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Registered Member #3026
Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54
Hi, Everyone
I am trying to drive an ignition spark coil with a microswitch activated by an eccentric on my small DC motor shaft. The coil is getting about 12 volts pulsating DC. I have a 0.1 mf capacitor across the switch. However, the spark I'm getting is barely visible! In a car, the coil is driven by the points -- just an on-off switch. Are these ignition coils designed to operate at a certain frequency? Why doesn't my set-up work very well??
I am trying to drive an ignition spark coil with a microswitch activated by an eccentric on my small DC motor shaft. The coil is getting about 12 volts pulsating DC. I have a 0.1 mf capacitor across the switch. However, the spark I'm getting is barely visible! In a car, the coil is driven by the points -- just an on-off switch. Are these ignition coils designed to operate at a certain frequency? Why doesn't my set-up work very well??
Thanks much! John M.
I will think you dont have enough current, are you running this with a battery? also if you runing with a battery check this site out it has a driver circuit.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
These coils are designed to operate at a certain frequency, or rather to have a maximum frequency.
What frequency are you driving it at?
For example, when Jaguar introduced their V12 engine, they had to have ignition coils designed to operate in excess of 5,000RPM X 12 (one spark per cylinder every second revolution) eg 30,000 per minute (I think, I've had a few drinks this evening, so check my maths) = 5kHz.
EDIT: The figure that is important here is the 'dwell angle'.....The spark gap (points) needs to be closed for a certain amount of time before the coil 're-generates'.
EDIT: Also, you need a condensor (capacitor) of the correct value for the coil to function effectively. I forget the typical values, though. It's a long time since I tuned engines (30 years).
Registered Member #3026
Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54
Thanks, Andre
I think you are right: I am using a laboratory, regulated power supply delivering a max of three amps! I plan to build the driver in the link you included. How can I power this driver to deliver six amps?? Would two lantern batteries do the trick?
I think you are right: I am using a laboratory, regulated power supply delivering a max of three amps! I plan to build the driver in the link you included. How can I power this driver to deliver six amps?? Would two lantern batteries do the trick?
I think the power supply has enough current, is just you need the correct driver circuit. it should work with the batteries and the power supply once you build the driver, post a video when you get it runing I will love to see.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
3A is not sufficient to drive a standard automotive ignition coil. 7A is typical for standard coils in a 12V system.
In the left frame we see a discharge across a 5mm gap with 7A pulsed primary current. The anemic effort on the right is the same gap and coil with 2A pulses.
If you are new to all this, I would advise you not to use any power supply you can't afford to replace, as high voltage spikes can sometimes travel back up the line and ruin your PSU. A 12V car battery would be a good place to start, and will provide plenty enough current.
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Ignition coil driver
