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I did this on both 955 and 1050 GT. I used epoxy resin in both cases.

On the 955 I completely rewound the whole stator. I isolated from the core on the burnt spot w/ 50g/m虏 glass fiber + epoxy. It lasted one year. After that I put an electrex UK one that lasted at least until I sold the bike. Didn't hear from the new owner about that since then. I think the winding process is crucial. Most of the damage appear at that time.

On the 1050 I only rewound one pole. The core isolation wasn't damaged. Still running well as I write.

The final work has to be coated w/ epoxy to avoid the windings to move and vibrate.

I didn't consider silicon because:
1-no professional winder does
2-it may squeeze down to the core on the core corners and destroy the enamel.

There is a lot of video showing how it's done. W/ machines and manually. For instance
 

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More details here:


13:37 : "after you get that epoxy shell out of the way".

I repare my RV exhaust mufflers w/ epoxy. So the best is to make a trial to check how the epoxy you get stand the temp. But it's pretty resistant.
 

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If burnt, contaminated, hot engine oil is a factor in the demise of a stator then fully synthetic oil might be a cheap preventative measure.

I don't think I'd have the patience to rewind a complete stator by hand.
 

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Discussion Starter · #27 ·
I did this on both 955 and 1050 GT. I used epoxy resin in both cases.

On the 955 I completely rewound the whole stator. I isolated from the core on the burnt spot w/ 50g/m虏 glass fiber + epoxy. It lasted one year. After that I put an electrex UK one that lasted at least until I sold the bike. Didn't hear from the new owner about that since then. I think the winding process is crucial. Most of the damage appear at that time.

On the 1050 I only rewound one pole. The core isolation wasn't damaged. Still running well as I write.

The final work has to be coated w/ epoxy to avoid the windings to move and vibrate.

I didn't consider silicon because:
1-no professional winder does
2-it may squeeze down to the core on the core corners and destroy the enamel.

There is a lot of video showing how it's done. W/ machines and manually. For instance
Thanks for the info Fred.

Interesting to hear about the outcome of your own epoxy repair efforts. Do you know where your 955 stator failed again after a year? I mean was it in the same spot you repaired, or somewhere else? (I'm assuming you mean it failed short to ground again.)

I was hoping for a similar repair situation to your 1050, but alas...

You raise a number of good points/considerations several of which I addressed earlier in the thread, eg.why use silicone when no professional rewinder would do it that way (as far as we know) etc.

It's somewhat experimental. Though of course I do want it to last for a while.

In response to your point 2 above - one of the key things here is that (apart from 2 pothole repairs) it will not be silicone riding on the metal core here. The silicone is providing an extra rubbery buffer on top of the original covering, to provide additional insulation and reduce potential for abrasion around the corners. There will also be another layer over the silicon before the first winding (though I need to play around with that a little).

I quite agree with you about the way the winding is done - it's important not to create invisible damage in the process.
 

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Discussion Starter · #28 ·
More details here:


13:37 : "after you get that epoxy shell out of the way".

I repare my RV exhaust mufflers w/ epoxy. So the best is to make a trial to check how the epoxy you get stand the temp. But it's pretty resistant.
I looked at all the videos you linked. I appreciate you were putting them up as 'for instance's, but for example at the point you mention above (13:37) he is talking about removing the huge external epoxy encrustations from that particular old stator, not the insulation layer on the core. In the interests of not keeping heat in I wouldn't want to put such a thick jacket of epoxy on the outside. He refers to the coating on the core as powder coat not epoxy and he doesn't attempt to repair it with epoxy where it is chipped through to the metal - he just says he wraps a bit of electrical tape around damage spots (but doesn't say what type of tape - which would have been the most interesting bit :) * ) He then uses a 2-part epoxy to impregnate the windings - I'm going to use an oil/temp resistant solvent based lacquer instead.

I'm curious about what stresses the magic winding machine might put on the wire (impressive though it is).

