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Old 12-29-2011, 11:50 AM   #196
C5! OP
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there is no direct thermal conductivity between the stator and the aluminum cover, as the stator touches the casing only along the fins you see here:
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Old 12-29-2011, 12:01 PM   #197
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As mentioned previously, I don't know if that stator (no.3) died for the same reason as the other ones, but if the fault is electrical, it appears it comes from the connection between the end of the stator wiring and the external wires, and if it would be overheating I would assume that the wiring should be turning black all around the stator, not only one side !!

Because if you look at the 2 following pictures you see that the wiring is ok on the outside side, and starting to chip on the inside side. So it appears that the heat is coming from the flywheel. (and thus not from the exhaust either)

here is the picture from the outside side, the side facing the cover.
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Old 12-29-2011, 12:05 PM   #198
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and here is the side facing the flywheel. We don't see very well for the quality of the picture (it's an iphone and not a camera sorry) but the varnish is turning black and chipping away.

Now the exhaust cannot be eliminated either because what is actually completely charred is the connection between the ending of the winding and the external wire. This part passes below a bracket in the cover and thus is in contact with the aluminum cover. Now hopefully we'll see when we unwind this part if the fault was electric or itjust melted and generated the fault.
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Old 12-29-2011, 07:18 PM   #199
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Possibly he's right, the Bosch guy said he thinks that about 100C is close to the upper operation limit but he did not know for sure. Maybe someone can figure out the proper values. That may help to find out how far we are away from -let's say - an acceptable temperature window....

Steve
You might be right...... But I find it strange though...... As that is an easy reached limit...... Even for room temp cured epoxys. The epoxy I use that require post heat cure has a upper temp limit of about 250 deg C. And wont break down until 325deg C. That same epoxy is in fact used in potting.....

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Old 12-29-2011, 07:42 PM   #200
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Ok, finally heard back from someone thats been helpful in the past.

Polyester-imide is what the F twin rotax stators are insulated with.

"Polyester-imide magnet wire is insulated with a Class H modified polyester resin. It has excellent thermal endurance, solvent resistance and exhibits a low coefficient of friction to improve windability. It requires mechanical or chemical stripping."

It is rated for a maximum temperature of 180C

Since theres some reference to Aprilia here, and it's something I have some new connections with, their 650 single and 1000 CC Rotax V twin stators are insulated with Polyester A / I Topcoat.

"Polyester-amide-imide magnet wire is a two-part insulation consisting of a modified polyester basecoat with a superimposed amide-imide outer coating. This wire exhibits exceptional windability, heat shock resistance, and ability to withstand overloads. Chemical resistance to most solvents and insulating varnishes is extremely good. It is not softened by refrigerants and extractions are essentially zero."

It is rated for a maximum temperature of 200C

On A side note, I don't remember seeing many charging system problems on old BMW F singles, which were actually built by Aprilia and rebadged by BMW.


I have never had any education specific to Parallel PM regulators (shunt type, stock for all of these) Or series PM regulators. Most of my education came from the automotive industry which does not use PM alternators.

That said, as an industrial electrician I had plenty of training with PWM motor controls, which seem to me to be similar to series PM regulators, and the problem is the large voltage spikes causing Partial Discharges (PD) in the coils or complete flashover and burn out.

Maybe theres some sort of new control technology, but any time we used PWM's, we wanted a motor with a magnet wire that said something like this "Polyamideimide For inverter duty applications, this insulation is designated for use in motors that may be subject to voltage spikes".

Neither the stator insulation BMW or Aprilia uses is known for spike resistance but particularly NEMA NW30, or Polyester-imide, what the F twin uses, is just plain bad at dealing with voltage spikes.

This may not be relevant. Perhaps series regulators some how avoid spikes, or maybe they aren't high enough to offset the benefits of lower heat. I simply don't know.


I do know that for me it wouldn't have mattered cause I use nearly all 400 available watts the F8 had to deliver either way.

Also 180 and 200C magnet wire is upper end to begin with and may explain why rebuilds aren't lasting long as 155C class is the usual to rewind car alternators with.



Without going too exotic...
Temperature Class: 240 C
Insulation Type: Polyimide-ML
NEMA Specification: MW 16C
Federal Specification: JW1177/15
IEC Specification: 317-7
Insulation Characteristics:
ML is a film coated magnet wire made with polyimide resin. It is a Class 240 C thermal life insulation with exceptional resistance to chemical solvents and burnout. It will operate at a temperature up to 240 C. The outstanding cut-thru of over 400C and its ability to withstand excessive overloads extends the use of magnet wire in extreme conditions. ML is unaffected by prolonged exposure to varnish solvents and it's compatible with virtually all systems


But I can say from experience, winding the above shit without cracking or bunching it is a PITA.

Sorry, still no answers, but more information.

