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Low Tension Ignition Explained -or- The Geek Strikes Again!

Elden DuRand

In Memory Of
Age
78
Last Subscription Date
12/22/2017
Group:

Again, having nothing better to do, yhis morning I went to the garage and did a study of low tension ignition using a storage oscilloscope.

If YOU'VE got nothing better to do, you might take a look at it. Then again, it's prolly VERY boring. I won't take offense if you fall asleep and take a nose-dive into your keyboard. Just don't hurt yourself! :)

DIRECT LINK:
http://home.cybertron.com/~edurand/Otherstuff/LT Scope Pictures/LT Scope Pictures.html

OR - you can go to my webpage below, click on "Other Stuff", then to "Low Tension Ignition".

Ain't indolence and bone-idleness great! :) :)

Take care - Elden
http://home.cybertron.com/~edurand
 

Attachments

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
Getting to the basics, Piston goes up the bore slowly, igniter goes click, points open, points flash with spark, stuff in cylender goes BOOM :eek: and the piston thingy makes a quick trip down the bore :cool: At least thats what its supposed to do :crazy: Thanks for the technical stuff Elden!
Andrew :D
 

Ken Majeski

Subscriber
Last Subscription Date
12/10/2019
300 Volts..... :eek: No wonder it's so Easy to get Zapped when messing with Low Tension Ignition... :(
 

VicP

In Memory Of
Age
86
Last Subscription Date
07/05/2010
Thanks for sharing the schematic and tools. Pictures worth a thousand words
Vic
 

Dick Welty

Registered
Elden,

You have the technical experience and equipment. I have not used a scope since 1963. I agree with your explanation.

You can correct me if I am wrong but I explane it this way.

As the current builds in the coil it is resisted by the inductance of the coil which resists the build up of the magnetic field thus slowing the process.

After the magnetic field reaches it's maximum strength due to the fact that the points are closed for a relatively long time.

The points then open causing the magnetic field to collapse at a very high speed.

If there weren't the inductive resistance the collapse would occure at the speed of light. 186.000 miles per second.

The fact that the inductive resistance to the collapse slows the collapse down is the reason that the current generated by the magnetic field cutting thru the coil is of a relative long duration.

The reason that the voltage is higher than the original voltage that was applied is that the speed of the collapse is so high.

I exlpain that by saying that if you spin a generator at 100 rpm and get 6 volts just think how many volts you would get if you could spin it at the speed of light.

The inductive resistance of course slows the speed of the collapse down significantly but it still happens very quickly.

The reason that a good fat spark is generated at the points is the fact that as the points start to open they are very close together and the spark starts to jump a very short distance as the distance is getting bigger the voltage is building and is now ionizing the air or air fuel mixture.

Ionized air is created when a voltage across an air filled space is sufficient to cause the electrons in the air molecules to allign them selves so as to allow current to pass. This is we see when lightining strikes either between clouds and the earth or some times between clouds.

Ionized air is a much better conductor of electricity than un-ionized air. thus allowing the total distance of the spark to increase untill either it becomes to large a distance for the voltage to sustain or the voltage drops below what is required to sustain the spark.

I also give an illistration of ionized air by describing a jacobs ladder as seen in the old Frankenstine movies where the spark climbs up the two electrodes.

The spark starts where the electrodes are close together and as the air is ionized it is also heated up causing it to rise.

As the ionized air rises the electrodes get farther appart untill the distance that they are appart so great that even though it is ionized it has a greater resistance than the smaller air gap where the spark started originally.

The spark then jumpes the smaller gap and the process is repeated.

If in fact the jacobs ladder was turned up side down the spark would stay at the closes point which would now be the top and would arch slightly upward in the middle.

I receintly purchased an original coil that was used on a 1907 Hicks engine. It weighs about 6 pounds and really puts out a spark when hooked up to a small 6 volt wetcell and an igniter.

I hope that this explanation is accurate and will help others to explane the process to people at engine shows.
 
D

Dennis

Guest
Thanks Elden, for the explanation of low tension igniton. I often wondered about the voltage output.
 

Elden DuRand

In Memory Of
Age
78
Last Subscription Date
12/22/2017
Dick Welty said:
You can correct me if I am wrong but I explane it this way.

As the current builds in the coil it is resisted by the inductance of the coil which resists the build up of the magnetic field thus slowing the process.

