Dwell calculations

[Flatline_Racing]

Would the resistance and inductance be measured off the Primary Winding or the secondary winding?

[Blue]

I'm trying to use Bruce's formula to compute the dwell setting for my ignition coil. Here are the values for my coil.

L=9.5 mH
R=1.55 Ohm

I have input several values of I. Here are the corresponding values for T.


I_______T
(amps) (ms)

1______.85
2______1.83
3______3.00
4______4.46
5______6.36
6______9.14
7_____14.37
7.7____32

How do I decide which pair of I and T is the best to use?

I graphed it in Excel, but there is no obvious point of inflection on the curve.

And for future reference, what is the right way to put a simple chart (like the one above) into a post?

Thanks for your help and advice.

[Bruce Bowling]

I'm trying to use Bruce's formula to compute the dwell setting for my ignition coil. Here are the values for my coil.

L=9.5 mH
R=1.55 Ohm

I have input several values of I. Here are the corresponding values for T.


I_______T
(amps) (ms)

1______.85
2______1.83
3______3.00
4______4.46
5______6.36
6______9.14
7_____14.37
7.7____32

How do I decide which pair of I and T is the best to use?

I graphed it in Excel, but there is no obvious point of inflection on the curve.

And for future reference, what is the right way to put a simple chart (like the one above) into a post?

Thanks for your help and advice.

For this coil it appears to have a slow charge time. You want a primary current around 5 - 6 amps before spark, but this leads to a dwell time of close to 9ms which will limit your upper RPM. You may want to see if 4 amps (4.5ms) works for your setup..

BTW, your chart was fine

- Bruce

[Blue]

Thanks Bruce. I'll try that and post my results back to the forum.

[ajay magge]

Hi, i tried using this formula but the actual dwell time vary a lot with theoritical values do u have any correction factors for this?