MTFCA Forum

I plan to make a little buzz-coil testing machine. It shall be something between an "K.R.Wilson" and a simple "Amps meter". I want to see if a coil is doing multiple sparks or not.

Well, I don't want to build up a hand cranked magneto with all this magnets, windings, ..., this is wasting a lot of money because I have to buy that parts.

My idea is applying either a rectified AC (so only positive half-waves, the negative ones are changed in their polarity), or by a pulsed DC voltage (simplified version). A little cam and a metal pointer will be mounted to a rotating shaft (driven by a little DC motor), the pointer is rotating inside a 90 degree scale made of metal and being connected to the high voltage output of the coil.

Principle (I am brainstorming)
The cam will press a micro switch and simulate the timer. At same time, the pointer is moving. Whenever a spark occurs, I will see it, so it works similar to the K.R. in this point, but it works only with one buzz-coil at a time.
When applying DC voltage, I see what happens in "battery mode", the coil permanently fires when timer is closed. When applying either pulsed DC or rectified AC, I will have four supplies per 1/4 revolution.

What I could not find out yet:

1. Timing of timer.
   How many degrees of crankshaft rotation is the buzz-coil connected to ground by the timer? It would save me a lot of trials if one here knows, otherwise I will have to measure the angle of very slowly turned crank from start to end of hearing a coil buzzing. (My tester will simulate 1 cylinder, so everything is related to 1/4 turn of engine crankshaft.)
2. How many AC Half Waves does the magneto produce on 1/4 turn of crankshaft?
   Should be 4 or 8. Four magnets on 90 degrees if I am right. But I am not sure about number of half waves produced. I don't have an oscilloscope in my garage to measure that, and garage is far away from my lab. So it will help if somebody already figured that out. From theory, magnets are mounted N-S S-N N-S .... S-N so I have 16 poles on one revolution (or 4 poles in 1/4 revolution). But how many half waves do I have?
3. I also would like to know how many rpm the engine does when it is idling and running on travel speed (approx 30 mph)

The rest is then relatively simple math. It would help me a lot. Thank you.

You are making too many speculations - the 60 Hz from the AC can do quite well (50 Hz in Europe).
Strobospark use that transformed down to 10 V AC.
I have troubles calculating what rpm 60(50) Hz is equal to - maybe somebody else can.

If I may. Search for a Dykes automotive book, one with the Model T supplement.
https://www.google.com/books/edition/Dy ... frontcover

To eliminate any reason for the dreaded double sparking, make certain the cushion spring is free to have movement. To add to the confusion, even the HCCT instructions state that double sparking is desirable for cold starts.

Personally I believe the concept for a mechanical design of the Huff system is as simple as one can get for an ignition. And when adjusted with the period information, you have reached optimum efficiently. Of course there is the make and break ignition.

But then what do I know after 50 years of Model T ownership?

"When applying DC voltage, I see what happens in "battery mode", the coil permanently fires when timer is closed."

No, it doesn't. The coil points are still vibrating/pulsing when supplied with DC. Each break of the points fires the coil. The fire is pulsed, in time with the each break of the points. With AC, each break of the points is timed to the AC pulse frequency.

"3. I also would like to know how many rpm the engine does when it is idling and running on travel speed (approx 30 mph)"


Also simple math. Knowing the circumferance of your tire, calculate how many revolutions are needed to travel 30 miles in 1 hour. Now you know revolutions per hour. Divide by 60 for revs per minute, then multiply that by 3.63, the ratio of a stock rear end, and you've got engine RPM's.

Magneto frequency = number of poles X engine RPM.

"Magneto frequency = number of poles X engine RPM." Not really. First frequency is a measurement of full waves of AC per second. There are 16 magnets on the magneto so 16 poles. But each pole only produces a half wave. Therefore there are 8 full waves per revolution of the crankshaft. Next is that engine RPM is revolutions per "minute". Frequency is in cycles (full wave) per "second". So if my math is correct the "frequency" of the magneto would be engine rpm x 8 / 60. Or in other words engine rpm / 7.5.

0 v, plus v peak, 0 v, minus v peak, 0v.

