Re: Science Fair Project

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Re: Science Fair Project
From: Tesla List <tesla-at-stic-dot-net>
Date: Thu, 13 Nov 1997 09:16:08 -0600
Approved: tesla-at-stic-dot-net

From:	Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:	Wednesday, November 12, 1997 10:20 AM
To:	Tesla List
Subject:	Re: Science Fair Project

> I know that this is probably a bumb questions that shows my ignorance,
but
> what is "12 volt square wave" . I get the idea it means just feed it
> bursts of electricity? I've read you can do this with a 555 timer- Is
that
> true, I would think the voltage would be a little high for a 555 timer...
> 			Matt
> 
You can use a 555 to generate pulses to turn a transistor on and off in the
primary circuit of the coil. That transistor needs a fairly good voltage
rating (>400 Volts) and has to carry 5Amps.  I would suggest a much lower
tech technique, the buzzer.

Hook a relay up so that the relay coil is powered through the Normally
Closed contacts. You can see how this would work. Assume the relay is OFF,
apply power. Power goes through the NC contacts and makes the relay pull
in. Now the contacts open, and the relay drops out, closing the contacts,
making it pull in, etc. The buzz frequency is related to the mass of the
armature and its spring constant.

Connect your ignition coil across the relay coil and you'll get HV pulses
out of the ignition coil. You will probably want to put a .01 to .1
microfarad cap across the contacts of the relay or they will erode in a
short time. If you can scrounge up an ignition points capacitor (or
condensor as they are called in the auto repair biz) that would be ideal.
They have the voltage rating, and are the right capacitance for the
application.

The relay should be a fairly sturdy one, with contact ratings better than
5-6 Amps (try for 10 Amps). Don't use the little dip relays.

Good luck.