Ballast resistor ...or not??

Getting ready to wire the ignition in my 40. A mid 60's 283 with a stock points distributor and a flamethrower coil. The coil is 12V 1.5 ohms and the instructions say no resistor is needed. Is that right? If so why ???
I'm an electronics idiot. Gary

 

You might just burn the sheeit out of your points with that coil and no ballast resistor. I'd upgrade to a Pertronix unit to run that coil, otherwise you will need a ballast resistor. The coil might just pull too much current for those points, causing premature failure.

 

1.5 ohms is way too low for a set of points. you'll burn them out pretty quick. go with the ballast resistor.

 

Give it a try. All you can do is burn a set of points. Buy another set and bring them with you. I put a few thousand miles on my Cad engine 48 Ford without any trouble before I went to a hot coil and resistor.
Don't listen to the electronic jerks.

 

Some coils have a built in ballast resistor, but Splinter is right about possibly burning your points anyway.

If you run a points ignition with no ballast resistor (and your coil doesn't already have one built in) you will eventually fry your coil. Don't ask me how I know this one, but it had to do with a '40 ford and a 283 . . .

 

Hey, I resemble that remark! I'm an electronic AND welding jerk!!

 

Dealing with that right now. Use the resistor. I'm having a little trouble with the "I" circuit on the Ford starter solenoid though. Damn thing runs without the "I" wire hooked and WON'T start withe it hooked up.

 

I'm running 1 on my roadster. Guess it's working nuthin happened yet. Rob

 

Actually this is a case where a system with a ballast resistor is always better with points ignition. You are better off using a coil designed for a ballast resistor. The benefits of having an external resistor setup is to be able to boost the spark during starting, to overcome the interval when the system voltage is reduced by the starter. By using a coil made for a lower supply voltage the coil is boosted during starting by bypassing the ballast resistor. The resistor is bypassed during cranking when the system voltage is pulled down by the draw from the starter, but after starting is complete the system voltage is reduced to the coil, which prevents possible overheating of the coil and unnecessary overheating of the points. I use a 6v coil with ballast resistor, so that during starting the coil gets 12V.

You might not NEED a ballast resistor with that coil you have, but for easy starting, every time, and long coil and point life, get a 6V coil and a ballast resistor.

 

My favorite is to run an MSD box with a matching coil and no ballast resistor on all of my hotrods. The MSD box burns the gas even with a BIG cam. You can run the MSD box with many different distributors. You might want to install a ballast resistor on the car but wire around it. In the event that the MSD box stops working, you can wire into the resistor and drive the car.

 

Not everyone wants to remain stupid.

If you have a 1.5 ohm coil (with no internal ballast), then you need a 1.5 ohm ballast resistor. You can bypass the resistor when starting, or at the race track.

For reliability, and extended life for a points ignition, most people will run a ballast. When the engine is chugging along at less than 4000 rpm, then there is no need for a hot spark.

The only time you don't run a ballast on a street car, is if you have a CD ignition (MSD box, etc).

 

I get so confused with this shit I decided to run a magneto. Why can't coil mfgrs state on the coil whether it has an internal resistor? Sometimes I think my dog knows more about ignitions than I do!

 

It's a voltage divider.

 

One would think that if the instructions state that no external resister is required, which is what he said they said, that the coil probably has an internal resistor. However that being said, what 29nash said, is the best advise of anyones here.

 

Do those instructions mention if that coil's OK to use with points? If yes, then use it with no resistor. If not, you'll have to get a different coil. But, some coils now don't need the ballast resistor

 

It just might be right. Some of the info presented is correct and some assumes that the resistance circuits or start voltage is self-correcting in a manner of speaking. I'd think if you're wiring it none of that applies. Your aftermarket coil is probably designed to run w/out a ballast which is why they stated that in the spec sheet. I'd think it has an internal resistance factor engineered into it vs an internal resistor so that it can be used in exactly what you have...a custom wired system instead of an OEM system. Additional resistance to the coil input as designed may cause excess heat and pre-mature failure. I hope that answers your question.

Also I'd think if you wanted electronic or Pertronics ign in your car you would have done so from the start.

 

anyone have a basic wiring diagram for adding a ballast resistor? i don't have one in my system yet, seems like i ought to (and explains why my new points have pitted up so quickly.....)

 

GND---->Dist<-----(-)COIL(+)----/\/\/\/\---->12 V IGN Switch

 

hahaha!!!!

I kept frying points in my 59 (Painless wiring, points, standard coil), so I added a ballast resistor. Then it would die as soon as I put it in gear. Took the resistor out, and replaced the points with Petronix and haven't had a single problem in over 2 years.

