Nelson Riedel, Nelson@NelsonsLocomotive.com
2/21/2010, last updated
The igniter on the shay uses a 6 volt battery
(4 D cells) and an electronic circuit to pulse a 6 volt motorcycle coil
Electrical I.) That
igniter has worked flawlessly. However, on the Heisler I want to
more standard 12 volt battery. That electronic circuit can't be
used on voltages greater than 6 volts. Rather than redesign
that circuit I decided to make a simple pulser using inexpensive
12 volt relays from Radio Shack. This design is
not original; similar designs have been around for years.
The igniter wiring diagram is shown above.
On the relays, terminals 7 & 8 are the coil. Terminals 1,3 & 5 are one
contact set and 2, 4 & 6 the other contact set.
The parts I used are:
Auto Coil --- Autozone
Duralast # C819. Any 6 to 12 volt motorcycle or auto coil is OK
Long electrode spark plug for
Salamander type heater from Ace Hardware
2 12 volt DPDT relays --- Radio Shack # 275-218
2- sockets for relays
---- Radio Shack #275-220
1 5 ohm 10 watt resistor ----- I used 2 Radio
Shack #271-132 10 ohm 10 watt resistors connected in parallel
1 ~ 0.2 uF capacitor --- I
used 2 Radio Shack 272-1053 0.1uF capacitors connected in parallel
Auto type spark plug
wire --- havent secured yet.
Push button normally open switch Radio Shack #
275-609 looks like what I used on the Shay.
On-off switch --- havent purchased yet- Radio
shack has a number of suitable choices.
Fuse holder --- will use Radio Shack #270-1237
mini blade fuse holder with #270-1089 3 amp fuse.
The operation is as follows:
1. When the push button switch is operated there is
a current path from the positive battery terminal through the fuse &
power switch then through the lower relay coil (terminals 8 & 7), through
Normally Closed (NC) contacts (tweminals 2 & 6) on the upper relay, through the push
button switch to negative battery. The current flow through the lower relay
coil will cause it to operate.
2. When the lower relay operates
there is a current path from the positive battery terminal through the
fuse and power switch and then through the upper relay coil (terminals 8 &
7) through the normally open (NO) contacts (terminals 4 & 6) of the lower relay
(which are now closed because the lower relay is operated) to the
negative battery terminal. Current flow through the upper relay coil
will cause it operate.
3. When the upper relay operates, the NC contacts
& 6) will open interrupting the current flow through the lower relay coil
causing it to release.
4. When the lower relay releases, the NO contacts
& 6) on the lower rely will open interrupting the current flow through
the upper relay coil causing it to release.
is Lower operates Upper operates Lower releases Upper releases.
The relays will operate and release rapidly which makes a buzzing sound.
coil (+) terminal is supplied power from the positive battery terminal
through the 5 ohm resistor (note that I used two 10 ohm resistors in
parallel to make a 5 ohm resistor). The () coil terminal on the coil
connects through NO terminals 3 & 5 of the lower relay to the negative
battery terminal. The opening and closing of terminals 3 &
5 on the lower relay is similar to that of points on older auto engines
and will pulse the coil causing it to put out a ~ 30 K volt pulse to the spark plug
causing it to spark.
The ~ 0.2 uF capacitor (two 0.1 uF capacitors in
parallel) limits the voltage spike and arching across the lower relay
contacts on terminals 3 & 5 which would eventually destroy the contacts
if the arching is not suppressed. The capacitor also serves
to shape the pulse delivered to the coil and on to the sparkplug making
for a much greater spark.
I found it best to wire up the
relays and get them to buzz and then add the wiring to the coil.
The photo shows all the parts except the power
switch. Ill probably tape the two large power resistors to the side of
the coil. The relay sockets were mounted in a scrap piece of thin
aluminum angle. The angle will be cut to the required length once I
figure out exactly how to mount it.
Several folks have successfully built
this pulser and I've seen it used on a propane fired Shay.