Bypass ballast resistor

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Graham Martin
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Joined: Tue Oct 22, 13 10:32 am

Bypass ballast resistor

Post by Graham Martin »

Hi can someone tell me if I can fit a coil with built in resistor and bypass stock one or will it cause problems
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Re: Bypass ballast resistor

Post by Dave999 »

depends on what you use as your igntion "swicther"
with points no probs

with mopar electronic probably no problem, cant guarantee the quality of the igntion box anymore... the box runs on 12 volts so should be fine

really depends on the resistance of the primary of the coil you choose, suggest one with 1.5 to 3 ohms

depends on your aims

what are you aiming for.... just removal of a device (the ballast) that will eventually fail......? perfectly reasonable aim....

I ran a bosch blue coil (air cooled VW favorite) with the ballast bypassed and a points igntion on my 6 cylinder... it may limit rpm range on a v8 but if you never go more than 5000 rpm i think it would work

currently i use a 4 pin HEI module (GM delco hella BW etc) and a lucas DLB198 (jag 6 and 12 with electonic igntion 1980s) with the ballast bypassed. its cheap it works and the jag v12 used a very similar igntion module so good for v12 jag good for 6 cylinder aussie engine

basic premis is

the coil primary resistance needs to be appropriate for the thing you use to switch the coil off and on, so you don't burn it out

HEI uses a low resiatnce primary 0.5-1.3 ohms and the module is expecting to supply 4- 8 amps

a 12 volt coil like the bosch above will have a primary resistance between 1.5 ohms and 3.5 ohms. its designed for a small 4 cylinder car with no ballast.

the coil has resistance designed in, to limit the current to 2-3 amps which is what a set of points or an older style electronic module expects to switch i.e low enough to give them some life, but high enough when combined with the correct coil to make a spark.

the standard mopar coil was just like the 12 volt bosch above but had most of the resistance removed and put in a seperate ballast resistor instead.
the coil could be used at 12 volts for a few seconds and at 8 volts for general running

at 12 volts it would allow excessive current/ amps to flow but at 8 volts ( with 4 of the 12 available volts used by the ballast) it allowed 2-3 amps to flow in the coil and through the device that is used to switch it off and on.

mopar coil was only run at 12 volts for the few seconds you were starting the car... i.e there was a 12 volt feed that bypasses the ballast that switched on when you click the key to start...

choose sensible coil, byapss the ballast and gap the plugs at standard and see how you go. big huge gaps not necessary.... you need just and spark power, its a case of diminishing returns really, a big 50KV coil for £150 does not make any more HP than a standard one if both reliably spark the plug... big red and shiny is just for braggin rights. nice matt black coil lasts longer by running cooler.

serious racing or running on LPG or massive turbo or massive high 12+:1 static CR different kettle of fish

the main drive for a ballast set up was the "bigger spark" at starting...good for v8 cars designed to work in -15*C to 40+ *c when equipped with the smallest lightest cheapest car battery they could get away with as standard....

your battery is unlikely to be so weedy...these days, and you live in a reasonable clement climate

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Graham Martin
Posts: 129
Joined: Tue Oct 22, 13 10:32 am

Re: Bypass ballast resistor

Post by Graham Martin »

Thanks for reply and great detail cheers
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