MTFCA Forum

Constructed an analogue meter that indicates which coils are firing, or not. Indicates both battery and magneto operation. Simple . (diagram from Ford Fix)

What’s the jumble of green wire?
How does it work?

I think you might be over complicating things. The spark can be checked with a screwdriver. If it’s not sparking switch with another coil. If the no spark moves it is the coil, if not it is likely a wiring issue. Takes longer to type than to do.

Andy

The Ford Fix diagram fails to show how/where the meter is connected. Also, there is no mention of the type of meter being used. More information is required.

If you have to connect the meter for EACH coil, I agree with Andy, it would be quicker, less expensive, and more simple to use a screw driver to check spark at the end of the plug wire. You then can rule out everything up to the spark plug.

The ford fix diagram is to show how the coils are wired for a Model T using a mechanical timer. The meter shown is based on a Radio Electronics, August 1966, article by Duane Sweet, Simplest Tachometer/Dwellmeter. The question - "What’s the jumble of green wire?" - is answered by having each of the wires connect to the timer side of the coils, as the coil is excited it sends a pulse to the meter as an active coil vibrates. The ford fix diagram has terminals from the timer, 1to 4, and that is where the green wires attach with clips. The probes with the clips are designed not cause interference between coils.

Here is a link to the article.
It's on page 45.

https://worldradiohistory.com/Archive-R ... 966-08.pdf

Someone, perhaps Joe Felin, created a display panel for his car which contained 4 small neon (I believe) lamps which would light upon receiving a pulse via induction which displayed as 4 somewhat solid lights (depending on speed) and misfiring could be detected through the pants and identified by an unsteady light on the dash.

Very clever and definitely useful to someone who really wanted to know about such things. For me personally, completely useless as I am still flexible enough to bend down and test the coils in place, and rarely have a need to do so anyway, and certainly do not wish to see 4 green flickering lights staring at me as I try to enjoy a non-modern, non-neon life while in my car.

To each his own

"To each his own"

Yes, a bit like replacing a mechanical rotor inside a timer with a micro chip.

Why use a meter to see if a coil is firing, when a screwdriver will tell the same thing?

Water pumps for ever!

I downloaded the magazine and I still can’t find the article. I have attached the index. Page 45 is the continuation of an article for a tachometer which is far from simple or a mess of green wire.
What am I missing.?
Is it April Fools Day?

Around here we do it this way.
“ Hold my beer while I touch these here wares and see which one ain’t a faring”

Dan

in WY, we finish the beer and then urinate on the plugs...that way, not only do we detect if they're firing, but also if they're double-sparking, too.

It's tough out here, man.

RE: neon bulbs

As someone mentioned, you can always use the screwdriver against the block/headbolt method to get to see if an individual plug is firing.

However, my dad always carries a nifty spark plug tester in his tool box. It's a small, pocket-size screwdriver with a neon bulb inside the handle. You just touch the screwdriver blade to the spark plug terminal.

More recently, I acquired one for myself at an estate sale. It's probably 50 years old but unused/brand new in the box. New ones are available online today.

If you are trying to find out if the cylinders are all firing at the same place, I can see the point. But, not sure if a meter would be the way to go for that.
My friend Bill (RIP), mounted a fixture on the hood rod with 4 small bulbs (not sure the type and may have been induction pickup). When he wanted to check and see if all 4 were firing, he would flip a switch. Made a nice little light show in the dark.

Something that I forgot to mention. The Meter has a 90 degree scale. When adjusted for use, I set the scale (using battery and coils to start) for full scale at 6 volts.

Connected, with all four coils connected, and the motor running at idle, I have the needle between 20 -25 degrees of the full meter.

From what I have read, the Model T has a dwell of 22.5 degrees. It must be a coincidence that my analogue meter that indicates which coils are firing, is showing that on battery my dwell timing is close to specs.

George

I am really trying to figure out what you're doing and reading the article didn't make it any clearer. As far as the 90 degree meter and 22.5 degree dwell, I think you're conflating a number of things, but again I cannot at all figure out what you're trying to accomplish, so maybe I'm all wet.

