Coils strong & weak spark

[John0]

I have a question for the coil experts. I've been rebuilding some coils, checking the primary & secondary winding's, and replacing the capacitor. I am using both an old amp type tester and ECCT tester to set these up correctly. I've done about 10 so far and 5 have a strong spark and 5 a weak spark. The resistance of the primary & secondary winding's are the same and have new capacitors.

The question is why when 2 coils are setup and tested the same, why the spark is a lot stronger on one than the other.

Regards John O, Perth, Western Australia

[Mike Silbert]

Adjusting coils is a balancing act with many factors at play.
There has been a lot of documentation and discussion about how to properly adjust the coils.
There is even a lot of discussion about the proper way to test and where to set coils.
A properly adjusted set of coils is one of the large factors in having a good running Model T Ford.
Working with someone who has experience in this is the best way to learn.
If you want to tackle this yourself here are some of the things that make a difference:

Capacitance value (and voltage)
Points condition
Points alignment
Points insulating fiber washer condition
Upper point drop
Upper point spring pressure
Lower point spring pressure
How far the spacers have sunk into the wood box
Gap from core pins to lower point
Type of core (pins or strips)
Primary winding count
Secondary winding count
Connection and wire condition (cracked and broken wires also)
Connection quality at button connections
And probably other things I forgot about.
There are some coils that just do not perform well.
Over the last 100 plus years they have been made in many, many, many batches by many, many people and "repaired" many times making it a very mixed lot today.

MTFCA makes a great set of books on how to restore parts but they will take a long time to get to Australia.
This is such a broad question is suggest you search "mtfca coil adjustment" and see if anything makes a difference.
Like https://www.mtfca.com/discus/messages/5 ... 1464833674
You will find a whole lot of information and styles and opinions.
Even how you are testing your coils makes a difference in what you are seeing for results.

More information and details would make it easier to get an answer for you.
Mike

[Moxie26]

Mike .... You could add this to your list, the cleanliness of the metal contacts, which would include the cleaning of the outer coil box contacts, cleaning of the top coil point mounting hardware including the posts and nuts and standoffs, cleaning of the upper contact adjustment spring and post with new insulator.....,.. .. past manufacturers of replacement coil point sets have been putting out items that have metal alloy strengths and weaknesses. Most recent with the last manufacturer, the upper bridge was of a thicker metal and also had the cushion spring rivet mount it with a better clearance, averaging about 0. 010 " .... Others have had thinner Bridges, various cushion spring clearances and I'm sure various tension settings..... The same with the vibrator spring tensions. Our fellow Model T. Hobbyists, on the most part, may not be aware of all the variables involved in proper coil recalibration, hopefully this information will bring some realization of what is involved.

[TXGOAT2]

One possibility is that the weaker coil units have high voltage shorts in the secondary windings. That might not show up on an ohm- meter test, but when actual high voltage is developed during coil unit operation, the short circuit would become evident in the lower output. It's best to limit the gap across which the coil unit throws a spark to about 1/4 inch. A good coil unit can throw a spark a lot farther, but causing it to do so risks breaking down insulation in the secondary winding.

[MKossor]

It may help to provide screen captures of the ECCT screen showing the results of the Capacitor test, single spark test results and multi spark test results for both coils to compare the differences.

[John0]

update, on further investigation I went over all the work I'd done covering the detailed points noted by Mike Silbert, (thanks for such a detailed reply), found that the biggest issue was the condition & quality of the points, I would not have expected it to make such a difference, it now looks like a buzz and a sparking of the contacts does not mean that they are working at the optimum.

careful cleaning and adjusting and replacing those that were obviously bad has shown me that this was the main issue causing a poor spark.

thanks for all the helpful suggestions

[Moxie26]

Good morning John... Well the dealings with coils with used points is different than replacing with new points. It really means to keep those used points in the same mounted position... The only way revive those points would be to spray with carburetor cleaner to remove any Gunk and also to use a double-sided Point file between those points to get your new surface that hopefully will be parallel with the current installation position, re sprayed clean..... And then electrically calibrated... . And this should be done after the installation of the new capacitor/ condenser and repotting..... And it's very likely we will be doing this if the supply of new points never goes to fruition. ,..... .. used points do not have flat surfaces. There will be tungsten transfer from one point to the other creating dips and hills, visible or microscopic,

[Mike Silbert]

And NEW points also need inspection, possible rework, and cleaning before use.
They are not always perfect out of the box.
They are hand made and quality will vary.

It's a good idea to inspect all used and new parts anyway.
Mike

[TXGOAT2]

Issues with the point set is probably the commonest source of trouble with coil units aside from proper adjustment. Points can be filed to remove minor pitting and corrosion, but the actual contacts consist of a steel base with a platinum overlay. If the platinum is worn or filed away to as to expose the steel, the points won't work well for very long. The springs and other hardware need to be in good condition and the entire assembly needs to be in good alignment. Running good points with a bad condenser or poor coil adjustment will cause the points to wear rapidly due to excess arcing and excess current flow.