Ballast Resistors

[Knockout]

Hello everyone,

I’ve just joined the forum and thought I’d say hello. I’m a bit of long-suffering builder (for various reasons) but if I tell you that I’m building a SYLVA striker I guess you’ll know just how long it’s been! I’m just getting back into the build now and about to make a final effort to finish the project. Anyway, if you don’t mind I have a question on ballast resistors and would appreciate your thoughts...

Basically, should I include a ballast resistor in my ignition circuit? From the research I’ve done I think that I should be fitting one as I have a 1.5 Ohm coil. But I’m not sure whether it would be just better to fit a 3 ohm coil and leave the resistor out. Am I likely to have starting problems if I go down this route as I understand the ballast resistor (well bypassing it) helps improve the spark for starting? What do people recommend?

By the way, the engine is a 1700cc crossflow currently still fitted with points (though I’m planning to fit an Aldon ignitor soon).

Cheers,
Chris

[MartinClan]

Originally Posted by Knockout

Hello everyone,

I’ve just joined the forum and thought I’d say hello. I’m a bit of long-suffering builder (for various reasons) but if I tell you that I’m building a SYLVA striker I guess you’ll know just how long it’s been! I’m just getting back into the build now and about to make a final effort to finish the project. Anyway, if you don’t mind I have a question on ballast resistors and would appreciate your thoughts...

Basically, should I include a ballast resistor in my ignition circuit? From the research I’ve done I think that I should be fitting one as I have a 1.5 Ohm coil. But I’m not sure whether it would be just better to fit a 3 ohm coil and leave the resistor out. Am I likely to have starting problems if I go down this route as I understand the ballast resistor (well bypassing it) helps improve the spark for starting? What do people recommend?

By the way, the engine is a 1700cc crossflow currently still fitted with points (though I’m planning to fit an Aldon ignitor soon).

Cheers,
Chris

If you are using good old fashioned points without out any electronic assistance you will almost certainly need a balast resistor and matching coil to assist with starting. The resistor is shorted out when the engine is cranking so you get a nice fat spark. After the engine has started the resistor becomes part of the circuit again to prevent the coil from overheating.

Robin (Old enough to remember what points look like lol)

[Knockout]

Cheers Robin, I figured it was something like that.

When I originally wired the circuit I did actually wire a resistor in to the circuit but it got very hot (like glowing red hot) whenever the ignition was switched on. I decided this probably wasn't a good idea and so removed it. Subsequently I managed to burn out the carbon bush in the top of the dizzy cap. Now I look back on it, I'm wondering if I managed to wire the ballast resistor in parallel rather than in series with the coil.

How hot do ballast resistors normally get? It was made of a ceramic material so I guess its deigned to take some heat??

Chris

[MartinClan]

Hi Chris

I can't remember what resistance a typical ballast resistor is now - but yes - they can get hot. I seem to remember the one I used was quite large (like about 5 cm long) and it had a mounting plate that you bolted to something to help dissipate the heat. Mind you that was 20+ years ago and my recollection is a bit vague now!

Robin

[Knockout]

Cheers Robin. Yeah the resistor I have is a similar size - I just thought that it was strange that it should be so hot all of the time. Anyway, I guess I should re-introduce it to the circuit. Thanks again...