* Actually one of my earlier ideas - which in some ways I now wish I'd followed up a bit more energetically - was to use a PTFE tape to overwrap the stator poles. I went off the idea at some point due to the possibility of it shredding around the edges but I think I might have jumped too quickly there.
 

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Discussion Starter · #29 ·
If burnt, contaminated, hot engine oil is a factor in the demise of a stator then fully synthetic oil might be a cheap preventative measure.

I don't think I'd have the patience to rewind a complete stator by hand.
Interesting thought. I don't know how much the accumulating horrors in the eng.oil (or just the type of oil itself) are a contributing factor to the weakening of the insulation, either on the stator or on the windings. The damage I've seen tends to look very localised but perhaps there is a general weakening occurring. I've just gone for general oil and temp resistance.

It's not a job for the impatient perhaps... though everything is a balance of opportunity costs :)
 

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I buy el cheapo stators off ebay. They don't last anytime at all, burning out the insulation on the flyleads and shorting out, usually near the clamp point. The stators themselves are actually quite good but I suspect he flyleads are added by a separate workshop and they don't use cable with insulation properly rated for the temperature they will be subject to. Buying small quantities of cable rated for at least 125掳C is actually quite difficult. I had one supplier send me cable advertised as 'suitable for hi-temp applications above 130掳C' and when it arrived I was dismayed to see it clearly printed with 105掳C along it's length.

Anyway I've done two units so far and both are holding up well (probably jinxed myself now).
 

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May not be of interest, but GL1000 alternators were PM also. The stators were pretty common to go out, but the real cause was not weak internals - it was the stupid plug that they used to connect the three phases to the rectifier. All three in one small plastic plug with sub-par connectors and located in the area of road moisture and battery fumes. The connectors would develop high resistance, get hot, melt the plastic plug body, and short out a phase which rapidly took out the stator. The "three yellow wire" fix became a common thing to do on any of the GL1000, 1100, 1200 'wings. Nothing wrong with PM alternators, but one must remember that they put out full power whether needed or not. Anything else is shunted to ground.
 

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Discussion Starter · #32 ·
I buy el cheapo stators off ebay. They don't last anytime at all, burning out the insulation on the flyleads and shorting out, usually near the clamp point. The stators themselves are actually quite good but I suspect he flyleads are added by a separate workshop and they don't use cable with insulation properly rated for the temperature they will be subject to. Buying small quantities of cable rated for at least 125掳C is actually quite difficult. I had one supplier send me cable advertised as 'suitable for hi-temp applications above 130掳C' and when it arrived I was dismayed to see it clearly printed with 105掳C along it's length.

Anyway I've done two units so far and both are holding up well (probably jinxed myself now).
That's very interesting - and the most specific info on how these stators tend to fail that I've heard so far (albeit an admittedly small sample..) ! And relatively nice easy fix.

Teflon insulated cable should be good for the flying leads (not just because it's used in aircraft :ROFLMAO: ) I've used it in the past for slim high current cabling of valve(tube) heaters in an amplifier. My cables were still good this time so no need to replace.
 

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Discussion Starter · #33 ·
May not be of interest, but GL1000 alternators were PM also. The stators were pretty common to go out, but the real cause was not weak internals - it was the stupid plug that they used to connect the three phases to the rectifier. All three in one small plastic plug with sub-par connectors and located in the area of road moisture and battery fumes. The connectors would develop high resistance, get hot, melt the plastic plug body, and short out a phase which rapidly took out the stator. The "three yellow wire" fix became a common thing to do on any of the GL1000, 1100, 1200 'wings. Nothing wrong with PM alternators, but one must remember that they put out full power whether needed or not. Anything else is shunted to ground.
Yes indeed - the plugs are often a weak spot.

