preventing failing stator

[ofstone]

I am a new owner of a yamaha vision ,83 (in holland just called XZ550)
and i luckily have not (yet) a burned stator.

Because of that problem and my electrical background i am trying to find out wat is going wrong with th stator and maybee to improve this.
One thing that i have already read on different websites is to solder the wires coming from the stator, but then stil some stators burn out even if they have a new one from electrex.
The stator burns out because it is dissapating to much power as i calculated(not verry acurately) 20 Amps, coil recistance 0,32 ohm, so voltage drop over 1 stator coilwill be 6.4 volts so power in watts is 20amps x 6.4 volts=128 Watts x 3 coils= 384 watts!!
This is generating a large amount off heat inside the coils.
The regulator in the rectifier even makes things worse, becouse it is regulating the voltage. The more rpm's the engine is making the higher the voltage output of the stator will be. The regulator is lowering the output voltage by diverting a lot off current to the chassis, becouse off the higher current the voltagedrop in the stator wil rise, and the output voltage will drop. But becouse voltage drop on the stator is rising and also the current the amount of watts dissapated inside the stator coils wil rise also generating even more heat.
This will not burn the stator directely but due to the warming up and cool down eevery time your engine is making high revs and overheating the coils the insulation wil weaken and cracks will occure in the insulation of the stator coils making chort circuit witch will burn the stator.
A possible solution is to add power resistors about 0.32 OHM (have to calculate this i first need to do some measurements) in series between the stator coils and the regulator rectifier.
This means that a lot of voltage wil be dropping over this resistors (and also will heat up the resistors so they will need a big cooling fin) and then the regulator will not have to divert a high current directely to the chassis.
Instead of the heat dissapating in the stator or regulator, the heat will be dissapated bij the added power resistors.

Still this is just theoretical and needs to be calculated and a little more electronics are needed to bypass the resistors when the engine is running on low revs or when driving slow, otherwise the voltage output wil probably be to low to charge the battery properly.

I am now drawing a schematic wich i am going to test for a PWM (puls width modulation) DC/DC convertor. Witch is going to replace my Regulator/Rectifier. The design will not have high tech. components but some standard components like resistors, capacitors mosfets etc.

I will keep you updated when i have some new information

[Walt_M.]

You have some interesting theories there. I have considered putting resistors in series with the stator output to the R/R and pretty much gave it up due to the physical size of the 100-150 watt resistors that would be needed. Also, they would get hot. I have a theory, unproven, that the stator fails when the R/R fails. I think the stator can live with being open circuited but it will overheat if it is short circuited. The overall design is pretty simple and, if everything works as it should, the stator will put out its 300+ watts and the R/R will regulate the system voltage according to demand and dissipate the excess to the frame. I have thought about putting some type of overcurrent relay in the stator output that would open the stator if the current went too high but that got complicated. What I have done is put a computer CPU fan, one of the larger ones 4"X4" (10cmX10cm) on the R/R and put on an LED volt monitor to keep an eye on the voltage so I can shut down or whatever is necessary to save the stator.

[ofstone]

 Walt_M You are right about the size and cooling of the resistors, thats why i am trying to make a sort of DC/DC convertor wich still needs cooling, but not as much as this resistors.
I think you are also right about the failing R/R if the 3 phase rectifier bridge shorts, or the regulator fails, causing a permanent connection to ground, then one or more of the stator coils will burn.
But as i read some people did only had a defective stator and not a defective R/R.
You are also right that the stator wil not fail when the coils are open. And will fail when they are shorted. Only when 1 or 2 coils are open and the rest is still good connected (melted connector between stator and R/R) then this will overload the coils that are still in use and eventually will burn them.
The idea of extra cooling the R/R is i think a verry good idea together with the voltage monitoring, then you can probably save your stator or the R/R, but then you would still have to walk home if the voltage monitor says the voltage is not ok.

The stator/rectifier/regulator system of the vision is simple, cheap (compared with other systems), but not very relyable.


