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Thread: Lithium Battery Tab Welder
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10th Apr 2021, 09:16 PM #1Most Valued Member
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Lithium Battery Tab Welder
Anyone have any good cheap Lithium Battery Tab Welder ideas or a links to what they think are simple good ones. Looking at putting tabs on some 18650 cells.
Nev.
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10th Apr 2021, 11:34 PM #2
Hi Nev, Guys,
Somewhere on one of my backup discs I have the instructions and construction notes for a microwave oven transformer design. It uses a capacitor bank and a timer, 555 ic, to discharge the capacitors via an SCR.
You have to remove the high voltage winding and hand wind a secondary to produce about 12 volts, then you select one or more capacitors to discharge into the weld via a two pronged hand held probe made from copper welding rods.
I don't remember all the details but I did start to modify a transformer to make a spot welder using similar circuitry. I'm sure that I found the details on line, not that I remember where, but I'm sure DuckDuckGo will find something.Best Regards:
Baron J.
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11th Apr 2021, 01:18 PM #3Diamond Member
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Haven't ever built one, but I liked these primitive "designs":
https://www.youtube.com/watch?v=1SMUFSiaV-8
https://www.youtube.com/watch?v=WSXHO7C1vaM
All low voltage, no transformer rewinding - a large capacitor or three, and a light bulb for safe charging.
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12th Apr 2021, 01:16 AM #4
I bought and use one of these:
https://www.youtube.com/watch?v=yyJZFzLnSGE
I have used it with a car battery and with a RC battery like in the video. Both work perfectly fine. Listen to his warming about using a battery that is too small and the voltage drop to 9V!!!! IMPORTANT.
I found it had no effect on the charge of the car battery at all, even after an extensive series of welds. So the power used is quite small (lots of amps but for just milliseconds). If you use a small capacity12V battery, its voltage could drop to 9V and the next weld blow the welder up!Cheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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13th Apr 2021, 09:06 PM #5Senior Member
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Never built one myself, but I gave a friend - who is an electronic / SCADA / computer engineer a microwave oven transformer, and he cut the secondary off, and made two turns (2 vots) of some fibreglass insulate (125c+ insulation) cable about 10mm diameter - that I gave him. The trick is you need the two electrodes very close together - on the new tab - with a bit of a "wrinkle" (on the new tab) between the electrodes so that the current flows across the tab, and the battery's outer case. I think this reduces the temperature rise inside the battery (temperature rise inside battery = explosion!).
I will go and see him next week.
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14th Apr 2021, 01:39 AM #6
Hi Guys,
The one thing that I haven't seen mentioned anywhere is that it is important to make sure that the battery contacts are clean ! Any oil, grease or dirt will cause a poor joint. The same applies to the nickel strip.
A modified microwave oven transformer makes a brilliant spot welder, being able to put several hundred amps into a joint. I bought a five foot 12 mm diameter copper earth rod to make make electrodes with. But you do have to be careful some earth rods are copper coated steel and are no good for this purpose.Best Regards:
Baron J.
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3rd Oct 2021, 07:55 PM #7New Member
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With two of those, there might be head room in voltage (29,6V nominal) and capacity (120A for 2 minutes or - in your case - 65A for about 4 minutes).
Both options have also peak power in excess, being rated at 50C this means that they can generate also up to 260 A (and for a second even twice as much).
In comparison, regular Li-Ion 18650 batteries are not built for those currents. They are built to get discharged in 30 minutes while 20 is already pretty extreme for them. Densely packed in a container they might easily overheat if stressed with upper position of pipe.
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