GS Stator

[Nessism]

Obviously very astute observation. If there are 280 watts available for "high-voltage" accessories then how much is there for "low-voltage" accessories? How does the charging system tell the difference or allocate for High voltage v.s. the standard loads? How high is high above 12V? 14.5V? How low is low below 12V?

The author's statement is obviously profound, it just bears some explanation especially considering it has nothing to do with the discussion on power dissipated in the stator.

The total amount of power the generator produces is important because power not consumed by the system is excess and shunted back to the stator. And this has everything to do with the discussion at hand.

Fact of the matter Jim you are overestimating how much power the generator produces and therefore how much excess is shunted back. Either that or your Electrosport stator IS significantly boosting power produced in your changing system because most UJM charging systems were making mid 200's watts.

[posplayr]

The editor wrote, "For high-voltage accessories the generator cranks out 280 watts".

Obviously very astute observation. If there are 280 watts available for "high-voltage" accessories then how much is there for "low-voltage" accessories? How does the charging system tell the difference or allocate for High voltage v.s. the standard loads? How high is high above 12V? 14.5V? How low is low below 12V?

The author's statement is obviously profound, it just bears some explanation especially considering it has nothing to do with the discussion on power dissipated in the stator.

[Nessism]

Reading though the March 1983 copy of Cycle magazine the other day, the Kawasaki KZ1100A3 shaft test. The editor wrote, "For high-voltage accessories the generator cranks out 280 watts".

[posplayr]

After a few months studying and dithering, I finally broke down - well actually before I broke down, hopefully - and decided to buy an SH775 to go with the new stator I'm winding. I blew one stator last summer when it got over 100 degrees here and the used spare I had looks like a homebrew with skinny wire, and it will inevitably get just as hot next summer. I ordered it from the local Polaris dealer for about $75, which seems about right as there's no shipping cost.

So now I need to buy the Furukawa [?] connectors that go with the SH775. Is there a recommended supplier, or do I just go fishing on Ebay?

The connector info is in the first post of this thread.

Cheap SH-775 Connector Source

[John Park]

After a few months studying and dithering, I finally broke down - well actually before I broke down, hopefully - and decided to buy an SH775 to go with the new stator I'm winding. I blew one stator last summer when it got over 100 degrees here and the used spare I had looks like a homebrew with skinny wire, and it will inevitably get just as hot next summer. I ordered it from the local Polaris dealer for about $75, which seems about right as there's no shipping cost.

So now I need to buy the Furukawa [?] connectors that go with the SH775. Is there a recommended supplier, or do I just go fishing on Ebay?

[OldVet66]

Googling around, I'm struck by the number of people who think that rewinding a stator for More output would make it more reliable and less prone to burning out. After all, it's only common sense isn't? Heavy Duty!

It might be true if you could increase the number of windings using the same size wire, but you can't because there is not enough room, you have to use a smaller wire gauge. That does change things a bit, for better worse I don't know. I do know that an over wound Electrosport stator and my Compu-Fire 55402 seem to be an excellent match and very reliable. I live in a much hotter place than I used to and my bike has not shown the slightest tendency to overheat stuck in traffic. I have given up once or twice and pulled off the road because I couldn't handle the heat but the bike seems perfectly happy to keep on keeping on.

[posplayr]

Googling around, I'm struck by the number of people who think that rewinding a stator for More output would make it more reliable and less prone to burning out. After all, it's only common sense isn't? Heavy Duty!

200 watts ia almost 1/3 hp; not a lot to lose in the scheme of things, but when you try to dissipate it in one place and cool it with hot engine oil… catastrophe. I was looking at the rewind specs for a Suzuki Cavalcade stator and it's something like 47 turns of 20ga as opposed to the typical GS 32 of 18g a, and the max voltage per leg is 90v @ 5k as I recall. What they had to do to keep up with all the farkles while lugging around, I suppose.

Back in the dim and distant 70's I recall that we'd install a choke coil from a Yamaha to keep the lights from blowing on over rev on Bultacos and suchlike. Is there any possible use for that as an 'attenuator' in a three phase system like ours? Maybe one coil per leg?

I started looking at this problem back in 2009 when I first started riding a street bike and was puzzling over my GS750EX charging issues. The traditional way to limit power from the stator is to control the field winding or the magnetic field that that is rotating about the stator. The XS650 uses slip rings to do that and has a field control regulator. There is an obscure device that (an engineer more expert at this stuff than I ) told me about; I looked it up (don't remember the name). It basically has another winding separately controlled on the stator. It makes it possible to counteract the fields that would otherwise exist and allow for (reduced) output control.

The GS stator doesn't have a whole lot of room for the winding it has much less adding additional ones. In addition the Series RR is here making it practically a non-starter to design a custom stator and potentially a rotor. Having mentioned that there are some guys, one of them a member here working on using super magnets in a smaller light weight rotor off a modern bike and adapting it to a GS. Same magnetic field for much less spinning mass.


