coil

[Fortyfiver]

Hi All
I am replacing the intermotor coil and have bought a viper 12 volt ballast coil upon checking the voltage to the coil it reads 10.5 so I assume the ballast has been bypassed, so can I still use the ballast coil or not, i have a piranha electric ignition fitted
Thanks for any help
Alan

[StagJonno]

Was the engine running when you took the voltage reading? If not, then you can't draw too many conclusions about whether or not the ballast has been bypassed. The ballast only drops the voltage when current is flowing and if the electronic ignition isn't allowing current to flow through the coil you'll see pretty much battery voltage..

If the Intermotor coil was working before, easiest check to do is to measure the resistance across the low voltage terminals and do similar with your new Viper coil (disconnected, of course). A ballast-type coil will have a resistance of approx 1.5 ohms, whereas an unballasted-type coil is approx 3 ohms. Note, as you're measuring pretty low resistances, worth checking the resistance of your test leads by putting the 2 probes together. Deduct the resistance of your leads from what you measure at the coils.

A ballast-type coil run at full battery voltage will have a pretty short life due to overheating.

[Fortyfiver]

No the engine wasn’t running will put the original back on and try it, I have no idea how to test for resistance, any advice?
Alan

[sujitroy]

disconnect the coil completely. get a digital multi meter and set it to resistance. first connect the leads of the multi meter together measure the resistance of the leads. then connect the same two leads to each terminal of the coil. measure the reading. then take the first reading and subtract it from the 2nd reading. YouTube is a great help.

[Fortyfiver]

This is the meter i have I’ve never used one before where do I set it to, give me a piece of gold and i can make an engagement ring but this is all new to me
Alan

[marshman]

Set it to 200 on the "Ohms" range - Greek symbol Omega - as indicated by the red arrow in the pic.

As others have said before measuring short the two test leads together and note the reading - probably 0.3 Ohms or something close. the measure directly across the coil terminals - make sure there are no wires connected to the coil. Note this reading. Subtract the first reading from the second reading and you will have the coil resistance in Ohms.

Roger

[Wheelz]

My method to test if ballast is in-circuit and working is to make sure current is flowing through the ballast and the coil as follows:

1. Temporarily short the coil NEG to chassis.
2. Switch on ignition and measure the voltage at the coil POS.**
3. If the voltage read approx half battery volts ie about 6 volts then the ballast and coil is as expected.
4. If the voltage reads battery voltage ie approx 12 votls then the ballst has been bypassed.
5.If the voltage reads about 9 volts then possible the coil is a non-ballast type.
6. Remove the temporary short.

** All voltages to be be measured with respect to chassis.

[Fortyfiver]

Deducting the 0.3 from touching the two leads together i have 1.0 on the old coil and 1.3 on the new one. I’m changing the coil, leads rotor arm and dizzy cap as the car suddenly died and had to be towed home, the breakdown guy said it’s a very weak spark from the coil so I’m starting there
Alan

[Fortyfiver]

Wheelz that was how i did it and got 10.5 volts
Alan

[Wheelz]

Wheelz that was how i did it and got 10.5 volts
Alan

With a 12V battery voltage, you should get about 8V if the coil was non-ballasted, and 6 volts if ballasted. So unfortunately 10.5 volts doesnt make much sense but it seems something is wrong unless the battery was 10.5 volts?

[Fortyfiver]

I’m getting 12.5 at the battery. I’m going to reconnect the original coil and start it as it does start but runs badly and check the voltage again. I assume when running you put the meter on the plus and to earth?
Alan

[Fortyfiver]

Just started the car I’m getting 13.5 with the car running on the plus with the meter grounded on the body and did the static test as per instructions and got 11.5 volts and 12.5 at the battery. It did start easy, I will investigate more in the winter but for now should I get a non ballast coil or stick with the new ballast one I bought
Alan

[StagJonno]

Personally, I'd repeat the tests using the new coil. I'm with Chris in finding the results from your earlier tests puzzling and inconclusive. Testing with the new coil may give some clearer pointers.

[Fortyfiver]

Will do, I’m assuming that it was all changed for the piranha ignition Thanks for the help
Alan

[MikeParker]

Wheelz that was how i did it and got 10.5 volts
Alan

Alan,
One way to get that voltage is to have a coil that doesn't need a ballast (i.e. a higher resistance, 12V coil) and have the ballast in circuit.
So you may have a 3.8 ohm coil (12V).
Mike