Pulser coil redux

[boscoe99]

Here is what I have found.

A pulser coil can be constructed so that it senses the orientation of the flywheel magnets (north pole versus south pole) and in so doing knows what ignition coil to send the charge coil voltage to at the appropriate time.

I am now guessing that the pulser coil assembly in certain Yamaha 25 HP models uses two magnets and two pickup points. The two magnets would have different polarity when installed in the flywheel. The upper magnet sensing north moving in one direction would fire one cylinder (but not the other) whereas the bottom magnet sensing south moving in one direction would fire the other cylinder (but not the first cylinder).

If one of the two magnets has lost it magnetism then it stands to reason that it won't be firing the cylinder that it is supposed to. The pulser coil is not detecting the magnet going by.

Does this make sense?

The Yamaha V4 uses two pulser coils to fire four cylinders. Each pulser coil fires two cylinders and it knows which cylinder to fire and when based on the polarity that it sensing from the magnet. Or so says Mama Yamaha.

[99yam40]

but as in the 20 HP motor we were discussing the motor has 2 pick up units 180 out from each other and both have 2 sensor/pick ups so both of the units 180 out from each other would get the same signal because the polarity of the magnets going by would be the same on each.

probably did not explain that to good, but maybe you can get my drift

[rodbolt17]

someone had more likker than me last night.

folks it does not matter much north VS south.
as long as the design of the diodes,and transistors( NPN vs PNP) work.
a two wire pulser is going to produce a sine wave of equal negative and positive polarity.
a single wire pulser is going to produce a half wave of either negative or positive polarity .
now the DCI may have various delay circuits.
but the pulser signal is eventually fed to an SCR gate.
this turns on the SCR and allows a discharge path for a charged capacitor to the ign coil primary.

once the SCR is on it stays on regaurdless of a trigger signal.
it turns off when current through it drops below a threshold.
that threshold is set by the electrical engineers spec for that device.

it is a stupidly dirt simple system.

[boscoe99]

No likker for me. Don't drink like I used to. Your comments about likker drinking should be directed at Yamaha. This is what they have to say. Their words. Not mine. But I don't disagree with them.

V4 CDI Ignition
The V4 Ignition System works like a basic CDI system with two major differences:
• One pulser coil fires two cylinders independently of each other.
• There are two charge coils: one for low speed and one for high speed.

In a basic CDI, one pulser coil sends the signal to fire one ignition coil. In the V4 system, only two pulser coils fire four separate ignition coils. This means that one two-wire pulser coil fires two separate cylinders at different times in the firing order. To fire two cylinders off one pulser at different times, the pulser must tell the CDI box when to fire a particular cylinder. This is accomplished by using direction of current flow. The direction of current flow, sometimes referred to as “phase,” is determined by which end of the magnet, North or South, passes the coil first. When the North end of the magnet passes the pulser coil first, current flows in one direction. When the South end of the magnet passes first, the current flows in the opposite direction. The CDI box senses which direction the pulser current is flowing. The direction of flow determines which of the two cylinders con*****ed by the
pulser will fire. By operating this way, two pulser coils can control the operation of four cylinders.

And yes, it is stupidly simple system. As long as the system is understood. Per Einstein, the theory of relativity is stupidly simply.

[rodbolt17]

a SINE wave consists of TWO currents. one negative one positive PER pass of the magnet.
\as I cannot post fancy graphics lets do this.

draw a straight line on a piece of paper.
label it 0v.
take a penny, place the bottom edge at the top of the line.
take a pencil and starting at the top of the line trace around the penny until you hit the line opposite where you started.

now move the penny BELOW the line and to the right.

starting where the TOP tracing stopped at the line trace the penny until it hits the line again.

this is a sine wave.

this is what you get when you pass a N/S mag past a coil of wire on an iron core.

this is how 4 capacitors triggered by 4 inputs to 4 SCR's can work with 2 two wire pulser coils.
2 trigger off the positive sine wave.
the other two trigger from the negative.

remember the A/C sine wave goes from 0v.
to a positive peak V.
then to a negative peak V.
then back to 0v.
it repeats.
the repeat is known as cycles per second or Hertz.

like most house wireing here in the states for standard lights.
120V at 60Hz.
means that wave goes from 0v to positive 120 then to 0v then to negative 120v then to 0V 60 times per second

[99yam40]

All of the magnets i have seen that were labeled with a N and S pole were flat bar type or horseshoe

when you get to the button magnets or round ones I would think the flats would be the N&S.
Can a button magnet have poles not on the flat sides?

how do you find out which is N & S poles on magnets that are not labeled?
only way I can think of would be to use a magnet with a known correctly labeled pole to see if it attracted or repelled the other pole in question.

Now if you install a button magnet on a flywheel with a certain pole facing out, you will not be passing one pole and the the other (opposite pole) by the pick up because that opposite pole is facing away from the pick up.
so does this mean that you only get 1/2 of the sine wave either positive or negative but not both?

[rodbolt17]

depends on the coil.
if you ground one leg of the coil you get a half wave out of the other.
if neither leg is grounded you get a sine or full wave.
in this 20 HP one leg is grounded on each coil.
that is why you test both outputs to ground.
Boscoe posted the wiring diagram.
it is not hard to trace the current paths,.

