can a 9v be used to heat a piece of wire without the danger of blowing up?

I am working on a costume that utilizes shape memory metal. I plan to use a 9v to briefly heat the metal to its transformation point of roughly 115F where it springs to shape but I would like to prevent any possibility of this momentary short circuit from blowing out the battery. I have yet to fully grasp the applications of diodes, transistors and resistors. is there any kind of simple setup someone may suggest? I've also considered the use of microcontrollers or relays but im trying to keep as simple as I can.

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There are tables for calculating the appropriate current needed to actuate a length of shape memory alloy (SMA) wire.

This page:

http://makezine.com/2012/01/31/skill-builder-worki...

sort of explains how that works, and points to this datasheet:

http://www.robotshop.com/PDF/flexinol-technical-da...

which contains the table.

Typical actuation currents are 100s of mA, and I would expect this to be too much for a 9-volt battery. I mean I don't think the battery is in danger of overheating, or "blowing up". Instead the danger is that it just won't work, and/or the battery will die very quickly.

By the way, the manufacturers of batteries write up datasheets for those too, e.g. the ubiquitous Zn/MnO2, 9-volt battery:

http://data.energizer.com/PDFs/522.pdf

In summary, 9-volt batteries are weak sauce. Nothing like what you see in the movies.

;-P

SideTracked350 (author)  Jack A Lopez3 years ago

Thank you I'll look into this carefully. It's not a 'Michael Bay' explosion going off in my pocket that concerns me. I'm more concerned about the expansion within causing a rupture and having battery acid dripping down my leg.

I used to start fires by taking a 9 volt and sticking it to steel wool, the 9v only has enough juice to do it one time before it goes dead.

A 6V lantern battery may be enough to move the wire and it will have plenty of current to do it several times.

iceng3 years ago

So, I used to be careless about dropping 9volt batteries in my pocket, and one day a battery shorted on some pocket change.

Suddenly there was a warm ( what is it ? ) to a realization that ( HEY its a hot battery against my leg ! ) it was a very quick drawer pull out that placed a hot battery followed by warm change on a nearby coffee table.

No skin burn, or fabric damage but I'm real careful about handling those 9_volt batteries these days, especially Lion batteries which could cause serious harm..

iceng iceng3 years ago

Take care that the attach point to your Nitinol wire does not slip off causing a spark to ignite a costume fire.

As for control use a power MOSFET sized 10X the expected current.

verence3 years ago

Can 9V be used to heat up a wire? Sure. ANY voltage driving a current through a wire will heat it up (except maybe supra conductors). Will it burn out your battery? Sure. As long as you don't take precautions. By limiting energy, temperature, time etc.

But really ... do you want to be in a costume that (at least partially) heats itself up to a temperature that can burn you skin? And that's bets case. Worst case, the depletion of the battery will be your least problem - e.g. if your costume goes up in flames - with you inside...

Of course, if you're talking about a PP3 9V block battery, well ... that should be safe. But it will have probably not enough power to heat up a memory metal wire anyway.

115F =46C. Toast-ie, but not really burn-ie.....and pretty unlikel-ie with a 9V battery....

kjsrocks3 years ago

DO NOT USE MICROS AND RELAYS FOR THIS

that could blow a bigger hole in your pocket than a nine volt would it self

I would just try it a nine volt shouldn't blowup but they are cheap enough

Maybe rickharris or kiteman knows about the battery.