AC or DC

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rjoynt
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AC or DC

Postby rjoynt » Tue Dec 05, 2017 3:59 pm

Which type does a magneto based outboard produce? Our Wednesday group is meeting tomorrow and that is going to be one of the topics. Any suggestions on any tests to do to either prove or disprove? It should be an interesting Wednesday!!!
Thanks in advance.

FrankR
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Re: AC or DC

Postby FrankR » Tue Dec 05, 2017 4:13 pm

Interesting topic indeed. First you need to ask AC or DC---where? At the spark? At the coil? or whatever. Actually, when it comes down to it, the answer is very complicated. A better topic would be on how the magneto produces a spark. You will then get into electricity generation, induced voltages, etc, etc.

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Phil B
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Re: AC or DC

Postby Phil B » Tue Dec 05, 2017 4:57 pm

The first image the waveform measured on the primary with no points or condenser (cheap digital scope, external voltage scaling) for three rotations of the flywheel, the second with points and condenser (polarity, scale may differ) for one rotation:

coil.jpg
coil.jpg (20.13 KiB) Viewed 310 times
Attachments
spark.jpg
spark.jpg (17.79 KiB) Viewed 310 times
[the Aerocraft & OMC boat guy; formerly "Silver Bay"]

JoeCB
Great Lakes Chapter President
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Re: AC or DC

Postby JoeCB » Tue Dec 05, 2017 8:14 pm

Very interesting, thanks Phil. At the risk of side tracking the OP... A question for Phil. Is it possible to superimpose the secondary circuit discharge on your second scan? Where would the ideal point of discharge occur relative to the big primary voltage spike? Perhaps this may be the ideal way to set the points in the magneto.

Joe B

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Richard A. White
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Re: AC or DC

Postby Richard A. White » Tue Dec 05, 2017 8:45 pm

This is cool stuff,


Joe, they make a timing tool for the OMC and a wheel for the Merc to set the timing, the antiquers get set by ear....LOL

Richard A. White
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http://www.richardsoutboardtools.com

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Phil B
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Re: AC or DC

Postby Phil B » Tue Dec 05, 2017 8:50 pm

I don't know how I could do it. The "scope" is a toy, and only has one input. I imagine with a real(er) scope, with the points not connected, you could attach a second input to the points, and get two graphs: one showing the coil output, and the other where the points are open vs closed.

mine is the previous version of one like this:
https://www.adafruit.com/product/468
[the Aerocraft & OMC boat guy; formerly "Silver Bay"]

FrankR
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Re: AC or DC

Postby FrankR » Tue Dec 05, 2017 9:11 pm

Nice toy though. Just for the heck of it, It would be cool to play around and see what difference would show up in case of a leaky condenser, dirty points, etc. Obviously, dirty points would show up very clearly in missing/low spikes (I suppose)

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VinTin
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Re: AC or DC

Postby VinTin » Tue Dec 05, 2017 9:48 pm

I believe the second scope photo shows the resonant frequency (ringing) of the inductor/capacitor. A leaky capacitor is going to shunt and reduce the amplitude of the voltage spike and resonant voltage. It is my understanding that this ringing results in a longer spark plug arcing duration. A capacitor that has changed in value would result in a change in frequency of the ringing. By collection some data from known good coils and capacitors (resonant frequency and voltage amplitude) it should be fairly easy to figure if a capacitor is out of spec.

debe
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Re: AC or DC

Postby debe » Wed Dec 06, 2017 6:45 am

These are the wave forms of coil primarys with an electronic module disconnected, then with the electronic module connected. The module was an Atom module on 2 different types of coils with different polarity triggering pulses. The Wipac coil was on a Seagull outboard. The Ryobi was a weed wacker.
WIPAC. pos.2.JPG
WIPAC. pos.2.JPG (97.5 KiB) Viewed 167 times
WIPAC. pos.1.JPG
WIPAC. pos.1.JPG (104.05 KiB) Viewed 167 times
RYOBI. neg.2.JPG
RYOBI. neg.2.JPG (95.04 KiB) Viewed 167 times
RYOBI. neg.1.JPG
RYOBI. neg.1.JPG (96.49 KiB) Viewed 167 times

debe
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Re: AC or DC

Postby debe » Wed Dec 06, 2017 6:53 am

https://www.banggood.com/DSO138-DIY-Dig ... rehouse=CN This was the DSO I was using & was around $30 Australian, & does require some assembling. I have found it quite usefull.


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