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Old 11-26-2011, 08:39 PM   #76
flying.moto
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Originally Posted by C5! View Post
I will definitely buy a new stator from this link earlier in the thread and I am thinking about this series regulator as well. I would really appreciate feedback from somebody who tried that, how it worked and if it didn't interfere with the other electrcial systems on the bike.
I'm planning to get that series regulator as soon as when/if i get the bike I'm looking at with a full testing/writeup to follow. but then again, you might beat me to it and then I will follow your lead! Good luck!

flying.moto screwed with this post 11-26-2011 at 08:42 PM Reason: spel chk failure...
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Old 11-27-2011, 12:27 AM   #77
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Originally Posted by LukasM View Post
A series regulator should fix it, or at least improve it. See the thermal images in post 22.
Hi Lukas. I like series regulators because they stand to improve fuel economy and I hate inefficiency.

As to solving early stator problem, they may help or could harm.

There are 2 common types of shunt regulators: "SCR" and "FET" Both do the same thing, the SCR type is cheaper, needs bigger heat sinks, allows voltage to move more and are electrically noisy. FET shunts are more efficient and produce cleaner power. They cost more to build and are more durable. Also they are not subject to thermal runaway.

SCR shunt regulators are the most common. The common failure mode for an SCR shunt regulator is thermal runaway. When SCR's get too hot they usually stay closed, at least until they burn up which in our application would be pretty quick. SCR shunts are slowwww. Under load they can not switch modes faster then about 1 ms. In 5 wire applications, like ours the voltage spike during high speed engine operation causes on SCR regulator to clamp prematurely which is why our system voltage is lower at speed then at idle. This voltage behavior is not by design or desirable. It has nothing to do with the stator, it's just what happens when a manufacture specs a 5 wire SCR shunt regulator without a 6th sensing wire.

The good thing about all shunt regulators is they are efficient at full output and hold stator voltages down nicely.

MOSFET (Magically Obliterated, Smoke and Fire Emitting Transistor) shunt regulators are much faster acting and can even hold system voltages stable with no battery connected. When a power FET fails, it usually does so with a small mushroom cloud of smoke but fortunately they are quite reliable. FET shunt regulators are more efficient and don't get as hot. FET's nearly always fail open. This isn't strictly desirable, but at least the chances of a single FET shorting and burning out a winding on the stator is very low, unlike with SCR regulators which MAY be what is causing some of the failures on our stators. FET's don't have to be matched because their normal tolerances are super tight owing to how they are built. Slight inconsistencies in how SCR's are doped can lead to one stator winding carrying more load then the others and early stator failures.

Series regulators are usually constructed with power SCR's because FET's can't handle as high of inverse voltage spikes. This isn't a rule and a very fine series regulator COULD be constructed using power FET's, but it would require more expensive components. Series regulators tend to be super electrically noisy. This can cause interference with components down stream and can also shorten their life. A bad battery connection or someone foolish enough to disconnect the battery while the engine is running will usually result in expensive electronics damage to the bike with a series voltage regulator. SCR shunt regulators aren't ideal for this but a whole lot better. A FET shunt regulated bike would run fine without a battery. This is of some concern on our bikes since the vibration of our engines is known for cracking the bus bar in the stock battery. Shunt, especially FET shunt regulators, but both to a great extent, are extremely efficient at transmitting the full power of the stator to the bike for charging and running loads. Series regulators convert a significant amount of energy from the stator to heat under full load conditions. I have only seen series type regulators used in industrial applications but those burned from 5 to 15% of the stators output.

Most importantly, regulating by opening the stator output, Stator voltage is going to hit about 200 volts on our bikes at 6,000 RPM. This is a value that I measured, it is not theoretical. High voltage breaks down the stators insulation and may lead to faster failures then what we are already experiencing.

I don't even know what is killing our stators prematurely on rotax twins. I suspect they are running too hot and that this is due to insufficient oil bathing, but I don't know this. It could be that what is happening is occasional thermal runaway and temporary shorting of one of the SCR's in the voltage regulator. Whichever is the case, will our stators hold up to high voltage better then high heat? It's going to take a bunch of people and 30,000 to 50,000 miles to find out, unfortunately.