I recall someone in past year? or two? or? posted their progress in developing a coil testing device that used a tuna can and rotating pointer to display the spark, basically a scaled down hcct pointer and brake drum. I think he used a cam operated switch to intermittently energize the coil and a small electric motor to drive the unit. For the life of me, I cannot find that thread, but it's out there, and it describes a very clever device. jb

So if the Strobospark is using the 60 Hz line frequency then that relates to about 450 rpm of engine speed or about 11 mph assuming 30" diameter tires and 3.63 to 1 rear end ratio. Or with 50 Hz would be about 9 mph.

16 magnets

16 pulses (revised back to my original wording after rethinking it; with each pulse being alternately +positive, and -negative, etc)

once a HCCT is spinning fast enough, a coil will/should fire 16x per full revolution of the crank/flywheel

as I recall, a KR Wison HCCT runs at roughly 160 RPM under electric power from a 1725RPM GE motor when it is fitted with the correct pulley (HCCT instructions are 150-175RPM)

If my math is correct, that would be firing a coil a little more than 42 times a second ((16*160)/60) at about 4V which is a VERY low voltage with an abnormally HIGH cycle rate for a single coil. This is why, in 1919, the HCCT was such a very robust test for a coil. As for RPM vs. voltage, it is linear - you double the RPM, you will double the voltage. Regardless of the voltage, though, the coil will always fire at the same amperage it is set to initially.

I should probably leave this last part out, but lately it seems that it has risen to the level of a sport, to make statements or speculations so far out in left field, I wonder if those making such statements will ever find the ball-park. It is one thing to honestly not know something, and seek answers, but to state things as facts that clearly are not, is not at all helpful to anyone. I am frankly less and less inclined to suggest a new hobbyist come here for information since so much is speculation and error masquerading as facts. Like a library, it's a great place to learn things, but until you get to know the authors, you never know if you're reading from the fiction or non-fiction section.

Rainer, I wish you luck in your quest for an answer to your problem.

A current pulse and a full AC cycle are two different things. One source indicates 146 AC cycles per second at 1000 engine RPM, which is about 25 MPH road speed in high gear. I assume that's about 300 current pulses per second, but assumptions may not get you far when dealing with a Model T. The coil primary frequency would be affected by how many times the coil points cycled during any particular magneto pulse. I'm pretty sure that the secondary coil output oscillation frequency would be very different from the primary coil frequency, and I'd think it would be much higher.

If you are seriously interested in the Model T ignition system, I suggest you take a look at these articles from past issues of The Vintage Ford:

“The Model T Ignition Coil – Part 1: The Ford/KW Ignition Company Story,” by Trent Boggess and Ronald Patterson, The Vintage Ford, vol. 34 no. 4 (July-August 1999) pp. 15-27.

“The Model T Ignition Coil – Part 2: The Ford Motor Company vs. the KW Ignition Company,” by Trent Boggess and Ronald Patterson, The Vintage Ford, vol. 34, no. 4 (September-October 1999) pp. 23-33.

“The Model T Ignition Coil – Part 3: A Chronology of the Ford/KW Coil Unit,” by Trent Boggess and Ronald Patterson, The Vintage Ford, vol. 34, no. 5 (November-December 1999) pp. 28-43.

Respectfully Submitted,

Trent Boggess

My comment was meant to just relate to the original question as to the "frequency" of the magneto, and not necessarily relate to the actual function of the Model T ignition system. I agree that to understand the ignition system those articles by Trent and Ron are the place to get answers.

jab35 wrote: ↑

Tue Dec 28, 2021 12:40 pm

I recall someone in past year? or two? or? posted their progress in developing a coil testing device that used a tuna can and rotating pointer to display the spark, basically a scaled down hcct pointer and brake drum. I think he used a cam operated switch to intermittently energize the coil and a small electric motor to drive the unit. For the life of me, I cannot find that thread, but it's out there, and it describes a very clever device. jb

That might be this thread viewtopic.php?t=3153

Steve Hughes wrote: ↑

Tue Dec 28, 2021 12:12 pm

"Magneto frequency = number of poles X engine RPM." Not really. First frequency is a measurement of full waves of AC per second. There are 16 magnets on the magneto so 16 poles. But each pole only produces a half wave. Therefore there are 8 full waves per revolution of the crankshaft. Next is that engine RPM is revolutions per "minute". Frequency is in cycles (full wave) per "second". So if my math is correct the "frequency" of the magneto would be engine rpm x 8 / 60. Or in other words engine rpm / 7.5.

