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Old 09-03-18, 10:42 AM   #1
swarf
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Question Lister 8hp CS Start O Matic 4 kw.

I would be very grateful for some help. I have a rotary switch to cut off the mains to my shed and switch over to the generator. (Double pole) Unfortunately this switch somehow allowed the mains to get connected back while the generator was starting up. There was a very loud bang and nasty smoke coming from the top of the generator. I cannot start it again on the batteries,(charged up) although it will turn slowly.
I haven't plucked up enough courage to take spanners to look at it yet.
It was a perfect working S-O-M. and all the control gear seems to still work.
So If any of you electrical minded men can give me any idea as what part of it went bang and if is likely to be repairable? Thanks, Chris.
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Old 09-03-18, 06:28 PM   #2
somian
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If smoke emerged from the box on top of the alternator the first thing to do is to take the lid off and have a look inside to see what looks charred. From what I remember the box sits over a hole where the wires come out of the machine itself, so It is possible that the smoke came through that hole from something in the machine itself.

One other question, is it a "fat boy" or "slim boy" machine, because the voltage regulation circuits differ, the slim boy has a current transformer and rectifier, whereas the "fat boy" doesn't. I believe the current transformer is in the end of the machine, but I may be wrong. Also check the battery fuse, though I doubt that is the problem.

Was there any smoke from the wall mounted SOM control box?
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Old 09-03-18, 09:25 PM   #3
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Thanks somian for your reply. yes i checked the control box and that is the only place that smoke came from. The battery fuse is intact. There is no signs of obvious burn out anywhere else.
Not sure what the difference between fat and thinboy. so I attach photos of the machine and top box..Thanks for the help. Chris.
Attached Images
File Type: jpg 2009_Fuel cut off solinoid.Alt. Cubicle open..JPG (84.5 KB, 40 views)
File Type: jpg C.S.jpg (101.6 KB, 37 views)
File Type: jpg 2009_CS Sideview..JPG (122.2 KB, 37 views)
File Type: jpg 2009_CS Complete side view. (2).JPG (118.5 KB, 34 views)
File Type: jpg 2009_Cubicle.JPG (128.0 KB, 42 views)
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Old 09-03-18, 10:18 PM   #4
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This link may assist in identification (bottom post on page).

http://www.stationary-engine.net/for...boy#post328092

Last edited by ListerHA2; 09-03-18 at 10:21 PM.
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Old 09-03-18, 10:20 PM   #5
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This link may assist in identification (bottom post on page).

http://www.stationary-engine.net/for...boy#post328092

Edit: What's on the data plate?
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Old 10-03-18, 02:10 AM   #6
AdeV
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This is just a guess... based on the fact it'll turn slowly (very slowly? Or just a bit slowly?), mains electricity has made it into the starter windings, and at some point they've melted & joined together. This will reduce the ability of the set to motor under 24v (hence the slow speed), and the smoke would have been the shellac insulation burning away. The reason the smoke came out of the top box was, that's where the hole is...

As I say, it's just a guess, but I think you're going to have to pull out the armature and inspect it for damage.
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Old 10-03-18, 11:46 AM   #7
Lucien Nunes
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I would conduct a number of tests before jumping to that conclusion. The resistance of the DC windings is very low, and it would take a very large mains fuse to pass enough current for long enough to damage them directly. Only one side of the mains is connected to the DC circuit except via the detection circuit, which is too light to pass enough current to damage the windings. It is possible that the AC armature winding is damaged and this has shorted to the DC winding, or damaged it by burning, in which case I would expect the battery current during starting to be sky-high and all sorts of distress apparent (e.g. SC contacts smoking) when attempting to start.

I would suggest testing the machine separately from the control box, to prove that when correctly connected it will motor at full speed and power. My hope is that you will find the control gear actually is damaged (I am not sure on what evidence you are saying it seems fine, as the set doesn't operate) and the machine is motoring on the shunt field only, in which case is will be very lacking in starting torque.

