flashing 3 phase generator 6

[holo]

I'm new to the forum.
I have a Kohler 15RMY62 208V 3 phase 15 KW generator that is producing 30 VAC (rms) at 1800 rpm.

The diodes and brushes have been replaced.

I disconnected the field windings from each other and they are 0.9 ohms each. The wiring has no visible signs of burning or discoloration.

I flashed the 4 pole rotor with a 12VDC battery thru the brushes when it was not running. No change.

Any help or advice would be most appreciated!

 

[holo]

waross, the 27 ohms were from the sliprings. Sorry, I should have made it clearer. No continuity between the slip rings and the rotor shaft or to the case.
The new voltage regulator and AVR board are from Kohler.
Here's a link with pics of the electronics.

http://www.fieldlines.com/story/2006/7/3/202447/2073

The boards and regulator have since been replaced and everything inside the box cleaned. All connections were unplugged and replugged.
I'll try varying the voltage and hopefully varying the amps also.
Thanks for the help!

 

[waross]

Hi holo;
I'm curious, and I may have missed something.
At one point I understood that the field resistance was 0.9 ohms X 4 = 3.6 ohms. This would be consistent with a rotary exciter, either with brushes or brushless.
At another point I understood the resistance to be 27 ohms.
This would be consistent with the field of a rotary exciter.
I don't believe that you have a rotary exciter.
However, despite the large manufacturers of generator ends more or less using the same values now, anything that works is possible with generators, particularly old generators or lessor known makes. In this case Kohler is well known so we would be looking at old.
If you have replaced the AVR with a Kohler replacement and the machine still doesn't work, there are two things to check.
1> When you changed the AVR, was there an electronic module connected between the output of the AVR and the brushes? If so it would be the static exciter. It should be checked or replaced if present. If possible verify with Kohler whether or not the machine uses a static exciter or if the AVR connects directly top the field.
2> Identify the power windings (1 to 4, 2 to 5, 3 to 6, 7 to 10, 8 to 10 or 11, 9 to 10 or 12.) depending on whether it is a 10 lead or a 12 lead machine. Check each individual winding for shorts or grounds. Then with battery excitation, check that each winding is developing the same voltage. This will give you a double check on the condition of the stator windings.

Double check also the RPMs and/or frequency.
Your machine shoukld be turning 1800 RPM.
respectfully

 

[ScottyUK]

If the measurement is being made using a multimeter, the carbon brushes will be giving incorrect measurement results because of the low applied voltage. How are you making the measurement?

The boards you replaced - are they the ones which are covered in a thick layer of dust or sediment? Are other parts of the controller in a similar condition? If so, a good clean may be a useful starting point. Electronic circuits can do wierd things if a vaguely conductive contaminant is present in a high impedance or high voltage part of the board.


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I don't suffer from insanity. I enjoy it...

 

[waross]

Sorry, correction/clarification;

At one point I understood that the field resistance was 0.9 ohms X 4 = 3.6 ohms. This would be consistent with a rotary exciter, either with brushes or brushless.

Should be,
That would be consistent with the main field coil winding, not the field of a rotary exciter.
That is the point of an exciter. The voltage regulator usually does not have the power available to excite the field directly. The AVR controls and excites the exciter and the exciter excites the main field.
I would expect the main field to have about 3 or 4 ohms resistance. I would expect the exciter field to have about 27 ohms resistance (more than 16 in any case).
There are exceptions and I suspect that your machine may be an exception.
It doesn't have a rotary exciter. If the field resistance is

I disconnected the field windings from each other and they are 0.9 ohms each. The wiring has no visible signs of burning or discoloration.

Then you either need a static exciter or a non-standard voltage regulator.
If the field resistance is 27 ohms the problem may be in the main windings, the wrong rotor may be installed, the speed may be slow, the air gap may be excessive, kohler may have supplied the wrong AVR, or other problems.
respectfully

 

[holo]

The field resistance was measured at 0.9 ohms by checking the start and end of each winding after the leads were disconnected from each other.