"Magneto frequency = number of poles X engine RPM."
I got the same formula (only in correct units from start).
When the engine is running 1200 rpm (I guess this will be approximately the case at 30 mph), the frequency will then be 1200 x 8 / 60 = 160 Hz or in other words, 320 Half Waves. So one half wave has a length of 1/320 second = 0.003125 second = ~3 milliseconds
From this length approx. 2/3 of the time the voltage is above 6 Volts (another estimation) and therefore usable by the buzz coil.As the voltage is lots higher than 6 V (somewhere around 20V, the rising and falling edge is very steep, so I can approximate it by a square wave.

So I know now the timing for testing one coil in a stroboscope way:
One coil will receive 4 pulses of ~24V within 12ms (interval time is 3ms), each pulse has a duration of 2ms followed by a pause of 1ms. Then a pause of 12 pulses (=36ms) follows (this are the other 3 cylinders). This will be relatively close to reality.

Adding a rotating pointer will give me the possibility to see double sparks, this is what I want to have. I will make a gap of 5mm between pointer and scale where the spark will jump over.



Thanks for your kindly help, it is much easier now.

Scott_Conger: I will use this setup like a "modern" version of a HCCT to run coils over long time (to test reliability of spark generation). Applying a variable voltage will allow me also to see if a coil is making troubles at lower or higher voltages or rpm.

Thanks again!

I believe waveform is pretty must sine and coils is supposed to work with 4V and upwards. Due to the nature of coils the current is pretty stable regardless of engine RPM and hence AC voltage varies as well as frequency.

Maybe you shoild read those 3 articles. They exists in print on the net.

Well Done Rainer, You are on the ball. It is good to see people thinking for themselves.
You could be Number Four.....n

Rainer,
Adding the pointer to the mechanism will give you the ability to determine the coil dwell. For every 600 rpm change in speed the firing time changes by 7.2 degrees at a dwell time of 2 milliseconds. The voltage applied can be dc or ac from a signal generator. The magneto will not work for this arrangement. It will if using an oscilloscope.
Dwell control is important for a properly tuned coil.

Several days ago I was brutally criticized for suggesting there is another way to set coils besides the ECCT, which I feel is very good but not the only way.

My criticizers (speedling) should read this artical and the article that Luke has been writing, which surfaced several days ago.

Art Mirtes

Rainer,
Adding the pointer to the mechanism will give you the ability to determine the coil dwell. For every 600 rpm change in speed the firing time changes by 7.2 degrees at a dwell time of 2 milliseconds. The voltage applied can be dc or ac from a signal generator. The magneto will not work for this arrangement. It will if using an oscilloscope.
Dwell control is important for a properly tuned coil.

Several days ago I was brutally criticized for suggesting there is another way to set coils besides the ECCT, which I feel is very good but not the only way.

My criticizers (speedling) should read this artical and the article that Luke has been writing, which surfaced several days ago.

Art Mirtes

jab35 wrote: ↑

Tue Dec 28, 2021 12:40 pm

I recall someone in past year? or two? or? posted their progress in developing a coil testing device that used a tuna can and rotating pointer to display the spark, basically a scaled down hcct pointer and brake drum. I think he used a cam operated switch to intermittently energize the coil and a small electric motor to drive the unit. For the life of me, I cannot find that thread, but it's out there, and it describes a very clever device. jb

Yes James, that was me. Here is the post on the MCCT (Motor Controlled Coil Tester): viewtopic.php?f=2&t=3153

Rainer,
I did spend some time using a little motor and switch to make a coil tester. For determining the time to fire it worked good. An improvement would have been to have the switch on for less time, so the measured current of one spark could be used.

But soon after I worked on that the FACT (Ford Arduino Coil Tester). Click this link for more info:viewtopic.php?f=2&t=3153. And I think that it hit the price point I was looking for.

If you have any questions don't hesitate to reach out to me.

All the best!

Matt