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Jeff Liebermann Jeff Liebermann is offline
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Default Rechargeable battery question

On Sun, 15 Apr 2018 14:18:39 -0700, mike wrote:

Lotsa people recommending tiny magnets to replace the button top.
I asked about the series resistance and was assured it wasn't a problem.
I spot-weld a tab on top and fold it over until it's tall enough.


I bought an assortment of magnets to replace the button top on an
18650 cell. They're not quite the right size, but work well enough in
my various flashlights. My spot welder died and I haven't bothered to
work on its replacement. When I get something working, I'll go back
to spot welding fake button tops (made by pounding a home made die set
with a big hammer). I measured the resistance of the magnet with a
ESR meter and found the resistance to be negligible. I forgot the
exact value. Bug me if you want the numbers.

So, where to get good 14500 cells? I have no idea. I just checked
Digikey and Mouser. Nothing found.


AS I recall, there was a ban on individual cells in the US.
Don't know if it's true, but it's still a BIG liability issue
for sellers. People seem to throw in any battery that fits
and make smoke.


I hadn't heard of any such ban and couldn't find anything searching
with Google. There are various limits to how many cells can be
shipped and how they should be packages, but no ban that I could find.
https://about.usps.com/postal-bulletin/2012/pb22336/html/updt_004.htm
https://www.ups.com/assets/resources/media/us_lithium_battery_regulations.pdf
http://images.fedex.com/us/services/pdf/LithiumBattery_Overview_2018.pdf
http://www.dhl.com/en/express/shipping/shipping_advice/lithium_batteries.html
http://www.iata.org/whatwedo/cargo/dgr/Pages/lithium-batteries.aspx
http://www.batteryspace.com/Lithium-Battery-Shipping-Regulations.aspx

You can't rely on anything you read on EBAY.


I prefer "Trust, but verify".

You can't even buy one and test it. The next purchase of the same
part from the same vendor may be completely different.


Well, I bought 10 cells on eBay twice from the same vendor and
received the same junk cells twice. Like these but from a different
vendor:
https://www.ebay.com/itm/202070101554

I just realized that I don't have any 14500 data, so I dug out the
West Mountain Radio CBA-II discharge tester and ran a graph:
http://www.learnbydestroying.com/jeffl/battery-tests/14500%20SkyWolfsEye%201200.jpg
The cell is labeled 1200 ma-hr. Nominal, normal, or typical for a
14500 LiIon cell is 750 ma-hr. My test produced about 225 ma-hr
capacity, which is well below 750 ma-hr nominal. The cell is junk.

Also, there's a problem. Capacity is measured at 0.2C. For a nominal
750 ma-hr rated capacity, 0.2C would be 150 ma test current. That
would require 5 hrs to run the test. It's also well below where I
normally run these batteries in my various flashlights. Testing the
battery at operating conditions makes more sense, so I measured the
current of my cheap junk Chinese flashlight at 850 ma and ran the test
at 850 ma which would only require 1.1 hrs. If I had run it at 150
ma, it capacity would have been somewhat higher, but nowhere near the
nominal 750 ma-hr.



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Jeff Liebermann
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Skype: JeffLiebermann AE6KS 831-336-2558