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Old 08-15-2007, 02:28 PM
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Resister mystery

OK I need electrical guidance with my ignition system
Basics are a small block installation in a 53 sedan (was 6 volt), when i hooked up the wiring I installed a 2.0 ohm resister going to the coil. I found my plugs sooting badly after a few around town trips. The coil is a Accel unit.
I put in new plugs and decided while under the hood to install a Pertronix breakerless ignition in the distributor. In reading the instructions ( I know I shouldn't do this, BUT I did) I find that the ignition needs a 1.5 ohm resister or more in the system. I measured the coil and find that there is 1.5 ohm in the coil so I have removed the external resister which would have given a total resistance of 3.5 ohms if left in place.
I got to wondering if the 3.5 ohm may have caused my plug problems and also
does anyone know if a stock coil has any resistance in the unit or is this the reason for the external resister on the Chevs?

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Old 08-15-2007, 03:06 PM
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I'm guessing you "had" points with the 3.5 ohms

purpose of the "normally" 1.5 to 2.0 ohms with points is to lower the coil input voltage (to between 6-9V) at idle where the points are moving open and closed so slow a full 12V would burn them up relatively quickly.....
as rpms increase, amps output from the alt over powers the resister so at around 2500rpms the coil is getting 12V and can make a 12,000V spark

put only 8V into a 100/1 wound coil, max spark is 8,000V at idle....
with 3.5ohms 12V becomes 3.4 volts at idle = a weak 3400V spark and less volts per 100 rpms increase driving in town at low rpms = sooty plugs

the pertronix needs a 1.5 ohm resistor for to many amps protection....

there are coils all they way down to .2ohm, how many ohms in the coil depends on what ign system it is used with and how many windings in the coil
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Old 08-15-2007, 03:38 PM
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Doc here,

Refer to your Installation Instructions concerning Ballast. Many differ.

IF your Using a Resistor with the Breakerless Ignition system (1.5 Ohms) , it is there to protect the module from spikes..You probably DO NOT need the resistor on the coil, this is where the instructions must be checked..

The combination of BOTH will give you poor performance..

BE sure the coil + wire is a proper gauge to support the coil under full load also, or you will swamp the coil at top end.


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Old 08-15-2007, 03:58 PM
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hey Doc....glad your back (and feeling better?????)
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Old 08-15-2007, 09:17 PM
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Thanks for the info. As to the instructions Pertronix states if your system has a resister, leave it in, but if no resister no need to add one. This is not good advice when you have an engine swap as in my case I installed what I was familiar with and this was a coil & resister system.
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Old 08-16-2007, 05:48 AM
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don't disagree....GREAT product.....same lousy instructions for 10 years+

"if" measuring the disconnected ign wire V* (to the coil) was step 1 and measuring the coil ohms was step 2**.....as written clearly for "how to" in their trouble shooting section.....before you do anything else....it would help alot of people!!!

*on points systems, Ford and Chevy mostly used a 1.5-2.0 ohm "resistance wire" (usually bright pink and soft insulation) in the dash plugged into the ign switch for 6-9V....chrysler mostly used a 1.5 ohm "ballast resistor" in the engine compartment for 6-9V....so for any old car, who knows what has been changed/swapped/butchered

**max "recommended" amps is 8.5 (also from the same trouble shooting section) so if you do have a super duper alt putting out 14+V and no voltage drop=9.3 amps....you don't want less than 1.5ohms!

also would be so easy to write: ignitor board 12V to 5V SS convert (red wire) will not operate with less than 8V...all they say is :"not enough voltage"...good grief!
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Old 08-19-2007, 08:09 AM
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Some newer 12V coils have built in ballast resistors. If you use an older external resistor on these, you will have a much colder spark.
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Old 08-19-2007, 06:21 PM
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Quote:
Originally Posted by ccb
Some newer 12V coils have built in ballast resistors. If you use an older external resistor on these, you will have a much colder spark.


Doc here,

ONLY if the system is points type..OR a Performance Coil that requires Module Protection..(like MSD) ...

An HEI like GM stock or aftermarket WILL not run / Run well , with ANY ballast Device in-line unless Specifically called for ( and I've only seen a few..) ...

HEI needs all the Power it can consume to provide the high energy spark to the system's Coil primary windings..a Ballast will cut that by at least 3 volts...it will run like "crap in a can..." It's like trying to run a foot race with a cigar in one side of your mouth, and 4 cigs in the other..It will cough and sputter, and stop to catch it's breath every few blocks or so..

IF you have a Ballast in line, no points, or require module protection (refer to installation text for this) , then REMOVE the resistor wire OR ballast..and/or internal ballast type coil..(unless prescribed by the maker!)



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