Battery Operated – Powering Nichrome Wire from Battery

battery-operated

I'm looking to power nichrome wire from battery. The problem I ran into is that desired length/width of the wire has very small resistance ~ 8 Ohm.

Several kinds of batteries I've tested have internal resistance much higher then that, which leads to wire staying cold and battery getting hot.

Is there any way to increase current drawn from the battery? Some kind of amplifier maybe?

Edit:

  • 1.2V(rechargable) and 1.5V one, while not getting hot itself did not provide enough power to heat the wire.
  • 3V did not provide enough power, even stacking 3 of them in series, only provided about 1V of voltage on the wire, and not enough amperage to heat the wire.
  • 9V battery did provide enough amperage to heat the wire, but at the same time got very hot very quickly itself.

PS. I was wondering if https://en.wikipedia.org/wiki/Joule_thief might work for this purpose?

Best Answer

  1. At a given ambient temperature, it takes a set amount of energy to heat the nichrome wire to fusion temperature, and then another amount of energy to melt it. Calculate the power required across your nichrome wire depending on the power losses and the required time-to-melt.
  2. Deduce what the required voltage and the corresponding current across the nichrome wire are
  3. Rule of thumb: choose a battery technology that has a capacity (in Ah) equal to or greater than the required current (in A) (10x greater for sustained use) if possible (otherwise step 4 is mandatory). Stack as many cells in series as required to make up the required voltage

AA batteries are usually quite good in terms of resistance (~0.2Ohm for alkaline) and current capability (up to 1 or 2A, not for long though). They wildly vary in specs depending on the manufacturer though, therefore if yours didn't work, you should try with a better quality one before trying the C and finally D type batteries.

  1. If the best stack you can afford (in terms of space, mass or whatever) can't provide the current or gets too hot, here is a potential solution: insert a Schottky diode that can handle the voltage and current in series with the stack (note that the stack voltage will be reduced by 0.2 to 0.5V), and duplicate that assembly in parallel as many times as required to reduce the current each stack has to provide. The diodes will prevent batteries fighting for the net voltage.

Note that this technique (step 4) is normally used to switch between power supplies, not increase the current capability. Only one diode will conduct at any time*, meaning that here the entire current will be supplied by one source before its voltage droops sufficiently to make another one conduct, and so on. This could work okay for this application though.

*: considering an ideal diode

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