Battery magnets.

Hey guys.
I've purchased an extension tube for my C8 as I'm going to stick an XHP50.2 in it, I've only got flat top batteries so bought some magnets too. Question is what happens if it get dropped side on? Is the magnet likely to shift and cause a short?
Anyone got any experience with these?
Thanks.
Thom

Yes, that can happen.

Hmm I might turn down a PU washer then to keep the magnet cantered correctly.

Is it possible to place one magnet on the far - (negative) end so that shifting will not touch positive?

That is why I add my own permanent button with a blob of solder on the positive. You must be good at it so it flows on quick, and does not heat up the internals of the battery. Then I file a little flat on it.

I have had a magnet shift and short, not fun. Got it apart without major damage, but a lot of heat happened.

I use some flat top cells in my Nitecore TM16GT, which has the physical polarity protection, so the battery has to go on the positive end of the cell. IMRBatteries sells some little insulators that are a lot like the paper reinforcement rings one can use, except they are thicker and designed for this use. Their original function was in rewrapping button top cells, but the center hole is just the right size for the magnets I use, and the paper is thick enough that it will keep the magnet from slipping off center. I actually tried to knock the magnet to one side before I put the cell into my light, and I couldn't get it to budge. I consider this a better option than trying to put a blob of solder on the end. Some people have the touch and the right equipment to pull it off, but Li-Ion cells are sensitive to heat enough so that I wouldn't want to try it, even though I have a lot of soldering experience.

Thom2022,
I had a similar situation in a light, and I ended up using one of these:

side view: (click on image to make larger)
http://bamavapor.com/Flat-Top-Battery-Adapter-990751/

and oblique top views:
https://store.indyvaporshop.com/flat-top-battery-adapter-p431.aspx
http://www.smoktek.com/Flat-Top-Battery-Adapter_p_922.html

the contact is either brass, or brass-plated. The plastic disc keeps the center contact from touching the sides (including if it's dropped, I'll wager). The circumference of the plastic disc might be too large for the interior of your light. I ended up rather crudely reducing the circumference of mine with some craft-shear-thingie.

Timothy, that sounds like a pretty good alternative, if you are not up to soldering. The only other sure way to feel totally safe for me would be buying the button tops. Fortunately, I am very comfortable with my soldering skills. I also use lead solder. The new lead-free stuff requires higher temperatures to flow, so not as good an idea for this.

I've used magnets for year on several lights and never had an issue with a short. However, it can still happen, and on some lights it is much more likely to happen. So you have to be aware of exactly what you're doing before going with this setup. Solder blobs are the most full proof thing once done properly. Most 18650's these days can take a LOT of punishment. Just look at LG or Panasonic spec sheets for the torture tests that they put these batteries through.

However, without proper soldering skills, it can still be futile and/or cause accident/incident which can be pretty bad, particularly if you bridge the + and - together. I was commenting on one of the modder forums that they should just solder-blob high drain cells and sell them, as it is a better solution even than most after-market button top cells which can be cheaply fashioned and restrict high-drains amperage flow.

I use magnets all the time when the positive terminal has a raised ring, which captivates the magnet if the light is dropped.

I recently bought a light that has batteries in line, and purchased button tops to make the connection from battery to battery. I wasn't going to chance dropping the light with a magnet between batteries that could be dislodged.

Just had a looksie and I e realised the inside of the battery tube is also anodised so I assume this should stop shorts? I'm also going to pick up some nylon washers from my local as they have them in 8x20mm which should fit with some light sanding.
I'm not happy soldering a blob to the battery as my iron is on its way out. I will eventually buy button tops but I'm not sure how well a C8 will deal with an XHP50 and a FET driver so I do t want to add unnecessary cost when it will be my only 2S light and I have too many 18650's as it is!!!

MAD777 said:

I use magnets all the time when the positive terminal has a raised ring, which captivates the magnet if the light is dropped.

Click to expand...

Not a terrible set-up, but consider this: You are probably thinking of dropping it on it's side. What if it hits the tail at a 45 degree angle. The spring in the cap will allow the battery to translate back in the tube, at the same time there is also a lot of lateral G's going on. Much harder to generate a short, but still not impossible.

Thom2022 said:

Just had a looksie and I e realised the inside of the battery tube is also anodised so I assume this should stop shorts?

Click to expand...

If only, but we are most concerned with the magnet getting across the battery positive to the outer contact ring on the back of the circuit board that is contacted by the non-anodized end of the battery tube (your negative path).

Only one magnet is being used between the two batteries.

Hondo said:

Not a terrible set-up, but consider this: You are probably thinking of dropping it on it's side. What if it hits the tail at a 45 degree angle. The spring in the cap will allow the battery to translate back in the tube, at the same time there is also a lot of lateral G's going on. Much harder to generate a short, but still not impossible.....

Click to expand...

Indeed, that would be the worst-case scenario. Makes a good argument for strong springs, too.

Thom2022 said:

Only one magnet is being used between the two batteries.

Click to expand...

Ah, I get it, you only have an issue between the two batteries. In most cases the flat top fails to contact at the head, requiring something to connect to the circuit board positive. So long as your insulator outside of the positive contact does not get torn, you should be fine.