I just don't see what the problem is that you're trying to detect and if you did detect something, what of it? If I have a coil or plug misfiring, I can see it, feel it and hear it. If I want to know which one it is, I hold down the vibrator on each coil until the malfunctioning one becomes apparent. Now as for the guy I mentioned earlier with the 4 neon lights on the dash, THAT provided information and if a non-steady light appeared, the exact coil could be visually determined while driving...but he still had to stop to fix it, and without the lights could have figured out which one it was by my method. And my method (the same method used by millions before me) works without meters or lights.

Everyone enjoys this hobby differently and I guess I just don't have the appreciation as some do, to tinker with this sort of stuff...carry on and have fun!

Detecting firing voltage at any particular plug would not prove that that plug was actually firing the cylinder consistently, since carbon or some other problem, like a cracked insulator, eroded electrodes, excessive gap, or any combination of these could cause intermittent or continuous misfire regardless of the firing voltage available to the plug. Two good spare plugs on board is not a bad idea.

We used to get non-functioning flourescent tubes and hook them to spark plug wires to make the tubes flash. (Split lamp cord may, or may not, provide enough insulation to keep you from flashing.)

[attachment=0]Scan1905metreoncoilboc.jpg[/attachment

It is time to put this discussion to rest.

The purpose or sharing the circuit was to show a way to identify problems with a vibrator or trembler coil. Matter fact there was a 1906/07 patent sharing a similar design.

Varley stated that the quality of current taken by a coil varies greatly according to the adjustment. To tight, large amounts of current, to loose very little current, if not adjusted properly no current and no spark.

I guess the 1906/07 use of a meter was a way to show if a coil was firing or not.

Be safe.

The patent was a setup to simultaneously increase or decrease vibrator tension for supposedly identical and interestingly, user variable current draw. The meter on the box was measuring coil current. Clever but impractical as the operator was expected to slide the bar such that the coils barely drew any current to save the battery(s) and then as power was needed, the bar could be slid the other way to increase current and subsequent spark intensity, which the patent referred to as "power". I would think that driving a car thus equipped would be more work than fun!

As for test apparatus, coil current is not a sure measure of whether or not a coil is actually firing. Anyone who has built enough coils can attest that coils can be rebuilt and set up perfectly with "ideal" (insert your desired value here) and still not have a spark that will jump a gap if there is an internal short. The old time HCCT would and regularly did, prove that out.

So it sounds like you built a device which monitors/measures average current draw of 4 coils or perhaps one coil at a time, I still don't know but it doesn't matter. If that is the case, then I follow what you're doing. I just had a hard time following what was happening.

FYI, testing if a cylinder is firing by shorting the spark plug to ground with a screwdriver is one of the most stressful things you can do to a Model T coil. The primary coil current increases markedly to very high values and is NOT advisable for that reason. Holding the points open with an insulated tool is far less stressful on the coil.

Contacting one lead of a small Neon lamp (NE2) via insulated screwdriver is a preferred indication high voltage is reaching the spark plug terminal but does not indicate the spark plug is actually firing spark in the cylinder under compression.

Mike:

It is my understanding if one has two large of a gap in the spark plug, one puts the ignition coil under a stressful condition.

Please explain how the primary circuit in the ignition coil is "harmed" by shorting the plug to ground.

Arnie

Arnie, that is correct; a Model T coil should never be operated without a suitable spark gap. The coil spark gap should not exceed 1/4" at ambient atmospheric pressure. The concern with wider spark gaps is the coil will spark internally to the coil winding causing a breakdown of insulation and possible carbon tracks which can become the path of least resistance rendering the coil unable to reliably produce spark at the spark plug under compression.

The theory is; demonstrating the ability of the coil to reliably and consistently produce spark that jumps a 1/4" spark gap at ambient pressure, the coil should be capable of reliably producing spark at the 0.025" spark plug gap under cylinder compression (45 - 60 psi).

Please explain how the primary circuit in the ignition coil is "harmed" by shorting the plug to ground.

Shorting the spark plug to ground with a screwdriver effectively shorts the coil secondary winding to ground during firing. The shorted secondary winding causes the the mutual inductance of the coil to decrease to very low value which in turn causes a very rapid rise of coil current to approximately twice the typical firing amplitude. The coil mutual inductance is dependent on the magnitude of the inducing mmf (A-T ampere-turns) produced by the winding, and if too large, will cause the iron core to saturate and the mutual inductance effectively reduces to that in air (ur~1). What that all means is the effective primary inductance drops to a very low value which results in the coil primary current rising very rapidly until the core saturates. An example may be helpful to understand this better.

