Ignition coils
Ignition coils
(OP)
I have read that all ignition coils are actually 6 volt coils. 12v cars just use a ballast resistor to step the voltage down. If they are all the same, why are some marked 12v and 6v, different part numbers, etc.





RE: Ignition coils
I'm sure different cars, number of cylinders, etc. dictated differant part numbers. Most of today's cars have the ignition controlled by the ECM, so the dwell (charging) time can be adjusted as necessary for a hot spark without damaging the coil(s). Of course this level of interdependence probably increases the variations and amount of part numbers.
RE: Ignition coils
The original question answer. Because of the design of the primary windings, and the ampacity of them.
RE: Ignition coils
6 volt for cars with nominal 6 volt electrical systems. I think the VW Beetle was the last to use 6 volts and they changed to 12 in 1972 I think.
12 volt for cars with a nominal 12 volt electrical system. System voltage is delivered directly to the coil whenever the ignition is switched on
8 volts for cars with a 12 volt nominal electrical system. System voltage is delivered directly to the coil when the starter switch is engaged, however when the starter switch is released, power is provided to the coil via a resistor. This is the system outlined by TheBlacksmith and is quite common. It mainly helps with cold starts.
Regards
Pat
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RE: Ignition coils
Most six-volt vehicles used ballast resistors.
To understand ballast resistor function/purpose you could refer to an old (forties or early fifties) Audel's manual. [Or, these days, maybe Wiki?]
RE: Ignition coils
RE: Ignition coils
RE: Ignition coils
Some run 12 volts with no resistor. Some run 6 volts with no resistor and some run 12 volts with a resistor. The ones that run 12 volts with a resistor are rated at 8 volts without a resistor. I never saw a 6 volt system with a resistor on the coil, but the only 6 volt system I have encountered was on old Beetles.
Regards
Pat
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RE: Ignition coils
RE: Ignition coils
RE: Ignition coils
http://www.weblube.com/12vOr6vCoil.html
(See attachment) for 6v electrical system wiring (ALL EARLY FORDS)
Pontiacjack show me some 'history' examples of a 6v system with a ballast resistor.
RE: Ignition coils
I've got a 6 volt '38 Ford tractor. At the moment it doesn't spark at all.
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RE: Ignition coils
RE: Ignition coils
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1) A ballast resistor (universal definition, not just automotive) has a high positive temperature coefficient; its resistance rises more steeply as a function of temperature than does the metal alloy of a 'normal' power resistor.
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2) At some point (early 1930's?) in the advancement of automotive engines (with breaker point and coil ignitions) excess heating of coils became an issue at low engine speeds (the impedance of a coil's primary winding is predominantly inductive, so RMS current value falls off with increased engine speed).
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3) See where this is going? 1) was applied to solve 2)!
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Whew! This surely would be easier if I just had a copy of a 1940's-era Audel's Guide to photocopy and post!
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Other pertinent facts:
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Since a coil primary (in the manner of any electrical path) displays both resistive and reactive impedance, the problem was sometimes approached by manipulating these impedance components within the coil proper.
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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.
RE: Ignition coils
RE: Ignition coils
RE: Ignition coils
Regards
Pat
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