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Author Topic: 3k Chinese alternator just stopped mid run  (Read 323 times)

tyssniffen

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3k Chinese alternator just stopped mid run
« on: December 25, 2022, 07:53:38 PM »
So, Merry Christmas to me. Alternator just quit during a run? I examine the wiring and it looked like one of the wires connecting the voltage regulator had melted? Disintegrated? Certainly was disconnected, so I reconnected it. Still nothing coming out. Voltage at the posts is only 12.6? Is this a bigger wiring problem, as in a winding problem? How did this suddenly stop working? nothing else seems wrong.
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ajaffa1

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Re: 3k Chinese alternator just stopped mid run
« Reply #1 on: December 25, 2022, 08:50:27 PM »
Merry Christmas from down under. Sorry to hear your alternator just died. Is this an ST type generator head? Was it under load when it died?
ST heads only have two sets of windings, one on the armature connected to the slip rings, the other is connected to four electromagnets around the inside of the housing. Test both with a multimeter, there should be a small resistance in each winding (10 ohms ish). If either is open circuit it`s probably fried. If both circuits are ok you may need to flash the winding to regenerate a magnetic field.

Good luck

Bob

tyssniffen

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Re: 3k Chinese alternator just stopped mid run
« Reply #2 on: December 25, 2022, 09:05:45 PM »
Yes this is an st. And yes it was under load when it stopped putting out power . Another update, I had another possibly old voltage regulator and I put that in position, and it started making 110 again, for a little while.
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tyssniffen

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Re: 3k Chinese alternator just stopped mid run
« Reply #3 on: December 25, 2022, 09:09:34 PM »
ST heads only have two sets of windings, one on the armature connected to the slip rings, the other is connected to four electromagnets around the inside of the housing. Test both with a multimeter, there should be a small resistance in each winding (10 ohms ish). If either is open circuit it`s probably fried. If both circuits are ok you may need to flash the winding to regenerate a magnetic field.

Are you saying I have to get in there with the case off and everything? Or is there a way to touch the windings without taking the entire outer shell off?
6/1 with 2 tank for WVO.  pushing power into off-grid house battery bank, in winter.

ajaffa1

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Re: 3k Chinese alternator just stopped mid run
« Reply #4 on: December 25, 2022, 09:26:16 PM »
You should be able to find the wires in the top box. two will go to the slip rings and two to the electromagnets. There maybe a third set of windings that produce about 9 volts to drive the small neon light on the front of the top box, you can ignore those.

Bob

tyssniffen

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Re: 3k Chinese alternator just stopped mid run
« Reply #5 on: December 25, 2022, 09:29:00 PM »
Thanks for all the help. Do I need to do that reading when the thing is spinning? Or will it always have that resistance?
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ajaffa1

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Re: 3k Chinese alternator just stopped mid run
« Reply #6 on: December 25, 2022, 09:33:02 PM »
No,  do it stationary. the resistance will be the same. I would expect to find resistances of between 5 and 20 ohm. This will confirm if the windings are still intact.

Bob

ajaffa1

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Re: 3k Chinese alternator just stopped mid run
« Reply #7 on: December 26, 2022, 12:16:22 AM »
Having thought about your problem It seems to me that you have suffered a catastrophic failure of the bridge rectifier, unusual but not unheard of. This caused a short circuit through the rectifier and burned out one wire.
Having replaced the bridge rectifier it generated power for a short time before failing again. I suspect that the burned wire was badly over heated and has failed. There are two short wires that connect AC voltage to the rectifier, replace them both as they have been overheated. Do not be tempted to replace them with lager wire, as a repeat failure with larger wires could well burn out the windings in the generator head. You might consider fitting an inline fuse in the circuit maybe 1 amp.
Let us know how you go.

Bob

tyssniffen

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Re: 3k Chinese alternator just stopped mid run
« Reply #8 on: December 26, 2022, 02:49:26 AM »
This is some high quality advice, thanks!

more details to see if this matches your thought:
- this ST 3k is only 7 years old; thus it doesn't have more than 700 hours on it. 

- I'm sure my habits are harder on this machine than ideal, but the thing has been inside it's shed and bolted down it's whole life. I spill enough diesel around that I don't think there's mice doing anything horrible in there either.

- when I noticed the loose wire, the attachment/terminal, which I believe was a little square with a hole, with the screw holding it down was just ... disintegrated.  it looked like failed solder, or aluminum foil flakes.  I have now reconnected it (as I said before) and it doesn't seem bad... just went and yanked on it, I can't see anything wrong with it. 

Are you suggesting that both that wire and the rectifier are bad?    Either of those would be a great problem over the windings obviously. 

WHY does something like this happen?

For some reason, I had that other rectifier - that other one I put in - but I don't know if it was a good spare or one I'd replaced.  If it was 'new' (sat on the shelf for 7 years) would it have failed like that so quickly?   

and, if your theory is correct, you would advise:
1. get another rectifier
2. get another wire where that one failed, put a 1amp fuse inline in it.






