mag85 Switch Cover vents...

FILIPPO said:

what do you think?

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Gryloc said:

I believe that your batteries produce a bit of hydrogen during the normal discharge (part of the reactions that take place). I believe that this occurs with alkaline and NiMH cells. What you are experiencing is just a build up of gases pretty much. The hot bulb may add to the pressure some due to expanding gases, but I do not know by how much.

Some sealed flashlights (noticeably 2-part bodied lights like the Streamlight ProPolymer and the various UK lights) have vents in them, as well as catalyst pellets containing platinum to remove the pressures do to this hydrogen.

I had a similar issue as yours, actually! I have a 2D maglite holding 6 AA NiMH cells. It was running 4 ~3W LEDs. I was camping when a friend was using the light. We heard a small pop/crack noise like the one a very small firecracker would make. We had no clue what happened. It was later when I noticed that the rubber switch boot was missing! Huh? It was later that I realized that the pressure in the Mag body was enough to pop it off. Luckily, I had a spare switch boot.

I experimented with this soon after by finding a way to pump air into the body using a small air pump. You could feel the rubber boot bulge when you touch it. It is weird. Eventually, it will pop and the boot will go flying. I experimented with making my own vent to release this pressure. I got a small pin and poked a hole into the center of the rubber boot. This allowed the boot to release its pressure when it bulges (through the tiny hole when it expands). It took larger amounts of pressure to pop it (overwhelm it). I believe that it retained its water resistance, but it was hard to prove (it was a tiny hole). When the switch boot is not bulging (normal), the hole should be partially closed. You can try the test and see what it takes to pop it. Just re-push the pin in a little further to widen the hole if it still pops too early.

Here is a doodle to demonstrate how I think the pin-hole vent should act, and from observation, seems to behave.

Code:

Normal    Bulged
 //          //
||          //
||   (air) ||
=|      <- >|
||         ||
||          \\
 \\          \\

With normal C/D cells, I bet the pressure is not an issue, but when you have 6, 8, 9, or 12 cells in a light running at high current, then it may become an issue. Well, good luck with the venting! Don't shoot an eye out! :laughing:

-Tony

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