After the magnetic field reaches it's maximum strength due to the fact that the points are closed for a relatively long time.

The points then open causing the magnetic field to collapse at a very high speed.

If there weren't the inductive resistance the collapse would occure at the speed of light. 186.000 miles per second.

The fact that the inductive resistance to the collapse slows the collapse down is the reason that the current generated by the magnetic field cutting thru the coil is of a relative long duration.

The reason that the voltage is higher than the original voltage that was applied is that the speed of the collapse is so high.
In the above faulty post, in the first picture, you see the waveform generated when there is no capacitor across the coil. The collapse of the field is VERY fast and all of the energy from the collapse goes into arcing at the points. This works very well for an ignitor system but just produces a weak spark and burns the points on a high-tension coil.

The second picture shows the damped oscillation that is caused by the combined inductive and capacitive reactances. This oscillation frequency is close to the natural frequency of the secondary thus making the high-tension coil resonant. The turns ratio and high Q factor of resonance is what makes the coil put out such a high voltage.

Please forgive me if I seem to be nit-picking but, after all, I'm just a Nerd! :)

Take care - Elden
 
Last edited:

Mike

Subscriber
Age
75
Last Subscription Date
12/14/2019
Elden,
What is the comparison between using a 6 vdc battery versus a 12 vdc battery? Is he discharge curve significantly reduced with the 6 volts?
 

Dick Welty

Registered
Elden,

I am confused. I thought that this thread was about Low Tension Ignition and not High Tention coils with primary and secondary coils.

I acknowlege that you are the expert so please clearify where exactly my low tension ignition logic goes astray.

Thanks,
 

Elden DuRand

In Memory Of
Age
78
Last Subscription Date
12/22/2017
Mike said:
Elden,
What is the comparison between using a 6 vdc battery versus a 12 vdc battery? Is he discharge curve significantly reduced with the 6 volts?
Mike:

Generally speaking, when you double the applied voltage, the curve remains the same but the discharge voltage roughly doubles, the energy dissipated by the ignitor points is roughly doubled and the life of the ignitor points is roughly halved.

Hope this helps.

Take care - Elden
 

Elden DuRand

In Memory Of
Age
78
Last Subscription Date
12/22/2017
Dick Welty said:
Elden,

I am confused. I thought that this thread was about Low Tension Ignition and not High Tention coils with primary and secondary coils.

I acknowlege that you are the expert so please clearify where exactly my low tension ignition logic goes astray.

Thanks,
Dick:

I apologize for being obtuse yesterday. I had just gotten back from a trip and was tired as you can see from my wierd string of posts on the subject. :eek:

For low-tension induction ignition, you are correct in that without a condenser, the field collapses much faster than with one. This makes the ignitor points arc many times during the short discharge of the inductor.

I think I was trying to explain that the fast collapse of the field does not make the high-tension induction coil (transformer) work better because there is no resonance and the energy is dissipated in the points (big spark) and not transferred to the secondary.

I don't have a function generator here so I can't put an auto ignition coil to test to find out what the resonant frequency of the secondary is. If I could do that, I could adjust the value of the condenser across the points to maximize the output from the secondary.

Thanks for your comments.

Take care - Elden
 

jimdes

Registered
yeah,thats the way it work. pure magic. the thing to keep in mind, is that youve got an oscilatinbg ac circuit here. transformers dont work on ac. so, what your condenser does is act like a spring. you ground your primary, the field collapses,bango the condenserstarts sucking up the currant,spits it back (decreasing frequency ac ) makes your coil a tranformer. boom youve got 15000 volt coming down those spark plug wires.
 

Harry

Administrator
Flash battery across low tension coil.

Blue flame = good coil. :)

Red sparks = bad coil. :mad:

Hold fingers across coil at same time.

Get knocked across room = good coil. :eek:

No jolt = bad coil. :uhoh:
 

Orrin

Registered
Last Subscription Date
06/25/2014
I've assembled a simple teaching aid consisting of a single 1.5 volt cell, an inductor (coil), a normally open switch and a neon lamp that requires about 90-Volts to "fire" (illuminate).

Basically, it is a simple low tension ignition system. When the switch is briefly closed, then opened, the neon lamp lights up. In other words, a 1.5 Volt "battery" causes a 90-Volt lamp to light.

It is a simple, but effective, way of illustrating "inductive kick."

Regards,

Orrin
 
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