First - OP - are you familiar and comfortable with using a multimeter to take resistance and voltage readings? Can you post high res pics of the inside of the two boxes and schematic?

Incidentally, the issue of the transfer switch applying mains to the set is quite a serious one, as the lack of electrical separation between a public utility and a private generator can create unseen hazards for people working on supposedly isolated sections of the mains. Strict standards apply to transfer switch design and construction and it would be wise to try to understand what went wrong with it.
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Old 10-03-18, 03:19 PM   #8
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Tanks for your reply Lucien. I was hoping that you would make a comment as you have helped me get out of tricky electrical situations before.
Well I have taken out the armature this morning and it and the 4 field coils 'look' ok with no obvious signs of burning, but i know that doesn't mean they are ok.
I have tried to test the resistance in the armature segments but without success. I think I need some help here and in testing the field windings also.
I have previously skimmed the armature and replaced all the brushes and had it working fully for about 12 years. That is only to really play with it.
I have found the sourse of the loud bang. It was the radio interferance suppressor. I attach a photo of it with the end blown out.
Attached Images
File Type: jpg DSCN0782.jpg (78.8 KB, 30 views)
File Type: jpg DSCN0783.jpg (75.8 KB, 25 views)
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File Type: jpg DSCN0789.jpg (93.3 KB, 25 views)
File Type: jpg DSCN0791.jpg (43.7 KB, 23 views)
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Old 10-03-18, 03:35 PM   #9
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Same sort of slip rings and associated brushes as my BKB alternator, no commutator on mine though.
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Old 10-03-18, 04:21 PM   #10
Lucien Nunes
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For test purposes that suppressor can be replaced with a bolt through a plastic bush, simply to connect the two cables together without them touching the casing.

There are two windings on the armature - AC (with sliprings) and DC (with commutator). There should be no continuity between them (with the armature removed from the machine) nor from either to the shaft. First check these three readings with the highest resistance range on the meter. Report any reading less than off-scale as this indicates possible insulation damage. Only a proper high-voltage insulation tester (aka Megger) would give a true indication of the state of the insulation, but if there are no signs of burning I don't think there will be any problem and would not waste time getting hold of one at this stage.

Next, measure and report the resistance of the AC winding between the sliprings using the multimeter on 200 ohm range.

It is hard to make meaningful tests on the armature DC winding using only a multimeter. The resistances are very low and it will be almost impossible to distinguish a good winding from a damaged one without special kit. In any case if the AC winding is OK I think it is very unlikely that the DC winding would be damaged.

Then the fields. I There are a few separate windings but I cannot confirm the exact arrangement without a clear picture of the schematic inside the box lid - perhaps you could post a pic? The most likely to be damaged is the shunt field, between terminal Z and the frame / A-. If the machine leads are at present disconnected from its top box, perhaps you could post a resistance reading? If they are still connected, you can simply lift the Z lead from the end of resistance SFR. and measure from lead to frame.

There is also the aux winding and the series, but neither is likely to have been damaged. I would focus testing on the most vulnerable parts.

To summarise:
Resistance from sliprings to shaft, sliprings to comm, comm to shaft (should be high), between sliprings (AC winding resistance), and field Z (while disconnected) to frame or A- if that is disconnected from the frame.

If this all checks out, I would reassemble the machine, bypass the damaged suppressor and attempt to motor it without any of the controlgear connected. Connecting the battery between SS and A- should see it spinning nicely. If it doesn't, then there is a serious problem to investigate. If it does, then we can progress to reconnecting SFR and seeing what it will generate, again without the automatic gear involved.

E2A: Please can you confirm what rating of fuse or circuit breaker protects the mains circuit that accidentally energised the plant, and how long it was energised for? Did that fuse blow immediately?
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Last edited by Lucien Nunes; 10-03-18 at 04:26 PM.
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