Why Do I Need A Ballast Resistor?

[Tom C.]

If I convert my points system to a Breakerless SE or Pertronix system, why do I need to use the ballast resistor since points are no longer involved?

[John D.]

Re: Why Do I Need A Ballast Resistor?

Tom, I don't believe that TI cars used a ballast resistor. John

[Jim T.]

Re: Why Do I Need A Ballast Resistor?

I don't have a Pertronix system, but from what I have read it should have a full 12 volts 100% of the time, so the ballast resistor or even resistor wiring in later cars is not required. Don't toss the points, they could come in handy some day on the road. I know.

[John D.]

Re: Why Do I Need A Ballast Resistor?

Tom, Ken Hanna of Lectric Limited has an excellent one wire system that you should highly consider. It's a lot neater and a whole lot better than some of the other stuff on the market. John

[Jack H.]

Do you still have a coil?

The ballast resistor was used to drop the drive voltage applied to the primary side of the ignition (points, condensor AND coil) to reduce the current flow through the circuit when the engine was actually running vs. in cold start mode. The use of a solid-state ignition system simply eliminates the points and condensor in the distributor by doing a precision electronic switching function vs. electro-mechanical switching. You still have electrical stress on your coil and the 'worst case' condition is ignition ON + engine not running where IF the points are closed, you're running max current, full time, through the coil's primary windings resulting in max internal heating.

Now, most of the add-in electronic ignition modules have some level of 'smarts' in them to defeat primary side ignition current fow until the engine starts/runs (certainly the Breakerless SE does...it's my favorite system for cars with a lift-window Delco distributor). So, systems like this will obviate the extra thermal stress of engine OFF/ignition ON, but when the engine IS running you're pushing more primary side current (albeit switched, coming in pulses) through the coil.

Bottom line, designers of these add-in ignition systems went to great pain to make them work WITH the ballast resistor present/functional. Why would you want to eliminate the ballast, make an obvious departure from factory stock under hood appearance, and COOK your coil as a result?

[David B.]

Re: Why Do I Need A Ballast Resistor?

Tom,

I installed a Pertronix II ignition system on my C-1. Per its installation instructions, you do not need a ballast resistor with it. The Pertonix II is a nice upgrade in that it maintains constant dwell over the entire rpm range, as well as other features.

If you wish to retain your resistor for appearance, you can attach a bypass wire to the underside of it(wink).

David

[Phil P.]

Re: Do you still have a coil?

hei no points no coil cook --- you make a good point --- but resistor and resistive wiring left with electronic systems --- tubes are out processors are in --- ballast takes the i load off of welding the points ---

[Richard S.]

Re: Do you still have a coil?

Tom,

I think Long Island Corvette Supply has NOS Pick Up coils. You might want to try one before you change out your TI System. You could always sell it later.

[John H.]

Re: Why Do I Need A Ballast Resistor?

Tom -

Without getting into the gory detail, the ballast resistor is there to reduce the voltage feeding the (+) primary side of the coil; as long as you use the stock coil, you need the resistor in its feed circuit, or you'll fry it, regardless of which conversion you use (Pertronix, Breakerless SE, Crane, etc.). Consult the instructions or manufacturer's tech line for whatever conversion you use to determine whether the conversion module requires a full 12 volts (like the Pertronix does) or whether it requires resistor-reduced voltage. All the conversions are is an electronic switch that replaces the mechanical switch (points) you have now; the coil still supplies the spark - the module only switches the secondary, just as the points did.

Some aftermarket coils (like the Pertronix Flamethrower) operate on a full 12 volts, but most don't; most still require the ballast resistor.

[Paul L.]

Re: Why Do I Need A Ballast Resistor?

As per John's comments.

[Tom C.]

Re: Thanks Everyone

I appreciate all of the responses to the above post. I understand now that I will be able to preserve a certain amount of originality in my TI 66 427/425 car by going to the Pertronix Ignitor II with the Flamethrower coil which does not require a ballast resistor.

I plan to post my entire TI restoration attempt (a horror story which is still ongoing) in detail since so many of you have asked me what went wrong.

Thanks again for the posts. Tom Cheairs

[David B.]

Re: Why Do I Need A Ballast Resistor?

Paul, John,

The Pertronix II instruction sheet says..

"The Ignitor II ignition can be used in conjunction with most ignition coils rated at 0.6 ohms or greater. For optimum performance purchase and install the Flame-Thrower II high performance coil."

"Recommended: Many vehicles cam equipped with ballast resistors or resistance wires. To achieve optimum performance from the Ignitor II ignition system, we recommended removal of these components. ... To remove a ballast resistor, (normally white ceramic blocks 3" to 4" long), disconnect all wires on both ends ...."