 

Since the OP said it was a Flame Thrower coil, I will assume that it is one of our PerTronix Flame Thrower coils. He said it is a 1.5 ohm, which it will say right on the coil label. 12v 8 cyl ignition with points should use 3 ohm resistance for optimum point life, so a ballast resistor needed in this case, since it has points.

Yes I work at PerTronix

 

Here's more shit to confuse you and to help explain to those who don't know electronics why they should shut the fuck up on accaision and defer to those who've studied the theory and application and not just "wired shit up".

Current and resistance are in inverse propotion in a curcuit. This is called Ohm's law, and is expressed as: I (currentin amperes or amps) = V (voltage)/ R (resistance in ohms)

So, for our example 12V (applied votage) / 1.5 (resistance in ohms of coil) = 8 AMPS.

kind of a fucking lot of current to run through an 18GA wire, right? So, we add another resistive load, a ballast resistor, of 1.5 ohms, add that to our other resistive load and recalculate the equation:

12/3= 4 AMPS

How about that? One little change and we were able to cut our current load in HALF! A lot more manageable for car wiring, and those poor little points, right?

Does that make more sense to you guys now?

(OK, and to the rest of you who know this stuff, I know this doesn't take into effect reactive and resistive capacitance from the condenser, or duty cycle of wire loading, but let's keep it simple for the kids.)

 

THIS IS GOOD
I'm speechless standing here in you elder HAMBers presence,,,Lets the Gods battle on!!!

 

Just bring an "optimum" set of spare points along in the trunk.

1.5 ohms doesn't sound like much, but in the ignition world, which commonly uses lower values in the form of resistance wire, it is a significant value.

I'm not going to argue that 1.5 ohms is not enough, as it may be a perfect setting for your spark plugs high voltage requirements.

I'm from a GM background, with the R post on the starter. It's just the way I wire GM's up if I use points. I haven't used points since about 1985, as I'm a CD ignition kind of guy now.

If I was going to use your setup of no ballast, I would then use a #10 wire from the ignition to the coil, and a #10 wire from the coil to the distrubutor.

This wire will have a lot of current flowing through it. As such it will generate a huge magnetic field. You will want to route this wire carefully, and not have that magnetic field pass by any relays or sending units.

Recardo out.

 

Without a resistor you could also burn out your coil. The real purpose of the resistor is to regulate the current in the coil between low and high speed operation. (At low speed the resistor heats up and resistance increases reducing current to the coil.)

(As a side benefit the resistor also reduces the rise time of coil saturation somewhat.)
-- edited to correct this comment --

You want about 3 ohms in the circuit (measured cold) when running points.

(I do not doubt that no resistor is necessary if running a pertronix system, but the OP is using points.)

 

Thanks for all the input guys, I guess I wasn't expecting this many different opinions (it's the HAMB don't know what I was thinking) but I will take all this in and see which works best. I'll be posting updates soon (40 progress) so you can see how it ended up. Gary

 

No one fights over HEI stuff anymore.

 

AMEN !!!
Ignition points WILL NOT last at 8 amps !!! Good answer ! This answer should go into a tech post!! EX :
Assuming the battery is 12 volts and 14 when running.
The first ballast at 1.5 will drop 6 volts, feeding 6 volts to the coil. The coil at 1.5 ohms will drop another 6 volts leaving a very small amount of voltage to arc the contacts. The lead wire coming from the distributor is also a calibrated resistance cable ( available at napa) and will resist the extra couple volts when the engine is started and the charging voltage goes to 14 etc.
Now assuming the condensor is the correct capacity the ignition should have a very usefull life in any car !!!!!!!

 

Right on. All you need to know when you're rolling off all those different colors of wire from the spool or from your Painless package.

I agree with the theories presented by Splinter and 440rr as well. Sadly these get off track sometimes and all the "wiried shit up" guys wanna help too, but the reality here is setting up a simple system that takes into consideration certain standards or practices of custom built stuff. Not many will incorporate a 'start circuit' with that special lil GM wire, some will add a resistor and use a stock coil, some will simply by a coil that should not need it and just wire as 'good ol, good ol' and it'll probably run forever with no troubles.

Similar to a starter on low voltage, running a ballast resistor where it's not needed can cause pre-mature failure of the system, and nobody here likes to suffer pre-mature capacitive discharge

 

Would you please then tell us a better way to analyze the circuit?

You need to make certain assumptions when doing any analysis. Thus far Splinter has presented the only rational explaination with clearly stated assumptions. I think they are reasonable good assumptions based on the wide margins of the involved variables.

I would mention that the resistor values involved in Slinter's analysis are not the nominal values measured at room temperature but the true value at normal operating conditions. I think it would be most reasonable of ballast resistor manufacturers to label resistors with their true values at operating conditions rather than nominal values.

Go with the 1.5 Ohm. I bet it will work like a champ.