confused

[1948jr]

on the old masseys with 12 volt gen. and 12 volt vr. i dont see any sign of resistors either internal or external. what keeps the points from burning up?

 

[JMOR]

(quoted from post at 09:57:00 12/05/13) on the old masseys with 12 volt gen. and 12 volt vr. i dont see any sign of resistors either internal or external. what keeps the points from burning up?

oints generally "burn" as a result of arcing which can be aggravated by wrong or bad condenser OR by too much coil current (your question). Typical correct current is around 3 1/2 to 4 amperes, when stalled. Coil current is a function of voltage (6 or 12 (7.2 or 14.4) and primary circuit resistance. Primary circuit resistance consists of coil winding resistance or coil winding resistance plus resistor resistance. In either case you can obtain the magic 4 amperes either with the proper coil primary resistance or proper coil+resistor values. I have coils ranging from 0.5 Ohms up to 4 Ohms primary resistance and the same 4 amperes can be obtained by using a 3 Ohm coil & 12v as can be obtained by using the 0.5 Ohm coil + a 2.5 Ohm resistor. In either case, we have 12/3=4. There are many roads to the same place.

 

[Bob (Aust)]

Why do you want a resistor if you have a 12 volt coil? :?:

I have never owned an engine with 12 volt ignition and 6 volt coil and resistor combination. For $15 or so, I'd rather have a 12 volt coil.

 

[1948jr]

you guys dont seem to be getting the POINTS you are not answering my question.

 

[Jason S.]

JMOR did answer your question. In simple terms the 12 volt coil that was installed has the resistor inside the coil. The resistor inside is extra windings of wire. You can use a 6 volt coil with the external ballast resistor or buy a 12 volt coil that has internally resistance in the windings. Either way you end up with the correct voltage to the points which is why they dont burn up.

 

[JMOR]

(quoted from post at 14:39:48 12/05/13) you guys dont seem to be getting the POINTS you are not answering my question.

gave you the answer......correct current level keeps them from "burning up"!
Maybe more hand holding is in order. You don't see a resistor in diagrams, so why not burning up? Well, just maybe someone used the correct coil, let us say with a 3 to 4 Ohm primary resistance, such that they obtain a safe/correct current level.

 

[1948jr]

now we are getting close. did they use a 12 volt coil with a built in resistor back in lets say 1964?

 

[JMOR]

(quoted from post at 15:13:20 12/05/13) now we are getting close. did they use a 12 volt coil with a built in resistor back in lets say 1964?

o the best of my knowledge, the ONLY car that ever came from the factory with a coil with a built in resistor was 1953-1955 Chrysler Imperial (AutoLite coil). Now, what virtually all posters are calling a "coil with built-in resistor" is in fact not! What they are is a coil wound with appropriate wire length & diameter & metal properties to yield those higher primary resistance measurements, such as 3 instead of 1.5 Ohms. I haven't a clue as to when the 3 & higher Ohm primary coil windings first appeared.

 

[Jason S.]

I said extra windings of wire inside the distributor...

 

[JMOR]

(quoted from post at 20:26:10 12/05/13) I said extra windings of wire inside the distributor...

ery good.

 

[Inno]

I'm pretty sure I have a coil which has "internal resistor" stamped on the side........or words to that effect. I'm not saying there is actually a resistor in there, just pointing out why people call it that.

 

[JMOR]

(quoted from post at 22:28:42 12/05/13) I'm pretty sure I have a coil which has "internal resistor" stamped on the side........or words to that effect. I'm not saying there is actually a resistor in there, just pointing out why people call it that.

hear you, but.......until someone cuts one open & pulls out that resistor, & shows it to me, I will continue to say that there is no resistor in the coil can. A resistor is a discrete component, it is not the resistance distributed throughout a length of wire. Not semantics, either, just fact. All the wiring in your house has resistance, but is wire, it is not 'a' or 'a bunch' of resistors connecting panel to outlets & lights.

 

[Bob (Aust)]

".... did they use a 12 volt coil with a built in resistor back in lets say 1964?"

12 volt coils have been installed on Ferguson tractors since the TEA20 went from 6 volts to 12 volts around 1949 - 1950. Whilst US built cars retained 6 volt ignition into the 1950s, UK and European cars were generally 12 volt ignition from the 1920s.

I don't believe there is such a thing as a "12 volt coil with built in resistor".

There are 6 volt coils, there are 12 volt coils; and there are those owners who are too tight to buy a $15 12 coil when they upgrade, so install a resistor in series with the 6 volt coil to drop the primary voltage back to 6 volts. Then wonder why they have starting and running problems........ :lol:

 

[Joe Scribner]

Hey Jmor ! I have in fact just for fun cut open
several old 12V coils that have said "internal
resistor" I have never found a separate resistor.

My shop teacher back in trade school explained it
to me this way. The different internal resistance
is strictly a function of the size and number of
the windings in the coil. The finer the windings
the higher the resistance and if you add more
windings you get higher resistance. It's pretty
basic science if you understand that any conductor
has a specific resistance to current flow.

 

[Inno]

They probably put it that way so as to keep it simple. Although they really should put a resistance value on the coil instead of saying "internal resistor". That would be much more meaningful.

 

[Bob (Aust)]

Why not simply mark the coil with the primary input voltage?



Why worry about primary coil resistance?

Primary input voltage is a function of the number of turns in the primary coil. Primary resistance is a function of primary coil wire diameter and length.

 

[JMOR]

(quoted from post at 15:28:23 12/06/13) Why not simply mark the coil with the primary input voltage?



Why worry about primary coil resistance?

Primary input voltage is a function of the number of turns in the primary coil. Primary resistance is a function of primary coil wire diameter and length.

ow! Nice clean looker you have there! None of mine have even come close to clean since they left the factory. As to marking input voltage, well.............that is just too simple ......and sometimes when they do, they lie. Example Ford 9N, 2n, 8N (front distr) coils marked 12v are not really.......they still need a resistor. Pitiful isn't it?

 

[Bob (Aust)]

That is a Pertronix 12 volt, negative ground High Voltage coil. I installed Pertronix electronic ignition over a decade ago.



Bob in Oz
'53 TEA20