flashing 3 phase generator
flashing 3 phase generator
(OP)
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!
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!






RE: flashing 3 phase generator
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: flashing 3 phase generator
I haven't tried hooking up a load.
Waffle iron? OK, I'll try it!
Thanks!
RE: flashing 3 phase generator
Could this be a voltage regulator problem? Does the rotor need to be flashed with higher voltage?
Again, any help/advice is very much appreciated!
RE: flashing 3 phase generator
Generally if you are getting 30V there is more than enough energy available to allow the generator to 'build' up to normal.
Yes it could absolutely be the VR. Generally that is where the problem lies.
First though you said 'rings' these are for the field then?
If that is so you may be able to provide some 'manual' field current and see the output rise. If you can and you see it rise dramatically never mind to 208V then you can probably assume the field is intact and the 'mechanical' generator is okay. At this point you would want to focus on the regulator. Again the regulator's job is to look at the output voltage and adjust the field current accordingly. If you could put an ammeter of some sort in the field circuit you could see if the VR was functioning. Make sure your ammeter is good for several amps. (DC)
Others will come along who sleep and eat generators. They will have some sage advice.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: flashing 3 phase generator
"If that is so you may be able to provide some 'manual' field current and see the output rise."
I'm not sure exactly what you mean. 12 volt battery flash to the field windings and watch the ammeter? If it works, the voltage would go high in several milliseconds. I'm allergic to sulfuric acid, so I'll fuse the battery. :)
Thanks
RE: flashing 3 phase generator
You totally lost me here.. Capacitor?
I am talking about providing field current with something. Disconnect the VR and just feed current to the field. A battery might work but you might need more than 12V.
I'm also talking about finding your existing system's field control wires to/from rings and inserting an ammeter in one. You should see some amps being provided by the VR.
Of course before this stuff with all power removed you should be able to confirm the field wining is not open. (Presuming you've already done this!)
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: flashing 3 phase generator
Being that yours does have brushes we can assume that you have a synchronous generator, which makes sense since you are expecting to run it in island mode. OK then, did you realize that a synchronous generator must have power applied to the exciter at all times? Flashing is just to set up an initial field on a brand new generator or one that has been out of service for a long time where the residual magnetism in the rotor is insufficient to provide enough power to the exciter system, and is usually done off of the same battery used to start the engine. In fact, the initial flashing on most small portables can be done with very little voltage, I have done it with a drill motor as a generator in a pinch (I won't go into details unless asked). After that the exciter circuit needs to take over on its own.
The 30V output you are getting is likely the result of some small amount of residual magnetism in the rotor. The fact that it can do that means you should have enough to get the exciter going. Is your exciter properly connected? You mentioned having replaced the diodes, are you sure all the wires went back onto the same terminals? Now that I think of it, why did you have to replace the diodes anyway? If they shorted, chances are some other part of the circuit was damaged as well. Does it have an output? Does it have a Field Circuit Breaker that may be open?
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: flashing 3 phase generator
You need to answer jraef's questions above to yourself in your troubleshooting process. Also, not being real familiar with Kohler model #'s, I don't know how old it is--how advanced of a voltage regulating system it has.
To do a conclusive flash while it is running, identify F1 an F2 wires going to the excitor. This is where you want to flash the DC in. If running a solid state regulator, you want to disconnect the leads from the regulator before doing this, or put a diode on the B+ line before flashing to avoid sparking surprises.
If you've confirmed diode installation/brushes/wiring to them is good, and flashing gives you a predicted result, investigate the regulation circuit it has. Check if sensing/power voltages are rising/falling when being flashed.
Any number of things it could be on these old small units. Just need to identify the key components, look for expected results from each, and lots of ohming to ensure all is connected from point to point.
RE: flashing 3 phase generator
First, if you try to flash the generator with the starting battery before you disconnect the voltage regulator, you will probably join a long list of people with blown voltage regulators.
But, your generator should boot up with 30 volts. It's when we are reading between zero and 3 or 4 volts that we consider flashing.
If you disconnect the voltage regulator you may connect the starting battery to the field.