I have only doine a few calculations trying to see if there is a clear answer to the trade of wire thickness and number of turns and it was not clear at all. I have not wound a stator and do not recall at all any of the wire measurements I may or may not have made. So sorry, but I won't try and offer an opinion for which I have not done an adequate preparation to offer a useful opinion.

I think there are subtle trades here and you have to look at the whole problem. For example Ed's common sense conclusion that a higher power stator will dissipate more heat is possibly wrong depending upon what Electrosports 20% increase power claim really means. The reason is pretty simple when you consider the saturation effects.

If max current is fixed by the rotor and magnetic paths, then the only way to increase power to the load(only through additional loads) is to reduce the resistance in the windings. The reduced resistance means more voltage is dropped across the load than across the stator; more power delivered.

On the other hand if Electrosport is actually only increasing voltage at low RPM then they did that by increased winding of thinner wire. So at high RPM and saturated current there will be more voltage drop in the stator and therefore more power dissipated in the stator for the boosted voltage.

The power dissipated in the stator is highly dependent on the temperature it is running. It is actually unstable. Higher power begets higher resistance which begat higher power. This probably explains partially why some stator burn and other do not and it seems to be a function of the way people ride.

I honestly do not know which it is. Probably the latter as I have quickly burned up electrosport stators using a MOSFET Shunt R/R.

To me the bottom line is get a SERIES R/R and all the problems largely go away. In addition it would appear that adding a sprayer will cool your engine as well whether it is SHUNT or SERIES R/R. You optimum stator winding will depend on your type of R/R. Trying to wind the statro to avoid using a SERIES R/R seems completely counter productive.

[John Park]

The next part of the puzzle is what is the actual power. The AC distortion plus the unknown resistance (due to unknown temperature) and the reactance of the coils make for several variables that make it hard to be an estimate to within 10% but the estimates show that power is larger than most expect and probably with a factor of two at least of the calculations.If the shorted stator was purely resistive then the power would be as estimated directly from a resistance estimate. However we know it will be inductive so teh number would need to be derated some. Eyeballing the scope output I would gander the current is out of phase with the voltage by about 22 degrees (PI/4) which would give a power factor of about 0.7. So derate the 581W by 0.7 and we are back to 410 watts. Shocking huh? Who would think that the SHUNT R/R - stator combination is dissipating more power (by almost a factor of two) that it is delivering to the load. Actually all you have to do is look at the burned up stators; it should be no big surprise.


The other very interesting thing I'm realizing is that the hotter the stator is the more power it will dissipate (I^2R increases with temp because R is increasing with temp and power factor increase with R). In the case of the SHUNT R/R this represents a lot of power, less so with the SERIES and my miraculous temperature drop is probably partially to do with my sprayer in combination with the SERIES R/R.

Googling around, I'm struck by the number of people who think that rewinding a stator for More output would make it more reliable and less prone to burning out. After all, it's only common sense isn't? Heavy Duty!

200 watts ia almost 1/3 hp; not a lot to lose in the scheme of things, but when you try to dissipate it in one place and cool it with hot engine oil… catastrophe. I was looking at the rewind specs for a Suzuki Cavalcade stator and it's something like 47 turns of 20ga as opposed to the typical GS 32 of 18g a, and the max voltage per leg is 90v @ 5k as I recall. What they had to do to keep up with all the farkles while lugging around, I suppose.

Back in the dim and distant 70's I recall that we'd install a choke coil from a Yamaha to keep the lights from blowing on over rev on Bultacos and suchlike. Is there any possible use for that as an 'attenuator' in a three phase system like ours? Maybe one coil per leg?

[posplayr]

Yes, but there is a relationship between the AC phase to phase voltage on stator and the DC voltage as rectified by the diode bridge.Being 3 phase means power output from stator is steady, there's some loss in diodes but it's a big stretch to think that the stator is pumping out 500 + watt if the r/r lets it. The ac line current would be in 20 amp range- the resistance voltage drop here plus the reaction of this current on the rotor magnets woukd be enormous. Even if you fiddled withmagnet wire size, can't see these things delivering much more than 350 watts AC to the r/r.

Tom, when the stator is shorted (by a SHUNT R/R), then the blocking diodes (or in the case of synchronous rectification it is FETS/SCR are open) then they are reverse biased so the DC output voltage is determined by the battery and the load and nothing to do with the stator AC.

There is certainly stator current and I have measured/published that back in 2010. I have directly measured the RMS current in one leg to be 17.5 amps RMS using the MOSFET R/R. The waveform is obviously not a sine wave but my Tektronix TDH730A scope with clamp on current meter will accurately (with a few percent) computer true RMS (per the definition of RMS) regardless of the waveform.

I used the 3 phase formulas to convert this to total power in all three legs to get 26 amps RMS. This may or may not be a good calculation. but the single leg amperage being at 17.5 amps RMS suggests that total current is actually quiet a bit higher. When I use the same formula on the SERIES waveforms I get a very reasonable 15 amps which corresponds to the measurable DC output current. That gives me more confidence that the single phase to three phase conversion is accurate.

