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Elementary Electronics Confusion
Old 06-08-2008, 05:15 PM   #1
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Elementary Electronics Confusion

I've had this nice Black Diamond LED headlamp for a while. What I didn't like about it was that a new battery cost almost as much as a new headlamp. Also, I couldn't use rechargeable batteries.

So today I modified it so that I could have a little pack of batteries in my pocket, with wires up to the headlamp.


The little battery that fits it is a 6V battery. So I set up a pack with four AA's, hook it up, and the thing immediately gets very hot. Even with three AA's it gets too hot. I now run it with only two AA batteries.

So why does that happen? Six volts is six volts even if the batteries have a potential of supplying more current. The current should be determined by the voltage, unless the small battery has a de facto limit on how much current it can supply.

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Old 06-08-2008, 05:54 PM   #2
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Doesn't make any sense Al. The only answer is the battery is limiting the max current.

Here's the data sheet on the 476 silver oxide battery.

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Old 06-08-2008, 06:12 PM   #3
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Two guesses: there are differences in battery internal resistances. Alkaline about 1.5 ohm @20 degrees C, Silver oxides are described only as "very low". Not likely the problem.

The other is a blown regulator IC, little square black thing with 6 or eight legs. Or other kind with three legs

LED run on low voltage, hence the need for regulators.

Try one alkaline, if it runs cool, and near normal brightness, then confirms blown (shorted) regulator.
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