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A project log for Unity Candle

Taking the idea of a unity candle to the next level

QuinnQuinn 06/13/2014 at 23:470 Comments

The ceremony control box:

The candle in this case is 3 feet high and 12 inches wide on top of a 3 foot stone pedestal, located about 15 feet beyond the ceremony space. The pedestal is made of insulation foam, cut and screwed together, with decorative paint to make it look like stone. The backside is open to allow installation and access. The candle on top is made of a section of galvanized steel ducting with an opening in the back for installation and to allow air to flow up through the shield.

This is actually only a decorative shell to a two stage release propane poofer. A common propane poofer releases the contents of an accumulator tank past a flame to ignite it. To increase reliability, and prevent the visibility of the open flame pilot, Hot Surface Ignitors were used. These are off the shelf parts used in the electric ignition on many gas furnaces and water heaters. A pair was used for redundancy, though in testing, a single ignitor always worked. The ignitors were mounted in a wind shield at the top of the primary accumulator output pipe which served prevent the wind from cooling the ignitor, as well as to shield the ignitors from any propane coming out of the second accumulator output pipe. The most noteworthy difference of this from most poofers is the use of a second output path that is not ignited. This allows the release of propane into the air above the poofer prior to ignition to create more of a burning fireball effect than a jet.

The basics of a propane poofer involve a propane tank with regulator the passes "high" pressure gaseous propane and fills an accumulator tank. In this case, the accumulator is filled to 60psi.(a standard regulator for a propane grill is 0.5-1psi) The accumulator tank has a high flow path for the propane to release under the control of a solenoid valve and out the top to be ignited. A 3/4" pipe path is used here as it is the maximum output size of the easy to acquire accumulator tank, and can empty the entire tank in about 1.5-2 seconds. The poofer is fired by opening the solenoid valve which quickly releases the stored propane in the accumulator to create the fireball burst. This system of using an accumulator is required because a standard liquid propane tank has a limited rate of evaporating the liquid into gas to be released and burned. This allows high volume bursts to be released very quickly. Further discussion of the principals of a poofer is left to the reader to research elsewhere.

The remaining part of the system is a controller which implements safety features as well as runs programmed sequences to correctly time the two solenoid valves. This was built from a surplus hand controller, with an arduino micro, additional buttons, and IO drivers and protection built in. This was designed to be very tolerant of electrical noise, spikes and electrostatic discharage without damage or incorrect operation.

During operation, there are several safety features. At the accumulator tank, there is a ball valve which can quickly close off the output as one emergency shutdown. At the controller, removing the cable functions as another emergency shutdown. The rest of the safety factors are for the flame effect operator and located at the controller. The primary is the positive manual enable. For the system to fire, an arming button must be held, which allows the operator to continually watch for site safety, and release if there are any issues. Releasing this button will prevent firing, as well as stop and shut down any sequence that is running. This arming button only makes the system active, as the keyswitches and main button for the couple actually fires the sequence. This allows the operator to be responsible for operation and safety of the system, while allowing the couple who are not responsible for the system to fire it. The controller also implements password protection, with it locked at powerup, as well as a single button to lock it.

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