Rewinding old 3-phase stator: Non-symmetrical layout

[Baluncore]

We don't know what goes on in the ignition coils magnetic circuit . Amp-turns in adjacent charging coils can put the squeeze on flux over there.

Maybe halving the number of turns on the 3PH end coils, on either side of the HT, is a window function designed to better isolate the power from the HT.

 

[Tom.G]

Here is a plot of three phases, two with peak amplitude ±1.0, one with amplitude ±0.9, plotted relative to the star common = zero.

Nice!
What turns count distribution did you use? Since you have come up with a way to simulate the darn thing, could you make a run with the 15 coils and the turns distribution as speculated in post 19?

 

[Kjell Amundsen]

First comment I have here is that there will be a reason for this. With mass-produced Motor vehicles (and the old RD350 was a popular machine in its time), the manufacturers have spent a lot of time getting it right, so stick to the original scheme, no matter how much it doesn't make sense to you or me.

Secondly, If the Yamaha is the same as My HONDA VFR800 the three-phase AC is fed directly into a rectifier and becomes DC, so any imbalance can only have an effect of the actual windings that you are repairing.

A Question, DO you know what fried the stator windings? Was it a failure somewhere else, and you have found and repaired it, OR was it just a time thing?. My experience is that the regulator rectifier and the stator windings go hand in hand, if one fails you should be examining the other to be sure it is ok before starting it all back up again.

Some background on the Regulator-Rectifier . (R/R)
I took a quick look at an RD350 Forum and it appears that the Regulator rectifier works on the same principle as used by a lot of other motorcycles. The Field poles are permanent magnets so there is no control over the output voltage. It changes with engine RPM. In order to get useable output at low RPM the Magnets must be specified to give at least 13 to 15 Volts at idle, and as the Engine RPM Increases the voltage will increase above this, and can get to a couple of hundred volts at Max RPM if the R/R is removed.
To keep the votage down to the correct level the R/R will start shorting the output of the windings through its semiconductors, to "Pull the volts down" . This is why there is a substantial heat sink on the R/R .
If the R/R is turning on incorrectly or Failed short, this could be the reason for the fried windings.
Just a thought.
I notice, like on other motorcycles, Third parties have started marketing phase controlled Rectifiers to remove this seemingly senseless "Shorting", in a bid to make life a little easier for the stator windings.

Forgive me if I have gone a little Off Topic.Tom

You are right about the R/R part.
I have read descriptions of poor and corroded connectors and groundings as the main enemy of charging systems like these.
That is - when the battery is charged and the bike is running with low load (no main lights on), the poor connections will thus have the potential to prevent the needed current draw to "pull the volts downs" just like you described.

This supposedly can cause the voltage to rise to unwanted levels - causing overcharging to battery and and hurt other things as well.
In my case however I do not know what went wrong and started it all.

But I remembered I did charge the batteries a couple of times while the battery was hooked up to the system + ignition on while doing some other testing.
Could that be the cause of a reveres current of some sort? Must check wiring diagram for that theory.
But I am sure there was something wrong before I started charging so often, otherwise I wouldn't be needing to in the first place. So there maybe the coils were partially dead already.
I will also check the R/R itself and post the results when done.

Regards
Kjell

 

[jim hardy]

Could that be the cause of a reveres current of some sort? Must check wiring diagram for that theory.

Correcting a mistake i posted yesterday evening (thanks @Tom.G )

When a battery gets hooked up backward and the sparks fly
observe that all six rectifiers are forward biased, if ever so briefly.
One or more if them will likely fail to a short circuit during that "oops " moment. Might fail open soon afterward if the battery is stout enough to melt the internal wire.

Two shorted as shown will let the battery, when reconnected properly, run down backward through the coils and fry them. Path is in orange.

Just one shorted will interfere with normal alternator operation but I've not enough hands-on experience to tell you what symptom to expect.
Open rectifiers will give low alternator output.
If you have access to a similar machine, measure both the DC and AC across the batteries with engines at same RPM.

Image courtesy of a pretty good article at
http://www.electrosport.com/technical-resources/technical-articles/how-motorcycle-charging-system-works

 

[Baluncore]

What turns count distribution did you use? Since you have come up with a way to simulate the darn thing, could you make a run with the 15 coils and the turns distribution as speculated in post 19?

In your post #19, you propose 14 coils giving 160t : 160t : 160t. Output will vary between 3/2 and √3. Ripple will be symmetrical.

The graph I posted had phase amplitudes of 1.00 : 1.00 : 0.90, which is the equivalent of 200t : 200t : 180t. That is very close to the partially compensated 180t : 180t : 160t, with amplitudes of 1.00 : 1.00 : 0.889

I wanted to see the effect of a minor phase imbalance on the rectified output when there is no neutral connected to the centre of the star. All I have done is simulate the 3 phasors, with normalised relative amplitudes and 120 degree separation. I then perfectly rectify the 3PH by picking the difference between the highest and lowest voltage phases, which gives the output voltage plot with ripple. Such a trivial model ignores diode voltages, RPM, flux, pole position, harmonic content and reality.

 

[Tom.G]

Such a trivial model ignores diode voltages, RPM, flux, pole position, harmonic content and reality.

Ahh, I see. Perfect for what you were after. I was a hoping there was something with more detail involved. (A case of 'If wishes were horses, beggars would ride.")

 

[jim hardy]

Such a trivial model ignores diode voltages, RPM, flux, pole position, harmonic content and reality.

But it sure gives one's thinking a jumpsart...

 

[Kjell Amundsen]

Hi all.
I thought I'd add some updates after finishing my diy rewind of the stator in question. I decided to go simple, and estimated roughly 40 windings for each core. Doing it by hand is not ideal as it was hard to keep the wires as tight as a machine would. I compensated with generous amount of transformer grade varnish to finish off and secure any slack. Anyway after testing and installing, the charging system produced around 12.9 Vdc at idle and 14.5Vdc at 4-5000 rpm with the headlights lit and measured at the battery terminals. 14.5V is at the high end of what is normally required and is slightly above factory spec. Probably due to a few more total windings and or less resistance in the copper wire (uncertainty when measuring old wire gauge due to varnish). I have not bothered to measure ac phase voltages so far. I think I will just leave it with that. Thanks for interesting inputs along the way on here.

 

[anorlunda]

Moved to our new DIY forum. This thread is a perfect fit for that.