Ignition coil resistance values

[Howard Wright]

Hi All

I’ve tested the resistance of two 6volt coils I have and obtained the following resistance values ( both coils give similar readings).

Between + and - terminals….. 1.1 ohms
Between - or + and HT terminal…. 8.8k ohms.

I believe from research that the 1.1 ohms is a little low?  Can anyone please confirm and tell me what effect this low resistance would have?

Cheers

Howard

[John Cornforth]

Hi Howard

In the past I have measured a standard Austin Seven coil as being nearer to 1.5 ohms when cold. With 6 volts applied, this gives a steady current of 4 amps. Because the points are only closed for about 50% of the time, the average running current is about 2 Amps. This is an approximate value, as coil temperature, battery voltage and inductive effects at higher RPM will all affect the exact value.

You possibly have "sports coils" which were designed for a higher primary current and greater HT output. The only downside is that points wear is increased, and there is more load on the A7's feeble dynamo.

The other possibility is that you have a little error in the resistance measurement, as accurate measurements are more difficult at low resistances. Maybe a quick check on a borrowed standard coil would help for comparison ?

[Chris KC]

My notes say 0.4 - 2.0 ohms is an acceptable range.
I understood all coils are "sports" coils these days.

[Bob Culver]

Seems about right. Digital meters read low ohms well. Are the coils labelled 6v? There are similar but not always identical 12v coils intended for use with a ballast and low reistance and low resitance 12v coils intended for electronic ignition applications.

[Howard Wright]

Thanks, John Chris and Bob

One of the coils is an old one that came with the car, the other new from the green spark plug co. I’m measuring with a digital meter and getting consistent repeat results.

It seems the values are within the acceptable range and the car is running well so I think both coils are useable.

I must have a fairly “dirty” (electronically) engine which causes interference with the LED lights. I have a .22 microFarad ignition condenser on the +ve coil terminal which seems to solve the LED flickering but I wanted to check in case anything else was causing problems. 

Any advice on suppressing interference gratefully received  .

I guess A7 engines are prone to electrical noise.

Cheers

Howard

[Roland Alcock]

I gave up on my LED bulbs. They were flickering or not lighting. 

I put it down to insufficient electricity due to voltage drop by the time the juice arrived at the light. 

I could overcome this with meticulous attention to the wiring or using inexpensive little voltage converter pcbs which filter out the noisy A7 electrical noise. 

It was easier to revert back to normal bulbs as I hardly ever drive at night. 

I also have another (unproved) theory that 6v led bulbs are really 12v ones which don’t work very well below 5.75 volts. 

Roly


————-
It seems the values are within the acceptable range and the car is running well so I think both coils are useable.

I must have a fairly “dirty” (electronically) engine which causes interference with the LED lights. I have a .22 microFarad ignition condenser on the +ve coil terminal which seems to solve the LED flickering but I wanted to check in case anything else was causing problems. 

Any advice on suppressing interference gratefully received  .

I guess A7 engines are prone to electrical noise.