Open circuit when batteries under pressure?

[Hack On Wheels]

Hi all,

I'm trying to troubleshoot a problem in a light I just put together. From the (admittedly limited) testing I've done so far, the batteries seem like a likely cause of the light working intermittently.

The symptoms are not entirely consistent, but it seems to follow the trend of being less likely to work the more pressure that is put on the batteries. I can get the light to work indefinitely by making a connection with the tailcap before I screw it in (conducts through the threads). As soon as I screw in the tailcap I can't guarantee it will work, sometimes it turns of right away, sometime I get the tailcap almost fully threaded, occasionally it will still work for a bit with the tailcap fully threaded in. Once it stops working the only way to get it to work again is to remove the tailcap and start over.

For reference, the light is a Minimag with a copper heatsink that has an SOB1000 converter mounted. The batteries are 2 Trustfire 14500 Li-Ions (unprotected), so I know the quality isn't the highest. There isn't much extra room in the battery tube once the tailcap is installed, maybe 2-3mm. I don't notice any heat (not any more than what is probably residual heat) when the tailcap is installed but the light isn't working, so I don't believe the batteries are being shorted either.

Really what I'm wondering is: are the batteries constructed in such a way that they could have an open circuit under enough pressure? Any input on this would be great. :candle:

Thanks!

 

[Hack On Wheels]

Well, I actually don't believe the batteries are at fault now. I found a couple more 14500s that I forgot I had and tried that out, they seem to have the same issues. I cut the tailcap spring down a bit and that seemed to help, but it is still terribly unreliable. I had insulated the converter from the heatsink with Kapton tape but that must have been damaged at some point. Either that is true and something is always on the verge of shorting (if it isn't shorting already) or I have a bad solder joint that is shifting as pressure is applied.

The whole thing is a bit of a ship-in-a-bottle situation, so I'm going to have to partially desolder the MC-E before I can remove the pill and check the converter for shorting or other issues. Hopefully I have time for that soon. After I've got the light working reliably I'm going to look into a dual stage Kroll switch mod so I can make the light a bit more practical.

 

[bstrickler]

Maybe try adding a compressed tinfoil spacer (as a quick test. compressed, to reduce the chance of poor contact with the tin-foil) at the base of the body, and see if that helps any. Also, stack the cells like you would in the mag, and see if the button top of the bottom one touches the bottom of the top one fully.

Another problem I've had in the past with minimags, is the tailcap spring, or the inside of the tailcal would (for some reason) become slightly corroded, and be very unreliable in brightness. If thats the case, let the tailcap sit in some vinegar for a while, and then sand it with some 400 grit sandpaper, then wash it, to remove the aluminum powder.

Try those solutions, then update us.

~Brian