The following is for the people that do not now a lot about electronics:
It works like this, imagine 2 barrels, one barrel ( representing the R/R) with a large hole in it about 50 cm above the bottom(representing 14.5Volts) and on the bottem a connection to the second barrel (representing the battery). In the second barrel there is a valve that can be regulated between ful open and close.(this represents the amount of current used by the motercycle for lights ignition etc.) also a man wil be filling the first barrel with a bucket.(this man represents the generator/stator). this man will only stop filling when the barrel is completely full.(representing the maximum voltage of the stator at 9.5K RPM) how much buckets the man empties in the first barrel depends on how much rpms the engine is turning. What happens is that this man wil keep on filling up the first barrel with water, once the water level reaches the hole in the barrel al the extra water he ads to the first barrel will flow away(current ''shorted'' to ground). The second barrel wil have a steady level, no matter how much water(current) is used. when the engine is making high revs, the man is working real hard with filling up the first barrel and is bringing more water than is used, so all the water wil flow away and wil not be used.(representing the heat in the R/R and stator)
What i want to do is to close the hole at 50 cm and place between the first and the second barrel an open/close valve, wich is operated by a second man. This man is only looking to the water level in the second barel and wil open and close the valve every 60 seconds but if the level is to high he will keep the valve opened for 10 sec and closed for 50 seconds, and when the level in the barrel is to low he will open the valve 50 seconds and keeps it close for 10 seconds. The open/close time wil be depending on the amount is water(current) that is used. The water level in the second barel will have a steady level and the first man will stop filling the first barrel becouse it is filled to the maximum height the man is able to fill the barrel. (maximum output voltage of the stator) Like this there is no water spilled so no extra heat is generated in the system.

Now back to the electronics.
i am planning first to rectify the output of the stator with a 3 phase rectifier. (maybe the original one can be used, but only the sensing wire should be removed then, because otherwise the R/R still wil try to lower the output voltage) and store the power in a large capacitor. The only problem is what the maximum peak voltage will be with an open circuit. What i mean is with only the rectifier and capacitor and no load attached. The maximum output voltage will determine the voltage of the capacitor type, and also the size of the capacitor.
If anyone nows this maximum stator outputvoltage at max. RPM please tell me.Then the capacitor is connected to a MOSFET (the valve between the barrels) and this valve will open and close to load a second smaller capacitor. The opening and closing of the MOSFET will be at a frequency about 10KHz and this voltage wil be a steady voltage. The opening and closing of the MOSFET will be done by electronics wich are still on the drawing board at the moment.

[Lucky]

according to the chat in the service manual, max output is achieved at 5800rpm, at 22.5A.

what that is for voltage I don't know, but it sounds like you would know how to convert it... hope that's what you want.
--Lucky

[Walt_M.]

Should be able to open the stator and get a max voltage output. I'm not sure where you are going with the capacitor but I do know that they can raise the AC voltage and that is not a good thing. If I eventually do lose my stator, I might look further into my overcurrent relay idea, I am pretty sure it would work but I haven't worked out the 'how' part yet. By the way, the object of monitoring the voltage is to detect the failure of the R/R, then decide whether to ride it home or disconnect the stator and ride home on the battery.

[Rick G]

I believe that are there are several scenarios for stator failure . first there is the shorted to ground by a  failed R/R . A contributing factor is the poor location of the R/R , it is far too hot, and in my opinion a fan only circulates the  superheated air  in the confined space behind the rear cylinder. Many of us have moved the R/R to locations which allow the  R/R  to  pass heat to lower its temp. In the stock location  it will actually absorb heat and NO electronic device works long or well if its over heated .  Mine is now located on the left foot peg / muffler bracket . I've had it in several locations but this is the easiest to do.
Of coarse the gang plug between the stator and the R/R  is a potiental sore point as the plus are differant , one is brass the other some form of cadmeum.
A further factor , that we are trying to investigate further,  is to graph engin oil temprature.  excess heat is caried away by  the oil , but if my suspissions  are correct he oil is actuallly ADDING heat to the stator , NOT carrying it away.  many other bikes use the same stator  and similar R/R  and have far better success , as far a stator life is concerned. there is some thing about the Vision that  punishes this item!

