[TR] Coil Resistance & Pertronics

[spamiam at comcast.net]

Dan,

The 1.5 ohm coil needs external ballast to bring the overall resistance to 
about 3 ohms.  In other words, the 1.5 ohm coil runs on 6V.  The purpose of 
that is to allow the ignition switch to sent power which bypasses the 
ballast when starting the car.  When the started is sucking lots of amps, 
the battery voltage sags to well below 12V.  This will make a standard 12V 
coil put out a weak spark, and start hard, especially if flooded.  Bypassing 
the ballast runs the coil at the equivalent of about 16V while cranking the 
engine.  That short duration of overcurrent will not harm the coil, but will 
assist in starting.

Conversely, the 3 ohm coil should not use a ballast resistor.  It if does 
have a ballast resistor, it will be effectively running on something like 8 
Volts, when it is designed for 12v.  You will get a weak spark in that 
situation.

If you run the 1.5 ohm coil continuously without a ballast resistor, you 
will burn it out and you will probably damage a pertronics that is trying to 
switch the coil.  In my humble opinion, the pertronics is JUST able to 
handle the switching current from a 3 ohm coil.  Doubling that current is 
probably going to be bad.

I have never used a pertronics in a ballasted system.  But here is what I 
THINK you need to do if you do use it in a ballasted system: The pertronics 
unit needs 12V, so it can't tap that from the + side of the coil the way it 
does when you have an unballasted system.  You need a separate 12V supply. 
All the other pertronics connections are the same.  When cranking the 
engine, you will probably be switching higher current thru the coil that 
usual, but for limited durations, this is probably not going to be a 
problem.

-Tony

-----Original Message----- 
Message: 1
Date: Fri, 15 Apr 2011 14:45:47 -0400 (EDT)
From: cofrog at q.com
Subject: [TR] Coil Resistance
To: triumph fot  <fot at autox.team.net>, triumph
<triumphs at autox.team.net>
Message-ID:
<521553293.229397.1302893147706.JavaMail.root at md04.quartz.synacor.com>
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I'm confused (again).? What coil resistance do I use with a Pertronix LU142A 
?Ignition?? I have two different cars and two different ?setups.? A street 
TR4 which has the 1.5 ohm internal ballasted ?coil and a TR4A racer with am 
external ?ballast and a ?3 ohm coil.? Both are negative ground.? Some folks 
on the web say use only a 3 ohm coil (unballasted?) with the Pertronix.? It 
appears my coil shot craps on the street car and took out the I gnitor.? So 
I'm double checking what resistance coil is proper.

I want to give kudos to Marvin at Pertronix who replaced the toasted LU142A 
eventhough it was out of warranty by a few weeks.?

Thanks,

Dan