Here is an example of normal Coil operation with proper spark gap. (Each vertical division is 5A, each horizontal division is 0.001 second) Coil current ramps up linearly (straight line) from 0A to 6.4A. The coil magnetic field increases steadily during this time until it is strong enough to pull open the coil points after 0.00186 seconds. The points open at this time which abruptly stops the flow of primary coil current and causes the magnetic field to rapidly collapse and induce high voltage across the coil secondary winging sufficient to generate spark across the spark gap.

Here is the same coil operated with a shorted spark plug to ground (secondary winding):
Note how the coil primary current rockets to over 10A in amplitude in just 0.0007 seconds because of the shorted secondary winding (loss of mutual inductance). Coil primary current continues to rise but flattens out due to magnetic core saturation. The coil primary current reaches 12.8A (twice the normal amplitude) before the points pull open the coil points to stop the flow of primary current and generate spark. Note that the magnetic field is plenty strong enough to open the points but the vibrator spring and attached contact has mass that takes time it to get physically moving. This test was conducted using a bench power supply not 12V car battery which can supply significantly higher current. Also consider the coil primary coil current could be higher if the coil points are not properly adjusted or malfunctioning (remember, something may not be operating correctly if the operator trying to troubleshoot coil sparking). This is why holding the coil points open using a non-conductive tool would be a better method of checking if a coil is firing spark at the spark plug compared with shorting the spark plug to ground using a screwdriver.

Mike:

Thank you for your explanation. However I do not understand the x or time axis. If each division is .001 seconds, the normal one took about .0095 seconds to build up to max current while the shorted to ground spark plug took about .0092 seconds to reach double the amperage.

Am I reading the traces correctly? If so, the time to reach max current(amperage) in the primary circuit for each case was about the same but the shorted plug resulted in about twice the amperage in the primary circuit. Is this summary correct, or am I not reading the time axis correctly?

I have been guilty of shorting spark plugs in the past as I did not realize that the amperage would increase in the primary circuit of the ignition coil doing it this way. Thanks for alerting us to that. Can you estimate what the maximum amperage the primary circuit can withstand for a short period of time?

I guess I will use my plastic comb to hold open the coil points to check for coil operation rather than shorting the plug out with a screwdriver in the future!

Arnie

Arnie

you can hold the coil points open and will not receive a shock. Nothing remotely dramatic is happening at the points and no comb is necessary. Given the average age of a T owner, that might even be considered a feature.

Arnie, The current and time scales in the oscilloscope screen capture refer to the large white boxes on the display. Each large white box is further divided in to 5 sub sections. For example, time on the X axis is 0.001 seconds (1ms) per large division and 1ms/5 = 200us per sub section within that large white box. Current is measured on the vertical Y scale and is 5A per large division or 5A/5 = 1A per sub division.

Sorry, I don't have test data on the maximum DC current the Model T coil primary can withstand. The popular lore is that a coil will overheat and tar melt out if left buzzing continuously on battery, especially 12V battery. That may be the case for poorly maintained or improperly adjusted coils.
I tested properly maintained and ECCT adjusted coil points and found they function to limit the coil current to a safe level even if left buzzing continuously for several minutes from the testing I conducted in this thread: https://mtfca.com/phpBB3/viewtopic.php? ... ly#p157543 although it is not good practice to permit a coil to buzz continuously for extended periods of time.

you can hold the coil points open and will not receive a shock.

Scott, there is sufficient electrical potential developed across operating coil points to pose a shock hazard. Weather you experience a shock or not depends upon several variables including one's skin moisture/resistance. Good electrical safety practices is to avoid contact with electrical conductors with voltage potentials in excess of 30V and use of safety guarding for voltages in excess of 50V.

Operating coil points that have been properly maintained and adjusted can develop voltages as high as 500V for very brief intervals as spark is initiated and remain at around 200V for longer intervals during the spark interval. Here is some measured data I took to illustrate.
A plastic fork with missing center elements makes a simple and safe tool for depressing the vibrator spring open on operating coil points. Just be very careful to not interfere with the normal opening of the coil points or that too can result in abnormally high coil primary current.

