12volt internal resistor coil vs external risistor?

axe55

Member
May be a silly question.....I possibility made a mistake, I replaced the coil on my vac. Its been coverted to 12 volt. I bought a 12 volt internal resistor coil from napa.& removed external resistor. Is that the correct way to go ? Or should I stick w/external resistor thanks in advance john
 
Well, on a 12 volt tractor your coil choices are:

A) A true "12 Volt" coil no ballast required.

B) A "6 Volt" coil + series voltage dropping (12 to 6) external Ballast Resistor.

EITHER will work fine.

One ADVANTAGE of a 6 volt plus ballast is if you have a working ballast by pass when starting feature it improves cold weather starting.

One DISADVANTAGE of that is extra connections and possible ballast problems or by pass circuit problems.

An ADVANTAGE of the true "12 Volt" coil is no ballast problems and less wiring connections and possible problems.

A DISADVANTAGE of the true "12 Volt" coil is no by pass starting system is available

NOTICE: What lay persons call an internal ballast coil isn't exactly correct. If you x ray or disassemble a 12 volt coil, chances are great there's no internal discrete stand alone ballast resistor hidden away and tucked inside there!!!

Now to your question: "Is that the correct way to go ? Or should I stick w/external resistor"

ANSWER (A) Its your tractor and your choice now given the information above, either will work fine.

(B) That being said, if you don't already have a working ballast by pass system (whereby a 6 volt coil and ballast and by pass can help cold weather starts), a true 12 volt coil makes most sense as there's no ballast problems and less connections to go bad.

Some may prefer a true 12 volt coil and others the 6 volt and that's fine and their choice. Some may tell stories why one or the other is bad based on an experience they had and that's fine and good information.

"I report, now you decide"

Now see what others think is the best way to go as no topics draw more opinions then electrical or legal questions.

John T
 
Actually, there is. Not in common use anymore
though. I'm talking about a discrete resistor.
Used in several old cars from 60 years ago.

A modern coil labeled with "do not use external
resistor" says so because it has extra resistance
already wired into the primary. Not a separate
"discrete" unit, but the extra resistance is still
there.
 
Glen, I've never seen or heard of (but that don't make it true lol) of any typical old tractor coils (6 or 12 volt) that contained an internal stand alone discrete ballast resistor tucked away inside the can. And yes, you and I and others have informed the fine gents here of such for years.

However, to my best "recollection" and that's not very good nowadays lol, I once saw a picture/diagram of a very old car coil that had a noticeable ring around the cans bottom and inside there was a separate compartment that indeed contained a discrete stand alone ballast resistor, but seemed like this was a 6 volt coil and the years were like somewhere around the twenties or thirties??? I don't recall any cars of the 40's and 50's and up or any tractor with such a coil, but again that don't make it true.

In over 15 years here Ive learned NEVER SAY NEVER AND NEVER SAY ALWAYS because someone may jump out of the wood work and yell GOTCHA LOL as some just love to do that.

Take care my friend, if you get time Id appreciate your input on my Electrical Service Grounding post over on Tool Talk

John T
 
Back in the "old days' of autos, many companies
used ignition coils with built in ballast
resistors and sometimes built in capacitors.
Delco, Atwater-Kent, and Remy certainly had
them. In the 1930s - Delco listed four
different type coils.

#1 ROUND TYPE WITH STRAW-COLORED SHELL - has no
condensor or resistor built in.

#2 ROUND TYPE WITH BLACK SHELL - built in
resistance unit but no condensor

#3 D-TYPE WITH BAKELITE SHELL - resistance unit
built into top of coil can.

#4 d-TYPE WITH BLACK SHELL - condensor and
resistance until built into end of coil can.
a173835.jpg

a173836.jpg
 

The 12V coils have twice as many primary windings as the 6V coil . That's it and this keeps the colts to turns ratio correct.
 
No, just smaller diameter (higher resistance) wire for primary. It is the exception that does not use 100:1 turns ratio, whether 6v or 12v. Not stepping 6v to 20KV or 12v to 20KV.
 
the average joe can't walk into napa and buy one of those 6 decade old coils.. so they are virtually non existant except in very very rare situations.
 
what coil did you get? Ic14SB?


no internal resistor.. it's primary is simply hte correct ohms for it's 12v application.
 
I posted a reply to this over on the main tractor forum. But, to repeat: there have been several versions used in the past. Chrysler used them in the 50s. Most were temperature sensitive and were used to provide higher starting voltage.

Since the old flathead 6 was used in a lot of ag and industrial applications, I wouldn't surprise me to see that used there also.

As mentioned on the other forum, don't use both an external ballast and one of those coils. Did that once, car wouldn't start worth a darn in cold weather!
 
As I recall Chrysler used an EXTERNAL Ballast NOT one that was built and enclosed inside the coils can like the picture JD was kind enough to post. Many many auto and tractor manufacturers used external ballast resistors. I liked that old Chrysler EXTERNAL ballast that had two different resistors in one big block firewall mounted.

Fun chat, good info, thanks

John T
 
The goal with any coil and breaker-point system
is to keep operating voltage down to around 6-8
volts during normal running with a 12 volt
system. That is to extend the life of the
breaker points. That's done by having a total
primary resistance around 3.2 to 4.2 ohms.
Lots of ways to do that.

