DIY Dangers
Know how long it can take for a full-fledged disaster to break out?
–> < --
About that fast.
I was powering a small audio amplifier tonight from a 12v lead acid battery. One of the benefits of SLA gel cells is that they can source incredibly high amperage, when called upon to do so. Normally, you don’t use it to do so…
However, when something bad (like your positive and ground wires getting shorted) happens, they can quite easily discharge a whole lot of power in a short amount of time.
I was about six feet from the amp and battery when the power leads shorted. The amp immediately went dead. I looked up, and couldn’t immediately spot the problem; I thought perhaps the radio station I was playing was having technical difficulties.
About two seconds later, both power leads (18in 26ga stranded copper wire with pvc, probably, insulation) vaporised in an enormous cloud of smoke. I jumped up, and by the time I crossed the room, the connectors at the battery (spade terminals with plastic insulators, and polyoleofin shrink tubing) had burst into flames quite spectacularly; fire was shooting up a foot from the poor battery.
I got the fire extinguished without difficulty, the windows opened and the room aired out. All that’s left of the power cable are the two battery connectors, the barrel plug at the other end, and about a gram of melted plastic insulation.
Elapsed time, from short to pillar of fire? Less than five seconds.
Something to think about, should you ever consider powering anything off a SLA cell. It’s also a marvelous demonstration of why fuses - which I didn’t have - are very good things, even on battery-powered equipment.
I don’t know for sure yet, but I suspect the amp survived; I built it with short-circuit protection, just in case. It’s all too easy to turn an electroltyic capacitor into a small but extraordinarily violent explosive device, and while the audible warning of a problem is perhaps useful, the extra couple parts required to prevent such a catastrophic failure are trivial enough to include that not adding them is just silly.
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