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Re: anybody know about ignition ballast resistors?

To: spamiam@comcast.net, triumphs@autox.team.net
Subject: Re: anybody know about ignition ballast resistors?
From: ZinkZ10C@aol.com
Date: Sat, 26 Jun 2004 14:23:56 EDT
In a message dated 6/26/04 1:01:49 PM Eastern Daylight Time, 
spamiam@comcast.net writes:

<< Well, I am really confused.>>


First what a ballast resistor does:

For a ignition coil to have enough zip at high speeds, the primary side must 
have a low resistance.  At high speeds the points are closed for a short 
period of time so the only way to build a strong magnetic field is high current 
( 
low resistance) 

At low speeds, the points are closed for a longer period of time allowing the 
magnetic field to build.  We can build a field over a longer period of time 
with lower current.  This reduced current makes for longer point life.

In order to reduce the curent, we insert a balast resistor.  The secret to a 
balast resistor is that it changes to a higher resistance at high current 
flow.  It is self limiting so you can think of it as a regulator for the 
ignition. 
 Some electronic ignitions ( GM HEI , Ford TFI ) use a current sensor built 
into the module to limit current.  Early Ford Duraspark and Chrysler electronic 
ignition use a balast resistor/wire.

Balast resistors are made from Nichrome wire ( like a toaster element ) Ford 
and GM had long used a balast wire in the harness, Chrysler used a white 
ceramic resistor.  There are a few different resistances and mountings. In 
theory 
things should be tuned using extensive testing, but in practice a generic 
resistor should work fine.  Be sure to contact Pertronix for a recommendation 
for 
total resistance, supposedly the ig module is sensitive to too low of a total 
resistance.
 

<<  It comes in the
 mail a few days later and it is a 1.5 ohm coil as well!!!!  The instructions
 inside gave a little more info.  It says that the coil can be used for RACING
 applications on non-ballasted 4 cyl cars, but that for street purposes the
 ballast resistor should be left in place.  Well, I have no ballast resistor. 
>>

For a racing application, the engine is running at high RPM most of the time 
and tends to have regular point adjustment,  in this case a balast resistor is 
not needed.

 
<< I guess that I should use a 1.5  ohm resistor to get the overall 
resistance to 3 ohms.  Is that true?>>  


I'd have to dig in some old ignition books, but this sounds reasonable.

<< What model car should I ask for a resistor at the local NAPA?  The speed 
shop has seemingly expensive ($11) resistors in 0.85 and 5 ohms, maybe a 2 ohm 
as well.>>

Is this $ 11 resistor a single unit with 4 prongs?  If so it sounds like a  
73 to ~ 80 Chysler electronic ig resistor.  Early Chrysler used the .85 ohm 
side for the coil and the 5 ohm side for the ig box.  Later Chrysler ~ 80 to 85 
used a single 2 prong .85 ish resistor.

<< I would think I could get it cheaper by not having it for "performance" 
applications.
 
Try a resistor for a 84 Dodge 1/2 ton pickup with a 318 V8. This will have 2 
prongs.
 

Harold





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