If a half dozen switch to series regulators AND the stator holds up for at least 30,000 miles, I'll go out and buy one because I would like the fuel savings, but I'm reluctant to lead on this one.

P.S. the thermal picture way above is nice, but makes no sense. The hottest part, the part the cross hairs are on, should be empty! Secondly, emisivity is a huge factor when using infrared measurement devices. If the bike was dustier on the second measurement, it would look a LOT hotter. Infrared measurements are only meaningful when conducted by someone heavily trained on how to use them. I don't know who took those measurements and under what conditions, but at the least, I can't imagine why the case would be much hotter in the center then where the stator bolts to it. That makes absolutely no sense to me. In any case, at the best of times, infrared surface measurements are horribly inaccurate. I'm interested in case temperature measurements, but a simple thermal couple measurement is going to be FAR more accurate and much less prone to user error. Thermal couples are also cheap if anyone wants to buy one to take measurements.

Wish I had something constructive to add, but I don't. Wait.... Maybe we could figure out a way to improve thermal conduction between the pole pieces and the case cover, also improve conduction between the cover and engine case. Aluminum bolts? Build up thermally conductive material between the cover and stator? Thermally conductive grease? Additives to make the engine oil more thermally conductive or synthetic which by nature is more thermally conductive? Just thinking out loud.

Good luck, I hope someone finds a solution.
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Old 11-27-2011, 06:49 AM   #78
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Quote:
Originally Posted by JoelWisman View Post
Hi Lukas. I like series regulators because they stand to improve fuel economy and I hate inefficiency.

As to solving early stator problem, they may help or could harm.

There are 2 common types of shunt regulators: "SCR" and "FET" Both do the same thing, the SCR type is cheaper, needs bigger heat sinks, allows voltage to move more and are electrically noisy. FET shunts are more efficient and produce cleaner power. They cost more to build and are more durable. Also they are not subject to thermal runaway.

SCR shunt regulators are the most common. The common failure mode for an SCR shunt regulator is thermal runaway. When SCR's get too hot they usually stay closed, at least until they burn up which in our application would be pretty quick. SCR shunts are slowwww. Under load they can not switch modes faster then about 1 ms. In 5 wire applications, like ours the voltage spike during high speed engine operation causes on SCR regulator to clamp prematurely which is why our system voltage is lower at speed then at idle. This voltage behavior is not by design or desirable. It has nothing to do with the stator, it's just what happens when a manufacture specs a 5 wire SCR shunt regulator without a 6th sensing wire.

The good thing about all shunt regulators is they are efficient at full output and hold stator voltages down nicely.

MOSFET (Magically Obliterated, Smoke and Fire Emitting Transistor) shunt regulators are much faster acting and can even hold system voltages stable with no battery connected. When a power FET fails, it usually does so with a small mushroom cloud of smoke but fortunately they are quite reliable. FET shunt regulators are more efficient and don't get as hot. FET's nearly always fail open. This isn't strictly desirable, but at least the chances of a single FET shorting and burning out a winding on the stator is very low, unlike with SCR regulators which MAY be what is causing some of the failures on our stators. FET's don't have to be matched because their normal tolerances are super tight owing to how they are built. Slight inconsistencies in how SCR's are doped can lead to one stator winding carrying more load then the others and early stator failures.

Series regulators are usually constructed with power SCR's because FET's can't handle as high of inverse voltage spikes. This isn't a rule and a very fine series regulator COULD be constructed using power FET's, but it would require more expensive components. Series regulators tend to be super electrically noisy. This can cause interference with components down stream and can also shorten their life. A bad battery connection or someone foolish enough to disconnect the battery while the engine is running will usually result in expensive electronics damage to the bike with a series voltage regulator. SCR shunt regulators aren't ideal for this but a whole lot better. A FET shunt regulated bike would run fine without a battery. This is of some concern on our bikes since the vibration of our engines is known for cracking the bus bar in the stock battery. Shunt, especially FET shunt regulators, but both to a great extent, are extremely efficient at transmitting the full power of the stator to the bike for charging and running loads. Series regulators convert a significant amount of energy from the stator to heat under full load conditions. I have only seen series type regulators used in industrial applications but those burned from 5 to 15% of the stators output.

