On 11/26/2017 9:32 AM, Ian Field wrote:


"~misfit~" wrote in message
news
Once upon a time on usenet Jeff Liebermann wrote:
On Wed, 15 Nov 2017 19:56:22 -0800, Jeff Liebermann
wrote:

My ESR meter is in my office so I can't measure the resistance of the
battery right now. I'll try to remember to check tomorrow.

I don't think there's a problem with pushing current through the
magnet if there is enough spring pressure on the contacts.

The 6mm dia x 1mm thick magnets show about 0.02 ohms measured with the
original Bob Parker ESR meter. It was fairly difficult getting a good
connection which required using two strips of nickel flat wire to get
a decent connection. I also had to apply some pressure to get a
reliable connection to the meter probes. Even so, the resistance
never climbed over about 0.30 ohms.

If you get some square magnets, you can wrap a piece of battery tab
material around them. Leave some sticking out so you can
solder a wire or put a clip on it. Works for charging all types
of batteries with magnet-attractive connection points. And the
current doesn't go through the magnet or depend on the surface
plating.

I don't have any square magnets and most everything that I could find
in the right size on eBay is round, but I'm sure they exist.

I'm (slowly) building a better spot welder suitable for welding tabs
onto batteries. I plan to buy some flat nickel wire at about 10 mm
width, and make replacement button tops in a small bench press, which
would then be spot welded to the top of recycled batteries.

Or, I could be crude, and just spot weld one end of a nickel strip to
the battery, and zig-zag the strip to simulate the button top. With
luck, it might act as a spring.

I used to do that until one part-unfolded as I put a cell into my
favourite flashlight, shorted against part of the top of the
flashlight referenced to negative and and cooked the switch into
oblivion. :-/

You can reduce that by coiling the strip in the direction that reduces
the length of unsupported strip. Coil can't fold over as easily.

If I have to - I tin a m3 nut and solder it on. some applications have a
contact spring at both ends, so it isn't an issue.