[panasonic]

All of the magnets i have seen that were labeled with a N and S pole were flat bar type or horseshoe

when you get to the button magnets or round ones I would think the flats would be the N&S.
Can a button magnet have poles not on the flat sides?

how do you find out which is N & S poles on magnets that are not labeled?
only way I can think of would be to use a magnet with a known correctly labeled pole to see if it attracted or repelled the other pole in question.

Now if you install a button magnet on a flywheel with a certain pole facing out, you will not be passing one pole and the the other (opposite pole) by the pick up because that opposite pole is facing away from the pick up.
so does this mean that you only get 1/2 of the sine wave either positive or negative but not both?

Rodbolt that is very good description of how a basic CDI works and how a Sine Wave is formed when a magnet passes a coil. I think we all know that pretty well and anybody who has seen or used a oscilloscope hooked up to standard house voltage should know what you are talking about...

What started this debate./discussion was me finding a dead disc shaped magnet on the inside shaft of my engine flywheel. I wish you could see the pictures. This does not seem like a standard magneto set up and we are just trying to figure out how it works. I don't think anybody is saying that there is something "new" going on here, just it is being done in a strange way from what most know.

99yamaha,

I have bunch of disc magnets and a old cheap compass and they are all magnetized n/s coming out from the faces. When I put the edge of any of these magnets towards the compass it swings around all over the place.

So going on what we know so far, that you need a N and S magnetic field to create the AC sine wave in a coil. It makes perfect sense that there are two disc magnets right next to each other. One is a N and the other is a S and they are both needed to induce the current in the trigger coils. This also why the trigger coil units on this engine have two posts on them so they can pick up the magnetic fields of the two separate magnets going by at the same time. How else can it work.

One of these magnets was dead ( or at least very, very, weak) on this flywheel so there is no way this ignition was going to work right. No way.

How did I determine that it was dead? Before someone asks. I simply touched them with a screwdriver, it stuck like shit to a blanket on one and nothing on the other. Then I took a paper clip and done the same, it barely stuck to bad one and I mean very slightly. So a tiny bit of magnetism maybe left in it.

Why it was only effecting the #2 cylinder and not the #1 I do not know the answer to that....and I think that is what 99Yamaha also is trying to figure out.

[rodbolt17]

was it a magnet or a hall effect device>
I dunno and Yamaha doesn't say.
I do know how to check the peak voltage output of a single lead coil though.
I don't know how that mag would degauss itself but I guess anything is possible.

[99yam40]

Why it was only effecting the #2 cylinder and not the #1 I do not know the answer to that....and I think that is what 99Yamaha also is trying to figure out.

Yes it is puzzling .

If one magnet is not inducing enough magnetic fields into the pickup coils it should affect both pulsers the same in my thoughts.

Once you get the good used flywheel installed you can measure the outputs of both pulser coils to see what they send to the CDI and record that for later needs if they ever come up.
Hope everything works as it should with the new Flywheel.
I just do not see how that one magnet would affect only #2 unless that second pick up point going by that bad magnet had its own signal wire or it sends an opposite signal than the other pickup as Boscoe99 said

was it a magnet or a hall effect device>

being others with flywheels for sale have told him that both had good magnetism I would think both should be magnets.
I hope they were not blowing smoke

[panasonic]

was it a magnet or a hall effect device>
I dunno and Yamaha doesn't say.
I do know how to check the peak voltage output of a single lead coil though.
I don't know how that mag would degauss itself but I guess anything is possible.

It is a magnet.

I got four separate people who had these flywheels on ebay to check them for me. I sent them a picture of the magnets in question and asked them all to touch a screwdriver on both the magnets and see if it would stick. They all got back to me and said they were magnetic. Unless all of them lied to me.

I have DVA for my meter now and will check the peak voltage out of each trigger when I get the new flywheel installed.

I am just as puzzled about how the magnet degaussed as well. But I read that a very small magnet, left in a very strong magnetic field (outer ring magnets on the rotor) in just the right position for a long period of time can lose its magnetism....Why only one of the two I don't know. This engine sat for 25 year's, never moved.

I tell you what. A buddy of mine got a scope and I will be getting a loan of it and having a look at the pulses from the triggers and out of the CDI as well.

Thanks for your response.

[panasonic]

Yes it is puzzling .

If one magnet is not inducing enough magnetic fields into the pickup coils it should affect both pulsers the same in my thoughts.

Once you get the good used flywheel installed you can measure the outputs of both pulser coils to see what they send to the CDI and record that for later needs if they ever come up

Yes I agree 100%

[boscoe99]

a SINE wave consists of TWO currents. one negative one positive PER pass of the magnet.

You are absolutely correct. Current flow first in one direction (positive voltage value rising and falling to zero) and then current flow in the opposite direction (negative voltage value rising and falling to zero).



A properly positioned single rectifier can capture voltage flowing in the positive direction only.



A properly positioned single rectifier can capture voltage flowing in the negative direction only.

It just depends upon how the voltage is captured when the magnet wizzes past the pick up coil the current flow could be in one direction or the other. Depending upon the circuit.

[panasonic]

You are absolutely correct. Current flow first in one direction (positive voltage value rising and falling to zero) and then current flow in the opposite direction (negative voltage value rising and falling to zero).



A properly positioned single rectifier can capture voltage flowing in the positive direction only.



A properly positioned single rectifier can capture voltage flowing in the negative direction only.

It just depends upon how the voltage is captured when the magnet wizzes past the pick up coil the current flow could be in one direction or the other. Depending upon the circuit.

Cool, nice diagrams for this post.