Saturday, July 14, 2007

Cordless batteries - "Do Not Overcharge"

OK, so you see some interesting cordless tool, buy it, get it home, then find the instructions say something like "do not overcharge battery". Of course the battery charger that came with the tool is a very slow "dumb" one that won't shut itself off when the battery is charged.

Of course the recommended charging time is something like 4-6 hours which is just long enough that you always forget to unplug the damn thing and don't remember that its still charging until a day or two later.

Sound familiar?

I finally decided to do something about this odious situation. Places like Home Depot and Lowes sell a little settable timer device made by Intermatic. The Intermatic timers come in several different maximum time settings. I picked one that runs from 0-6 hours. The Intermatic timer works just like a standard 2-pole switch from an electrical point of view.

I came out of an existing GFCI receptacle (on its line-side so that the Intermatic and downstream receptacle are protected by the GFCI), into a box with the Intermatic timer that switches the hot, and into another box that contains an ordinary receptacle.

Now I can plug a cheap dumb charger into that receptacle to the right of the Intermatic timer, set it for whatever charging time I want, and walk away knowing the battery pack won't be overcharged.

This whole project took under a half hour and maybe $20 worth of materials. I already had the boxes, covers, receptacle and some short lengths of EMT and wire on hand, so all I really had to buy was the Intermatic timer. Even if you had to pay an electrician to do this, I would expect the cost to be in the $100 range.

The nice thing about this approach is it doesn't block an existing receptacle with one of those hokey plug in timers (which aren't very robust, and often don't support having a ground prong). The Intermatic handles higher current, and all the downstream receptacles will be fully functioning 3-prong ones.

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