As you say, the stators are designed to cope with being shorted as that's how shunt regulation works - but that also makes it less clear how shorting out a phase at the plug would cause the stator to fail. It's conceivable perhaps that a slight increase in current due to the regulator being taken out of the circuit could push the stator over the edge, but it would have to be on the brink of failing already, it would seem.
 

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Discussion Starter · #34 ·
So...Next step.

Snipped off any particularly knobbly bits of silicone.

Experimented with fibreglass winding tape as an additional layer on top of the silicone but it was slightly wider than the bobbin and in general too bulky.

The remaining space after the rubber coating is already a slight concern, especially since I'm intending to use larger diameter wire.

Tried trimming the tape down but then all the escaping strands of fibregass were unmnageable and it was in general a right pain to try and work with small pieces in the narrow slots - and still too bulky anyway.

In an effort to make it look even worse I therefore used the Krapton (TM) tape as a final belt-and-braces core isolation layer. It's thin and the crinkles will pack down ok when the windings go on. There's a double layer of it.

Automotive tire Rim Auto part Machine Circle
 

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Discussion Starter · #37 · (Edited)
Why are you using thicker wire? is that how the output is increased with these?
In theory (I haven't tried it it personally in a real situation) it can boost the output but it is only one of the limiting factors in the available output of a generator like this.

If you increase the wire diameter you will tend to force more of the coil turns further away from the core in each pole piece. That will tend to worsen the magnetic coupling, causing a decrease in output. Furthermore if it forces you to have less turns due to space limitations then it will mean less voltage generated - which could be an issue at low RPM.

Personally I'm doing it primarily as part of measures to reduce heat generated in the windings (the other measures being changing to use a series type Reg/Rec, LED headlights etc.). I'm hoping the lower resistance will also help offset inefficiencies that may be introduced by adding thicker insulation layer on the core as well as the thicker wire itself - both of which push the coils away from the core. I haven't bothered to try and calculate the relative strengths of the positive and negative effects however, so I'm slightly flying by the seat of my pants.

(Not all of the heat is generated in the windings, some comes from the ambient engine temperature obviously, but also some heat is generated in the stator core laminations themselves by eddy currents.)
 
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Discussion Starter · #38 ·
The GL1000 regulators just shunt one phase (partially) to ground. Shorting two together dumps them into each other.
Ah - right. That does change the picture... In danger of getting too parochial here in sprintland!
 

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In theory (I haven't tried it it personally in a real situation) it can boost the output but it is only one of the limiting factors in the available output of a generator like this.

If you increase the wire diameter you will tend to force more of the coil turns further away from the core in each pole piece. That will tend to worsen the magnetic coupling, causing a decrease in output. Furthermore if it forces you to have less turns due to space limitations then it will mean less voltage generated - which could be an issue at low RPM.

Personally I'm doing it primarily as part of measures to reduce heat generated in the windings (the other measures being changing to use a series type Reg/Rec, LED headlights etc.). I'm hoping the lower resistance will also help offset inefficiencies that may be introduced by adding thicker insulation layer on the core as well as the thicker wire itself - both of which push the coils away from the core. I haven't bothered to try and calculate the relative strengths of the positive and negative effects however, so I'm slightly flying by the seat of my pants.

(Not all of the heat is generated in the windings, some comes from the ambient engine temperature obviously, but also some heat is generated in the stator core laminations themselves by eddy currents.)
Thanks. I've got a very basic idea of how they work but don't really understand it so that helps.
 

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Wildly in general, the number of turns determines the Voltage, and the wire size determines the Amperage that can be handled. PM alternators (given good field magnets) tend to be limited by speed and their regulators. Switching to series regulators is a more efficient way of dumping excess. Switching to LEDs doesn't reduce the load on the stator, but does give more power available to power other added electrical loads. On bikes with limited stator output (like my RD400c), that can be important. But, any excess still has to be handled. On excited alternators, the regulator controlss field current, controlling magnetic field and therefore output power.
From what I read the Sprint has at least a 300 Watt alternator, which should be plenty.
 
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