[ofstone]

The capacitor after the 3 phase rectifier will indeed raise the DC voltage, but this will be no problem, since the DC voltage is going to be lowered by the DC/DC converter. Its pupose is to make sure every coil of the stator has the same load, whithout the capacitor it is possible that one coil can be overloaded. and this system will create current pulses and then the capacitor averages the current drawn out of the coils. For the over current protection maybee it is possible to use an overcurrent relay for standard 3 phase engines. the advantage of that is that they can be bought off the shelf, do not need external power, When the relay monitors over current on one or more it will disconnect all 3 phases, and most of them have an extra contact what you can use for an lamp on the dash, so you can see if the relay has tripped, and then you can simply reset the relay with a knob on the relay.(if you find out why it tripped) The price could be the only problem but these things are used a lot in companies using electrical ac engines and maybe you can find one second hand.

[Rupert]

KISS - keep is simple ..

Just an over current relay or something would be sufficient surely, otherwise alot of time and planning will be in your near future. R/R shouldn't die THAT often once it's moved to a better location  :-/

[ofstone]

So the stator only fails if the R/R fails?
I read that sometimes the stator was burned but the R/R whas still working well.
Has somebody measured the temperature of the R/R while riding? When the temperature is over 110 degrees celsius it surely will damage the components, becouse most electrical components have a maximum core temperature of 150 degrees celcius.

As i understand nobody knows fur sure what is causing this failing of the stator R/R.

It is probably a combination of some factors that is causing a failure, BUT to much heat is definately one of the factors, so that is why i am trying to make a stator/regulator that keeps everything cooler.

[Lucky]

Ok, here's what we know about stator/ r/r failures:
The most common physical indication of stator failure is a melted connector between the R/R & stator.  weather this is cause or effect we haven't decieded.

The most probable scenario is shorted stator windings (broken down insulation) heats up the output wires, melting the connector. the burned connector creates resistance, creating more heat & shorting the wires (I think you can see where this is going)

The cavet to this 'theroy' is that the insulation breaking down may not be the cause, it could also be crrosion in the connector.  this has also affected the other connector on the R/R that goes to the bikes harness, primarily melting the shunt ground wire.

the solution is to eliminate the connectors altogether and solder the wires directly. since the bad parts need to be replaced, generally Electrex parts are used. they are cheaper and more reliable.

You didn't think this was the end of the story did you?  lol.  Even with replacing the parts, soldering the wires, and moving the R/R to cooler air, we still have failures (although they seem to be fewer and further between...)  I've been working with Ritzo at Electrex and have convinced them to investigate the possability of producing heavy duty parts for us. we're just waiting on the oil tempurature data from Rick to continue.

so that's the story, so far...
--Lucky

[Rick G]

Pray for some decient week end weather out here, so I can get  get some meaning full readings!~

[Lucky]

You and me both buddy, you & me both...lol

Isn't there a Lords prayer for Visionarys?
"Yea though I ride through the vally of the shadow of death, I fear no rain, sleet, snow or gloom of night..."

Oh wait, that's the postal thing...

[Walt_M.]

Hate to dash your melted connector theory but if the stator windings start shorting out, the current output would be reduced and the output wires would be cooler. I hadn't looked at the current output graph lately and was beginning to think extended running at higher RPMs where the current is above 22 amps might be part of it but the output at 5000 RPM is 22 amps and I run there most of the time. I'm sticking to my R/R fails and kills the stator theory.

[George R. Young]

. . . I'm sticking to my R/R fails and kills the stator theory.

Had 3 stator failures roughly 5 years apart, the regulator/rectifier was and still is fine. My own theory is that the current flowing in the stator wires heats them up and eventually breaks down their insulation. Looking at the goop that Yamaha puts on the wires, it goes in looking good and comes out looking carbonized.

[Brian Moffet]

"Yea though I ride through the valley of death, I fear no fried stator, no failed RPM limiter, and no gunk my my carbs."

Okay, so I don't know much of it anymore :-)

Brian

[Lucky]

Yeah, Yeah, that's the way it goes, I thouoght I was close!  :)

[ofstone]

It is not very clear what is going on, but as i already told, i think heat is the greatest problem. And if we prevent everything from heating up it will last longer or even forever. Better cooling is not possible or effective enough.
If we can lower the stator output current, the amount of produced heat will be much lower.

