Ignition - Relay alternative

[Kane2oo2]

hey all
I am currently using an ignition coil to create a spark, by tapping the negative lead on/off the input. I have tried to use a relay so that a push button could be used, but this just seems to create a spark across the internal contacts and so no spark occurs across the spark gap.

So what im wondering is ...is there an alternative to the relay which would still be able to operate at these high voltages?

Thanks
Kane

 

[stevez]

Ignition coils were originally "fired" by "points and condenser" and the "points" were little more than a pair of contacts that were opened by a cam, held to the surface of the cam by a spring that allowed the points to open/close/open/etc as the cam rotated.

In that old system the condenser (capacitor) was required for best spark. Yes, there was a spark across the points as they opened and it did burn the contacts which is why we had to file the points or replace them periodically. First electronic ignitions used points to trigger electronics that fired the coil however points were replaced by better systems eventually.

Note that the spark on the secondary (high voltage side) will occur only on opening of the contacts. Closing of the contacts builds the magnetic field that collapses on opening of the contacts. For repetitive sparks you need to open/close the contacts over and over. Guess what - they used to do this with a device called a vibrator (no idea if this had a secondary recreational use then) that was a relay that buzzed open/closed - providing pulsating DC to a coil or transformer for generating the higher voltages needed for vacuum tube supplies.

You might employ a solid state circuit to trigger the coil driven by a timer or square wave oscillator. Realize that there will be substantial current drawn by the primary and that you might need to protect against voltage spikes. For guidance search on solid state ignition or electronic ignition conversions. Its seems that in racing the old point type distributor is still popular - likely because it's so easy to understand.

Good luck.

 

[jbeng]

Here's a circuit which has worked for me. It's basically the "vibrator" circuit that stevez described. It uses a pushbutton switch and a double-pole, double-throw relay. Here's how it works: When you push the switch, the current flows thru one set of the relays normally closed contacts. This causes the relay to energize, pulling in the contacts. When this happens, the relay breaks it's own power and releases. This happens very quickly and will continue as long as you hold the switch. The relay will make a buzzing (vibrating) sound, the speed of which is limited by the mechanical parts of the relay. The second set of contacts (used to control the ignition coil) are simply along for the ride... they make and break at the frequency of the buzz. Also, like stevez said, these relay contacts will likely burn out eventually. This method can generate some pretty hot sparks between the contacts of the spark gap. Be careful ... it can pack a punch! JB

 

[Kane2oo2]

thanks for the replies

when you say the contacts will burn out eventually... how long a period are we talking?

the circuit will only be operated for a max of 3-5 seconds each time.

 

[ante]

Kane,

This circuit will power your coil without burnt contacts:


Ante :roll:

 

[audioguru]

Ante,
No diode across the coil?

 

[spuffock]

A diode across the coil will kill the spark.
No diode across the coil will kill the transistor.
You can't win.

 

[tansis]

Here is an old fashioned way of doing things...

 

[jbeng]

when you say the contacts will burn out eventually... how long a period are we talking?

I really can't answer that one ... my contacts never burned out. But, switching that amount of current will almost certainly have an adverse effect on the contacts eventually. JB

 

[Kane2oo2]

tansis - how does that work then?
is it just using the contacts inside the motor to make/break?

thanks
Kane

 

[ante]

audioguru,

A diode across the transistor is good. I found the circuit on the net and it is supposed to work as is. Haven’t tested it!

Ante :roll:

 

[ante]

There are some that gets away with no diodes.
Here is some info on ignition coil drivers:

http://www.powerlabs.org/igncoildrivers.htm

http://www.geocities.com/CapeCanaveral/Lab/5322/coildrv.htm

**broken link removed**


Ante :roll:

 

[Kane2oo2]

well....i've been testing something else today.

i have a relay which is on an IR detector circuit, and using a tv remote to trigger it. and this is connected to my Ign'n Coil.

and what i have found is that if i click the relay on/off at around half second intervals ...the ignition coil will spark after 8 clicks (4 seconds)... and this happens consecutively.

what does this mean?

how come it triggers in this way?

Kane