Testing voltage to the points on the Sportfour Imperial

[Buccaneer]

Have my voltmeter hooked up directly to one set of points on this battery
ignition Evinrude. It’s running just under 10 volts, which still seems high,
as I’m now using a 3 ohm resistor before the ignition coil.
Not sure what to believe.

VIDEO……..

https://youtu.be/9MtCafA_OKs

Prepare to be boarded!

[crosbyman]

I am no expert on your engine type but… JMHO…..if you measure voltage on or across point that open an close the voltage will be at max value  during the open air gap of the point because by ohms law….. the highest voltage appears at the highest resistance point (air gap)  of measurement in a series circuit.

your  meter is  only showing you a value  made up of PEAKS ( when the gap opens)  and  something (when the gap closes)

analog or digital meters are to slow to react (damper)  to these fast fluctuations and the only way to “see” what you have is with  an oscilloscope..

https://youtu.be/-arFz0cI5jQ

 

if you feel adventurous Amazon has lots of  inexpensive scopes  below 75$

 

 

 

 

 

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[Buccaneer]

Interesting Crosbyman, but I think in my case, that scope would be a little
bit of an overkill.

Prepare to be boarded!

[crosbyman]

agree the one in the utube is to much $$$$$    but a small inexpensive single trace scope  is all you need for OB work . up to you.

Joining AOMCI has priviledges 🙂

[Buccaneer]

 

Regards to “overkill”, I’m not referring to the price, but
rather that it would seem like using a $1000 gold plated
toilet seat, when the Ohm’s Law should tell me what
size resistor I need.
I just don’t think I have quite the right information in
my calculations perhaps?

With the current volts to the points with the engine running,
V=IxR

I have, between the ignition resistor and primary coil resistance (3 + 1.3)
around 4.3 ohms, and if the voltage to the points is running just under 10 volts,
that calculates to an amperage of 2.3 amps current.

2.3 amps x 4.3 ohms = 9.89 volts, about what I currently have at the points.

When I tried using the 2 ohm ignition resistor, and having a total resistance of
3.3 ohms, the current must have ran at a higher amperage. During that test,
I checked voltage at the coil “Bat” connection, and was running 11 volts,
but in testing at that location, it’s not taking into account the resistance
of the primary coil……. hence, my two test weren’t “apples to apples”.

Then there’s the question, do I calculate the primary resistance of both
coils in the coil tube for my equations, or just the one? I only did
the one.

With all my calculations, I’m stumped why, when using a 3 ohm ignition
resistor, I’m still getting almost 10 volts to the points!

 

 

Prepare to be boarded!

[Gary Haight]

Do you know if there is an IDEAL voltage to the coils? I know the ballast resistors in the Chryslers was used because of the oil filled metal can coils that would get hot.  Is it possible that the ballast resistor is there to just regulate the voltage to the coils because of the voltage fluctuation with the generator voltage? I don’t know and I am just questioning what the voltage should be.

[Buccaneer]

From what I know, points ignition systems with 12 volt systems,
had a ballast resistor, or other type, usually around 1.7 ohms,
depending on the type of coil used. This was to lower the voltage,
and hence the current going through the points so they didn’t
burn up.
The generator will change the equation somewhat I presume,
when it’s putting out 13.5 volts, etc.,
I read somewhere that nine volts to the points would be okay,
but I’m currently at 10 volts.

Prepare to be boarded!

[crosbyman]

I am not certain V=IxR  because  current in a coil is not a simple curent flow as in a  plain  old resistance .

A “coil”offers not only the pure wire resistance  it actually opposes  the flow  of current  because of  its  inductive resistance.

gets tricky  to make  current calculations  because the formula is a tad more complex .

If I recall….. in a capacitor …current actually moves faster while  voltage follows    later.

In a coil  voltage rises faster  while current is held up by the magnetci build-up in the coil (inductive reactance)

lots of good articles on the net on the subject…

that said play safe &  just reduce the current to protect  points and coils while  producing a good enough spark on the plugs.

jmho

Joining AOMCI has priviledges 🙂

[Buccaneer]

I seen a video earlier regarding cars, that said to measure the ignition voltage
(with the engine off) with the volt meter hooked up to the coil “Bat” side,
and have the other side of the coil grounded.
That would tell you how much the ignition resistor is dropping down
the voltage, but I presume one would only want to do that test
for an instant or risk blowing the coil?

 

Prepare to be boarded!

[Gary Haight]

What about using a dual ballast resistor like the Standard Ignition RU-12. I believe one side is approx. 5 ohms and the other side is approx. 1.2 ohms. You could use the 5 ohm side and if needed, add the 1.2 ohm in series. Just a thought. They are not too expensive.

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