Odd problem with my keychain light

I just picked up a new version of the Coast G10 AAA light. I have had an older version for a while, and I like the size of these lights. I find most single AAA lights to be too small. Anyhow, I went to put in a NIMH cell into it, and when I do, the light will not shut off!! If I put an alkaline cell in it, it works fine. A NIMH battery works fine in the old version. I tried swapping the end caps/switches on both of them, and the new one did the same thing. Could this be some sort of problem with the circuitry or regulation on this light? If I screw the end cap / switch on the light halfway, it works! I have never run into this before!

If you have a caliper check the size of the cells. Sounds like everything is over compressed with the ni-mh making the switch short out therefore keeping the circuit closed at all times.

I actually thought of that, but I cannot see a difference in size. I have also tried 3 brands of AAA NIMH cells (Duracell, Eveready, CVS Brand). I do not have a caliper, but if there is a difference, it is VERY minute! I may try exchanging it for another.

What happens if you leave the tailcap off and short the negative end of the battery to the body?

EDIT: Ignore that, I forgot that not turning off was the problem. Does the switch feel the same with alkalines versus NiMH, i.e., can you feel the click as the switch goes to on and again when it goes to off?

Yamabushi said:

What happens if you leave the tailcap off and short the negative end of the battery to the body?

EDIT: Ignore that, I forgot that not turning off was the problem. Does the switch feel the same with alkalines versus NiMH, i.e., can you feel the click as the switch goes to on and again when it goes to off?

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The switch feels exactly the same. I was thinking that the spring inside the light was possibly bending over and touching the side of the light so I rolled up a small piece of paper and put it inside, then slid the battery inside the paper. It still did the same thing. Maybe the rechargeable cells are just a tad bit longer because it works OK if you slightly loosen the endcap. I just have never run into a problem like this.

I had this happen. It was because the bottom of the eneloop is all contact area, alkalines have the wrapper that comes around the bottom. Hope this makes sense.

jonnyfgroove said:

I had this happen. It was because the bottom of the eneloop is all contact area, alkalines have the wrapper that comes around the bottom. Hope this makes sense.

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You hit the nail right on the head! The outer rim bottom of the switch apparently is touching the negative contact of any NIMH cell I put into it. If I put a piece of tape over the bottom of the battery, then cut a hole in the center of it so the spring from the cap makes contact, it works fine. I have never seen this before and looks like an odd design flaw in the light. I may still look into exchanging it tomorrow, but from just looking at the cap/switch, I bet the new one will do the same thing.