What does a coil tester do and how does it do it? I see a lot of talk about properly setting up a spark coil requires a coil tester, but no one ever says what it does or how. I don't mean you attach the leads to the coil and crank it while watching the meter. I would like to know information like...does it provide a regulated current at a specified voltage while you watch an amp meter? Does it put a load on the secondary? you know, the physics of the procedure.
Steve
Steve
The hand cranked coil tester is basically a magneto just like the one inside the Model T engine, an ac ammeter meter in series with the primary winding and a spark gap similar to the one on a spark plug.
The magneto output is wired to the bottom terminal of the ignition coil just like in the Model T car when the dash switch in in the magneto position. The upper side coil terminal (timer) is wired to an ac ammeter which replaces the timer in the car. The spark plug terminal is connected to the spark ring.
As the coil tester handle is cranked the magneto output operates the coil just as it would when operating in the car. The sparks jump the gap around the spark ring. The spark gap is set to 1/4 to 5-16 inch gap because the spark will jump this gap in free air, as opposed to compressed air in the cylinder.
When properly adjusted the coil will fire every 22.5 degrees of flywheel rotation (on every positive and negative peak of the magneto ac output) and the meter will read the current flowing in the primary circuit which is normally set for 1.2-1.4 amps.
Coils with newly replaced points may be adjusted for correct operation.
The beauty of this device is that it operates the coil exactly as it would be operating in the Model T car AND excites the coil with the worst case low level magneto voltage (approximate 4-6 volts ac) and when cranked at 60 rpm the points are being operated at an approximate engine speed of 1900 rpm. If the coil will operate in this test environment it will operate very well if the cars magneto, wiring, spark plugs and timer are working properly.
Using the hand cranked coil tester is the only way you can properly adjust the upper coil point cushion spring adn vibrator balance so you can see 16 (and only sixteen) individual sparks at the coil tester spark ring.
Do not let anyone try to tell you can assure proper coil point operation using a buzz box tester because you cannot see the time and space relationship of the spark with only a single spark gap. On the hand cranked coil tester you can see each of the correct sixteen individual sparks at the spark ring.
The Model T coil is a trap for logicians. By that I mean it looks simple, but you have to know the few secrets of adjusting them correctly and you will be surprised at the difference when they are set correctly. When they are right they are great and when they are not right I will be thr frist to admit they are terrible. This in my opinion is why they get such a bad rap.
How about some of you guys who have been through this process of getting your coils properly working provide your of your experiences?
Here is a photo which may help.
Ron Patterson
The photo agian.
had mine properly adjusted and the difference was like night and day.