spudnuty said:
This is from a current thread in "basics":
http://groups-beta.google.com/group...to+topics&_doneTitle=Back&&d#d32a8f0214ad3b43
and the DIY spot welder:
http://users.frii.com/katana/spotweld.html
I've done this for a long time. I replaced batteries in pro movie
camera belts but those were soldered together. At least that's the way
we did it. More recently I work on my own stuff, mostly Makita 9.6V
sticks. I've been using a big soldering gun with the tip cut off.
Pressing the open leads against the work firmly makes a lot of cool
sparks but heats the work area so that it takes solder nicely. This
method wouldn't do well around sensitive components. There's another
guy working on heat sinks that uses a BIG iron. I also reassemble the
batteries first and make the middle connection at the bottom last. This
avoids most short circuit problems. I also don't leave out the
cardboard sleeves and the plastic washers between the cells.
Richard
Short Answer: I've been workinng on and off on the problem for a couple
of decades. Here's the result:
http://nm7u.tripod.com/homepage/welder.html
I stopped working on it when a Unitek CD welder fell into my lap.
Long Answer:
Welding something with an electrode on each side and no worry about
temperature is pretty easy.
Welding with both electrodes one side and not being able to heat the
metal is MUCH more difficult. You need a LOT of power for a short time.
The current has to go thru the contact points and the battery case, not
the metal strip. Nickel is most used, but I've found .005" brass from
the hobby store to work pretty well. Contact area is critical. Too big
and it won't weld. Too small and it burns thru. You're on the right
track when you get a weld that can't be pulled off without tearing the
strip and the battery is still cold to the touch.
One thing that helps is to cut a slot in the tab material between the
electrode contact points. That increased path resistance forces more
current thru the battery. If you cut it longitudinally, you can make
the path length thru the tab arbitrarily long.
If you use a transformer and run if off the AC line, you need to worry
about saturation in the core. I solved the problem by using zero
crossing turn on and running an integral number of cycles.
You can have ZERO.Zero resistance in the welding path. I was improving
the setup by taking out a couple of milliohms at a time. You'll see a
lot of soldering on my system. That's all mechanical. No current goes
thru a soldered joint.
My welds were working but they were extremely sensitive to time,pressure
and number of cycles of AC line. More turns on the scondary gives you
more voltage and less sensitivity to time/pressure, but increases the
input amps proportionally for the same output amps.
Oh, I was sucking 40 amps for six cycles out of a 15A house breaker.
Talk about dimming the lights ;-) I was about to give up and add a
third secondary turn when the Unitek fell into my lap.
The Unitek CD welder is MUCH more forgiving. It dumps a fixed amount of
energy and is relatively insensitive to contact resistance. That's
relatively. Still have to be careful, but I can make 10 good welds in a
row without much trouble. Couldn't do that with the microwave transformer.
Wear safety glasses and an old shirt. A mis-weld sprays molten metal at
you. Keep a flashlight handy so you can find the fuse box when it blows
;-) Blows caustic stuff at you when you blow a hole in the battery.
Been there done that.
mike
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