One is with a "6 volt" coil with maybe 2.6 ohms
on the primary windings and add an additional
1.8 to 2.2 ohm resistor outside somewhere.
Total resistance = approx 4.4 ohms. That's why
John Deere used the same coil on 6 volt
tractors and 12 volt tractors. No extra
resistor when used on 420s but with an added
external resistor when used on 1010s. The
added resistance for the primary windings
(where the battery power goes) can be all
inside the coil can - or part inside and part
outside. It's the total resistance that
counts.

When you buy a coil made for 12 volt breaker-
point systems only - and it says "no external
resistor" it means all the needed resistance is
already wired inside the can. That's all. If
you installed such a coil and then added an
extra 1.8 ohm ballast thermally reactive
resistor (or a carbon wire resistor) - the
engine would still run. Max voltage potential
would be lost though and problems might show up
in cold starting or high RPM use.

One bonus to external resistors is they can be
mechanically bypassed for over-volting during
cold starting. Or with some they vary in
resistance according to load and act like
voltage regulators. That's why some will start
to glow red and smoke if you leave the key on
without the engine running and breaker points
not operating.

Here's a brief general history of self-
contained ignition coils used in autos and
tractors in the USA. I did not author it. Good
read though, if interested.

General Motors vehicles used the same 6-volt
non-resistor ignition coil from 1923-'54. When
they converted to 12-volt in 1955, the coils
were 12-volt and externally resisted. The same
coil was used from 1955 right up until 1975;
however, a resistance unit was required on GM
vehicles newer than 1963. General Motors
changed to their "coil in the cap" electronic
ignition in 1975.
Chrysler products used the same firewall-
mounted coil from 1935-'42, but differences in
the ignition switch and cable that attached to
them changed every two years or so. You could
interchange the coils if your cable and switch
assembly could be reused. Mopar changed to the
standard 6-volt coil mounted to the manifold
when they began automotive production again
after WWII in 1946. These 6-volt units did not
require an external resistor. The same coil was
used from 1946 up to 1955. When Chrysler
converted to 12-volt in 1956, they used an
externally resisted coil, which was used right
up until 1978, even in the electronic ignition-
equipped vehicles. Point distributors required
a two-terminal resistor with 1.2 ohms of
resistance, whereas electronic ignition
distributors used a four-terminal resistor with
the 1.2 ohms primary and a secondary circuit of
.5 ohms resistance. A "tan top" electronic
ignition coil was used from 1979-'94, but it
used the same four-terminal resistor and will
also retrofit any 1956-'78 application.
American Motors borrowed several different
ignition systems from various sources, and the
AMC coils were the same units as the donor
ignitions used. From 1951-'55, the Chrysler 6-
volt internally resisted unit was used; 1956-
'59 cars used the GM externally resisted 12-
volt coil. The 1960-'62 V-8 models used a
Prestolite Distributor with a Chrysler
externally resisted coil (and resistor), but
the six-cylinder engines used two different
systems: a GM externally resisted unit (the
same coil and resistor used on 1955-'63 GM
cars) on the Delco distributors and a Chrysler
internally resisted coil on six-cylinder cars
with a Prestolite distributor. By 1963, AMC had
settled on Delco parts for their American-built
cars and Prestolite for their Canadian-built
vehicles. They continued to use the GM ignition
coil with external resistor until 1974. They
then tried the Prestolite and Holley electronic
ignition system used on International Harvester
trucks for a few years. From 1975-'77, Jeep,
International and AMC used the same
photoelectric sensor-based ignition system but
still used the same Delco-style externally
resisted coil. They later abandoned the
Prestolite system in favor of a Ford electronic
ignition setup. This system used a Ford "blue
top" electronic ignition coil which did not
require an outside resistance unit.
In conclusion, there were only about 10
different ignition coils that covered about 90%
of the American-built vehicles on the road from
the 1930s to the 1980s.
 
(quoted from post at 18:39:23 11/10/14) As I recall Chrysler used an EXTERNAL Ballast NOT one that was built and enclosed inside the coils can like the picture JD was kind enough to post. Many many auto and tractor manufacturers used external ballast resistors. I liked that old Chrysler EXTERNAL ballast that had two different resistors in one big block firewall mounted.

Fun chat, good info, thanks

John T
ne model for three years:

An interesting aspect to contemplate is that even without a temperature dependent ballast resistor, just the heating of the copper coil winding (70 to 200F) will increase its resistance (133%) enough to reduce current by 25%, which decreases spark energy by 43% or stated another way, at 200F the energy is only 57% of room temperature energy. It is no wonder that there are so many complaints of running troubles when hot.
 
souNdguy, I checked the box, it's a lc14sb....Thanks everyone, I really appreciate all the input..... you guys know your coils....I know I've asked some simple questions...Use to be able to go to the local parts store, hardware store etc. the counter guy had all the answers.... Not any more, its answer their dozen questions & they grab it of the shelf...Of all the forums I'm on, the tractor guys are the most helpful. thanks again
 
JohnT, Jmor, JDemaris, thanks for mentioning the chryslers... next time im at my bldg. I'll check the coil on my 66 chrysler imperial. I dont remember a resistor... it has a after market electronic ignition. Thanks again
 
To check 12 volts systems and assure that the breaker points are operating at 6-8 volts as was indicated one would connect a voltmeter across the coil terminal to the distributor and ground. Is that correct?
 
It will usually say on the side if a ballast resister is needed or not. If it says none required, then by all means run it without. If one is required, it will over heat and crack if you run it without the resistor.
 

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