Apologies for the thread drift. For those interested in more details on the Model T ignition coil spark anatomy, see this thread: https://mtfca.com/phpBB3/viewtopic.php?f=2&t=22868

Note that many hit and miss engines used a "low tension" magneto with very low nominal voltage capability. However, when these were connected in series with a coil similar to a Model T primary coil and a set of mechanically operated points inside the combustion chamber, they could provide a nice spark. I doubt if the voltage would get as high as can be obtained with a step-up type coil when the points cycled, but it would get substantially higher than the highest measured voltage from the magneto absent the induction coil. The system worked well with no secondary winding, no vibrating points, and no capacitor but was not suited to higher speed engines operating at higher compression.

I don't see how holding the screwdriver to check spark on the outside of the plug, which would be creating a spark gap, or even the second or two shorting the plug would hurt the coils? Is it any different than, if the plugs were dirty, preventing any spark or any of the many other issue that could happen to plugs that would prevent them from firing? Besides, wouldn't holding a screwdriver against the plug be just allowing the current to flow to the block, only without the spark? Yes, I understand that firing the coils without a path to ground can hurt them, but I don't see shorting in this manner being the same thing.

Geeez! All I wanted to do was show a simple - Go. No Go- devise that would indicate that four coils in the T ignition system were firing or creating a pulse, a damper wave, a hertz wave. a spark.

If any one looked at the suggested article, they would see a pulses from a printed source that looks like a coloured high tech digital pulse representation. of what the - Analogue meter that indicates which coils are firing - simply shows.

My gosh life with a model t sure has become complicated....

Given that a stock T tuned by ear will go just as well as stock T tuned with a microchip.

Before closing, any one still set points with this product?

Given that a stock T tuned by ear will go just as well as stock T tuned with a microchip.

In Reality, there is a Huge difference between a Model T engine that "Runs" and a Model T engine that runs well. Properly tuned coils for equal and consistent firing Time is very often the only difference. Its difficult to appreciate just how well a Model T engine can run if you've never experienced one.

It is really hard to believe that "ear tuning" is still a thing. It was not true when Dyke's and others published it around 1910 or so, and the advice never got better.

Trying hard as I might, to agree with it, I will give you the benefit of doubt that when this advice first came out, trembler coils did not have a cushion spring or rivet, and the resulting variability they brought when comparing or adjusting one coil to another. With simply a vibrating element, if they were close in pitch, then they might have been close in amperage, but "close" is miles apart at 1000RPM. Additionally, without a cushion spring, those coils were far more problematic in their functioning over time and sometimes a very short time at that. Cushion springs and extended contact time/travel was a revolutionary change to coils and with it brought multiple variables into the audible sound a single coil can and will make when properly adjusted. A set of 4 done to amperage or TTF can have quite a variation. A set of those coils which will allow you to charge up a steep hill at will, once re-tuned by ear might at best get the grandkids to the ice cream if it's down hill all the way.

If a person believes an "ear tuned" T runs as well as a T with properly tuned coils, it can only be because they have never actually experienced the difference or were asleep in the passenger seat during the demonstration.

I have been reading his post for a good number of years, he keeps going back to Dykes and pre-1914 coil setup for examples when post 1914 coils are being talked about. I don't see how the setup/adjustment of the early coils even applies to post 1914 type? They don't even have the same amp draw between them or operating characteristics.
Take the coils out, set them up on your HCCT, clean the plugs, attach the wires, lay them on the head and see if they all spark. That meter setup will not help with a high speed under load test.

Mr. MKossor,

Do you know what RMS is and what the RMS output value is of correctly working model T Alternating Current magneto? If you do, then do you think 12VDC is the correct DC voltage to drive the Model T ignition coils if using a DC source?

R/Mark

A magneto can produce 20 plus VAC

see: http://www.mtfca.com/discus/messages/29 ... 1175535079

Do you know what RMS is and what the RMS output value is of correctly working model T Alternating Current magneto?

Yes, the RMS value of alternating current is also know as the effective value: equivalent to the same DC current that dissipates the same value of power in a resistive load.

The RMS output value of a correctly working Model T magneto depends upon the engine speed and load. That makes it difficult to determine the health of the magneto. The St. Louis Magneto tester and ECCT are both specifically designed to measure the magnetic field strength of the magneto as opposed to a particular out out voltage or current of a specific load at a specific RPM.