How to test canister type coil?

[36tudordeluxe]

How would I test my coil with ohm meter to see if it has been damaged or is still good?

[Old Henry]

[BUBBAS IGNITION]

Old Henry has got it picture perfect.

However the specs are for a six volt only unit. Later coils ( 12 volt) need to be approx 1.5 ohm across the primary...

[rotorwrench]

The Ohms test only gets you in the catagory of "it might work". The old testers used for this had systems to apply voltage to heat the coil up and then it was subjected to several tests to insure proper function. The old Sun type coil testers are getting harder to find now days. More modern equipment would scope it to see if normal paterns were present during operation. THe oscilloscope with a good old distributor testing machine would run a complete diagnostic but only folks like Bubba maintain that type of equipment in the modern era.

[JM 35 Sedan]

rotowrench is correct about heated windings being necessary to properly check coils by checking resistance. Cold resistance checks on windings may not show shorted or grounded conditions that can occur during normal driving conditions. It usually requires heat and expansion of components inside the coil housing to allow these failures to occure and to be detected. Heating in an oven allowing enough time for heat to penatrate to center of coil windings or resitance heating by applying a controlled voltage for the correct time will also work.

[tubman]

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This is all good information for me. JM, to what heat should we bring the coil temp?

[Mtn Wudy]

So....Can I use the 1.5 ohm "Test" on a Stock Tan Ford coil ??? I have a Mallory hanging off of the original bracket on my 48 with a stock Ford dist.......Thanks to everybody that takes the time to clarify "STUFF" for us all...Carl

[JM 35 Sedan]

Originally Posted by tubman

This is all good information for me. JM, to what heat should we bring the coil temp?

I would suggest taking the maximum of the normal operating temperature range these flathead engines typically run, plus a few degrees more. So, if I consider the normal operating temperature of my '35 fordor engine to be 175°F to 195°F, I would think heating the coil to something in the range of 200 to 210°F would be sufficient.

[Richard in Florida]

Originally Posted by Old Henry

In broad strokes, coils meant for 6-volt systems measure about 1.5 ohms across the primaries. Coils usable with 12 volts measure about 3.0 ohms due to an internal resistor.

[Richard in Florida]

Originally Posted by BUBBAS IGNITION

Old Henry has got it picture perfect.

However the specs are for a six volt only unit. Later coils ( 12 volt) need to be approx 1.5 ohm across the primary...

Say what?

[rotorwrench]

FoMoCo continued to use the same basic coil for the 1956 models with 12-volt and continued that for some time. There was only a slight difference in the primary value. They just had to utilize a ballast resistor to control the amperage & voltage for it to be reliable. Only coils of the modern era use the higher resistance primary and many of those use an electronic trigger.

The coil primary winding on my old 51 Mercury car is rated at 1.05 to 1.15 ohms but it is a can type. The older coils before the 8BA era are a lower value yet but not by much. Coils that have added resistance generally have no warning printed on the case to use an external ballast like the older ones made for 12-volt vehicles did.

[Brian]

Slightly off original topic, but related; how much difference does these ratings make anyway? The reason I ask is because on both my '35 and my 8N tractor, I have converted to 12 jolts and still run the stock 6 v coils. Simply reverse the wiring to suit neg ground and they run sweet as! These are no name black bodied coils with goldie colored tops. They do not seem to care about primary voltage.

[BUBBAS IGNITION]

Originally Posted by Richard in Florida

Say what?

Thats correct Richard, the early six volt coils helmets etc were spec-ed at .6 of a ohm. Henrys chart shown is perfect for early six volt coils. 1.5 ohm is a fairly standard 12 volt reading and often used with a ballast resistor.
The later 3 ohm coils are typically designed for a four cylinder ( although we use them on 8's as well some times (especially lower rpm units).
The Bosch blue ( 3 ohm) was designed for the VW beetle and used for years as a factory unit.

Another problem with the 3 ohms unit is the wattage (heat) is contained into one unit where a 1.5 with ballast will divide the wattage between the two parts . Per the oem design side of the world....

Thats concerning the above discussion, when you add in later model electronic systems ( factory) we use another low ohm breed of coil with a very much different design of induction etc.. Another world, the unit lite Mallory is a electronic switching moduel be not really high voltage in the sense of the word...

[BUBBAS IGNITION]

Originally Posted by rotorwrench

FoMoCo continued to use the same basic coil for the 1956 models with 12-volt and continued that for some time. There was only a slight difference in the primary value. They just had to utilize a ballast resistor to control the amperage & voltage for it to be reliable. Only coils of the modern era use the higher resistance primary and many of those use an electronic trigger.

