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MG Midget and Sprite Technical - Coil ohms?

How do I measure the ohms(?) of a coil?

I have a digi multi meter, but I'm unsure how to use it to do the above! I also understand that the pertronix thingy prefers 3 ohms or more, is that correct?

Thanks
AndyB (looking less like I know what I'm doing, with each passing day!)
a borris

I take it we're talking primary resistance. A coil has two - primary and secondary.

Put the digital voltmeter onto resistance measurement (Probably marked with the ohms symbol). There will be several resistance ranges to choose from and you want something like 0 to 10 ohms so that 3 will be a reasonable way up the scale. Then to measure the primary resistance put one probe onto each of the coil's spade terminals. To measure the secondary put one on the case of the coil and the other down the HT lead hole.

Haynes tells you what these should be for a standard setup. I know nothing of a Pertronix.

Ant
Ant Allen

Thanks Ant.

AndyB
a borris

Andy

as Ant says measure the resistance between the LT terminals, this will give you the coil resistance the Pertronix requires

A quick delve into my old AA patrol manual give these figures for various "types" of coil (Not specific to a Joe Lucas or a Bert Ducellier or Harry Bosch etcetera)

12 volt basic coil (unballasted) 3-6 ohms @ 20Kv output
12 volt ballasted coil 1.2 - 3 ohms @ 30Kv output
12 volt electronic ignition 0.3 ohms @ 60Kv + output

the little white book also gives the secondary windings as 3,000 to 14,000 ohms regardless of system

The secondary windings are measured betweeen the king lead post (the middle bit) and the negative LT terminal
This is because the two share a common ground inside.

A further note whch is useful reads

resistance can only be measured with the component out of the circuit, so disconnect the wires to the coil before you test the coil


HTH
Bill sdgpm

Measuring such low ohmic values should always be performed by knowing the lead resistance and subtracting it from you measured value.

Before you measure the coil put the leads together and note their resistance can be 1 or 2 ohms. This figure should be subtracted from you final result so that you are only measuring the coil resistance.

As Bill states it depends on the coil what the resistance will be. From out point of view we either use the ballasted coil 2 or 3 ohms or the non ballasted which will be between 3 and 6 ohms
Robert (Bob) Midget Turbo

Basically Andy, approx 3 ohms is fine for what you need.
Cheers John
JOHN HALL & JULIE ROBERTS

Bill wrote:
> The secondary windings are measured betweeen the king
> lead post (the middle bit) and the negative LT terminal
> This is because the two share a common ground inside.

I didn't know that. I've had trouble before now when my coil came loose and the AA man cleaned up the bracket mounts and tightened it all up and it worked again. That wasn't a Spridget.

Ant
Ant Allen

This thread was discussed between 28/05/2009 and 29/05/2009

MG Midget and Sprite Technical index

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