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I want to be able to create a set of candles that light automatically (for a presentation) however it's almost 100 candles and I need an inexpensive solution. I know that nichrome wire get's hot when you pass current through it but can it get hot enough to start a candle. I figure that I could wrap the wick with the wire to get it started (I don't need it to out afterward).

The question is: can I heat up nichrome wire enough with less than 12 volts of electricity?

stevenvh
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    In case anyone is wondering, I said candle but I really mean Deeya. I want to be able to reignite a deeya even if the wind or rain blows it out. –  Oct 07 '11 at 00:28
  • 1/4 watt resistor - pass ~10W to it. – Vorac Sep 13 '12 at 10:49
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    @Vorac, yea but then I'll only be able to light it once ;) –  Sep 13 '12 at 11:43

4 Answers4

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I would look at purchasing some type of electronic ignition module (e.g. like those used for pilot lights in heating/hot water systems) but here are some thoughts regarding nichrome:

The 12V question - yes, if the supply can source enough current. Nichrome will vary in ohms per metre for different gauges. I have some nichrome wire here somewhere that is around 10ohms per metre (28AWG IIRC, see resistance table at bottom), which says it can be used up to around 1100 degrees centigrade.
I'm not sure of the exact temperature needed, but parrafin wax usually ignites around 199-249 C according to this page.
If we assume say 400 degress will be sufficient to start the ignition process (I'm guessing here, you will need to do some more research, or just try it out and see what works best) then using the table below we can calculate ~2A is needed for 28AWG (so your supply needs to be able to source at least 2A)
For ~10 ohms per metre and 12V, this would be 12V/2A = 6ohms, so 1m * (6/10) = 0.6m. So 60cm of 28AWG Nichrome wire across 12V should heat to around 400 C.

Nichrome Temperature

nichrome temperatures

Nichrome Resistance

nichrome resistance

Oli Glaser
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    @OliGlaaser - As with all Oli's answers - good stuff. But needs thinking more about. 60 cm = 2 feet of wire is far too long for what he wants. And 24 Watts is higher than needed. On that basis 1 Volt will heat 5cm to the the same using the same wire - ie 1 or 2 a AA NimH - and that's too long a length. Using eg 32 gauge or thinner will get you as hot at less current or a higher temperature for the same current. eg a much shorter length of 32g wire will heat to 1000C at 2A at about 5 Volts. – Russell McMahon Oct 06 '11 at 03:26
  • @Russell - This was an example using the 12V mentioned to show how to calculate. I was assuming the OP would work out the practical side of things and adjust to suit. For example it may be possible to use one long wire for all candles (e.g. if all in a line, depending on size/shape of candle) but I'm not a pyrotechnics expert :-) – Oli Glaser Oct 06 '11 at 06:45
  • Higest AWG I could find on amazon is 49 AWG. Resistance ~500Ohms per foot. that should do the trick? –  Oct 07 '11 at 00:35
  • @kurtnelle - it will be pretty thin so might be a bit tricky to work with, but anything that fits in with how you want to do things should be fine. If you are looking at making separate short filaments for each candle then a very thin wire is best for the reasons outlined above. I would maybe get a couple of different gauges and experiment a bit - also check the igniters from Talon mentioned in Steve R's answer - I think they are just a "ready rolled" nichrome filament with leads. – Oli Glaser Oct 07 '11 at 09:17
  • @Oli - Come to think of it, yea it might be really thin; I'll def get different gauges. Also, I saw the Talon igniters however I need repeatability; if the "candle" outs then it should reignite. –  Oct 07 '11 at 09:31
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Summary

  • Yes, you will be able to make it work

  • either by using nichrome wire on th wick directly

  • or if that is not consistent enough, by using a match head. to light the candle and lighting the head with nichrome.

  • The voltage is not what counts, it is the energy that matters. You will probably want a Watt or two per candle to do it well. Many batteries will do this.

Nichrome melts at 1400 C which is well above candle ignition temperature. Wikipedia article on Nichrome

However, the properties of the wax and wick may make the practicalimplementation tricky. Getting rapid and consistent ignition may be "tricky".

What would work far better is to use nichrome wrapped around a match head. Embed a match head and igniter loop in each candle next to the wick. (Long long ago I used to ignite match heads using copper wire wrapped around them, to form an igniter for other material. It worked well and fast.

Voltage is not the main issue in ignition. To get temperature rise you need power and/or energy. Power = Watts = volts x amps. Energy = Watt-seconds = power integrated over time.

You will probably need a Watt or few to get fast ignition. The nichrome or similar wire can be sized to give the right power level at the available voltage. Another suitable wire is "constantan" which is made of 55/45 Copper-Nickel. It is commonly available and AFAIR has a higher resistance for a given length and diameter than Nichrome.

Per Watt, at 6V you need about 160 mA, at 3 V = 1/3 amp, at 1V = 1A.

AA NimH batteries can provide currents of this magnitude. Be awwre that resistance in the leads and in any connections can drastically alter the result at low voltages.

Wikipedia comment on flame temperaure says 1400C at core and 1000C mean.

This page says the wick ignites at about 240C and the wax vaporises at under 650C.

This very nice fore investigation paper says wax will flash at 204-270 C, the fore point is 238-260C !!!

This says Tmax in flame is 1400C as others do, but main value is its many references

Russell McMahon
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A popular igniter used by firework enthusiasts Talon will work if you only need one ignition.

SteveR
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With all the math and tables you can figure out theoretically what should work. My experience with Ni-Chrome and paraffin is practical. MANY times when Ni-Chrome is used it burns out at the point it is bent or rolled, ie, the point at which it is to perform its work (light the candles). There are also way too many variables here with wind, relighting, etc. If you watch them try to light the big candles inside Church on any given Sunday they are using a direct flame and sometimes it lights right off, others you stand there until it does. My solution to lighting the first time right away is to use a hair dryer to loosen up the paraffin on the wick and roll a little plasticized black powder from a sporting goods gun shop reloading supplies onto the wick. Wrap it with the Ni-Chrome. You will be getting a little flash but if the Ni-chrome burns out you'll get that anyway.

Joe Hass
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Bill Bailey
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