P.S. Potting and varnishing are not the same thing. Once the varnish fails and causes shorts, the resultant short will cause the stator magnet wire to exceed 800C and sometimes even melts the copper so like 1100C. Potting just keeps the magnet wire from moving around and abrading.

P.P.S. Denso makes the PM rotor and stator of these and many many other motorcycles, but they are a goliath company with a tun of off the shelf products and ability to cater to any buyers design. In quality control and design, Denso makes Bosch look like a bunch of fools.
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Old 12-29-2011, 08:16 PM   #201
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Thanks for the data Joel. The saga continues.
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Old 12-29-2011, 08:19 PM   #202
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Just another item to keep an extra on hand with this bike...
Going to need an extra shelf.
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Old 12-29-2011, 09:32 PM   #203
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Originally Posted by C5! View Post
As mentioned previously, I don't know if that stator (no.3) died for the same reason as the other ones, but if the fault is electrical, it appears it comes from the connection between the end of the stator wiring and the external wires, and if it would be overheating I would assume that the wiring should be turning black all around the stator, not only one side !!

Because if you look at the 2 following pictures you see that the wiring is ok on the outside side, and starting to chip on the inside side. So it appears that the heat is coming from the flywheel. (and thus not from the exhaust either)

here is the picture from the outside side, the side facing the cover.
Interesting thread for sure.

I worked at a fractional hp electric motor mgr 38 years ago, so the idea of winding copper wire around steel annealed laminations is not new. In looking at the photo I could not tell if there was an insulator between the windings and the metal. In making motors the stator metal was coated with epoxy for isolation. Edge thickness of this isolation was important as the windings were tested to assure a hi- pot test of 1800 volts.

I was the reliability mgr for a while so we did testing of locking the rotor and life testing in it's application. Failure often occurred with a room of smoke with fried windings.

I would imagine the designers did testing to assure that the design would be good but full load in a hot ambient with rock protection may not have been in the testing plan.

In the case of some windings turning black seems a possible shorting to the laminations (gnd) should be investigated. That short would cause excessive current and heat IMO.

One other rule of thumb was that organic finishes on windings life decreases by 1/2 for every 10 degrees C over 150 degrees C.

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RidingAgin screwed with this post 12-29-2011 at 09:34 PM Reason: Typo
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Old 12-30-2011, 12:03 AM   #204
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You might be right...... But I find it strange though...... As that is an easy reached limit...... Even for room temp cured epoxys. The epoxy I use that require post heat cure has a upper temp limit of about 250 deg C. And wont break down until 325deg C. That same epoxy is in fact used in potting.....

ErlIng
Referring to Joels post #200 it seems the Bosch guy did tell me bullshit.

So considering that temperatures around 150 to 180 C (300-350F) would be still acceptable we can drop the idea of overheating due to high ambient temperatures in combination of heat radiaton of the exhaust pipes. I can not imagine that the rotor gets that hot just due to the mentioned reasons. What do you think? I mean if the engine is designed that way why is there obviously no cooling for the stator coil? Or does the oil cool the stator and we just dont know how it works (a schematic of the oil system could help)?

I worked as car technician and then changed over to aircrafts so I know all kinds of engines and motors with pistons, rotary pistons and turbines. Oil temperatures in piston engines do not exceed 120C (250F) under normal operation conditions. Measured at the correct measuring point, which is not the sump, drain plug or at the dipstick.

As reported theres not much oil cooling the stator, right? No nozzels spraying oil at the stator and not enough oil in the engine housing that could cool the stator. Is this a poor desing or what is the idea behind? Why does BMW say use mineral oil (instead of synthetic)? Why is the F8 equipped with an oil/water heat exchanger (it is not an oil cooler, literally), its not high revving and it has a huge water cooler. There are bikes with more power and smaller radiators having no oil cooler....

Strange.... and I have no clue what else we could try :(

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Old 12-30-2011, 01:04 AM   #205
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Ridingagin, All the cooked ones I saw with my own eyes had fully cocked, so I couldn't determine the primary failure point with my eyes.

That said, it never has looked like a very quality stator. I say this with a grain of salt cause I'm educated in car alternators and industrial motors, not motorcycle stators.

This however is my observation. The finish on the core is thin epoxy looking stuff with pretty sharp edges. There are no sleeves or insulators of any kind protecting the magnet wire from grounding on the core other then the thin epoxy like finish.

Steveman, I wouldn't rule out ambient temperatures inside the case or of the case itself, nor oil cooling or the lack there of. The magnet wire itself generates a lot of heat. That heat leaves by convection, conduction, and radiation. The warmer the case, oil, and gases are, even though still bellow the maximum temperature the magnet wire insulation can take, the slower the magnet wire can shed heat through the above named dynamics.

Also, for the types of insulation above, whats listed is the maximum RATED temperature. They SHOULD hold up to the maximum rated temperature for a considerable while, but not forever and NOT if they have any flaws or were at all damaged during the winding process. Its a non linear slope, how long they will take whatever temperature.