As some people said, at 5000 RPM ... 22 AMPS! Where is all that current going to.
It is not the dashboard, or the headlight or the engine, and when the battery is full also not there.
The regulator is ''absorbing'' that current to lower the output voltage. this is also why the regulator rectiefier heats up. (that is also coused by the voltage drop over the regulator.

Estimated Power consumption bike:
engine (ignition) 2.5 A?
Headlight          5 A
Rearlights         1.5 A
Dashboard        1.5 A?
battery (full)     3A  If its higher when full the battery boils
over)
So total power is: 13.5 A

That means on long high speed riding contioniously 22-13,5=8.5 amps is whasted into heat in the regulator. and i even think i have rated the ignition, dashboard and battery current to high.

Lets see how many heat is generated inside the stator:
22Amps.
stator coil resistance 0.32ohms  Voltage over stator coil= 22*0.32=7.04V  
power 1 stator coil= 22*7.04=154.88W
3 stator coils total= 154.88*3=464.64W
So 464,64 Watts are heating up the coil.

Now see howmany heat is generated inside the stator with 13.5Amps.
stator coil resistance 0.32ohms  Voltage over stator coil= 13.5*0.32=4.32V
power 1 stator coil= 13.5*4.32=58.32W
3 stator coils total= 58.32*3=174,96W
So only 174,96 Watts are heating up the coil.

That is a huge difference of 289.68 Watts

I have a heater using 500 watts for heating up my caravan for hollidays in the winter, so you can imagine almost the same amount of energy is heating up the coil and the engine oil, and also wasting a lot of energy from the engine power(and also fuel!).

That is why i am trying to make a design so that the power is not wasted into heat, when not needed.

My first idea of using some kind of PWM step down converter is maybee not so good idea, but a college of mine gave me an exellent schematic of a compact cheap PWM voltage regulator. But the only problem is that a large coil for filtering the power wil be needed in that design.
I am looking to another design wich will regulate the voltage when it is an AC voltage, and then is giong to be rectified.

Maybee it is possible to use the old R/R and then only a few components are needed to make some sort of pre-regulator so that the R/R is not wasting so much of energy.

The only problem is that i dont know how the orriginal regulator ias build, So if someone has a schematic or Knows wich type of regulating it is using, then i can check is that is a good idea.
I know the regulator is diverting current from each coil before it is rectified, but the question is how.

[Lucky]

Quote: "Better cooling is not possible or effective enough"
 
That's what Rick & I are working on (ok, mostly Rick) an oil cooler for the Vision. The hard part is the adapter, the rest is easy...

[Rick G]

The  early Suzuki 550's had a stator failure problem.  the general concessis was that the oil ran too hot to absorb enough (or even any ) heat from the stator , causing a breakdown  in in the insulation .  
 I'm a retired HVAC tech. (heating, ventilation , air conditioning)  so I under stand a little about heat transfer.  Basicly , heat goes "down hill"  , that is from a hot place to a cooler place. It may be a  temprature of 250 deg. f.  passing heat to a 105 deg.F  medum . (This is typical in Air conditioning applications)
So , if the oil is  so hot , relative to the stator temrature , no heat will transfer ( in fact,  if its hot enough heat will transfer the wrong way!)  As soon as possable, I will take some readings  on oil temps I'm persuing the idea of an oil cooler , BUT, Jason Morris  (whose opinions I respect very much)  has warned me that the oil pressure can drop to a dangerous level , if a cooler is added .  I will add a oil pressure guage , like luckys, befor  attempting to install the cooler. The only other option that comes to mind is a separate pump to circulate the oil.  We will see. I 'm, glad to see ofstone coming at the problem from a different direction.

[Rupert]

If the oil pressure drops by adding an oil cooler, wouldn't adding more oil help to bring the pressure up again?

Or simply put the cooler low down so that oil will simply sit
in the cooler but the heat will be vented to the air thanks to
the surface area of the cooling fins, which in effect will also
cool the remaining oil in the sump to which the cooler is attached?
Or would this be too low for the cooler to be attached?
Just a thought.