Most importantly, regulating by opening the stator output, Stator voltage is going to hit about 200 volts on our bikes at 6,000 RPM. This is a value that I measured, it is not theoretical. High voltage breaks down the stators insulation and may lead to faster failures then what we are already experiencing.

I don't even know what is killing our stators prematurely on rotax twins. I suspect they are running too hot and that this is due to insufficient oil bathing, but I don't know this. It could be that what is happening is occasional thermal runaway and temporary shorting of one of the SCR's in the voltage regulator. Whichever is the case, will our stators hold up to high voltage better then high heat? It's going to take a bunch of people and 30,000 to 50,000 miles to find out, unfortunately.

If a half dozen switch to series regulators AND the stator holds up for at least 30,000 miles, I'll go out and buy one because I would like the fuel savings, but I'm reluctant to lead on this one.

P.S. the thermal picture way above is nice, but makes no sense. The hottest part, the part the cross hairs are on, should be empty! Secondly, emisivity is a huge factor when using infrared measurement devices. If the bike was dustier on the second measurement, it would look a LOT hotter. Infrared measurements are only meaningful when conducted by someone heavily trained on how to use them. I don't know who took those measurements and under what conditions, but at the least, I can't imagine why the case would be much hotter in the center then where the stator bolts to it. That makes absolutely no sense to me. In any case, at the best of times, infrared surface measurements are horribly inaccurate. I'm interested in case temperature measurements, but a simple thermal couple measurement is going to be FAR more accurate and much less prone to user error. Thermal couples are also cheap if anyone wants to buy one to take measurements.

Wish I had something constructive to add, but I don't. Wait.... Maybe we could figure out a way to improve thermal conduction between the pole pieces and the case cover, also improve conduction between the cover and engine case. Aluminum bolts? Build up thermally conductive material between the cover and stator? Thermally conductive grease? Additives to make the engine oil more thermally conductive or synthetic which by nature is more thermally conductive? Just thinking out loud.

Good luck, I hope someone finds a solution.
very very interesting discussion.
I will not rush anymore about adapting a series regulator, I think there is some research to be done.
as for the failures, i also agree about the lack of cooling. It would be interesting to get statistics about where the failed stators happened, one for my part is in the tropics where I live, and I think I noticed that some of the failures in teh US where in the South, Arizona etc... maybe there is something to investigate there.
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Old 11-27-2011, 09:03 AM   #79
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Very interesting indeed.

This is what I found late last night: http://www.apriliaforum.com/forums/s....php?p=2598642 and i stated reading with page 18... but one guy on there did approach this with more or less scientific side, but(!) for some reason i did not see him test it for voltages "to the redline" but only for stator loads. The report he made does show quite a large voltage spiking when series switch is "off" and that is only at 2000 RPM. Check it out here

I'm not sure if you guys found this discussion but it was an interesting read even after following this thread since these guys seem to have already tried/trying everything. It would be interesting to talk to some of them, and i'm thinking of contacting some of them too. Apparently this is how some people have been coping with similar issues on different bikes. Some seem to have experienced stator failures with FET shunting types as well. Where others have not seen or maybe have not reported any failures with series type R/R's. I personally would seriously doubt the insulation of the winding wires can't handle 200-250 volts. Just think about 220v motors, and welder transformers. The only thing that puts an "if" in that statement in my mind is the exposure to oil. Heat does not concern me as much if it is kept below 75-80C (just my personal "memory" limit from the times i dealt with buzzbox welders a lot, not a researched number). On the other side, can the series R/R handle the spikes and not loose its' circuity to the voltage? It does seem to have been paired with similar style "alternator" so it may be ok.

And others are saying they retrofitted extra oil line with a spray nozzle to cool the stator!

South AZ or not, this should not happen. I wonder if this engine/bike has been "hot box" tested in a desert... like cars.

p.s. thank you Joel for measuring voltages. was 200 volts the highest you have seen? It probably goes higher closer to the redline... i would think.

Anyway, those are my current thoughts for what they're worth.

