Diode across coil?

[tbirdtbird]

Pete, maybe a magneto does need a cap. Won't argue. But I have worked on a lot of early mags like from 1910 and if there was a cap it sure was hidden away.....

[tbirdtbird]

I'm sure of it. Maybe one of them can give a quick synopsis that the rest of us can understand

[Tom Wesenberg]

IGNITION WITHOUT A CAPACITOR

Some of the old hit and miss engines used what was known as low tension ignition. The contact points are inside the combustion chamber and connected to a 6 volt battery and coil wired in series. When the points open a spark is created by the coil's collapsing field, and this fires the gas mixture. In this case you want a big spark across the points, so no condeser is used.

[Mike V. Florida]

Originally Posted by Tom Wesenberg

IGNITION WITHOUT A CAPACITOR

Some of the old hit and miss engines used what was known as low tension ignition. The contact points are inside the combustion chamber and connected to a 6 volt battery and coil wired in series. When the points open a spark is created by the coil's collapsing field, and this fires the gas mixture. In this case you want a big spark across the points, so no condeser is used.

Also see Wright Bros. first engine.

[MrTube]

Interesting replies from some.

Thank you all for responding. I do have an electronics backround and do understand LC circuits.

I was talking with an electrical engineer where I work about this and his opinion was the capacitor was needed but he wasn't 100% sure and my opinion was it was there only to prevent burning of the points. We primarily work with RF here in the 2.4 - 5.8 GHz range.


Looks like he was right and I was wrong.

[MrTube]

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Originally Posted by tbirdtbird

I'm sure of it. Maybe one of them can give a quick synopsis that the rest of us can understand

This may help.

http://youtu.be/6qrOoes_At8

[MrTube]

Originally Posted by Patrick L.

That extra couple feet of wire means nothing to a condenser/capacitor installed on the firewall. Electrons are pretty quick little critters. They get where want to go in less than a nano-second.
All I can say is, if you think a diode will work in place of the condenser then try it and post the results. I'd recommend having an extra condenser and set of points on hand for when you decide to drive the car somewhere though.
Plus I think about the only folks that can understand this are Charles Kettering or Nickola Tesla.

Not sure if I can agree with that statement at least not in general. Very often a fraction of an inch effects how a circuit performs.

Those squiggly lines on the PCB are most likely for timing. If you open up a PC you will find this all over. They are referred to as meanders

[tbirdtbird]

Not that critical in this case. I have run caps on the firewall in an emergency in several cars just to get going quickly

[Purdy Swoft]

Originally Posted by tbirdtbird

Not that critical in this case. I have run caps on the firewall in an emergency in several cars just to get going quickly

I agree !!! Some of the older guys did it all the time. I've had one of mine set up this way for years just for the hell of it because I( knew that I could. I didn't do it because I thought that I had to or because I thought it was the best way to go. I was shown this setup back around 1960-61 and always considered it a novelty. I probably won't be driving the car that I have setup that way to Cali-phone-ya to see Bill but it has worked for many years on my sept 29. I run the A&L condensers in the rest of my model A's except the two that run Mallory distributors.

[tbirdtbird]

http://youtu.be/6qrOoes_At8

ha ha this is a joke right

My dog ate my slide rule and i could make no sense of it.

Someone who understands it so well that they don't need equations to explain it might be able to step up and enlighten us

"You might want to click on some of the posters profiles before making a statement like that. Many of the posters have a electronic background and can quote L-C formulas in there sleep. "

My point was missed. Formulas are for engineers. For the rest of us a simple verbal explanation would do wonders.

[Purdy Swoft]

Being a common man, BS credentials never meant much to me.

[MrTube]

Originally Posted by tbirdtbird

http://youtu.be/6qrOoes_At8

ha ha this is a joke right

My dog ate my slide rule and i could make no sense of it.

Someone who understands it so well that they don't need equations to explain it might be able to step up and enlighten us

"You might want to click on some of the posters profiles before making a statement like that. Many of the posters have a electronic background and can quote L-C formulas in there sleep. "

My point was missed. Formulas are for engineers. For the rest of us a simple verbal explanation would do wonders.

No need to be sarcastic.

How about this one.

http://youtu.be/hqhV50852jA

[Mike V. Florida]

Originally Posted by MrTube

Interesting replies from some.

Thank you all for responding. I do have an electronics backround and do understand LC circuits.

I was talking with an electrical engineer where I work about this and his opinion was the capacitor was needed but he wasn't 100% sure and my opinion was it was there only to prevent burning of the points. We primarily work with RF here in the 2.4 - 5.8 GHz range.