Usually it takes 12 to 24 volts on the field to get full voltage at no load. It often takes twice as much voltage on the field to give full voltage with full load.
by the way, I have succsesfully flashed a 35 kw set with a 1.5 volt "D" cell in series with the voltage regulator. It doesn't take much. (The voltage regulator probably helped a little.)
It sounds as if you have regulator problems.
respectfully
RE: flashing 3 phase generator
* If a little knowledge is dangerous, then I am the safest person in the world *
RE: flashing 3 phase generator
RE: flashing 3 phase generator
RE: flashing 3 phase generator
Good call JIMGEN.
respectfully
RE: flashing 3 phase generator
OP said all 4 pole coils measure 0.9 ohms each. That gives a total of 3.6 ohms with 8.33 amps field current.
Given the equal resistances of the 4 pole coils, I would rule out any turn shorts.
The turn short can also be confirmed by doing ac pole drop test. (Apply 110 V AC across field winding terminals and measure the voltage drop across each pole coil. Equal voltage drops will rules out turn shorts)
* If a little knowledge is dangerous, then I am the safest person in the world *
RE: flashing 3 phase generator
A very common but by no means universal specification for voltage regulators for small generators is Minimum 16 ohms field resistance.
If the field is good, it is possible that the voltage regulator has been replaced with one which requires a minimum of 16 ohms.
respectfully
RE: flashing 3 phase generator
The rotor checked out at 27 ohms. My book for single phase unit shows the reading should be between 2.5 and 4.5 ohms. This sounds too low. I'm guessing it should be the same for three phase because both operate on DC voltage to the exciter rings.
With the electronics disconnected and the rotor hooked to a 12 volt auto battery, I get 46 volts out. Can't get the ammeter to work. There does not appear to be a short in the rotor.
Your help is greatly appreciated!
RE: flashing 3 phase generator
High rotor resistance (27 ohms as against 3.6 ohms) indicates some high resistance connection either in between poles and or in the rotor leads.
* If a little knowledge is dangerous, then I am the safest person in the world *
RE: flashing 3 phase generator
ed,
"The turn short can also be confirmed by doing ac pole drop test. (Apply 110 V AC across field winding terminals and measure the voltage drop across each pole coil. Equal voltage drops will rules out turn shorts)"
Voltage drop across each pole should not necessarily equal. It should fall within tolerance value.
holo,
Better send your generator for thorough check up if you desperately need it.
RE: flashing 3 phase generator
I did some googling on your model number. I found some of your other queries and got a little new information.
Apparently, your generator has a static exciter. This is not common on a set this size. The only other one I have seen was an old Caterpillar.
A static exciter may have the voltage regulator built in, or it may be basically a power amplifier controlled by a standard voltage regulator.
Voltage regulators for that size set are pretty generic and/or interchangeable.
HOWEVER, a standard, off the shelf AVR (automatic voltage regulator) will not have the current capacity to properly energise your field directly.
From the field resistance values you have supplied, and the voltages you found when testing, I strongly suspect that your problem lies in the static exciter.
You will need 31 volts in to get 120 volts out at no load. possibly twice that at full load. You will need close to 20 amps.
The 27 ohms is a worry. You should measure the rotor resistance at the slip rings and NOT through the brushes. There will be a non linear voltage drop across the brushes that will cause serious errors if you try to measure field resistance through the brushes with a multi-meter.
One other thing to check is the connections of the output or power leads. This is a long shot but it is something that should be verified.
For a DC supply you may use batteries. 6 volts, 12 volts, 24 volts, etc. The output voltage should be proportional to the input voltage.
You may also use a variable AC source and a bridge rectifier. The relatively large inductance of the field winding will act as a quite efficient filter.
respectfully
RE: flashing 3 phase generator
The new voltage regulator and AVR board are from Kohler.
Here's a link with pics of the electronics. ht
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!
RE: flashing 3 phase generator
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
RE: flashing 3 phase generator
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...
RE: flashing 3 phase generator
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
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
RE: flashing 3 phase generator
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!
RE: flashing 3 phase generator
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
RE: flashing 3 phase generator
"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.
