[Moses]

I loved Roger's video on calculating the self capacitance and self resonant frequencies of an inductor.  I tried to duplicate this in order to measure these values on an oil filled ignition coils primary and secondary. These are autotransformers so the non exposed end of the secondary is connected to the primary (usually at the negative primary terminal).

I can't seem to get it to work well with this inductor, should I be using a smaller resistance?  I am using a 10 meg ohm resistor pulled out of a microwave oven capacitor.

Thanks for any help you guys can shed on this! I am using a Hantek DSO5202P 200mhz two channel scope and a FeelTech FY6600-60M signal generator.

[Roger@kainkalabs]

AFAIK the inductance of ignition coils are quite high and so the SRF is very low.
So put the oscilloscope trace first to 100ms/div and see if you get at least the beginning of a sine-wave.
You can also use smaller resistors like 1 Megohm because of the very low frequencies.
An ignition coil has a primary and a secondary coil.
Try both separately (and measure beforehand if they are still OK with a multimeter in ohms-mode).

Roger

[Moses]

AFAIK the inductance of ignition coils are quite high and so the SRF is very low.
So put the oscilloscope trace first to 100ms/div and see if you get at least the beginning of a sine-wave.
You can also use smaller resistors like 1 Megohm because of the very low frequencies.
An ignition coil has a primary and a secondary coil.
Try both separately (and measure beforehand if they are still OK with a multimeter in ohms-mode).

Roger

Hello Roger, 

Thanks for the reply!

I have only tested the primary of the coil so far because my current LCR meter only goes up to 20 Henries (The primary is 5.27 mh and the secondary is about 49h (but I can't test it with that meter)).

(The ignition coil has one side of the secondary connected to the primary at the negative terminal of the primary. It's an autotransformer). 

Before I saw this reply I changed my probe to 1x and I now get this which looks good.  Only the frequency measures to 370khz no matter what input frequency I set my square wave to.  That seems high to me, but maybe fine. I swept the coil in that vicinity with a straight sine wave and no resistor and I do seem to get the highest voltage in that vicinity.  

I am experimenting with stepping down high voltage static electricity off my quadruple Bonetti machine (not to use the machine as a generator, I know these machines are like 1% efficient at most, but rather to do a proof of concept for harvesting high voltage static electricity off the surface of an aircraft.)  I am using the ignition coil(s) as a step-down transformer(s), and I am operating it sort of like a reverse spark gap tesla coil.  I found as can be seen in my "Stepping down ultra-high voltage" YouTube video, that the only way to get efficient energy transfer is to operate in resonant mode like this, so now I want to maximize that by matching the old secondary resonance frequency with the old primary (remember I am running the coil in reverse).  

https://flic.kr/p/2ktbuyN (Here is the waveform I get with the probe in 1X).
https://flic.kr/p/2ktb7c7

[Roger@kainkalabs]

Of course the frequency of the square wave doesn´t change the resonant frequency. It only serves to start the resonance repeatedly.
The SRF depends on the inductance and the self-capacitance:
https://de.wikipedia.org/wiki/Thomsonsch...sgleichung
Good luck with your experiments

[Moses]

Of course the frequency of the square wave doesn´t change the resonant frequency. It only serves to start the resonance repeatedly.
The SRF depends on the inductance and the self-capacitance:
https://de.wikipedia.org/wiki/Thomsonsch...sgleichung
Good luck with your experiments

Thank you!