"Alternative: The Ignitor II can also be installed in applications retaining the ballast resistor or resistance wire."

Pertronix does not require the use of the Flamethrower coil for removal of the ballast resistor in their instructions (04/01 printing date).

I am running the Flamethrower coil on both of my applications so perhaps that is why I haven't run into the trouble mentioned, but I haven't found a reference from the factory literature that requires the use of it when the ballast is bypassed. Have you seen something to that effect?

What am I missing here?

Thanks,
David B.

[Jack H.]

Re: Why Do I Need A Ballast Resistor?

What will 'work' and what's within factory original spec for optimum longevity are two different things. Competent designers always built safety margin into their systems, but it's NOT a good idea to alter the system such that it's working in its safety margin loci...

Primary ignition current is a function of working voltage. The lower the voltage the lower the current flowing through the coil's primary and the distributor's points. In the case of an add-in solid state ignition system, you eliminate the points leaving only the coil.

The worst case stress for a coil is points closed, ignition ON, engine OFF; there you're driving max current with a 100% duty cycle through the coil's primary windings AND the car isn't in motion to produce a convection cooling air flow. That's when you see ballast resistors getting too HOT to handle and coils heating up.... Some solid state ignition systems (the Breakerless SE for one) have 'smarts' in them to detect this optimum stress sitution and automatically squelch the flow of current through the primary to extend coil life.

Now, when the engine starts, the ballast is switched in and primary ignition voltage drops in lock-step. Plus, the fan is running providing an underhood cooling air stream. AND, the primary side of the ignition is being switched (ON/OFF with plug firing order). So the RMS level of primary side ignition current is reduced (lower voltage + current switching). This reduces the overall thermal stress on the coil.

A coil is simply a step-up transformer housed inside a case and immersed in an oil bath to promote heat transfer. When you get it too hot for its designed thermal dissipation silhouette, two things happen and neither is good!

(1) The transformer's core laminations begin to separate causing a loss of magnetic permablity (energy transfer efficiency from the primary to the secondary winding).

(2) Eventually, the transformer's windings will distort, short together and in the long run go open circuit as shorted windings decrease the winding resistance, and increase current flow beyond coil wire's diameter for current handling.

Factory original coils were designed and selected for a given application KNOWING the ballast resistor was there. So, when you drive them with a higher voltage, you're 'pushing' the thermal dissipation envelope!

How long can you go before there's a problem? Well, it depends on your driving habits, the wear profile of your existing coil and the ambient conditions you expose it to. If you're careful (avoid long periods of ignition ON/engine OFF and high underhood thermal dwell), it's possible your coil will last indefinitely. BUT, you ARE pushing the envelope!

Now, the old timer dirt racers knew the el cheapo 'hot spark' trick and many ran the track without incident. What's the dirt racer's trick, you ask? Well, they discarded the ballast resistor (full battery voltage) and swapped the original 12V coil for an earlier 6V coil. That effectively drove the primary side of the ignition system +2X hotter insuring a crisp spark under WOT + max RPM conditions.

Yes, they were pushing the design safety margin of the envelope to/beyond its hairy edge! But, these were pros who knew what they were doing, didn't leave the ignition ON/engine OFF and KEPT the car in motion when it was running. Plus, they did periodic maintenance changing out engine components known to be wear prone because they wanted to STAY on the optimum peak of the car's performance profile....

So, that's what you were missing. Any more questions?

[David B.]

Re: Why Do I Need A Ballast Resistor?

Jack,

Thanks, I always enjoy/appreciate your electrical explanations.

In summary then:
1. The Pertronix II includes a feature which "Senses if it is incorrectly wired, or if the key is left on without the engine running, and shuts itself off to protect the circuitry and the coil." (manufacturer's description)
2. You point out that if it did not have this feature, it could damage an OEM coil.
3. The Pertronix II manufacturer's literature recommends deleting/bypassing the resistor, regardless of the coil being used for best performance.

Therefore, no problem deleting the resistor when using the Pertronix II as I see it.

David

[John H.]

Re: Why Do I Need A Ballast Resistor?

Dave -

Where they say "we recommend removal of those components" (ballast resistor or resistance wire), they're referring to the power feed to the MODULE, so it gets a full 12 volts. They are NOT referring to the power feed to the COIL, except in the case of using their Flamethrower coil. That's where the confusion (and fried stock coils) starts. It would be very simple to write the instructions correctly and clearly to separate the discussion of feed requirements for the module vs. for the coil, but they haven't mastered that yet .