EDIT: I wonder if this stator on the F800 is Y or Delta connected... from how i read this Y would have more of voltage spiking capability while D would have more of current capacity (and possibly less spiking because no coil is "open" at any time?). Maybe the Harley stators they sell with Compufire regs are wound in D configuration? Correct me if I'm wrong, if someone has better information...

EDIT2: well, it seems like Delta wound stators will not like low-rpm conditions as well as Y wound ones...

flying.moto screwed with this post 11-27-2011 at 09:35 AM Reason: missed clarification...
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Old 11-27-2011, 01:28 PM   #80
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Quote:
Originally Posted by JoelWisman View Post
...

P.S. the thermal picture way above is nice, but makes no sense. The hottest part, the part the cross hairs are on, should be empty! Secondly, emisivity is a huge factor when using infrared measurement devices. If the bike was dustier on the second measurement, it would look a LOT hotter. Infrared measurements are only meaningful when conducted by someone heavily trained on how to use them. I don't know who took those measurements and under what conditions, but at the least, I can't imagine why the case would be much hotter in the center then where the stator bolts to it. That makes absolutely no sense to me. In any case, at the best of times, infrared surface measurements are horribly inaccurate. I'm interested in case temperature measurements, but a simple thermal couple measurement is going to be FAR more accurate and much less prone to user error. Thermal couples are also cheap if anyone wants to buy one to take measurements.

Wish I had something constructive to add, but I don't. Wait.... Maybe we could figure out a way to improve thermal conduction between the pole pieces and the case cover, also improve conduction between the cover and engine case. Aluminum bolts? Build up thermally conductive material between the cover and stator? Thermally conductive grease? Additives to make the engine oil more thermally conductive or synthetic which by nature is more thermally conductive? Just thinking out loud.

Good luck, I hope someone finds a solution.
Thanks for the education on regulators ... I'm going to have to read it twice more to understand everything you said

I was scratching my head at the thermal picture as well ...
I am wondering if the part in the cross-hairs was the bolt in th end of the crankshaft which would be hotter (maybe?) than everything else?
Not sure...

A better oil bath would help ... I was looking at the starter gear train and wondering if it was pressure fed with oil....
and if so could some of that be squirted on the stator but it seems the answer is no and no...

Better thermal conductivity between the stator and the housing would help for sure ....
Some sort of thermal grease (industrial version of what they use between computer CPUs and heat sinks) would help at least a bit... one of those fancy finned housings like they sold for the 1970's bikes that could be thermally grounded to the stator would be cool...

The only other thing I have thought of is rewinding the stator with wire that has lower resistivity...
The heating is result of I^2 * R heating so if we could reduce the resistance of the stator windings they would not produce as much heat....
Either use a larger gauge wire (it it would fit) and/or select a wire alloy with lower bulk resistance, there are a few available .... might cost an arm and a leg though...
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Old 11-27-2011, 04:47 PM   #81
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I have far more questions then answers, but here are the few I have:

Flying.moto, the stator on our bikes is a 3 phase Y configuration.

I found my notes from tests a long time ago, no easy feat lol, 213 volts RMS was the open circuit voltage at 6,000 RPM, but 1ms averaged peaks were 394 volts. I did not test at higher RPM because It was my stator I was testing and I was concerned about going higher but most certainly that voltage will climb somewhat linear to increases in RPM.

A few additional notes: I measured the temperature of engine oil in my sump after a hard ride on a hot day and it was 124 C which is another reason that thermal image way above makes no sense. Our thermostat isn't full open till about 100c and the oil is always going to be hotter then the coolant. I would suspect we are going to have to work with stator temperatures south of 140c at the very least. Also, my normal knowledge of induction wire is in air or pure oil. Our oil contains a lot of carbon and often also contains water. Combustion byproducts include water and engine oil may contain quite a bit of water, especially when it's cold and even more so if the bike makes regular short trips. This is to say nothing of bikes that are submerged in water which happens to mine occasionally.

In an oil cooled transformer, the addition of just a little water really drives the insulation resistance down.

I am very leery of greatly raising stator voltages under these conditions. Further, experience with other stators will only tell so much. A stator that say honda uses may be built to withstand voltage better then ours, or it may not. I simply do not know.

