Shoutout to the guy who taught me about battery math the hard way

So I was finishing up a job in Springfield, a full system with six motion sensors and a siren. I put in fresh batteries everywhere, tested it, everything worked great. Two weeks later, the client calls saying the siren is dead. I go back, check it, and sure enough the battery is totally flat. My boss, who's been doing this for thirty years, just looks at me and says, 'Kid, you ever add up the draw?' I hadn't. The siren's spec sheet said it pulled 500mA in alarm, but I never thought about the little bit it pulls just sitting there, listening for a signal. That standby current, over two weeks, was enough to kill a standard 9V. I felt like a total rookie. He showed me how to calculate the total daily drain and pick a battery with enough juice. Has anyone else had a system eat a battery way faster than you thought it would?

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3 Comments

emery_lane6mo ago

Seriously, you're supposed to do that math every single time? That sounds like a waste of time. Most gear these days is way more efficient. I've slapped in standard batteries for years and never had a call back. Your boss is just being old school and making things too hard. Sometimes you just get a bad battery from the factory, that's all it was.

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karen1656mo ago

But what if @emery_lane's boss is right this time?

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colemartinez5mo ago

Honestly, that standby drain seems pretty tiny. I get the math, but how often does it actually matter in the real world? Sounds like you just got a dud battery or maybe a sticky sensor kept the circuit awake.

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