Any way to make spring of flashlight not scratch battery?

[johnny13oi]

Hey guys, my flashlights scratch the bottom of the battery like crazy with the spring, I have a feeling eventually it'll scratch all the way through or damage the battery somehow. Any suggestions on some way to minimize this or stop it completely?

 

[Christoph]

bend the tip of the spring in away from the battery slightly or a small file to the edge will do it.
C

 

[cnjl3]

"Ditto" on the small file.
Better yet use a dremel to taper the edge of the spring or
do the "resistance fix" and solder your wire to the spring edge!

 

[Paladin]

I fold up a small piece of tin foil, place it centered on the negative end of the cell, and the sharp tip of the contact spring holds it in place. Bending or filing makes more sense but the 0.035 spring in my Z48 tailcaps is pretty darn hard to bend, I was worried about breaking the spring loose from the tailcap is why I use the "foil pad" method. Even if it shifted all that can happen is the light might come on.

Paladin

 

[DonShock]

I smooth the contact end of the spring flat; sometimes with a grinder, sometimes with a sander. Then for extra protection, I add solder to make a smooth continuous surface where it contacts the battery pack.
Here's a picture of the finished product:

 

[Dinan]

I put a small piece of aluminum foil on the spring on the tailcap... this isn't bad is it? It seems to solve the scratching of my RCR123's.

 

[Curious_character]

I always put a dab of Nyogel on the spring where it contacts the battery. Besides reducing oxidation, I'd expect it to reduce scratching some.

c_c

 

[Codeman]

I use a burnishing tool. While the results aren't as refined as DonShock's approach, the ultra-fine scoring gives a smooth finish without having to use a two-step process.

 

[Fallingwater]

Can it actually scratch its way to the inside of the battery? This sounds rather unlikely to me... well, not within a century, anyway.

 

[johnny13oi]

Oh some of my protected Li-ion's the PCB is at the bottom and doesn't seem to made with anything particularly strong. It looks like maybe after about 50 or 100 times the PCB will be penetrated and rendered useless.

 

[abvidledUK]

Some cheapy CR123 torches just use a raised dimple on the base, no spring.

Definitely not recommended for RCR123's.

 

[scott.cr]

This is how I do it... a spring-loaded plunger!

 

[Patriot]

Hey!! That's an outstanding idea Scott.cr! It wont damage the batteries and it looks like it would have very low resistance too. Can you give us any details or specifics of it's contruction?

Thanks

 

[scott.cr]

Can you give us any details or specifics of it's contruction?

It's basically a 6061-T651 aluminum bushing with a spring-loaded brass plunger. I made it in my mini lathe and it's a simple job. The spring I usually use is taken out of the Maglite's lamp holder assembly; it's the perfect spring rate for *123 cells and it solders to the brass plunger.

The tailcap in the picture is held together with a C-clip, but in the later ones I've machined I thread the ID of the cap and the OD of the bushing and thread them together to reduce the parts count. And, it looks nicer.

Just in case anyone's curious, this is a 2C Maglite running three CR123s and a ROP "low" lamp. The CR123s are in a Delrin holder.

I make these for CPFers on a case-by-case basis... PM me if interested.

 

[lctorana]

Funny.

I actually think that for the spring to scratch the bottom of the battery is a good thing.

 

[johnny13oi]

Now why would it be a good thing? Maybe there's more to it I don't know. I just like to preserve the life of my batteries.

 

[lctorana]

Now why would it be a good thing?

Because it makes better contact.

Don't try to tell me you haven't roughened up the bottom of a cell with a file or something to get a bit better contact, at least once in your life.

 

[johnny13oi]

Because it makes better contact.

Don't try to tell me you haven't roughened up the bottom of a cell with a file or something to get a bit better contact, at least once in your life.

Only time I've tried that was when I was trying to solder a battery to make a pack and I tried filing away the nickel or whatever coating and hoping that it would make contact with it. It took A LOT of time but finally worked. And only other time was for a big car battery, but those things are like .. solid metal contacts right?

 

[65535]

For mechanical connections the flattest smoothest contact is the best, for soldering or brazing even welding the parts must be rough in order to increase surface area.