Heisler Igniter
Nelson Riedel, Nelson@NelsonsLocomotive.com
2/21/2010, last updated
02/21/2010

 The igniter on the shay uses a 6 volt battery (4 D cells) and an electronic circuit to pulse a 6 volt motorcycle coil (see Shay Electrical I.)  That igniter has worked flawlessly.  However, on the Heisler I want to use  a 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 --- haven’t secured yet.
 

• Push button normally open switch – Radio Shack # 275-609 looks like what I used on the Shay.

• On-off switch --- haven’t 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 (terminals 2 & 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 (terminals 4 & 6) on the lower rely will open interrupting the current flow through the upper relay coil causing it to release.

This sequence is Lower operates – Upper operates – Lower releases – Upper releases. The relays will operate and release rapidly which makes a buzzing sound.

The 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. I’ll 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. 

 

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