Looks like he was right and I was wrong.

You weren't wrong you did not have the whole story.

I spend many years at Comsat in CT., Directv latin america in Fl, in the uplink centers. C,L,KU bands.

[dlfrisch]

For a lot of years, I taught electrical trades - theory and electrical construction. L = symbol for induction and C= symbol for capacitance (LC). A quickie.... we used to use capacitors across some traffic light controller points to protect them from to much arcing and opening that special circuit. We did use diodes because we didn't need or rely on any residue currents. Like most of us - they are older controllers and not too may around yet. Most systems are solid-state and real reliable. (glad I'm retired and play with my Harley and my "A" now! )
As per Wikipedia -
An inductor-capacitor circuit (LC circuit) is an electric circuit composed of inductors and capacitors. A second order LC circuit is composed of one inductor and one capacitor and is the simplest type of LC circuit.
A second order LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. The circuit can act as an electrical resonator, an electrical analogue of a tuning fork, storing energy oscillating at the circuit's resonant frequency.
LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal. They are key components in many electronic devices, particularly radio equipment, used in circuits such as oscillators, filters, tuners and frequency mixers.
An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance. Any practical implementation of an LC circuit will always include loss resulting from small but non-zero resistance within the components and connecting wires. The purpose of an LC circuit is usually to oscillate with minimal damping, so the resistance is made as low as possible. While no practical circuit is without losses, it is nonetheless instructive to study this ideal form of the circuit to gain understanding and physical intuition. For a circuit model incorporating resistance, see RLC circuit.

[PC/SR]

Ok,I'll try a very cursory and much simplified explanation:
When the points open, current continues to flow into the condensor (The "C")until it is fully charged. Because of the component design and matching of the condensor and the coil (the "L") the current oscillates back and forth at the speed of light until the voltage in the primary circuit builds up to about 4-500 volts. This voltage is sufficient to induce enough voltage out of the secondary to jump the spark gap, say 7-10,000 volts.
Why the voltage builds up from the original 12 volts has to do with the properties of electricity in a tuned, resonant (LC) circuit (essentially a short circuit) which allows voltage buildup, and the extraction of energy from the magnetic field of the coil. Try this link. http://www.fas.harvard.edu/~scphys/c...E1b/E1b_3b.pdf

[hardtimes]

I do not have a degree in electronics, and think that most here do not either. So, with my little understanding of DC auto type electricity, I like pictures to help with my meager second order LC circuit understanding. If you have ever observed an oscillascope connected to a running auto electrical system, the 'picture' given of this LC circuit in action....really helps to understand some of what's said here. Do not know if this old machine even applies to current(ha..yeah intended,eh) auto systems...even tho they are still DC electricity ?
And, if you've never heard of and/or seen one of these old auto analytical machines in action, I recommend it. For those with often asked question...such as, how do I determine what is going/gone wrong (if anything) with my ignition system,i.e.-condenser, points,coil/ spark plugs, etc..., get a guy who has an scope, have him hook it to your A / whatever old car with pts/plugs/cond, and have him explain what it is that you're seeing.
Pictures are good for lighting up and completing YOUR circuit !!
Oh, btw, it will show you why / how condenser functions as a NECESSARY part of this system.

[hoop98]

Electronic Ignitions don't seem to need the capacitor across the transistor when it opens. ?



The backward diode will reverse conduct and clip the primary voltage at 600 to protect the circuit.

[emf]

Points need a capacitor, in part, because the switch (points) is mechanical and the capacitor helps reduce metal migration. The mosfet circuit above is solid state with no moving parts, hence no metal migration...

Frank

[hoop98]

Originally Posted by emf

Points need a capacitor, in part, because the switch (points) is mechanical and the capacitor helps reduce metal migration. The mosfet circuit above is solid state with no moving parts, hence no metal migration...

Frank

More than metal migration, you won't get a high voltage spark without the cap/cond. You will get a spark across the points. If you look at a grounded plug outside the combustion chamber you will see a weak yellow spark with no snap. With the condenser you will see a snappy blue spark.

Proper sizing of the condenser reduces metal migration, too much or too little capacitance will change which point gets the buildup.

[Mike V. Florida]

Originally Posted by hoop98

Electronic Ignitions don't seem to need the capacitor across the transistor when it opens. ?



The backward diode will reverse conduct and clip the primary voltage at 600 to protect the circuit.

The schematic is not meant for use in a car