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jpsmith123

Wed Mar 19 2008, 09:13PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

I'm wondering, does anyone know what the typical range for the self-resonant frequency of a "HEI" type ignition coil would be?

From the few specs I've been able to find (for a few manufacturers specific parts), it looks like secondary inductances are in the range of 30 H or so, but I have no idea what the capaticance of the windings might be. If it's in the neighborhood of a few hundred pF or so, then the frequency will be somewhere in the range of 1 to 2 kHz I would think.

For straight AC drive (sinewave) I wonder what kind of primary drive voltage I could use in this frequency range without saturating the core? It would be nice to know # of turns, core cross-sectional area and Bsat, but I suppose the only way to find out is get one and look at it.

Proud Mary

Wed Mar 19 2008, 11:17PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I was unable to measure the inductance of an ignition coil with my Peak Atlas LCR meter because its high series resistance - 7K5 - made it out of the range of the instrument.

My solution was to stick the secondary in one collector leg of an emitter coupled two PNP transistor oscillator, and measure fo, which wobbled around 950Hz. Discounting the bit of extra capacitance of the oscillator circuit, I assumed that the secondary design fres was 1 kHz.

Measuring L (684uH)and R (1R4) of the primary, I discovered its time constant to be about 500us - which corresponds to a square wave of 1 kHz.

So I concluded that the ignition coil had been designed so that the secondary would resonate at the shortest dwell time, ensuring there was still enough spark power at high speed.

jpsmith123

Thu Mar 20 2008, 12:40AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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I'm not sure I understand your notation, Harry...are you saying the resistance was 75,000 ohms or 750,000 ohms? If either, that sounds way too high...by one and two orders of magnitude, respectively; or at least way too high compared to some of the "high performance" coils I'm looking at such as this one:

Here's one with only 360 ohms of resistance in the secondary (but they want a lot of money for it).

Wolfram

Thu Mar 20 2008, 12:03PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

7k5 is the common way of writing 7.5 kilo ohms, or 7500 ohms.

jpsmith123

Thu Mar 20 2008, 02:23PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Thanks. For some reason I thought he transposed the k and the 5 or something...it's been a while since I've used those abbreviations.

Proud Mary

Thu Mar 20 2008, 03:42PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

jpsmith123 wrote ...

Thanks. For some reason I thought he transposed the k and the 5 or something...it's been a while since I've used those abbreviations.

In this system, you just substitute the decimal point with the decimal multiplier K, M, G, T and so on. e.g. 2M2 indicates a value of 2.2 megohms. 4G7 would mean 4.7 gigohms. It is often used in component marking, because it uses fewer letters and occupies less space.

Tesladownunder

Sat Mar 22 2008, 01:36PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

No idea of inductance but I have just swept a frequency gen through an ignition coil and watched the output into a neon tube. For constant voltage in the highest voltage output was at 20kHz and fell off rapidly after that. It was one of the more modern type as opposed to the older Bosch can type.

8000RPM in an 8 cylinder 4 stroke is how many Hz?

TDU

jpsmith123

Sat Mar 22 2008, 07:00PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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TDU I take it that your coil is one of those with an E core?

ramses

Sat Mar 22 2008, 09:20PM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

TDU, i would guess 533hz.

8 cylinders fire every 2 revolutions since it is a 4 stroke engine, so 4 fire in one rotation. multiply that by the 8000 rpm, then divide by 60 since the 8000 was in rpm, not revs per second.

sorry if i mislead you,
ramses

quicksilver

Wed Mar 26 2008, 10:40PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I was at a junk yard very recently and found some HEI coils inside several Continentals (I believe) and pulled the best one of three. Is there any advantage to using this over other varieties of coil? Many "cans" are designed to be used with both electronic and "points" style distributors but an HEI is not as flexible: correct?

The oil in the "can-type" coil minimized internal arc I am told....would the dry HEI be more prone to this?

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