Battery Selection for Brief Short-Circuit Pulse

Hello, first post, please bear with a newbie!

I want to send a pulse of high current from battery(s) to an array of very fine filament wires (e.g., miniature christmas bulb-like) wired in parallel, such that they individually melt/vaporize in less than ~0.1 sec, thus popping balloon(s) to which they are attached. The idea is to pop as many balloons as possible using the least number/smallest mass of batteries, no larger than AA/C/9V size range, preferably (but not necessarily) rechargeable, with enough capacity (say, 2AH or better) to be used many times before discarding/recharging.

I am presuming that the critical parameter here is the short-circuit current (or equivalently, the internal resistance) of the battery. From what little research I've done thus far, it seems like NiCd's may be the best choice for max current, although if NiMH's are reasonably close, I would prefer them to avoid the 'memory' effect inherent in NiCd's. The lithium batteries I've investigated so far all incorporate a current-limiting (1-2 amps max) safety device that would seem to make them inappropriate for this application, despite their high energy density.

Thanks for any info/insights-
SunMesa

LiPO batteries for radiocontrolled models are designed to consistently discharge at 30C - i.e. a 1 amphour battery can discharge at 30 amps - and they're so cheap now.

Just don't discharge below 2.5 volts when at rest.

Or use a Supercapacitor e.g. 5 Farad at 2.7 volts and charge it from a conventional battery.

Perhaps try a 1000uF cap in parallel with a battery of the desired voltage? That ought to produce a fast current surge. NiMH or Nicad should be fine. I wouldn't worry about memory effect.

Out of curiosity, what are you using for a fine filament wire? Even a small wire, such as 30 ga, can take a number of amps before it blows.

MikeAusC said:

LiPO batteries for radiocontrolled models are designed to consistently discharge at 30C - i.e. a 1 amphour battery can discharge at 30 amps - and they're so cheap now.

Just don't discharge below 2.5 volts when at rest.

Or use a Supercapacitor e.g. 5 Farad at 2.7 volts and charge it from a conventional battery.

Click to expand...

Hi Mike,

I did find some LFP (LiFePO4) batteries, 3.2V 2.5Ah, that allegedly can discharge at an incredible 48C (120 amps!) for up to 10 sec. You have to solder on a special copper terminal if you want to run at that current level, but that's no big deal. They're lightweight too, 2.6 oz.

I was originally going to use capacitor(s) rather than battery(s), but we also have weight/size constraints, and (unless I'm way oversizing the capacitors) the batteries seem to be the more compact/lightweight solution, and also should need less frequent charging.

Steve K said:

Out of curiosity, what are you using for a fine filament wire? Even a small wire, such as 30 ga, can take a number of amps before it blows.

Click to expand...

Hi Steve,
The prototype thus far literally uses miniature christmas bulbs with the glass removed, don't know the wire diameter but it's much smaller than 30 ga. The final design may incorporate something more robust, maybe 40(?) ga Nichrome wire.

I was wondering if you could use the little heater elements that are used to start model rocket motors. I don't have any personal experience with them, but I believe they are designed to be powered by common batteries, and are widely available. They aren't designed to fuse, though (I think)... is that a problem?

Steve K said:

I was wondering if you could use the little heater elements that are used to start model rocket motors. I don't have any personal experience with them, but I believe they are designed to be powered by common batteries, and are widely available. They aren't designed to fuse, though (I think)... is that a problem?

Click to expand...

We have a severe time constraint... the balloon must pop less than 100 msec after the current starts. That's why I'm overwhelming the filament with current... don't want to wait around for it to heat up.

For the fastest response, a heater with the smallest thermal mass would be the goal. The filament in a bulb might be the solution, but I imagine there are issues of ruggedness (easy to break a filament, especially when it'll be in contact with a balloon) as well as the difficulty of removing the glass envelope.
I'd suggest visiting a hobby shop and seeing what they have available. The little rocket motor igniters couldn't cost much.
http://www.estesrockets.com/rockets/engines/flight-supplies/302301-model-rocket-igniters-6-pk
$5.59 for a package of 6.

I'm guessing that the igniters are just nichrome wire. Were you able to find a supply of nichrome wire in bulk? That's probably the best solution in the long term... either that, or a solenoid with a needle point at the center.