JR, I can't see the crank being hotter then oil. Normally the oil runs hotter then the crank owing to heat absorbed from the head. Also I just can't see aluminum or even magnesium, whatever the cover is made out of, having that sharp of temperature differences. What I suspect we were seeing is a change in emissivity. Perhaps there was a sticker or flat painted graphic in the center and the surrounding area was shiny. In any case, that thermal image means nothing to me.

In any case, I don't dispute and can absolutely confirm that a series voltage regulator will run the stator cooler any time demand is less then 100%.

There are actually two common types of series regulators. "series resistive" and "series switching". Series resistive regulators would not allow the stator voltages to go nearly as high, would be less efficient at reducing stator loads, have huge heat sinks and double as a waffle iron. Series switching will be noisy as hell, run very cool, be efficient and allow stator voltages to go through the roof.

What would be really nice is a hybrid voltage regulator. Actually I could design it and even get components, but I don't have any resources for a custom board and heat sink.

A schematic would be better, but I have no apps for generating such on this computer. 2 zener circuits for precision reference voltages, say 14.18 volts and 14.22 volts. 1 op amp triggered by the lower voltage zener for driving 3 FET's through a 10 ohm resistor to ground. the higher reference zener driving an op amp to 3 more FET's that break the series. You would need a feedback circuit to compensate line voltage fluctuation to the zeners but these are simple, and since were going all out, 3 SCR's set up to avalanche at 15 volts as a redundant safety. I'd build it 6 wire so regulation was done by a sensing wire straight to the battery that carried no current to cancel out the annoying loss in voltage as load went up. Heck, for a few pennies more we could add a circuit to flash an LED green yellow or red for system voltage. Leave the avalanche diodes on load sensing so loss of the sensor wire wouldn't cook the bike. Perhaps $50 retail for the components less the custom board and heat sink and that assumes we used over spec'd components.

The results would be that the stator was never completely disconnected from load, RMS would still go pretty high but insulation piercing spikes would be halved, yet the system would go into series regulation to run the stator cooler and improve fuel economy. I'd probably also get sued for violating someones patent unless someone else already thought of this so long ago that the patent is up which is likely :)

P.S. Larger gauge wire will fit on the stator with the same number of turns but this isn't everything. The magnetic field is only close to or at saturation with max back EMF at redline. Increasing winding size will also up current nullifying some of the I*R heat reduction. In addition to that, I don't know how much additional current if any our stock regulators could handle.

As to oil feed to the stator. I don't know that there is any though I would sure hope there is. The crank is charged so theres either a nozzle at the end of the crank inside the rotor, or there is not. Assuming there is a nozzle. perhaps varnish buildup is causing a reduction? If there is no oil nozzle directed on the stator, well I know why they are failing lol. I would shutter to add a nozzle if none currently exist. Drilling on the crank and tapping a finite oil supply is beyond my engineering skills and testicle size.
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Old 11-27-2011, 07:11 PM   #82
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Originally Posted by JoelWisman View Post
....

P.S. Larger gauge wire will fit on the stator with the same number of turns but this isn't everything. The magnetic field is only close to or at saturation with max back EMF at redline. Increasing winding size will also up current nullifying some of the I*R heat reduction. In addition to that, I don't know how much additional current if any our stock regulators could handle.

As to oil feed to the stator. I don't know that there is any though I would sure hope there is. The crank is charged so theres either a nozzle at the end of the crank inside the rotor, or there is not. Assuming there is a nozzle. perhaps varnish buildup is causing a reduction? If there is no oil nozzle directed on the stator, well I know why they are failing lol. I would shutter to add a nozzle if none currently exist. Drilling on the crank and tapping a finite oil supply is beyond my engineering skills and testicle size.
Thanks Joel!

I have no clue on the IR readings either ... seems screwy...

I thought I understood that the current created in the stator would be proportional (on a first order basis anyway) only to 1) the number of turns of wire, 2) the strength of the magnetic field, and 3) the speed at which the field was changing ... So it was on that basis I was thinking that heavier/lower resistance wire would be our friend...but I'm not 100% on that ...

I'll not be drilling any holes in my crankshaft either .... If the motor design has some provision for sending oil in to cool the stator I've seen no evidence of that ...