 
« Last Edit: December 26, 2022, 02:57:37 AM by tyssniffen »
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ajaffa1

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Re: 3k Chinese alternator just stopped mid run
« Reply #9 on: December 26, 2022, 07:59:46 AM »
Yes, I would recommend getting a new bridge rectifier, better still buy two so you have a spare, they are cheap. As for the wiring I haven`t seen it so I was just speculating on the worst case scenario. Some ST heads are wired with aluminum rather than copper ( it`s cheaper), while aluminum is a great conductor it does corrode and cause problems.
The problems with rodents, mud wasps and ants are global problems and we suffer just as much in Australia as elsewhere, vigilance and regular maintenance are the only solutions.
Why do rectifiers break down? Rectifiers get hot when in use, they should have a large heatsink to dissipate that heat. The heating/cooling cycle causes microscopic cracks that eventually lead to failure. If you buy a new TV plug it in and leave it on it is probably good for 10 years, the more often you turn it on and off the quicker it will fail.
I am guessing at the value of the inline fuse required, without knowing the resistance of the field winding I can`t do the calculations. Based on Ohms law: V=IxR  where V is volts, I is current in Amps and R is the resistance of the field windings in ohms. So dividing the voltage by the resistance should give you the required fuse amperage.
Silicon rectifiers have an almost unlimited shelf life, if it was one you swapped out because it was breaking down or was of poor quality  it could fail very quickly.

Let us know how you go

Bob




38ac

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Re: 3k Chinese alternator just stopped mid run
« Reply #10 on: December 26, 2022, 01:05:52 PM »
I am very surprised that the original rectifier lasted as long as it did, most fail very quickly. Both of mine did in about 10 hours. Luckily the knowledgeables here on LEF put me on to these 5010 bridge diodes which are dirt cheap and reliable if they have a heat sink. I bought a bag of 20 on ebay for like $25 USD maybe 10 years ago. You can you can mount them on the fancy aluminum heat sinks sold for the purpose or simply attach them to the metal box with a screw. What you cannot do is not have a heat sink of some sort.
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tyssniffen

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Re: 3k Chinese alternator just stopped mid run
« Reply #11 on: December 26, 2022, 05:26:29 PM »
I am very surprised that the original rectifier lasted as long as it did, most fail very quickly. Both of mine did in about 10 hours. Luckily the knowledgeables here on LEF put me on to these 5010 bridge diodes which are dirt cheap and reliable if they have a heat sink. I bought a bag of 20 on ebay for like $25 USD maybe 10 years ago. You can you can mount them on the fancy aluminum heat sinks sold for the purpose or simply attach them to the metal box with a screw. What you cannot do is not have a heat sink of some sort.

Ok, I'll get new rectifier(s).  more questions created though:
I found the ones you reference:
https://www.aliexpress.us/item/2251832449962468.html?pdp_npi=2%40dis%21USD%21US%20%240.95%21%240.84%21%21%21%21%21%402103222016720751812772647e2079%2110000001113346307%21btf&_t=pvid%3A0e4d991c-e5f6-4ce2-9788-17f432c97328&afTraceInfo=32636277220__pc__pcBridgePPC__xxxxxx__1672075181&spm=a2g0o.ppclist.product.mainProduct&gatewayAdapt=glo2usa&_randl_shipto=US

and also ones that match what I had in there:
https://www.stationaryengineparts.com/ST-Alternator-Bridge-Rectifier.html

question 1: which is better?


question 2: if installing those KBPC5010s, how do you match up the wiring? (I see 2 labels, AC and +, but which post goes with which wire?)

question 3: what do you do for a heat sink with those?

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tyssniffen

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Re: 3k Chinese alternator just stopped mid run
« Reply #12 on: December 26, 2022, 06:05:31 PM »
PS - anxious, so already pulled the trigger and ordered 8 of those little KBPC5010s.   Very interested in hearing about mounting choices.

also, just to circle back on the windings possibility to understand the thinking.... how does that failure happen?  and what does it look/act like?  If that 2nd rectifier I popped in there was good, but the windings were fried, it shouldn't have made any more AC, even for a minute, right?   


« Last Edit: December 26, 2022, 06:23:35 PM by tyssniffen »
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38ac

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Re: 3k Chinese alternator just stopped mid run
« Reply #13 on: December 26, 2022, 07:02:58 PM »
The bridge rectifier such as shown by Stationary Engine parts are the style that fails a quickly. The little square 5010 bridge diodes last a long time. The bridge diodes are usually marked + and AC (or a wiggly line for AC) The other AC terminal is opposite the marked one and the -DC I terminal is opposite the +. Some bridge diodes are not marked at all but one terminal is turned 90 degrees from the other 3. That one is DC+, opposite is - and the other two are AC Your old rectifier shoukd be marked so you can transfer the wires. If not I'll have to dig out my ST manual to tell you how to trace the wires.3
« Last Edit: December 26, 2022, 07:05:03 PM by 38ac »
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ajaffa1

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Re: 3k Chinese alternator just stopped mid run
« Reply #14 on: December 26, 2022, 08:07:15 PM »
Well done on ordering new rectifiers. The ones that ship with these ST heads are garbage. A few years back I did a tear down and rebuild of a brand new ST head, I posted a lot of info and pictures showing how to do it. I replaced the rubbish bearings, skimmed the slip rings which were not concentric with the shaft, replaced the cheap carbon brushes, rewired the top box and fitted a new rectifier with an aluminum heatsink. Later I fitted an automatic voltage regulator.
Aluminum heat sinks can be found on ebay and other sites, old computers all have nice heatsinks on the processor chip. Drill a hole in the back of the top box, bolt the rectifier to the inside of the top box with the heatsink on the outside where it will get good airflow

The wiring is pretty simple there are two wires that can be traced back to the slip rings, these are the AC feeds to the rectifier, it does not matter which way you wire them as long as they both go to a rectifier lug labeled AC. The other two wires go to the field windings and are positive and negative, on mine the positive was the red wire. I do not know if your wiring has spade connectors or screw lugs, fortunately the rectifiers you ordered are compatible with both.

I think the fact that it generated AC for a short while with the replacement rectifier indicates that the windings are probably OK.

How do rectifiers fail? A bridge rectifier contains four diodes, the symptoms vary depending which of the diodes has failed and if it failed open or closed.

Best of luck, let us know how you go.

Bob