The Stovebolt Site Forums The Shop Area The Electrical Bay When do you need to use a ballast resistor with points..??

Well this is the first time on the electrical forum....usually stay on the greasy side of the forum.

I have a variety of gasoline engines from Allis Chalmers WC 45 with 4 cyl. gas engine..... played with some 216 Chev and now a 261 rebuilt chev circa 1959.

The AC tractor cooked the old original coil.... the fact that it was old, bumped and deeply dented did not help. when I purchased a new 12 volt coil.... it says printed on the isde of the coil that it can be used for 6 volts or with a resistor it can be used for 12 volts.......

What did I buy a 6 volt coil that can be used for 12 volts and should I go back and look for a real 12 volt coil...???

Now I have just been starting the new rebuilt 261 and I am not using a resistor.......the 12 volt coil is from Accel.... High capacity of some kind..... will it need a resistor or will I burn the points like I did in the tractor....??

I can't figure out when and why you need to use the darn resistor.... they are cheap enough so the cost is not an issue.

I have a Pertronic kit for the 261 but have not installed it yet.... I have read on the forum that this would be a solution
but it will not answer my question of why and when to use a resistor.... do I need a special capacity resistor or just a run of the mill model similar to what Chrysler products use to have in the 70s.

Thanks for your patience and answers.

Bob C.

RAC1812,

On a 12 volt system, the ignition was designed to run around 8 or 9 volts. This is obviously below the actually running voltage of the system.

To reduce the voltage to the ignition, several methods were used...a coil with a internal resistance built in, a resistance wire that goes from key to coil, or the traditional white ceramic ballast resistor you are probably describing as seen on the MoPar rigs around the '70's, and bazillions of Chevrolets.

Without the reduced voltage, the points will burn and wear at a accelerated rate. I actually don't know if the coil proper will generate more heat and fail faster, but I suspect so.

So....if your system is 12 volt, then some device needs to be on board to drop the voltage to the ignition system.

Your coil statement is interesting. I have only seen coils marked specifically for 6 volt or 12 volt. If you see the impedance specs for the different coils, they are quite close regardless of voltage, so I really don't know the answer to that question.

Stuart

I have been in the old farm tractor business for many years and now restoreing old trucks. I agree, when a 12 volt battery is replacing a six volt system the six volt coil still can be used with the use of a resistor. this is done to reduce the voltage down to four to six volts. Even the twelve volt systems including the coils marked 12 volt almost always need the voltage reduced to four to six volts. Many 12 volt coils have a resister included in them. some do not and thats when you run into trouble. The advantage is that with a twelve volt battery the spark or current to the coil is always at it's consistant level and not reduced when turning the engine over with a six volt battery. If the weather is cold ot the battery is not up to parr then the ing. system is robbed of the proper level of current to the coil causing a weak spark to the spark plugs. Weak spark results in starting trouble. I as a pratice almost always use a resistor to any twelve volt upgrade.

you stated that you have a pertronix conversion and they run on full voltage so there is no need to drop voltage to the points because you won't have any. i can say ballast resistors are needed for a points style ignition as i experienced years ago stuck along side the road wondering why my 69' firebird kept going through points(always kept extra in the glovebox) after i was instructed to install a ballast resistor back into ignition system problem was solved.

There are no points in a Pertronix system. I received conflicting advice from Pertronix technical support regarding their 12v Ignitor (I) on a 1960 261 engine. They also gave me some conflicting information/mumbo-jumbo regarding the required resistance in the coil (1.5 ohms is what I finally gleaned from their advice). I bought one of their Flame Thrower (I) coils and have not been using a ballast resistor with the Pertronix unit since 1998.