A clever regulator that both keeps electrical noise away from the DME, and keeps the stator from running at 100% duty cycle seems like the easiest way out ... I'd hate to install an aftermarket regulator in an effort to save a $150 stator and end up frying the computer ................
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Old 11-27-2011, 07:19 PM   #83
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Thank you, Joel, for digging up your notes! With 400+ volt spikes i'm not sure i'd go further up in RPM either.
It does make sense that we have a Y configuration stator. It leaves me to wonder if it was connected in Delta config. how would it behave at low rpm...

Regarding oil temps in the sump at 124 degrees, i am amazed. Seems a bit on the red line so to speak. What this bike could really use then is an external oil cooler. It should not be hard to hook up by replacing existing oil/coolant heat exchanger with a machined block with some fittings on it. I will look at my manual CD when i get home to see if that part is easily removable. Maybe with cooler engine temps we will not need to screw with stators/RRs to begin with. Or maybe can getaway with the use of FET shunt type if its that more efficient, although the stator would probably heat up the same... Still, seems like an easier solution. Rotax probably was onto something designing that heat exchanger to begin with - a bandaid fix for hot running oil system? I can't say i have seen such a part on any bikes i've dealt with.
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Old 11-27-2011, 08:39 PM   #84
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Be careful trying to adjust engine temps. On some stationary CAT engines if the coolant and oil temperature are not at the correct ratio the pistons will sieze. I don't think that will happen here as the clearences between the piston and liner are probably larger, but the engine was designed to run at a specific temperature and messing with that could cause unintended consequences.

If Rotax is like most companies, the electrical guys and the mechanical guys don't speak with each other and the stator might not be designed for the temperatures the mechanical were shooting for in thier design. However, I would think that there are ways to get a stator to live in hot enviroments.

As far as thermal properties of oil in the crankcase, I'm sure most models use clean oil and then a fouling factor is added for the impurites and coking. The only sure way is to devise a test and measure the results of clean oil vs dirty engine oil. However a model and some luck may get us close enough for this project.

I think your comments on the thermal image of the Aprilla are spot on Joel. Without knowing the details of the surface and who was taking the image, interpretation of the results are a crapshoot.
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Old 11-28-2011, 05:13 PM   #85
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There's a huge write up about this issue on the F800S bikes failing stators in this month's BMW ON (owner's news) magazine. It's a good read. Sorry I dont have a way to scan it in.
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Old 11-28-2011, 05:25 PM   #86
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There's a huge write up about this issue on the F800S bikes failing stators in this month's BMW ON (owner's news) magazine. It's a good read. Sorry I dont have a way to scan it in.
Did they offer any solutions?
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Old 11-28-2011, 05:32 PM   #87
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There's a huge write up about this issue on the F800S bikes failing stators in this month's BMW ON (owner's news) magazine. It's a good read. Sorry I dont have a way to scan it in.
synopsis??
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Old 11-28-2011, 06:39 PM   #88
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Interesting! I do believe current members can access it online, who's got it?
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Old 11-28-2011, 08:01 PM   #89
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If you mean the December issue, tain't up on the MOA site, yet.
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Old 11-29-2011, 06:34 PM   #90
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The Dec issue showed up in the mailbox, today.

Synopsis of the article:

Voni's bike (F800S) displayed charging problems while on a trip. Paul noted the DC measurements he made. They managed to get the bike home.
He described the difference between the F bike alternator and the ones on the rest of the BMW lineup.
He went through the logic of troubleshooting the problem.
Then he described the tests he ran.
He decided to order a stator from Rick's Motorsports Electrics.
The article ended with the bike on the lift waiting for the part.

Nothing that hasn't already been talked about on this forum. He checked continuity of the windings, measured AC output of each winding and discovered that one was lower than the others, 50v compared to 75v. The article will be informative for anyone who hasn't paid attention to the issue, but there's as much or more info on this forum.

Edit: Paul has also written about the rear drive failure Voni's bike suffered and the cam chain tensioner failure of one of their F bikes (that may have been his F650).

Bicyclist screwed with this post 11-29-2011 at 06:40 PM
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