Coil and points

M

Mike B

Well-known member
I see everyone says that without a ballast resistor to drop the voltage from 6v to roughly 3 volts, the coil can overheat and you can burn up the points....is the destruction of the points due to the coil over heating or?

Reason I ask is because (as far as I know) there is no difference (material wise) in 12volt points vs 6 volt points, and 12volt systems get about 8 volts or so at the coil when running.

Just curious, been bugging me for years:)
 
Mike B wrote:>>> Reason I ask is because (as far as I know) there is no difference (material wise) in 12volt points vs 6 volt points>>>

Good point Mike B. 8^) Sorry I couldn't help myself.

Seriously though, I'd guess that the ballast resistor is more for current or amperage control than voltage control. Amperes kill points, not voltage between them.

Jack E/NJ
 
I see, I think...must be a difference between 6v and 12v resistance accross + and - through the coil?
 
I think you're right, Mike. It's Ohm's Law! 8^) Resistance equals volts divided by amps. So if you have the same point amperage for both systems, the resistance of the 12 volt coil should be twice that of a 6 volt coil.

Jack E/NJ
 
Mike B said:
is the destruction of the points due to the coil over heating or?
Click to expand...

You've got cause and effect backwards. The overheated coil doesn't burn the points.The coil overheats because it's drawing too much amperage, and excessive amperage burns the points. The points are nothing more than a switch in a circuit. The more current that switch carries as it makes and breaks the circuit, the faster the contact points become pitted and eroded.

Bob
 
Fords are about the only ones that used a resister from 1932 thur 1948 and that was .5 ohms and using a stock coil.Most others 6 volts coils Don't use a resister.Ohms law "amps x .5 ohms resister= voltage so 3amps x .5 = 1.5 volts +or - .
What voltage is left from source = coil voltage. 12 volt coils used
1.5 or 1.35 ohms resisters and Say Cadilac and other GMs and other didn't use any resister.If you leave your key on and not running you can heat up the coil.I can see whats happeing here people are using what the have and it does,nt work.
 
Are you saying that the resistor needs to be in the circuit or not?? I just started my 41 pickup ( 41 engine ) first would not start, very weak spark, came back later and started fine, moved several more times and started every time, I asked on old forum how to get better spark, what do you think is causing weak spark ? ( can I take a jumper wire from neg. side of battery and connect to plus side of coil and see if spark is better, use fire wall push button to turn over, with key on???? ) thanks Bruce
 
You need the resister that belongs with car.You could have loose wires poor contacts ect.It seems the old ford coils are repairable and would be the best thing to do.If the old coil were to start to draw more current there would be more amps in circut,so if it was and increase of 1 amp the voltage at coil would be less.I had a 46 with 6 cylinder and had 12 volt and used tube coil.If you have 6 volt and were to use tube coil no resister is needed.
Use a 1949 thur 1955 Ford 6 volt coil.
 
The Ford points are large and made of good material. These points are larger and better than a 25 amp commercial relay. The points in a distributor work the same as a relay except the points make and break thousands of time a minute where a relay in most cases is used for short cycles such as blowing the horn or a relay in an air conditioner in a home is on for long cycles not fast interruptions. An arc is struck as the relay engauges and an extended arc is drawn as the points open. The size of the arc depends on the voltage and amperage load across the points. The capacitor helps absorb some of the arcing as the points open. The point size determines the amount of amperage points will carry. High amperage on small diameter points will get hot and damage and weaken the metal arms or springs the points are attached to as well as the points. This is similar to small battery cables that get hot. Higher voltage will cause the spark or arc to jump a longer gap like the high voltage at the sprark plugs. The higher voltage along with the amp load is what causes the arc burn marks on the points as well as a bad condensor. Ford coils have about a 3 amp draw. I tested the ignition on a 39 someone converted to 12 volts prior to a trip from Peking China to Paris and found no resistor. I knew the local Napa store owner and he gave me his box of condensors to find what I needed. I added resistors until it would only start with a shot of starting fluid and it ran very poorly. I added resistance until it started and ran good keeping the resistance as low as possible. This car completed the tour and was getting ready for a trip around the world several years later. We put the distributor on the Heyer stobe machine without touching it and reset the dwell which wasn't to bad and it was put back on the 39 and completed the trip around the world as well as several other shorter trips and is still running perfect. We had installed 2 rebuilt 46 type coils on a bracket next to each other so if there was a problem they could easly switch coils, this was never required. The best coils are the original Ford coils rebuilt by Skip Haney. The original coils had problems almost from when these cars were new in hot weather when the coils got hot. The insulation breaks down and causes internal leakage. When cooled for 20 or 30 minutes the coil worked again. This was 99% of the vapor lock for the past 70 years, it takes about 20 minutes to replace a fuel pump, the coil cooled and people though they fixed the problem. 99 % of ALL old Ford coils will break down on the coil tester when they get hot. The first indication on the car is rough running when hot and very hard or will not start until they cool down. Even the worst coil will start when cold. G.M.
 
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Just to add a bit. The inductor coil only will induct a higher voltage spike when there is either AC current or faking it with a half wave pulsating direct current, which it what the breaker points simulate. The condenser is a fairly large capacitor that acts like an accumulator in a hydraulic system it builds and stores a charge until the breaker points open then it all kicks out at a high velocity. This keeps the points from arcing too much and gives the secondary winding enough jolt to induct a quick high voltage spike. That spike will go the path of least resistance (spark plug gap if all is well with the high tension leads). If any one has ever handed you a charged condenser you will experience that spike!

Coil temperature control is best handled with a ballast so that it doesn't start drawing more current as it gets hotter thus decreasing efficiency and deteriorating spark performance as well as the coil innards. Bad condenser won't kick out a good spark and will aid in burning the points. Too bad most condensers made today are crap. The manufactureres in China & Mexico don't care if they work. What are we going to sue them? Good Luck. I buy 2 or 3 condensers when I buy one set of points just to make sure I can find at least one good one in the bunch. Sometimes you get lucky the first time.
 
I realize that there's no one answer, and it will vary with coil type, brand, design, etc., but are there any thoughts on just what a safe coil operating temperature would be? As common as infrared thermometers are now, it would be no big deal to check coil temperature and adjust amperage with a ballast resistor to keep it within a safe range.

Bob
 
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