In any case, winding a stator is always a flawed procedure that works because of "defense in depth" I'm sure the magnet wire is dipped more then once in the hopes that flaws won't line up and so its more resistant to abrasions, cracks, bubbles, and what have you. The core is epoxied and though not here, usually the channels are tubed or spaced to prevent grounds here.

What I'm saying is it's not a matter of doing it right or wrong. It's never perfect and is rarely terrible, and every little thing helps to make the stator last longer.

I don't know if these stators are dying from heat, voltage spikes, movement, solvent damage, heat shock, poor winding, overload, or what.

Either way, it's no different then the guy that smokes like a chimney, drinks like a fish, stresses day in and day out and enjoys blow every weekend. Perhaps he will die of cancer, or maybe his cause of death will be a heart attack, but the real underlying causes were all of the above with age and heredity kicked in.

No matter the ultimate cause of stator failure, improving any of the things that age stators will increase it's life. No stator lives forever, they will all die, we just want to make them live longer.
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Old 12-30-2011, 02:03 AM   #206
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Steveman, I wouldn't rule out ambient temperatures inside the case or of the case itself, nor oil cooling or the lack there of. The magnet wire itself generates a lot of heat. That heat leaves by convection, conduction, and radiation. The warmer the case, oil, and gases are, even though still bellow the maximum temperature the magnet wire insulation can take, the slower the magnet wire can shed heat through the above named dynamics.

No matter the ultimate cause of stator failure, improving any of the things that age stators will increase it's life. No stator lives forever, they will all die, we just want to make them live longer.
Well, ...assuming that BMW will not do anything to help finding an acceptable solution we then should reduce our efforts to find the cause(s) and put even more effort into reducing the stator coils temperature, meaning all following points could (and most likely will) reduce stator temperature, thus extending its life cycle

.) reduce exhaust tubes temperature (heat shield, heat wrap, coating etc.)
.) reduce engine temperature (different thermostat, bigger waterpump rotor, free airflow to radiator)
.) use different regulator (compu-fire may work)
.) use stator from Camro or other brand or rework existing one
.) reduce maximum alternator power
.) improve contact surface between stator coil and engine cover

anything else? By the way has anyone done the regulator mod?

Steve
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Old 12-30-2011, 04:11 AM   #207
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on harley stators 180C did not last, 200 did better, they also tend to fail after 30 K miles

Rod
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Old 12-30-2011, 04:04 PM   #208
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Well, ...assuming that BMW will not do anything to help finding an acceptable solution we then should reduce our efforts to find the cause(s) and put even more effort into reducing the stator coils temperature, meaning all following points could (and most likely will) reduce stator temperature, thus extending its life cycle

.) reduce exhaust tubes temperature (heat shield, heat wrap, coating etc.)
.) reduce engine temperature (different thermostat, bigger waterpump rotor, free airflow to radiator)
.) use different regulator (compu-fire may work)
.) use stator from Camro or other brand or rework existing one
.) reduce maximum alternator power
.) improve contact surface between stator coil and engine cover

anything else? By the way has anyone done the regulator mod?

Steve
The oil level is above the bottom of the flywheel right?
If so ... perhaps several small holes drilled thru the flywheel at an angle of attack such that they would "push" oil into the interior where the stator is located? You'd want to avoid drilling through the magnets which might not be possible....
I'm sure I'm doing a crappy job of explaining what I'm thinking.........

Maybe this will need a picture...........
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Old 12-30-2011, 08:34 PM   #209
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It seems to me we still do not know the real root cause of these failures.

While there have been several bandaid ideas ..like wrapping the exhaust pipes, using aftermarket bits to cut the power output in half...and the associated heat, etc etc. These all likely help some what....but many of us will still have premature failures that are very expensive.

We need the BMW designers, who truly know the electrical design parameters,of the regulator, stator and armature, the environmental conditions within the engine to step up and diagnose this problem....and share that info with their dealers and customers.

Let the chips fall were they may..but then we will know the best way to a real fix.

This blog, and others are interesting, but after a couple of years now still have not led to proper solution.

Is it time we sent letter to BMW? something else?
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Old 12-31-2011, 07:22 AM   #210
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... Is it time we sent letter to BMW? something else?
I was going to make some snide comment about threatening the Germans with having to financially support the Greeks and Italians for all eternity ... if they don't fix this problem but maybe I'll pass on that and stay on topic ...

Probably step one trying to get someone's attention would be to collect a list failed stators with along wiith some statistics like miles on the bike, typical riding conditions (hot cold lots of electrical load or not... etc.) amount of time the bike has been in service VIN number owner's name/contact data in/out of warranty etc. I we had those statistics, the list was long, and mileage figures were as short as they seem to be then ... maybe we could get some action?

Otherwise I don't think the conversation would go very well.............
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