Lesson About Power

For the past several months I’ve been learning to fly a quad copter UAV and trying to get First Person Video streaming over WiFi. This has meant that I’m spending a lot of time working with batteries and small electronics.

This last weekend I was lucky when a shorted wire was noticed before it caused significant damage.

Melted wire next to it's power supply

Melted wire next to it’s power supply

I was standing around talking when my friend asked what was smoking. I spun around to find the smoke coming from a box of cables and batteries. I flipped the wires out of the tailgate of my vehicle onto the ground. You can see the insulation is completely melted from the wire in the foreground.  I was extremely lucky that no further damage was caused.

The battery pack that caused this is a 4 cell pack producing 4.8 volts with a 2000 mAH capacity.  Each cell appears to be the same size as a AA battery. Nearby were several 3 cell LiPo batteries that produce 11.1 volts and have 2600 mAH capacity.  The LiPo batteries are a different form factor from the NiMH that I’m using.

Because I need to power both my BeagleBoard and the USB hub at close to 5 volts, I had soldered a plug for the hub into a wire I already had for powering the BeagleBoard. I wasn’t able to get the wire and its insulator to fit inside the strain relief, so for this weekend, I just left everything open, deciding that if things worked properly I could produce a better looking solution later.

A short was likely caused by a piece of bare metal from a prong on a wall plug resting against the plug where I’d neglected to use insulated heat shrink tubing. The rapid discharge of the battery obviously supplied more current than the wire was designed for, and the heat. If the heat from the first problem had melted the insulation on the larger and higher discharge LiPo batteries, my entire vehicle could have caught on fire. Perhaps actual fire could have happened with just this battery if I’d simply not noticed it for a longer period of time.

I am taking this as a reminder that even small low voltage batteries can create significant problems and should be handled with care, and for me it was lucky to learn on a small scale when I only lost the ability to run the wireless tests I wanted to run in the field that day, and not losing anything of significantly more value.