My high altitude balloon needed a reliable and lightweight device to release the balloon in the case it remained neutrally buoyant.
I saw some implementations with a nichrome wire (melting the rope), but I don’t like it: too much current, big MOSFET, another battery pack. And let’s say it: not enough spectacular, and dangerous ;) So I decided to make my own pyrotechnic device.
For the fuse I used a very thin wire from a regular kitchen steel wool. With just 200mA it start to melt and burn. I put the fuse in one end of a plastic tube (from a ball-pen tank) and just a wire loop in the other. And YES!… black powder in the middle. Guaranteed an spectacular balloon release with very little power!