Nichrome wire troubles

JamesIzzard

Hello all...
I have been having some trouble with some nickel/chromium resistance wire I have brought to act as a heating element, it is 0.375mm dia. and I am using 100mm lengths. I had originally intended to heat it up with a standard 9V battery, but it is behaving strangely when I connect it to the +ive & -ive terminals. It seems to heat up very quickly at first, as it should, and then stop heating and cool down after the first few seconds. It is definately not flattening the battery, becuase if I wait a while and try again, the same thing happens.
Is this something to do with it shorting the battery, and is it even possible to heat wire like this with a 9V battery, ideally so it glows red. (I am trying to make a cigarrette lighter)
Apologies if this is a stupid question, electricity really is not my strong point :)

NoTime

Welcome to PF.

When you draw too much current from a battery it can create a depletion zone and the battery will act like it is dead.
Disconnected, new carriers can migrate to the chemical interface and the battery will recover.
In general, this greatly shortens the usable life of the battery.

A standard 9V battery is far to small for your application.
The max output is about 50ma to achieve rated lifetime.

JamesIzzard

Ahh Ok right, that sounds like exactly what has been happening.
In terms of heat output of the nichrome wire then, is the current or the voltage more relevant, and why, and also I don't know where to start looking for equations to help me work out the nescessary voltages/amps needed to heat the wire to the nescessary temperature, could anybody point me in the right direction.
Sorry about asking for what I am sure is basic knowledge, I am more in the field of force mechanics, and am pretty new to electricity.

NoTime

E=IR.
Or Voltage = Current times Resistance.
As you can see from that, all the values are related.

Power dissipated in the wire heats it.
P=EI.

pantaz

According to this table: http://www.wiretron.com/nicrdat.html
Your wire requires almost 1.5 amps to reach 400 F.