The insert that comes with the Pertronix states that if you have a ballast resistor installed to leave it installed. I installed a Pertronix yesterday and the truck was very hard to start and ran like crap. Fiddled around with the advance and strained my eyes trying to see the timing marks on the flywheel but these old eyes couldn't "call the ball" or find the triangle. Today I put the points back in, re-gapped them and the engine starts right up and runs like a top. Perhaps I ordered the wrong Pertronix electronic ignition. Anyway, that's a whole another story.

I've posted this before but this is one of the best links I have found on Ingnition Systems and has some very good information on this topic.


Don

Actually Don the condenser (capacitor) serves two puposes:
1: It charges up with elecrical energy each time the points open and reduces arcing across the contact points as they seperate. Which results in extended point life as you indicated. However:
2. The primary function of the condenser is to collapse the magnetic field within the coils primary windings each time the points open by discharging stored voltage usually around 250 a.c. (yes A.C.) The release of this capacitated voltage causes a rapid collapse of magnetism from the primary windings across the secondary windings as it heads for the laminated iron core in the center of the coil which results in electromagnetic induction in the secondary windings boosting the magnetism and voltage in the seconadry windings to between 10-20 thousand volts.At the same time this process occurs the polarity of the elecrical energy is reversed (in the secondary windings). IE: positive to negative charge. Ultimately producing high voltage 10-20K Volts with a negative charge at each spark plug gap leaping from the center electrode to the side electrode of each plug.If the sole purpose was to extend point life, the engine would start and run without a condenser, but it will not. Doubt It? Try to start a breaker point equipt engine with the condenser removed.
Just FYI
Best Regards

Agreed, but then again it's a matter of perspective as the points are still being protected from the high voltage. I'll quote from the same linked source again.

The collapsing magnetic field not only collapses through the secondary coil, but also through the primary coil. The collapsing field induces a few hundred volts in the primary coil. These electrons have to go somewhere, they are just trying to get to ground by the easiest means possible. If they were allowed to jump across the points, they would burn them out in as little as 100miles. They see the condenser as an easy way to ground but what it really does is store them for a fraction of a second. Meanwhile the points have opened far enough that the 300 volts or so, can't jump across them.

WillsLimo,

Can you explain your "yes, it's AC voltage" statement for me, I didn't think alternating current could be found under the hood, not less in the vicinity of a transformer (coil).

Stuart

Hey Stu, I think what he is saying is that the current is flowing in one direction when the field is building and reverses direction when the field collapses.
Denny Graham
Sandwich, IL

Boy I have been away for a few days.... never expected this much action....

Summary of what I learn and will apply.....

Make darn sure I have the proper Pertronix for the Chev application. Talking here of a 1959 261 Chev truck in a 40 chev, a Canadian Pontiac 261 with Pertronix in a 43 and a Chev car 235 on points in a 1945. The engines are all installed in Canadian army trucks... plus a couple of old AC tractors on points.

Make sure the engine runs well on regular point system before experimenting with Pertronix.

Ballast resistor may not be needed with Pertronix as no points are invloved.

Next time I purchase a coil I will verify that it has a "built in " resistor......for simplicity.

Said ballast resistor is by-passed during the period the starter is energized at start up.....ballast comes in to play during running cycle to insure life of points system.

Our practical conclusion.... because of the design of the engine compartment...if you think modern designs are bad.... you ain't seen the engine compartment of our trucks..... we fully intend to make sure the engines run well on points.... then migrate to Pertronix before we install the sheet metal......

Once the cab is installed, for emergency situation should the Pertronix fail...... we will carry a fully loaded dizzy in the spare box..... pull out... push in... fiddle with timing and get back home...... any and I mean any kind of routine maintenance would require the whole nose sheet metal to be removed on my truck...... not a side of the road job.

Interesting about the 9 volts design of the coil/ignition system. Those of us working on Ford flat heads V8 army trucks of the same vintage usually run with an 8 volt battery for greater punch on startups...... and although the design is basically a 6 volts system the original generators puts out about 9 volts and manages to keep the 8 volts battery fully charged.

Thank you all very much for your help.

Bob