Weak sparks when bench testing coil

[sagaboy]

Using a fully charged 66 Amps battery, I wired it up with the negative on one end of a 1.5 Ohm 12 volt coil with no internal resistor and the out-put (centre of the coil) connected to a spark plug with normal gap of 0.28 The spark plug was grounded (the screw head) to the negative of the battery and a grounded wire was place 2 mm near the spark plug.
Next
I simply apply the battery positive by--touching one end (positive side) of the coil, I can see sparks coming out of the spark plug--BUT--somehow, the sparks are pretty weak and no where near or as strong (blue white) as it should be.

I remove the coil from my working car that is running fine, the sparks were really strong (blue white) when I test it by using a crew driver to flip the contact point to create the spark.

Any reason why the sparks are weaker when the coil is out of the car?

[Dale M.]

No... Other than the pulses will be sharper and better spaced when using a distributor.... Mount a distributor in a vice and adapt something to spin it like a electric drill.....

Also any weak or poor wiring will cause you grief... Be sure you have it "right"...

Basically this should be all you need.....



Believe the polarity of battery and points are wrong.... But its a "concept" graphic and not a true wiring diagram...

Dale

[Ol'fogasaurus]

And don't forget about the important job the condenser does.

[fusername]

true, but without the condesnor this will work on the bench. it will eat points eventually, but no big deal I would think for a few quick tests. a failed condesnor can give you grief by kinda sorta shorting out the points. AFAIK the condesner has zero effect on the spark, but stops a spark from forming inside the points themselves as they open. or minimizes the spark, there is still a spark, just smaller and softer than it could be w/o one.

[Piledriver]

For the record, the spark happens when you disconnect the juice.
(points open, magnetic field collapses)

make sure the polarity is right, it makes a huge difference (+ on 15, gnd on 1)

[sagaboy]

I have hooked-up an analog amp meter between the + battery to the coil and noted that the maximum current flow to the coil is about 2 amps

[sagaboy]

...make sure the polarity is right, it makes a huge difference (+ on 15, gnd on 1)

Technically, a distributor coil is just some primary copper winding to magnetically induce a high secondary voltage to jump the spark plug gap hence doesn't matter whether which side of the coil is connected to the battery + or -

[Ol'fogasaurus]

Recommendation; If you can find one, or maybe your library might have one: Petersen Publishing did a book called Ignition and Electrical Systems No 5. Library of Congress Catalog Card No. 73-79968, IBSN 0-8227-5014-7. Copyright 1977 and it was edited by Spence Murray who is an Ol' Tyme Hot Rodder.

My copy is older than most of you and is an updated version; it pretty tattered and falling apart from age and use. It deals with what most of you would call either old $#it or yep, that's what I got ignition systems. If you are still running points and condensers then it may be of some use to at least read and understand. I do keep it in my library for referencing back to.

While it is more towards US systems the basics are there of other systems. Among other (old) things it covers coils and how to test them and discusses points and condensers; e.g., how/why they work, what they do and some of the reasons they fail.

One thing I do remember about testing coils (its been a long time since I have had one fail), even shops that have the equipment to test them will say that the tests may not always be conclusive as the can be just hard to test accurately. I have taken coils I suspected to several different shops and got different results/opinions from each place.

Lee

[Piledriver]

...make sure the polarity is right, it makes a huge difference (+ on 15, gnd on 1)

Technically, a distributor coil is just some primary copper winding to magnetically induce a high secondary voltage to jump the spark plug gap hence doesn't matter whether which side of the coil is connected to the battery + or -

Technically that is true if you ignore how they are wound and how sparks jump from "hot" to cold preferentially or from sharp points on a spark plug.

Or, swap the wires on the 1 and 15 terminals on your car, and see how it drives.

It will idle fine, but don't be surprised if you can't clear 30 MPH, the weak spark will blow out under any load.

Reality frequently delivers surprising results.

[telforddorr]

The condenser is critical to the operation of the Kettering style ignition system. In operation, the coil produces proportional voltages (~1:100) on both the primary and secondary windings of the coil. The primary voltage is thus several hundred volts when the points open. The problem is that points (or whatever you're using to emulate the points) just can't open fast enough to keep from arcing and dissipating a significant amount of the energy stored in the coil's magnetic field (this leads to 'burned' points). The condenser absorbs this energy for a short time, allowing the points time to open far enough to avoid arcing (or more accurately, arc at the spark plug rather than at the points). The condenser's absorbed energy is ultimately returned to the coil.

Solid state points replacement modules do not have this problem as the driving transistor can turn off quickly, and withstand the multi-hundred volt pulse from the coil primary winding. This is why the condenser is removed when a solid state ignition module is installed.

Bottom line: hook up a condenser to your test bench circuit to emulate the one in the distributor. It should make a significant difference in the circuit operation.

[sagaboy]

Re: "Bottom line: hook up a condenser to your test bench circuit to emulate the one in the distributor. It should make a significant difference in the circuit operation."

I will give that a try--never cross my mind that the condenser plays a part when bench test the coil capacity to produce the correct sparks.