Engineering Question #8942

Brent Secondiak, a 36 year old male from Medicine Hat asks on July 8, 2013,

I am attempting to determine if the spark given off from a TASER, would be enough to light a candle with prolonged exposure. And why or why not this would work. I would suggest that the spark isn't great enough to light the wax vapour but I am looking for a more scientific answer.

viewed 2987 times

John Jones answered on July 9, 2013

A TASER generates a voltage of about 50,000 volts and a current of about 3.5 mA. This corresponds to a power of 175 W. In normal operation, the TASER doesn't produce a spark; it fires two metal darts which stick into the target, or his clothing, and the current then flows between the two darts. Some TASERS can also be used in `stun gun' mode. In this mode, the stun gun generates an arc between two electrodes. This arc is powerful enough to ignite butane gas from a lighter -- the sparks generated in gas lighters are typically at lower voltages, about 1,000 volts. Lighting a candle is much harder, because you need to heat the wick enough to vaporize some of the wax; then the spark ignites the vapour.

How much energy do you have to deliver to a candle wick to vaporize some wax? Let's suppose we have a gram of wax. To vaporize it, we first have to melt it; this will take about 200 Joules of energy. Then we have to vaporize it, which will take another 200 Joules. So if we can deliver 175 W of power to the wax, we should be able to vaporize a gram of it in just over two seconds, neglecting the facts that the hot wax is going to be losing some heat to the environment at the same time as we're trying to heat it up, and that a lot of the energy of the spark is going to be wasted in heating the air rather than the wax.

So lighting the candle looks like it might just barely be possible. One way to make it easier would be to light the candle with a match, let it burn for a little while, then blow it out and try using the TASER to light the wax vapours that will still be rising from the hot wick.

Brent Secondiak answered on July 9, 2013

I did some testing today and the results were very interesting.  If the wick is very dry and completely void of wax ( cheaper candles) they will light and relight with relative ease.  If the candle has a waxy wick, it will not light, even if it was previously burnt.

The Taser was the model X-26, rated at 50,000 volts and an amperage of 3.5 mA.  The Taser was used in Drive Stun mode, which means no probes were involved. The dry (unwaxed) candle wick was held between the two contacts on the Taser, and it lit in approximately one second. The wax covered wicks were tried multiple times at 5 second internals with little to no success.