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Will 2.5 volts be enough to heat a small segment of NiChrome wire up to/over 100 C? If it helps, the power is coming from a 8.1 kJ 2.5v 2600 F super capacitor which can unload very quickly.

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## 12 Replies

steveastrouk (author)2011-01-09

2.5 Volts, into 1.4 Ohm, is 2.5^2/1.4 W, or 4.4W., or 4.4J/sec. That will last a fair time - 2600 J/ 4.4 J/sec= 590 seconds, or 10 seconds shy of 10 minutes.

How HOT it will get is complicated, but if you assume its completely lossless - you can work out how long it will take to warm up, if you know the thermal mass, which is the mass x specific heat capacity, and you assume a rise in temperature of 100 C then Joules needed = mass x SHC x 100.

Steve

lemonie (author)2011-01-08

Yes.
But if you want to know "how long is a piece of wire" then you'll have to tell us what wire it is. Also - for how long, and how much heat do you want to take out of it?

http://www.aircraftmaterialsuk.com/data/electronic/alnicr.html

L

LiquidLightning (author)2011-01-08

About 1cm long, 18 gauge, NiChrome, about 3-4 seconds, and 2.6 kJ.

lemonie (author)2011-01-09

Should be quite achievable in energy terms, if I read the wire gauge right it'd be ~1.4 ohm per metre, giving you 0.014 ohm for 1cm.
But that means you'd need to limit current or it'll get too hot very quickly (or will it? for a single-use ignition it'd work)
Maybe some constant-current supply, but at low voltage I don't know.

L

LiquidLightning (author)2011-01-09

The wire won't be bare, it would be in a small amount of water.

lemonie (author)2011-01-09

That makes a difference. You're really asking about heating water then -
How much water?

L

LiquidLightning (author)2011-01-10

No, I'm not asking about heating water, I need the actual wire to get hot, but not above 100 C. The water is just there as a coolant for it to not exceed 100 C.

lemonie (author)2011-01-10

Water has a high heat-capacity, in terms of how hot things get with current water makes a big difference.
What's it for?

L

steveastrouk (author)2011-01-09

The "2.6kJ" is almost irrelevent, because thermal mass here is insignificant.

Steve

Kiteman (author)2011-01-08

It depends how thick the wire is.

LiquidLightning (author)2011-01-08

18 gauge.

frollard (author)2011-01-08

depends on the resistance = amps = watts = energy, which can be used to determine the temperature change of a given weight of wire at a certain heat capacity.

ohms law