The next part of the puzzle is what is the actual power. The AC distortion plus the unknown resistance (due to unknown temperature) and the reactance of the coils make for several variables that make it hard to be an estimate to within 10% but the estimates show that power is larger than most expect and probably with a factor of two at least of the calculations.If the shorted stator was purely resistive then the power would be as estimated directly from a resistance estimate. However we know it will be inductive so teh number would need to be derated some. Eyeballing the scope output I would gander the current is out of phase with the voltage by about 22 degrees (PI/4) which would give a power factor of about 0.7. So derate the 581W by 0.7 and we are back to 410 watts. Shocking huh? Who would think that the SHUNT R/R - stator combination is dissipating more power (by almost a factor of two) that it is delivering to the load. Actually all you have to do is look at the burned up stators; it should be no big surprise.

The only way to put a finer point on this is to do a direct power measurement of P = I X V. My meter will do that but I would need the leg to neutral voltage not the leg to leg voltage. That is because leg to leg is shorted and so it does not represent the true voltage across the coils. Just the shorting voltage of the R/R.

The other very interesting thing I'm realizing is that the hotter the stator is the more power it will dissipate (I^2R increases with temp because R is increasing with temp and power factor increase with R). In the case of the SHUNT R/R this represents a lot of power, less so with the SERIES and my miraculous temperature drop is probably partially to do with my sprayer in combination with the SERIES R/R.

[DimitriT]

FYI According to this site:

http://www.vstromhellasforum.com/t29828-topic

Suzuki has switched to using a series RR in the 2014 Vstrom DL1000.

[tom203]

Unfortunately you are mixing stator current with DC output voltage.
....

Yes, but there is a relationship between the AC phase to phase voltage on stator and the DC voltage as rectified by the diode bridge.Being 3 phase means power output from stator is steady, there's some loss in diodes but it's a big stretch to think that the stator is pumping out 500 + watt if the r/r lets it. The ac line current would be in 20 amp range- the resistance voltage drop here plus the reaction of this current on the rotor magnets woukd be enormous. Even if you fiddled withmagnet wire size, can't see these things delivering much more than 350 watts AC to the r/r.

[posplayr]

Well Jim, on my first 850 I wired the charging system with the R/R output line straight to the battery with a 15A fuse in-line. The bike ran fine this way until I decided to up rate to a 20A fuse just to be safe. Pretty sure my charging system isn't even getting halfway to your 581. Oh well, nevermind. I'm just an electrical heathen. You're doing the "new math" and this just doesn't compute in my head. My manual says "240 watts max output" from my charging system anyway so I'm good living where I am. You do as you like but my boat is staying right here.

You were questioning the number but not the calculation right? It is not new math unless multiplication is new math. It is ohms law with a little three phase power thrown in. And to be doubly redundant the spec power in the manual has nothing to do with how much power is burning up the stator. The manufactures have been dutifully oblivious to stator power and so you should probably be able to guess they did not spec it out in the manual.

[Nessism]

Ed , You have not figured out from in yet huh?

if on the other hand you have anything to debate about the calculation lets hear it?

Well Jim, on my first 850 I wired the charging system with the R/R output line straight to the battery with a 15A fuse in-line. The bike ran fine this way until I decided to up rate to a 20A fuse just to be safe. Pretty sure my charging system isn't even getting halfway to your 581. Oh well, nevermind. I'm just an electrical heathen. You're doing the "new math" and this just doesn't compute in my head. My manual says "240 watts max output" from my charging system anyway so I'm good living where I am. You do as you like but my boat is staying right here.

[posplayr]

One thing that occurred to me is that the oil flow to the cover would probably be considerably higher on a Twin because of the balance shaft bearing that dumps into the front of it. Whether that results in more oil getting to the stator is not assured, but it should help somewhat. It also adds a bit more heat sink to the cover as it's longer. It doesn't seem as though you would get the same high oil temps either, as the sump is pretty huge - 2.6-2.9 liters - and the pan area is more or less similar. I've done in a few stators on twins, but it took about 35,000 miles and usually a duff battery to do it.

As I understand it, the number of turns on a pole determines the voltage when the magnet is saturated. Basically like the output side of a transformer. I'm planning to rewind a stator soon, and had planned to go with three rows of ten [18ga] because that's what I've seen on stock stators, but since I spend almost no time in town and rarely below 4000 rpm I'm wondering if dropping that by ten percent would still give me enough idle voltage and put less strain on the system.

Is there a linear voltage/turns ratio at play or some other formula? How critical is wind number? Is there a 'right number'?

It is linear till it starts to saturate and a Lille more and it is maxed out no more current power limit; and yes the same physics for a transformer.

[posplayr]

581 watts out of a GS charging system? Humm...

Ed , You have not figured out from in yet huh?

if on the other hand you have anything to debate about the calculation lets hear it?