RE: flashing 3 phase generator
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.
RE: flashing 3 phase generator
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
RE: flashing 3 phase generator
This is going to take a few days.
Thank all for the comments! This has been quite a learning experience.
RE: flashing 3 phase generator
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. )
RE: flashing 3 phase generator
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?
RE: flashing 3 phase generator
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
RE: flashing 3 phase generator
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.
RE: flashing 3 phase generator
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
RE: flashing 3 phase generator
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.
RE: flashing 3 phase generator
RE: flashing 3 phase generator
The relays in the foreground are not new. They seem to function correctly. I've switched their positions without any change in voltage.
RE: flashing 3 phase generator
RE: flashing 3 phase generator
RE: flashing 3 phase generator
Just FYI. I'm in the laborious stage of reverse engineering the board now. best.
RE: flashing 3 phase generator
RE: flashing 3 phase generator
RE: flashing 3 phase generator
Sorry for the delay getting back, but I had a great weekend.
Re., Zig-Zag connection vs. Double Delta;
On one of the pictures that was posted of your generator, there was a diagram of the zig-zag connection for single phase.
This site has a diagram of a double delta connection.
http://www
The site also has a chart crossing the metric numbering convention to NEMA numbering convention.
I have seen a lot of various problems with a lot of generators.
I have never seen a problem that could be solved by changing from DD to ZZ or ZZ to DD.
DD is symetrical, and ZZ is not symetrical, but in practice, I have not observed any difference.
ZZ was used for years by many major manufacturers, DD is now becoming more common.
It may at first appear intuitively that the side with the two windings may have greater voltage drop, but a vector addition of the voltage drop shows it to be equal to the single side.
The main difference I see is that on an old set, with damaged or missing wire marking, the ZZ may be changed from 1 Ph. to 3 Ph. or from 3 Ph. to 1 Ph. quicker and with less chance of mistake, than the DD.
With appologies to the EU folk, virtually all the sets in the NEMA world start with three phase star connections.
If a set arrived from the factory wired for 3 Ph. delta, it may be easier to convert to DD than to ZZ.
By easier, I refer to the number of connections that have to be opened and reconnected.
respectfully
RE: flashing 3 phase generator
The relays are usually for automatic starting and motor protection. Although this is important, the relays seldom affect the generator.
The exception is on old sets that may have a "flashing" relay. A flashing relay will be interconnected to the Automatic Voltage Regulator.
respectfully
RE: flashing 3 phase generator
RE: flashing 3 phase generator
I am sorry for the delay, I've been short of time the last couple of days.
Allodola has just supplied the missing piece of the puzzle.
I am not surprised to see 30 volts out if the relay is flashing the field with 12 volts.
For some reason, your flashing relay is not transfering control to the Automatic voltage regulator.
What you are refering to as the shutdown relay is probably an AVR control relay.
In many of the older sets the AVR did not have an "Under Frequency Roll Off" feature. (UFRO)
Without the UFRO feature, the regulators would fail in a matter of a few minutes if the engine was operated at reduced speed.
It was recomended on many sets that the voltage regulator not be turned on until the engine was up to speed and that the voltage regulator be turned off before stopping the engine.
A shut-down relay connected to the AVR would not be unexpected on an old machine. The shutdown relay may be frequency dependent. if an old capacitor has failed or is failing the relay may not be functioning properly.
Note: I say may. There is not a lot of standardization from one make to another on the old generators in that size range.
AVRs with UFRO usually have a setting for 50 Hz. or 60 Hz.
Often it is jumper selectable.
I hope this helps.
respectfully
RE: flashing 3 phase generator
Also pondering the necessity of a Propane leak detector in the housing containg the Gen set, electronics and 20 year old 4 cylinder LP Wisonsin engine. Any thoughts on this?
Allodola
RE: flashing 3 phase generator
I have also delt with ASAP. They are very helpful and their original Kohler parts are cheaper than the dealers.
Instead of using an overvoltage relay, could you use an MOV? www.digikey.com has them for cheap.
RE: flashing 3 phase generator
Am certainly open to suggestions of an easy reliable protection approach. Ciao