Before beginning it is very important that you note that the output (secondary) side of a Buzz Coil is extremely high voltage and is very dangerous. That voltage is going to be exposed on "open to fingers" terminals in this tester. Handle it the way you would handle a live spark plug!
The items you need to build this tester are:
- Plywood rectangle about 300mm x 400mm (approx 12" x 16")
- 12 VDC Volt Meter (at least 12V)
- Zero centre 3 Amp Ammeter (at least 3A)
- 3 Amp fuse and fuse holder
- 6VDC or 12VDC Sealed Gel Battery or Dry Cell
- 12 AWG Automotive wire
- 10 AWG Copper Spark Wire (not silicone)
- A set of spark gap terminals (can you spell "nails")
- Heavy Duty Alligator clips for terminating the wires at the buzz coil ends
- 12VDC 10Amp Toggle Switch - do not use a household fitting!
- You might consider adding a DC Earth Leakage Detector
The spark gap should be set at about 7mm (1/4"). This gap is of course much bigger than the gap in a spark plug as it is in the open air where the resistance to the arc leaping from terminal to terminal is much less than if it were in a compressed combustion mixture within a closed combustion chamber. Thanks to Roy Rice for the picture.
To test a buzz coil, wire it into the tester as shown in the diagram in the following order:
- Spark Connection
- Negative Connection
- Positive Connection
Now that you have finished your tester, you can use it to test and adjust your coil.
As an added fun thing to do, you could get some steel wire (such as piano wire, or a guitar string) and make two vertical feelers at the spark gap which start about 7mm (1/4") away from each other then bend away. You've just made one of those interesting spark gap machines you often see in old horror and science fiction movies! Note that not all coils will be strong enough to make one of these work.
A further note is that this unit is a very effective spark gap transmitter and will disrupt television, radio and other such devices which are close to the unit.
The photos in this article are © Copyright Roy Rice 2001 All Rights Reserved.