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6 volt vs 12 volt coils

S

Sopp

New User
I have a box full of coils without any markings on them. How do I test to find out which are 6 volt and which are 12 volt? Also, how can I test to find out if some have built in resisters? These are just standard automotive type ignition coils.
Thanks for any help.
Sopp
 
6v 1.5 ohms 12v 3 ohms.You wont find any coils with a built in resistor, no room inside plus the heat of the resistor would over heat the coil.
 
A coil IS a resistor. The coil made to run on 14 volts, and start on 9 volts - and be wired with no extra "ballast" resistor is what is called a "12 volt" coil by many.

If one coil measures 1.5 ohms across the primaries, that part of it IS a 1.5 ohm resistor, etc., etc.

Historically, in the 1930s-40s, some coils did have an extra resistor built inside the can. Not something you see anymore.

Ignition coils specs (a few)

1992 Subaru 12 volt system breakerless: 2.4 ohms across primaries

NAPA IC-12 Echlin 2.1 ohms primary, 8.9 ohms secondary. For 6 or 12 volt systems

NAPA IC-14 Echlin 3.25 ohms primary resistance (no external resistor used) 12 volt system.

NAPA MPEIC14SB same as IC-14, just cheap Chinese. $18.69

NAPA IC-27 Echlin 2.2 ohms primary, 6.38 ohms secondary, for 6 or 12 volt systems

A500 12 volt 2.6 ohms primary, 9.8 ohms secondary
12 volt systems

Deere 6 volt (as used on 430, 1010) 2.6 ohms prim, 7.12 secondary

Hot Spark brand coil - HS06HEC - HEI, CDI and electronic ignition systems requiring a coil
with 0.6 Ohms primary resistance. 11.6 K ohms secondary. For 6 and 12 volt systems

Mallory 29219, 6 and 12 volt system coil - primary 1.4 ohms, secondary 9.8K ohms.

Accel coil for points, 1.4 ohms primary resistance, 9.2 k ohms secondary resistance,
42,000 volts maximum voltage. 6 and 12 volt systems
 
There were some coils that actually contained discrete internal resistiors buttttttttt that was more older cars and some had like a ring/junction mark visible on the exterior where the resistor was separated and contained inside but that was more for older autos and I havent seen them on tractors of the 30 to 50 vintage.

What some call "Internaly Ballasted" coils isnt quite correct, the greater resistance is made up of more wire turns or higher resistive wire NOT an internal discrete resistor.

Many farm tractor coils that have say 1.25 to 2+ or so ohms primary (between lil + and - terminals) are for use on 6 volt while if they have 2.4 to 3.5 ohms those are 12 volt coils. Of course they are designed to produce a spark at much reduced cranking voltages and still operate and not overheat at the raised charging voltages

Hope this helps, get out your ohm meter and check them out

John T
 
Copper wire has its own resistance.Wire size and the number of turn wound determine the voltage.An ignition coil with a 9 ohm secondary resistance wont work,in any case we are dealing with reactance since coils produce an alternating voltage.
 
(quoted from post at 20:17:48 09/04/10) A coil IS a resistor. The coil made to run on 14 volts, and start on 9 volts - and be wired with no extra "ballast" resistor is what is called a "12 volt" coil by many.

If one coil measures 1.5 ohms across the primaries, that part of it IS a 1.5 ohm resistor, etc., etc.

Historically, in the 1930s-40s, some coils did have an extra resistor built inside the can. Not something you see anymore.

Ignition coils specs (a few)

1992 Subaru 12 volt system breakerless: 2.4 ohms across primaries

NAPA IC-12 Echlin 2.1 ohms primary, 8.9 ohms secondary. For 6 or 12 volt systems

NAPA IC-14 Echlin 3.25 ohms primary resistance (no external resistor used) 12 volt system.

NAPA MPEIC14SB same as IC-14, just cheap Chinese. $18.69

NAPA IC-27 Echlin 2.2 ohms primary, 6.38 ohms secondary, for 6 or 12 volt systems

A500 12 volt 2.6 ohms primary, 9.8 ohms secondary
12 volt systems

Deere 6 volt (as used on 430, 1010) 2.6 ohms prim, 7.12 secondary

Hot Spark brand coil - HS06HEC - HEI, CDI and electronic ignition systems requiring a coil
with 0.6 Ohms primary resistance. 11.6 K ohms secondary. For 6 and 12 volt systems

Mallory 29219, 6 and 12 volt system coil - primary 1.4 ohms, secondary 9.8K ohms.

Accel coil for points, 1.4 ohms primary resistance, 9.2 k ohms secondary resistance,
42,000 volts maximum voltage. 6 and 12 volt systems
Click to expand...

Yes but.....................ohms is a DC value. And 99.9999% of the time that's enough.
An ignition coil is supplied with pulsating DC. A coil's performance is more of an Impedance "XL" value used with AC equipment. Characteristics of the iron core and magnetic path also affect the amount of stored energy and "charge time".
 
Thank you for the quick replies.
I will test my coils and see if they can be identified by their resistance.
 
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