The resistance measured through the slip rings, with the brushes and holders removed, was 27 ohms. I will check the voltage between each lead today.

My Fluke meter is showing about 64 Hz on the output. Since it's a 4 pole unit, I am assuming the rpm's are around 1800.

The entire unit was covered in contamination.
I cleaned all the the wiring, connections and original boards. The kill switches were also disconnected to eliminate them from the equation.

Once again, thanks for your comments!

 

[waross]

By field resistance do you mean the rotating field or the stator. Something is not adding up here. The rotating field has four poles. Four times 0.9 ohms is 3.6 ohms, not 27 ohms.
We usually call the stator windings on your type of genset the main windings or the power windings. When you say field windings, we think of the windings on the rotor.
respectfully

 

[holo]

"The rotating field has four poles." This has 27 ohms across the slip rings without brushes.

"We usually call the stator windings on your type of genset the main windings or the power windings." The main windings are 0.9 ohms. 12 wire main winding.
Sorry for the confusion.

 

[DaveScott]

Holo, have you checked what the voltage is across the sliprings, when everything is running in the normal wiring setup?
Have you checked the current through the slip ring circuit when everything is running in the normal wiring setup?
You have previously mentioned that with standard setup, you get 30vac, and if you apply 12V to the field, you get 46Vac.
It seems to me that your AVR is probably not giving any, or very little field current, for some reason.

 

[waross]

I agree with DaveScott;
It is starting to look as if you have an AVR problem. Check for brushes sticking, loose or broken pigtail leads on the brushes, surface contamination on the slip rings, and anything else you can think of that may introduce resistance into the circuit from the AVR to the field. If this is an old machine, check the wires. There may be internal corrosion in the wiring to and from the AVR.
Check the output of the AVR. 63 volts is a common maximum voltage for a small AVR. You may have to load the output with a 60 watt or 100 watt light bulb to get a good voltage reading.
respectfully

 

[holo]

I think I may have found the problem, or at least one. V7 and V8 wires, which are from the generator powers the AVR. Both are putting out intermittant voltage readings. Looks like it's time to take the generator apart and look.
This is going to take a few days.

Thank all for the comments! This has been quite a learning experience.

 

[Allodola]

Hello from another new member prompted by this thread. I too am several weeks in to troubleshooting the exact same Kohler generator 15RMY62 prob from 70’s-early 80’s that came with the house I just moved into, worked OK for a year then started blowing reset switches, I have decent small electronic skills, and helpful pals and initially diagnosed dysfunctional VR board (B-258296) which combines the SCR module and Voltage regulation on one board. Replacement is $570 so am in process of rebuilding the old one, highest failure parts first, I can replace every part for less than $100, although some of the values are a bit tricky to determine. I have briefly had it working 100% then re-failed am in to the next layer of relays and connectors, already did the basic rotor/stator checks.
The route of my evil was layers of mouse doo-doo and urine. Its amazing this (conformally coated) board lasted as long as it did!
Anyway, I have the Kohler book on this model including coil and control wiring,and some trouble shooting, if you need it, I can copy the pertinent bits, but this does NOT sadly include a schematic of the VR board, which I would love to have if anyone has it. It is Not available from any Kohler dealer even the usually helpful Buckeye folks, they just don’t have it. Sort of an OEM part. So I will probably have to reverse engineer the board, but that would not give me definite component values on those with markings eroded by rat wee-wee. Anyway I will try to help if I can, though am not (yet ) a generator specialist, and may ask for advice also. It is definitely a "static" excitation of field, it has a relay to "self flash" on start up but it is not clear if it really needs it, 30V is denitely what you get with unexcited (residual) rotor field. Keep us posted Holo. Oh yeah, mine is pre-wired for single phase operation, both 120 and 240. (V9 disconnected, internally wired armatures for single phase. )

 

[holo]

Hello Allodola,
I now have a manual coming from Kohler. It probably does not show the board schematics. I have a few pics of the cleaned board that shows every part except one chip. If you need them, let me know. They are ~1.5 mb each.

