:29 PM »
Carl,
You don't need a harmonic winding-  CGG has an inexpensive AVR that will operate on one of your 120V legs.
But before you do that:
Did you retest your AVR after testing with the Variac?  That would remagnetize the head and may make it work again.  It really could be as simple as it just not having enough residual magnetism to start.

tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #10 on: September 25, 2015, 02:40:01 AM »
Carl: I agree with Bruce , run it up with the Variac to correct voltage , then load it up for a while and reconnect every thing and see what happens. It would help me at least to know what the voltage at the brushes is no load, half load, and full load under Variac and or AVR.
 You are having fun! ;D
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carlb23

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #11 on: September 25, 2015, 08:55:01 PM »
I ran it under a 3kw load with the varaic and it worked well.  I did re-install the avr after the load test with the varaic but no joy.  no voltage at the brushes at all

I will have to look at CGG and see about their avr if all else fails. 

Seems like a simple solution to my problem

tiger

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #12 on: September 26, 2015, 03:06:38 AM »
 A common point of failure may be the input connections to the AVR. Might be worth tracing back to stator windings and checking for cold solder joint or bad crimped connection.
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carlb23

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #13 on: September 26, 2015, 12:32:18 PM »
Tiger,

I spoke to Tom @ CGG yesterday and had a nice long conversation with him.   We went through a few things and the determination is still the same the harmonic winding is bad.  He suggested using the ST115 avr (which Bruce had mentioned in an earlier post) and felt confident that it would work since the generator puts out full output using the varaic to feed the brushes.

The cost of the avr is quite reasonable and worth trying rather than take the generator apart again at this point. 

Tom was very helpful and just an all around nice guy to deal with

BruceM

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Re: Rigid RD90800s 8kw 3600rpm generator
« Reply #14 on: September 27, 2015, 03:25:34 PM »
Glad you got it sorted out, Carl. The Variac test is a very useful one.  Bill Rogers told me about that here years ago, when I was just starting to learn about the ST heads and needed help troubleshooting. 

Tom at CGG does provide excellent product support.  Something rare these days.

Best Wishes,
Bruce