The coil primary winding on my old 51 Mercury car is rated at 1.05 to 1.15 ohms but it is a can type. The older coils before the 8BA era are a lower value yet but not by much. Coils that have added resistance generally have no warning printed on the case to use an external ballast like the older ones made for 12-volt vehicles did.

Todays cars use a very low resistance coil with electronic trigger as well as total current control.

[BUBBAS IGNITION]

Guys,

I think that sometimes a post needs some re-alignment as the information gets pretty far out on a given topic.
This post is also on the hamb board and started with a bad running engine etc.
My intent has been to help the orginal poster get his car running correctly.
Look up the hamb post from poster and study it over and you will have a better feel for whats happening here...

Post is here :
http://www.jalopyjournal.com/forum/s...d.php?t=871179

[Binx]

Well before it goes off the subject of testing a coil and on to other things, I'd like to suggest he jump the coil to the battery to eliminate an ignition switch problem.

Lonnie

[36tudordeluxe]

I'm showing 1.7 ohms across the terminals, room temp. was 68°. My system is 12V.

[rotorwrench]

Many of the current vehicles have a coil for each cylinder so they only have to make one ring of the bell for every two revolutions of the crank. The single coil had to work a lot harder and generated more heat. Things have changed a lot even since Ford & Chrysler started to field electronic ignition systems back in the 60s. The early ones were a lot less reliable than the ones made today but at least a person didn't have to worry about burned breaker points. They just had to worry about the car quitting for no reason on a hot day. I have had that happen several times since my first transistorized ignition system in an old 64 T-bird I used to have. A person had to wait until the car cooled down a bit then it would usually start back up. After that, it was off to the parts store for a new trigger module.

[TomO]

The ohm meter test of a coil only lets you know if it is open or shorted and if it has an internal ballast resister. It can pass the ohm meter specs and still not deliver the correct spark. With an electronic ignition it is important to be using the coil specified for the module.

A quick test for spark problems is a lawn mower spark tester available at NAPA. It has an adjustable gap and connects between the plug wire and the plug. Set the gap at about 1/4" and run the engine while watching the spark. If the spark disappears when your engine is running rough, the problem is upstream from the plug wires (plug wire, distributor, coil ignition switch, grounding, etc). If you have a good spark when the engine is running rough, the problem is downstream from the distributor or fuel related.

[Ronnie]

Some good grass root testing here.
http://mgaguru.com/mgtech/ignition/ig108.htm

R

[36tudordeluxe]

Just found Mallory tech. sheet that comes with the Mallory coil, it states " all Mallory Unilite distributors & Mallory Breakerless distributors both need minimum amounts of primary resistance of 1.4 ohms or higher to remove the ballast resistor. Any coil with LESS than 1.4 ohms of primary resistance, MUST use a ballast resistor." I'm showing 1.7 ohms of resistance across the terminals on the coil. I think I will bypass the ballast resistor and see if it runs any better. Any thoughts?

[BUBBAS IGNITION]

Originally Posted by 36tudordeluxe

Just found Mallory tech. sheet that comes with the Mallory coil, it states " all Mallory Unilite distributors & Mallory Breakerless distributors both need minimum amounts of primary resistance of 1.4 ohms or higher to remove the ballast resistor. Any coil with LESS than 1.4 ohms of primary resistance, MUST use a ballast resistor." I'm showing 1.7 ohms of resistance across the terminals on the coil. I think I will bypass the ballast resistor and see if it runs any better. Any thoughts?

Sounds good assuming we havent already hurt the module.

Using a .6 ohm coil and 12 volts we would have a current flow of 20 amps.

A 1.7 ohm coil would draw 7.05 amps

And a 1.7 ohm coil with a 1.7 ohm resistor would draw 3.52 amps.

All three would run ok however the 20 amps would overload the module !

I dont remember , did we replace this module before ?????

[BUBBAS IGNITION]

See the post for discussion .......

[36tudordeluxe]

Originally Posted by BUBBAS IGNITION

Sounds good assuming we havent already hurt the module.

Using a .6 ohm coil and 12 volts we would have a current flow of 20 amps.

A 1.7 ohm coil would draw 7.05 amps

And a 1.7 ohm coil with a 1.7 ohm resistor would draw 3.52 amps.

All three would run ok however the 20 amps would overload the module !

I dont remember , did we replace this module before ?????

Yes, you replaced module after I fried it by using the Mallory E series coil. Am even more confused now as the coil I have in the car now is a Mallory with a brown top which I believe is the 29216 coil, yet it shows 1.7 ohms, brown top should read less than half that amount.