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Kohler Electric Plant 15R61 low output


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  #1  
Old 12-23-2018, 04:43:07 PM
mrh0t mrh0t is offline
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Photo Kohler Electric Plant 15R61 low output

Gentlemen, and/or Ladies,

This may be a good question for any old timers out there. This is my vintage (but I think not as old as me) Kohler Electric Plant, model 15R61, that I've owned about 15 years. The SN is 230934, and it's Spec 6701B5.7 The 15KW genset has internal windings to start the 4 cylinder Waukesha model 180GKB-5G gas engine on the front end. My local generator guy estimated it to be from the 1970's. If anyone can confirm that, or has a better idea as to it's age?

Except for the water pump, which got noisy and had to be rebuilt earlier this year, it starts right up, and it's been trouble free as long as I've owned it. It's single phase, and outputs 120V on each of it's two legs. Just recently it stopped putting out 120V, and now has only 4 or 5 volts on each leg. I checked the brushes and cleaned up the rotor, but no change. I was told these units used a coil to control voltage, instead of a voltage regulator? There is that big ol' coil inside the control box. Please see the photos.

I can't find anyone locally who's interested in working on this unit, so if anyone could point me in the right direction, I'd appreciate it.

Merry Christmas and Happy Holidays to all,
Harry
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  #2  
Old 12-23-2018, 05:07:16 PM
I like oldstuff I like oldstuff is offline
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Default Re: Kohler Electric Plant 15R61 low output

Lots of things to check.
Firstly, take the round cover off the end of the gen. You'll likely find a couple wire wound resistors that are adjustable via a sliding contact that touches the wires. Make note of the positions on the sliders. Take them off and clean the little pip that contacts the wires. Also clean the resistor wires with scotchbrite or fine sandpaper. Put it back together and see if it puts out power.

Those old selenium rectifiers (green finned thing in the control box) tend to fail with age. See if you have DC coming off of it. Should be the pinkish and yellow wire.
Also check the connections of your last pic for loose or corroded joints. The big wires coming from the generator into the terminal block.

Hang in there, the smart guys will chime in soon.
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Old 12-23-2018, 07:08:44 PM
Vanman Vanman is online now
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Default Re: Kohler Electric Plant 15R61 low output

Definitely concur- the resistor under the brush cover is the first thing to check.

You'll want to replace that selenium rectifier with a silicon unit. In this application, when that rectifier fails open while the set is under load, the compounding transformer that supplies it will be destroyed and will then have to be rewound.

Failure of this circuit will not prevent the generator from building up and generating, however.

While the set is running and generating but with no load, there are only a few volts dc on the auxiliary field winding, supplied by the rectifier. This increases in proportion to load, up to perhaps 40 volts at full load.

Keith
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Old 12-24-2018, 12:18:09 AM
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Default Re: Kohler Electric Plant 15R61 low output

Thanks Keith for bringing up the transformer failure should the rectifier croak. I forgot about that scenario to let the magic smoke out.
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Old 12-26-2018, 02:54:26 PM
mrh0t mrh0t is offline
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Default Re: Kohler Electric Plant 15R61 low output

Thanks Keith for your reply. I see the two wire-wound resistors, and the adjusting band has rusted through on the top resistor. The old band has a dimple in it for making contact with the resistor wires. Not a great design, but it is what it is. Should I fashion a replacement band, try to recreate the dimple, and solder it back on the lead, or try and replace the whole resistor? The old band left a good rust stain on the resistor, so I can get it very close to the original position if I make a replacement. Can you tell me the purpose of these resistors? Do they balance the output somehow?

I'll check the voltage at the rectifier when I get this problem fixed.

Best'
Harry
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Old 12-26-2018, 02:59:41 PM
mrh0t mrh0t is offline
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Photo Re: Kohler Electric Plant 15R61 low output

Forgot the photos
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Old 12-26-2018, 03:08:35 PM
mrh0t mrh0t is offline
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Default Re: Kohler Electric Plant 15R61 low output

I'm confused, ha, ha. "Oldstuff" was first to be thanked!

Now, thank you Keith, for the rectifier info. I'll try and see if I can find any specs on it.

Harry
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Old 12-26-2018, 03:14:56 PM
Zephyr7 Zephyr7 is offline
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Default Re: Kohler Electric Plant 15R61 low output

You can actually buy new bands for those wirewound resistors. I’d just make one out of a piece of brass strip. Easy to make the dimple, drill a hole in a piece of wood, ideally hardwood, then use a nail or awl to press in the dimple using the hole like a die underneath the strip.

You can clean up the wire on the resistor by polishing it a bit with paper towel. Make sure to wipe parallel to the wire, not across it, to prevent damage.

Bill
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Old 12-26-2018, 05:10:31 PM
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Default Re: Kohler Electric Plant 15R61 low output

There ya go, you found the problem and yup, either source new bands or make them. Take the resistors out to clean the windings. Take ALL the wire connections apart in that gen end and clean them up. It's an oldie so there's probably resistance in many of the connections and solder joints that could heat up and fail.
Once assembled you can slide the bands to fine tune your output voltage. *Shut it off when moving them so you don't get zapped.

Also carefully pull out on the end bearing seal and with a needle on your grease gun pump grease in it.

For the rectifier something like this will work just fine. I'm assuming yours is 3 phase.
https://www.ebay.com/itm/Bridge-Rect...-/271997001394

If your machine is single phase then something simple like this. You'll have a spare.
https://www.ebay.com/itm/2Pcs-1000V-....c100642.m3226
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Old 01-06-2019, 09:36:38 PM
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Default Re: Kohler Electric Plant 15R61 low output

His Selenium rectifier is a single-phase. They probably only tapped off of two legs to get the feedback for field boost.

I would NOT waste any time in getting that Selenium out'a there... it's probably leaky as a cracked 5-gallon bucket.

Two white wires go to AC terminals... they're marked with a tilde ~, and it doesn't matter WHICH way you connect those.

I believe red goes to + and yellow goes to -.

IF you connect the DC backwards, as you add more load, voltage will drop...
...don't ask how I know...


you can make a nice replacement strap by cutting a strip out'a a piece of copper pipe. If you don't have fancy tools, cut a piece of pipe about 4" long, hammer it flat on the back of your bench vise, then take a sharp cold chisel and cut a path along one of the folded edges. Once you've cut that clear, open up the pipe to a flat piece, then use the chisel to cut your strip... cut it a smidgen wider than you need, and clean it up with some 200 grit sandpaper.

Make the dimple by placing the strap on a piece of hardwood, and dull the tip of a fair sized nail...give it a light whack with a light hammer, it'll look professional. Wrap it, bend it, mark it, drill it and call it OEM.
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