testing a coil inquiry

[donQ]

A 9/02/2014 post was made regarding bench testing a coil . Tom Wesenberg made a reply suggesting placing a condenser across the coil terminals, then connecting a battery to one terminal, and simulate opening and closing of the points by momentarily touching a wire from the other battery terminal to the other coil terminal.
This as usual, is good advice, but I'm curious as to why the condenser is used in this sort of bench test.
donQ

 

[tbirdtbird]

it won't throw a 1/4" spark without it, just a tiny weak orange blip

google search "Kettering ignition points system"

such as
http://en.wikipedia.org/wiki/Ignition_system

 

[Mike V. Florida]

Most don't realize that the condenser does more then just keep the points from pitting. To be real simple, they "back feed" into the coil boosting the output.

 

[Kevin in NJ]

Still that is not a good test.

I got some practice testing coils from the days of owning a V8 60hp 39. Coils tested good when first connected to the coil tester. Then I would let them heat, that is leave the current flow through the coil. Then retest and the spark would just sputter.

You have not tested the coil unless you have heat soaked it. I have seen it in coils from the A's on through to 65 Mustangs.

 

[tbirdtbird]

i agree

 

[larrys40]

I concur that a coil needs to be load tested with voltage applied to heat it up to ensure that it will pass a stress test . I use a ford heyer stroboscope , test for 1.2-1.4 ohms on the primary and 10-12 kv on the secondary on straight pole, and more on the slant poles . The stroboscope uses an air motor with a breaker point setup to simulate operation on a car to produce the open/close of the voltage to the coil to produce the spark. You could create your own tester with some ingenuity. I'm thankful I've had these machines as they have been indispensable to strobe distributors, test coils, and condensers . Like sun's old slogan says... "Test, don't guess"

Also, don't take for granted every new coil and condenser is good. They aren't.
Best of luck
Larry Shepard

 

[BRENT in 10-uh-C]

Also, don't take for granted every new coil and condenser is good. They aren't.

Boy, ain't THAT the truth! I too owned some nice looking coils that ran "ugly" on an engine and I only found it once I purchased a coil tester. Somewhere here in the archives is several pictures of my unit showing coils being tested both before and after heating.

 

[donQ]

Thanks for the input fellas. When I've tested coils in the past, I've hooked a condenser from the + side of the coil to ground, not to the other terminal. The comments regarding checking the coil health with the coil at operating temperature are right on the money.i've has engines that would start and run and then quit after about 15 minutes running due to the coil failing at temperature.
donQ

 

[Tom Wesenberg]

I've never had a coil failure, but have seen customer's cars fail when they get hot. This was mostly 60's Fords with the small coil, and 70's and 80's MoPars where the control box for the coil failed when it got hot. I'd carry a quart of water and pour it on the control box to make it back to the shop.

 

[ctlikon0712]

I have one of these, I haven't had the opportunity to use it yet. Tom, are you familiar with this particular unit? What are your thoughts?

 

[Tom Wesenberg]

I haven't seen that unit, so can't help, but it looks like a quality piece of test equipment. The picture is too small. but is that an ALLEN? You might find instructions on the internet.

 

[fiddlybits]

I just rip em open and look inside to see if they are good.....


(funny, they all seem to be bad after that..... )

 

[ctlikon0712]

Tom, it is a SUN # AA 6881 So far these are the only instructions that I have found. Thanks anyway. I remember that you made your own coil tester and I was impressed.
As always I appreciate your input.

 

[Tom Wesenberg]

It's nice that you have the manual for it. Usually these old pieces of test equipment have dried dirt and grease on the wires and clips. I spray WD-40 on them and rub them with a cloth rag to clean them.