A project log for Unity Candle

Taking the idea of a unity candle to the next level

QuinnQuinn 05/05/2014 at 18:580 Comments

Ignition is handled using a Hot Surface Ignitor.  These are frequently used in modern gas driven furnace's and hot water heaters, and are available on the parts market, around 30-50 USD.  Simply power them to rated voltage(some are 120VAC, some I believe are 80VAC), and they will heat up glowing red hot.  The surface will exceed the ignition temperature of propane, so when propane and oxygen contact it, they will ignite.

A shroud was made with a length of galvanized steel ducting to mount the HSI.  The shield serves to protect the HSI from the wind, which may cool it faster than it's heater can add heat.

I just tabs into the duct to mount the HSI, and other tabs to form a mounting on the barrel.  It is attached to the barrel using a simple pipe clamp.  The HSI is screwed in with a sheet metal screw using it's mounting tab.

I made tabs on both sides so that a redundant HSI could be used.  I understand these are fragile and prone to breakage, so I wanted a backup.  The second is not mounted at this time.  I used the included ceramic wire nuts to connect the HSI leads to an AC line cord.  In testing, flames occasionally swirl around the shield when low pressure releases happen, in the area of that line cord.  For extended usage, high temperature wire should be used.  I will monitor how the standard PVC line cord does, and replace if needed.

The HSI is mounted just at the edge of the gas flow out of the opening in the pipe, and about 4" up.  In testing, this position occasionally did not ignite when running at higher pressures.  It may have to move higher up, or more into the stream.

I bent and hammered over the top and bottom edges of the ducting to reduce sharp edges.