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Kohler 33rz high output part 2


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  #41  
Old 11-08-2019, 06:36:44 PM
Birken Vogt Birken Vogt is offline
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Default Re: Kohler 33rz high output part 2

I tell customers to expect 15 years out of a piece of equipment. Any more than that is gravy. You will expect to call the repairman more often after that. At least since it is Kohler you can just call them and have a new part right away.
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  #42  
Old 11-08-2019, 07:27:51 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

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Originally Posted by Birken Vogt View Post
I tell customers to expect 15 years out of a piece of equipment. Any more than that is gravy. You will expect to call the repairman more often after that. At least since it is Kohler you can just call them and have a new part right away.
except I get to play the repair man part. I'm retired now, low income I'm sure you heard the story.

on the bright side, got back cover and magnet removed so I can actually see the scr heat sink in plain view.

tomorrow, weather permitting I plan to take some photos and get the scr removed.

also spoke w/ Anthony Misiti of FlightSystems. They don't make the scr assy any more but might have a rebuilt one I can try out. Wait and see
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  #43  
Old 11-08-2019, 07:45:30 PM
LWB250 LWB250 is offline
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Default Re: Kohler 33rz high output part 2

The FRactivators, or SCR assemblies, are pretty robust. Failure rates, even when they were relatively new, were low. If I had to swap one out more than what I could count on one hand in a given year it was pretty normal. And that's seeing these things on an almost daily basis.

As with anything electrical, electronic, mechanical, etc., stuff breaks.

I know the components that are on that heat sink, and I can tell you that they are very well designed. The potting compound is primarily there to both anchor the components due to centrifugal forces as well as to aid in cooling.

Be glad it's not one of the earlier FRactivators that were a hybrid device. I can't begin to imagine what those cost these days, or if they're even still around. The heat sink built with the discrete components was a big step up in reliability and cost.

FlightSystems are good people, so if they've got something you can use I would feel comfortable doing so. I never used them much in my Kohler days in the field, but when I was doing Onan early in my career I used a lot of their stuff, especially the boards for the LT and AT transfer switches.

Dan
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  #44  
Old 11-08-2019, 10:47:30 PM
Zephyr7 Zephyr7 is offline
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Default Re: Kohler 33rz high output part 2

Solid state stuff ages just like other stuff, it just sometimes takes longer. I repair old HP test equipment fairly often, and I see bad semiconductors periodically. Usually it’s the capacitors that die, but not always. The custom hybrids and chips are the big problems since they are no longer available, so if they die you’re usually stuck.

As others have said, the SCR assembly is pretty robust. I thought I had a bad one once, but it ended up being a flaky regulator board that I rebuilt. The fast response system is a rather clever way to build a brushless generator end that still has “real” external voltage regulation. On the big gensets this is accomplished with a magnetically coupled electrical circuit, but in smaller units you usually had brushes before the fast response system came out.

I think you just got unlucky here. I’m not sure what you could do to a fast response generator to cause the SCR assembly to die early since it’s pretty well protected from all the usual stuff that can damage electronics. About the only thing I can think of is to block the ventilation paths so that the generator end runs too hot for an extended period of time.

Chances are you’ll only replace that SCR assembly one time and never have to worry about it again. There are some electrolytic caps on the regulator board that are easily replaced if you want to bring that board back up to near-new performance just to be safe. It doesn’t take long to replace all the caps, and it’s maybe $10 worth of parts, if that, even when using top end components.

Bill
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  #45  
Old 11-11-2019, 05:32:15 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

is there a way to bench test the head sink assy using a dvm on ohm and diode test settings?

while this might be over kill in the testing dept. I want to make sure as best as I can that this part has truly failed.

I'm looking at 5 connections, 2x ac, gnd and f- f+. I suspect since I'm getting full output from the genset that there is likly a short from ac to the f connections
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  #46  
Old 11-11-2019, 06:54:13 PM
pegasuspinto pegasuspinto is offline
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Default Re: Kohler 33rz high output part 2

There is a test procedure in the book
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  #47  
Old 11-12-2019, 03:49:17 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

In TP-5353 page 7-9 there is a test procedure that calls for a know good scr assy and photo board. It that the procedure you are referring to ?
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  #48  
Old 11-12-2019, 04:01:28 PM
Birken Vogt Birken Vogt is offline
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Default Re: Kohler 33rz high output part 2

Looking at page 7-5 I wonder if while bench testing if the gate wire was connected and disconnected the problem appears or disappears it could be surmised which is the problem. Or simply temporarily cutting the gate wire on the rotor and seeing if the problem persists when running. But don't quote me on this.
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  #49  
Old 11-12-2019, 04:27:28 PM
Zephyr7 Zephyr7 is offline
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Default Re: Kohler 33rz high output part 2

Is there a schematic anywhere showing the innards of the heatsink assembly? I could look at it and recommend a testing procedure.

SCRs are interesting in that they can be electrically controlled as to when they turn on, but once on they latch on and stay on until the current through them drops below a cutoff threshold. Usually SCR assemblies will include some snubber capacitors too.

Normally to test an SCR you trigger it on, make sure it latches on, then interrupt power and make sure it doesn’t stay on when power is restored. All you need is a power supply, light bulb, and a resistor (for triggering), but you need to know the circuit configuration to be sure you’re testing things correctly. There is surely more in that module than just one SCR.