What's your ohms reading across the sliprings and power windings?

 

[waross]

These are 12 lead generators.
12 lead machines are easily converted to single phase. V9 should be connected and there is no internal wiring unless it has been rewound and changed from the original.
You lose 1/3 of the KVA, but the KW will equal the (New) KVA.
Power factor rating will be 100%

EG. Three phase ratings:
15 KW
18.75 KVA
80% PF
Same machine, single phase;
12.5 KVA
12.5 KW
100% PF

For a machine that is originally rated at 100% PF.
15 KVA
15 KW
100% PF
Same machine, single phase;
10 KVA
10 KW
100% PF
respectfully

 

[Allodola]

Waross, you are correct, thanks for the clarification. The "book" has V9 disconnected from the VR board bus, presumably not needed for the Voltage reg function, but is in circuit as an armature. The "internal" wiring I mentioned really referred to the configuration of the 12 leads into that single phase set up that is niether Wye nor Delta (whats it called?), it is internal only in the sense it is "inside the box"!
Holo, is your board the one with the SCR units and heat sinks all on the one board with the rest of the VR? If so I would love to see the pictures, might help me clarify a few things. Thanks. I will be going deeper into my unit as soon as I get a lightning free evening! I'll see if I jotted down thr resistance measurements or re check them for you.

 

[waross]

The single phase connection is called a "zig-zag" connection. Not to be confused with the transformer of the same name.
Another connection that is becomming common in newer sets to supply single phase from a three phase machine is the double delta connection.
The double delta is a symetrical connection.
If I have to convert a three phase machine to single phase, I use the double delta if the leads are well numbered. All the leads must be accurately identified when changing to the double delta.
On an older machine, where there may be some doubt about the lead numbereing for any reason, I use the Zig-zag connection.
The windings may be identified and the final connection checked with a multi meter, even if the numbering has been lost, when changing to the zig-zag connection.
Both connections have been used by the major manufacturers. I am not aware of any difference in the end result. Both connections work well.
respectfully

 

[holo]

Allodola, a few pics of the dirty boards are listed in a url earlier in this post. You can see if that's what you need. If it is, I'll figure out how to post the clean ones.

warcross, I understand the zig-zag. How is the double delta wired? What are the advantages of double delta vs. zig-zag? Nothing from Google.
Where should V9 be connected?

My generator seemed to be wired in 208 3 phase open delta. Presumably, it was being used in place of a single phase 240v circuit. Anyway, It's wired single phase now.

 

[Allodola]

Holo, your set up is identical to mine except you have the seperate "SCR module" (The thing on the side with the red disc Varistor that looks like a capacitor.) So prob not worth the effort to upload the board pic. BTW the Electronics including the control mechanisms/overload resets are much more vulnerable in general than the generator itself, so I would really make sure your board is capable of puting out F1 and F2 to the field, Make sure the Voltage/overcrank rset switches are in correct position, not shorted or needing to be reset, crud can even mess up the mechanics of the toggle switch action. On re-read you did say you got a NEW VR. did it include a new SCR module (is that what you meant by the diodes" were replaced?

 

[holo]

Yes, the VR is new and so is the bridge rectifier diode that's connected to F1 & F2.(far side of the pics mounted to the wall.)
The relays in the foreground are not new. They seem to function correctly. I've switched their positions without any change in voltage.

 

[Allodola]

Well, relays are pretty tough. I was talking about the stuff in the box with the meters and the reset switches. At one point, you mentioned "disconnecting" some of the "kill switches". Those might be part of the correct operating of the relays, i.e. the thermal time out switch for overcrank etc has an open and a closed set of connections. Ain't this critter fun?

 

[holo]

Allodola, I disconnected the kill switches for the external engine circuits. I think they all short to ground. Might be the case. I'll hook up one at a time and see what happens.