Lotus Elan

ignition ballast

PostPost by: street » Mon Apr 20, 2020 9:42 pm

I have post going regarding starting issues, ballast keeps on cropping up, i can verify my coil is standard Accu spark (will upgrade to Lucas gold), which i put on not knowing if I have a ballast system or not. If you do not know if it runs with a ballast or not is there a method of establishing this.

Im sure there are many out there who have the same question.

All help appreciated.

Many thanks
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PostPost by: Craven » Mon Apr 20, 2020 10:10 pm

As a basic check, a 12volt coil has a resistance between + & - spade terminals of nominal 3 ohms.
A coil designed to operate with a ballast resistor has between + & - spade terminal of nominal 1.5 ohms. From this the nominal value of ballast resistor is 1.5 ohms. this may be in the form of a obvious separate resistor or a resistance wire integral to the loom.
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PostPost by: miked » Mon Apr 20, 2020 10:15 pm

A ballast system has a resistor in the vincinty of the ht coil with it's associated wiring. There will be an extra wire from the starter solenoid to bypass the resìstor during cranking.
The resistor can take the form of a wire wound ceramic type. Usually in a little metal frame.
Accuspark actually do a kit with the resistor and matched coil.
As i recall, in the 70's Ford used to do a pink resistive lead in the harness for the ballast. I doubt anything like this being found.
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PostPost by: mbell » Mon Apr 20, 2020 10:23 pm

+2 would have two power wires, white/red and white/yellow, going to the coil in a ballast system. One wire, white/yellow I think, goes to the solenoid and supplies 12v during starting. The other, white/red, goes in side the car to the tacho and supplies power while running.

There would normal be a resistor connected between the red/white wire and coil if running as ballast system. From factory it was normally external to the wire but might be in the wire also.

Also possible to have both wires just connected to a 12v coil and it function as none ballest system.
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PostPost by: HCA » Tue Apr 21, 2020 8:43 am

Post a picture of the wiring on your coil, and another of the starter solenoid for a definitive answer.
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PostPost by: Bigbaldybloke » Tue Apr 21, 2020 2:29 pm

Take the wire off the coil, turn on the ignition and measure the voltage, if its about 9v you have a ballast resistor somewhere, if its 12v you do not. If 9v then briefly energise the starter and it should jump up to around 12v at the coil.
If it doesn't jump to 12v and you have a 9v coil you won't damage anything but starting may be unreliable especially if your battery is a bit down. If its 12v all the time and you have a 9v coil it probably wont last very long!

Looking at the wiring is theoretically ok but you don't know what some previous owner has done, maybe wires unused now in the harness from the starter solenoid, mine certainly did, found them taped back when doing some tidying up, still connected at the starter solenoid end.
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PostPost by: Craven » Tue Apr 21, 2020 4:06 pm

[quote="Bigbaldybloke"]Take the wire off the coil, turn on the ignition and measure the voltage, if its about 9v you have a ballast resistor somewhere, if its 12v you do not.
Not so, if the coil is disconnected there will no current in the circuit, no current no voltage drop so 12 volts all the time.
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PostPost by: Bigbaldybloke » Wed Apr 22, 2020 12:00 am

Quite right Craven, brain fade on my part, must have this virus or something.
Would need to try it with a dummy fixed resistor in place of the coil and points, so not so easy. could probably use a headlamp bulb In place of the coil and see if it’s dimmer than when connected to a known 12v supply such as the starter solenoid input from the battery.
A 60 watt headlamp bulb draws 5A so using
V=IR or R=V/I gives R of approx 2.4 ohms so not far away from coil resistance.
Probably easier to just trace the wiring, well it was a thought!
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PostPost by: Craven » Wed Apr 22, 2020 10:49 am

Change in voltage at the coil + when the solenoid is operated is a good idea, but with a points system on/off this might not too easy to see.
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