Bill
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  #50  
Old 11-12-2019, 05:09:20 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

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Originally Posted by Zephyr7 View Post
Is there a schematic anywhere showing the innards of the heatsink assembly? I could look at it and recommend a testing procedure.

SCRs are interesting in that they can be electrically controlled as to when they turn on, but once on they latch on and stay on until the current through them drops below a cutoff threshold. Usually SCR assemblies will include some snubber capacitors too.

Normally to test an SCR you trigger it on, make sure it latches on, then interrupt power and make sure it doesn’t stay on when power is restored. All you need is a power supply, light bulb, and a resistor (for triggering), but you need to know the circuit configuration to be sure you’re testing things correctly. There is surely more in that module than just one SCR.

Bill

All I can find is wiring diagrams. A typical policy for corporations not to release too much info, giving them just enough to have the service tech resort to replacing boards than components.

I had the same issue with a furnace induction fan motor, instead of board repair (probably $10 in parts) you replace the entire fan assy $175(used)

Last edited by toddbailey; 11-12-2019 at 06:51:47 PM.
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  #51  
Old 11-12-2019, 07:10:49 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

I'm still in the process of removing the scr from the gen housing.
It took the better part of an hour just to get one of the bolts removed still have 1 left that is well hidden behind a stator.
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  #52  
Old 11-12-2019, 08:43:52 PM
Zephyr7 Zephyr7 is offline
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Default Re: Kohler 33rz high output part 2

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Originally Posted by toddbailey View Post
I'm still in the process of removing the scr from the gen housing.
It took the better part of an hour just to get one of the bolts removed still have 1 left that is well hidden behind a stator.
It’s a huge pain to get to that particular part.

I’ve always found that when working on gensets, and big UPS systems too, a good assortment of 1/4” extension bars that includes a few really long ones (my longest is 18” or so) is VERY helpful for reaching those deeply embedded fasteners.

BTW, a trick I use when replacing those deeply embedded fasteners is to attach them to the socket with some electrical tape. I go about 1/2 to 2/3 of the way around the socket, enough to hold the bolt straight, and attach the tape about 3/4 to the socket and about 1/4 to the bolt head. The goal is for the tape to pull off of the fastener and stay on the socket after you get the threads engaged. This way you can use the socket and extension bar as a very long bolt holder when reinstalling the deep bolts. It’s best to use the good 3M colored tape for this since it tends to not leave residue behind.

Bill
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  #53  
Old 11-12-2019, 11:27:14 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

thanks, but ...

the electrical connections and 2 of the 4 mounting bolts are easy to get to. the other 2 are hidden and have no room for anything except an open end wrench. and even that is becoming a pain. if i had my way the engineers would have been fired for this design.
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  #54  
Old 11-13-2019, 08:25:13 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

whew after several days I finally got the scr heat sink assy removed fron the genset. And now I know why it was such a pita to get it removed.

it's a fairly old part 258766 that was replaced by the 258545.

I did some dvm tests and didn't see any issues, hi resistance across ac to ac and ac to ground and 30 & .6/ meg ohm f to f terms.

I have a bench test where you wire up the photo board and src pack.

once I get this done I'll comment further
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  #55  
Old 11-13-2019, 08:49:39 PM
pegasuspinto pegasuspinto is offline
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Default Re: Kohler 33rz high output part 2

diode check from AC to + and - terms

this is basically a bridge rectifier probably with 2 of the diodes replaced with SCRs. If the SCR's short, it would test just like a regular bridge.
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  #56  
Old 11-13-2019, 09:41:31 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

Thanks for the reply.
With out an internal schmatic I am basically doing black box testing and really can't say if the values I obtain are meaningful, valid or indicate a failure
Since the issue is with full excitation I am hoping to find low resistance across 1 or more terminals. once the replacement arrives I can do a proper a/b test but i'm still guessing at this point.

there is a bench test I plan to follow where the scr pack and photo board are wired up and tested with 110 vac source and a light bulb.

Last edited by toddbailey; 11-13-2019 at 10:11:33 PM.
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  #57  
Old 11-14-2019, 08:11:43 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

well this was interesting, wired up the bench test and the fuse blows before I can shine a light on the phototransistor

I'll try this again once the replacement assy arrives.

Last edited by toddbailey; 11-14-2019 at 08:22:16 PM. Reason: typos
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  #58  
Old 11-14-2019, 09:50:30 PM
Birken Vogt Birken Vogt is offline
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Default Re: Kohler 33rz high output part 2

Replace the fuse with a 100 watt light bulb and try again. It will not blow but the worst that will happen is that it will glow.
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  #59  
Old 11-14-2019, 10:08:21 PM
toddbailey toddbailey is offline
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Default Re: Kohler 33rz high output part 2

I think you might be looking at a different test diagram that I'm using

there is a 100 watt light bulb across the 'f' terminals

the photo board is wired to the scr pack and a power - fused 110 ac is applied to the 2 ac terminals.
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  #60  
Old 11-14-2019, 10:37:17 PM
Birken Vogt Birken Vogt is offline
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Default Re: Kohler 33rz high output part 2

No, I really mean replace the fuse with a light bulb in the power supply wire. If something is shorted or drawing too much power the worst that can happen is the bulb will glow brightly. If it glows dimly you will have some power continuing down line to do your tests with. More of a curiosity thing, the blown fuse tells you a lot already but it would be interesting to see what the light bulb does.
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