Why bypass the resistor wire?

[WhatTheFisaMOT?]

Hey all,

I know that a common mod to do is to bypass both the resistor wire and wire off the starter and just use a 3ohm coil with a direct feed from the fusebox, but I was wondering what is the benefit of this, because you lose the hotter spark for cold starting? Is the resistor wire unreliable? Would using an external block type resistor be better?

Thanks, Lukasz

[Jon Tilson]

Only because the bypass feed comes from a rather wobbly small terminal on the starter solenoid and then
via the gearbox loom connector plug, both are good places for it to go awol, which means your car won't start.
With a 12V nominal coil and electronic ignition there is no issue....

Also the 6V coil feed is not a good supply feed for the electronic ignition.

Jonners

[soe8m]

Not using a ballasted system is indeed degrading your ignition system. When all connectors are clean it works perfect. The only better option is to use an external resistor because due to time the original resistance wire gets unreliable.

The route of the bypass wire is the same as the starter wire. If one of them is wobly or dirty the only wire that causes a non starting vehicle is the starter wire itself. Not the bypass wire.

Starting at 12v on a 12v coil is the same as starting with a ballasted system without the bypass. Same spark but without the benefits of a ballasted sytem.

So keep it ballasted is the best.

Jeroen

[Jon Tilson]

Jeroen is for once wrong....

The small terminal at the solenoid is weak. I have had several cases where a car spins happily but wont fire or almost fires as the cranking stops....and its why I go 12V coil now and unballasted on most of my slants....

When its working right though I accept the ballasted coil gives a silghtly fatter spark, but electronic ignition makes
up for this. Its also a bit kinder to the condensor in a points system.

Jonners

[soe8m]

And what happens with the spark if you replace your 30 years old ballasted coil by a new ballasted coil instead of a new 12v one?

Jeroen

[Jon Tilson]

If you have a bad contact at the starter motor it will make no difference...

Jonners

[tinweevil]

I agree with Jeroen in the the OE setup is superior. I agree with Jonners that the oe wiring is weak (so maintain it). Britpart ignition works fine with OE voltages, mine has done 28,000 miles so far.

[soe8m]

If you have a bad contact at the starter motor it will make no difference...

Jonners

You are saying that a ballasted system without bypass has a weaker spark than a 12volt coil on 12v. That is not true.

Starting with a ballasted system less the bypass is the same as starting with a 12v coil. When you have almost no spark when starting at a ballasted sytem you have a deffective or a wrong (12v) coil fitted.

Lots of people do fit A coil and most of the time a wrong one. A 12v coil on a ballasted system causes a permanent weaker spark. A ballasted coil on a 12v system does cause permanent a bigger spark but due to the bigger current electronic ignitions can frie. Inferiour coils can also frie due to the bigger current what goes through. Good old points with fiber will last less and new aftermarket ones with plastic can even melt the plastic after 10 minutes running.

A 6 volt coil on a 6 volt car does also start and run so a ballasted coil with a ballast resistor does also start and run. The advantage is that you CAN use a bypass that puts during starting 12v on the coil so a bigger spark when starting.

The best ballasted coil is a red bosch one. Lucas coils are not that good and a lucas sports is even not as good as a standard bosch. if you electronic ignition can switch low resistance coils you can use a red bosch. These can handle easy the 12v current and if you ignition is up to it, like the 123 you can run permanent 12v on a red bosch ballasted so have the advantage of a very big spark all the time.

Years ago i did test on an ignition tester various coils, makes and ages. Lucas were one of the least performing ones.

If you don't like to use the starter connection for the bypass you can add a 5 pound normal automotive relay for the bypass. That is what for example all Jags have from 1970-

Jeroen

[xvivalve]

As the OE solenoid end caps are no longer available, the reconditioned starter motors I supply have a close match which has two normal sized fishplate connectors rather than one normal and one small, giving a much improved connection.

[Jon Tilson]

What you say about fitting incorrect coils is true Jeroen but the point of a ballasted system is to get a bigger spark when the ballast is bypassed for starting.
If you dont bypass the ballast a 6V nominal coil will produce a weaker spark when the voltage drops to about 10-11V during cranking. This is why the spark is weak
when the terminal connection at the starter solenoid that feeds the bypass breaks down.

An electronic ignition should always be fed from a 12V supply. If you feed it from the + lead of a 6v coil it will not trigger reliably.

Jonners

[soe8m]

First an electronic ignition must never have it's feed on coil plus. That is a very unstable feed because of the pulsating current through the coil. The best is at the fusebox.

Jonners you are wrong. A ballasted coil with the resistor has the same spark as a 12v coil on 12v during running.

Both setups have the same voltage drop during starting when there's no bypass. Both have a slightly weaker spark then at normal running.

Can you explain why a ballasted setup suffers more voltage drop than a 12v coil?

Jeroen

[Edin Dundee]

"The move away from automotive ballast resistors gained momentum with the advent of transistorized ignitions, with their attendant reduction of turns-ratio of coils. The resulting lower inductance values of the new coils' primaries resulted in smaller primary current variation with engine speed." - trawled from the net.

I've also read hints (but that's all) that the HT side running from a 6v primary can collapse/form quicker than if it were running from a 12v primary.

So that's an argument for both voltages.........

[tinweevil]

Sorry Jonners, Jeroen is correct. A 6v coil has half the resistance of a 12v coil therefore takes double the current and their power consumption, field strength and release potential is equal* (and to aside to Bill for a moment, this is why I don't believe your second quote). As the voltage drops during cranking a wet-finger-in-the-air 25% drop vs nominal 12V battery voltage (i.e 3v) would be halved in voltage by the ballast resistor so a ballasted coil sees a 1.5v drop. Exactly equal to 25% of the 6v coil working voltage. Therefore a ballasted system with a broken bypass is exactly the same as a 12v coil system working perfectly.

A ballasted system has the advantage that normally the ballast bypass isn't broken so instead of seeing 6V minus 25% during cranking it will see battery cranking voltage which in my experience is usually about 9V. Thus a 50% boost in power rather than 25% cut.

This is why I mentioned my experience with Britpart above. I may have been lucky in mine coping with double the intended switched current for 28k miles but I doubt it. Electronic ignition running a ballasted system is without doubt in my mind the best possible system. And if a Britpart blows every 28,001 miles who cares at the price?

Bills first quote rings true and I think becomes beneficial as revs increase and so the coil does not have time to reach saturation. Don't shoot me if I've got that backwards, I need to sleep on it.

* I'm not sure which is the more magnetically lossy system, far too much alcohol under the bridge since I studied that. I feel that it would not be significant in this discussion though.

[Jon Tilson]

If it were just ohms law here I would agree. But induction coils are non linear and volts etc build up exponentially. We also have rise times to consider.

During starting experience show a 6V coil will not start an 1850 or Sprint without the ballast bypass,
Same car starts quite happily with a 12V coil in place. The 6v coil needs the extra boost.

I'm sure there are graphs around to show this....if not I'll do some myself if I can be bothered.

Electronic ignition may well help a 6V car by helping the rise time.

Jonners

[soe8m]

The discussion yes or no has lost my interest but a complete ballasted system does not consume more current than a 12v coil. The total resistance of the ballasted coil AND resistor is the same as a 12v coil. An electronic ignition does not "wear" more. Only when a ballasted coil is fitted WITHOUT the external resistor or resistor wire causes a double current.

Some electronic ignition modules CAN switch a low resistance coil like the 123 or the black Lumenition optronic modules. Only a ballasted coil is not designed to have that current throug it and needs it resistor. Only the ballasted bosch can cope.

Jeroen