Is it possible to bench test fire a coil using a battery charger? I mean checking the spark strength from the high tension cable, checking the "zap" that would go into the distributor cap?
Try a 9volt flash-light battery Hook up a switch on the neg. of coil side to minus on the battry. then flick the switch to check if you have spark /K ............................................ Taildragger&fenderless
To test a coil just hook the plus to 12 volts. every time you touch the minus to ground a spark will jump from the wire in the top of the coil.
Well, here is what I have found. The charger has 5, 10, and 50 amp positions. I began with the 5 amp position and grounded/broke the ground on the - side of the coil. The charger "jumps" to a higher amperage as the coil is grounded, to about 15 or a little more amps on it's own while in the 5 amp position. I tried 3 known to be good (resistance tested) plugs. The gap had to be reduced to @ .010" to get any spark. The high tension wire I used passed the resistance test also. I tried 3 coils, all of which passed primary and secondary resistance tests. The charger works properly, it will charge a battery OK. I tested an new coil as above, same outcome. I put that new coil in the car, and while cranking it fires to about .030 gap, the car runs OK with the new coil. I am not getting why the charger will not just energize the coil on a bench test with the same charge as when the coil is wired into the car.
I think I agree that the coil should bench test the same way it does on the car. But I'm guessing that when you're bench testing the body of the spark plug isn't properly grounded. Try also running a test lead from the negative side of the charger to the threads on the spark plug.
Is the ground from the plug to the negative side of the coil substantial? Regardless of what the charger says it's putting out, it's probably wrong. There is usually built in protection circuitry. Try a car battery and jumper cables. Ground from battery, to coil, and to spark plug. Touch positive battery to positive coil momentarily, and when released, it should spark. Coils are designed to work at 9v. Do you have a meter? Try it with a 9v battery first, and see it it builds up to 9v when you touch it to the coil as described above. If not, then car battery, I guess.
A car battery can supply hundreds of amps....a charger can only supply much less. If you add a capacitor to the circuit, you might get a different result with the charger. A capacitor stores energy, sort of like a very short life battery.
That is a good thought, and I did that very thing. The spark plug body was grounded (held in the bench vice), and a ground wire was attached from the vice bolt to the plug body, and then that ground wire was then attached to the ground wire on the charger also. The ground wire was 14 gauge, same as on the car wiring.
The coil takes a lot of current for a very short time, every time it fires. The average current is not very high.
When your checking it on the car is there a capacitor in the circuit? Believe the capacitor is required to get the proper voltage rise. It is an capacitor/inductor circuit.
My understanding of the function of the condensor (capacitor) is as follows. The condenser acts as an alternate path for the current flow when the breaker points begin to open, which causes resistance across the points to increase. Without the condenser, the points would arc and burn the contacts rapidly. Since electricity "follows the path of least resistance", the current flow "sees" the path to the condenser as less resistance than the contact points as they begin to separate. So, the condenser (capacitor) absorbs the current, becomes 'charged' and, when the points close again, the condenser harmlessly 'discharges' into the coil primary winding......and is ready to go when the points open again. Condensors are rated in farads (microfarads) and a capacitor that is not correctly matched to the ignition circuit components will not be as effective at reducing point arcing as one that is well matched. The over or under capacity of the condenser can be determined by which side of the contact points have the 'barb' and which has the 'pit', assuming the coil polarity is correct. Ray
That's just part of what the condenser does: "When the points open to break the ground contact the primary current must stop flowing, and the magnetic field in the Coil will collapse. The collapsing magnetic field forces current to continue flowing in the same direction momentarily, and that current will charge up the capacitor. Forward inertia of this forced current raises voltage at the capacitor momentarily to about 300 volts, at which time this high voltage stops the current. The current then reverses direction, being driven backward by the high voltage at the capacitor. After the charge in the capacitor is depleted, inertia of the current in the Coil continues to drive the current in that direction to charge the capacitor in opposite polarity. The cycle then reverses. The result is an electrical ringing like a bell which reduces rapidly with time. The initial 300 volt spike in the primary winding will drive an output in the secondary winding up to 30,000 volts. The output current going to the spark plug will likewise ring in harmony with the input current, for as long as the output voltage is high enough for current to jump the spark gap under compression. Assuming the initial spark ignites the fuel air mixture, combustion pressure will rise rapidly, and the spark will stop almost immediately as voltage falls. By now it should be obvious why the capacitor is an essential part of the ignition circuit, and the engine will not run without it."
I'm not sure about that explanation. Without the capacitor, I've seen voltage spikes of hundreds of volts across the points with an oscilloscope, and once the capacitor is placed across them, the arcing almost disappears, and the voltage drops to battery voltage. This is just what I observed, and my teacher explained the purpose of the capacitor was to stop those voltage spikes that would burn up the points.
That is what part of the function of the capacitor is, but that's not all of it. Find out for yourself, disconnect the capacitor and see how it runs. That should solve the question. And if you saw one running on an oscilloscope connected up properly you should see what a lot of people call the "ringing" . If you don't want to believe how points ignitions work, it fine, but some people might want to know what is going on.
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