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kWeld - "Next level" DIY battery spot welder
#21
@spinningmagnets: Nice write-up! Very well done! Cool
Proceed with caution. Knowledge is Power! Literally! Cool 
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#22
No question, spotwelding is the better method.
But if someone decides to solder then it's fine as well. It's just a matter of a big enough iron. High power is helpful but mostly it's about a very chunky tip that can hold a lot of heat. The negative terminal is the chassis of the cell and is therefore a bigger heatsink. But if you have a proper iron than it's as easy to solder as the positive terminal.

But yes, definitely a nice write-up!
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#23
I've been researching this hard, and it looks like if someone does not want to use Hobbyking LiPo, then a common 12V lead-acid car starter battery is the only viable option. It works well, and...they might be bulky and heavy, but...there it is...

I am now looking into if a 6V old car starter battery, or a 6V golf cart battery might also work...
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#24
Well, you need any source able to put out enough current in the region of ~1000A. Good quality RC LiPo batteries work, so do most 12V LA batteries because they are designed to supply high currents as well.

6V batteries will probably work as well, if the cells are as big as on the working 12V batteries. The voltage isn't important. As long as it is enough to power the circuit then 6V is just as fine as 12V and it is just a matter of the maximum current the cell can put out.

Other options I've considered:
High drain 18650s, 40p configuration. The internal resistances of these cells are maybe a bit too high, but with 40 in parallel it evens out maybe.

LiFe cells, cylindrical 38120, 38140 or 40152, will probably work as well. 5p to 7p configuration will probably be the right amount. Or prismatic cells, depending on their size less than 5p.

Supercaps or Ultracaps, big capacitors of some sort. They might work as well, but I don't know enough about their specs and don't have proper sources for these, so I'm not sure. But I guess some people are already thinking about using them as a power source.
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#25
Do you really need a 1000A power source to use kWeld? I've been watching a couple of videos lately (namely, this one) that seems to get the job done using a 330A 12V lead-acid battery and just a solenoid relay with completely manual switching. Wouldn't kWeld automatically lengthen the duration of the weld if less current was available?
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#26
Well, strictly no, you don't. However you want a powerful supply to keep the pulse time as low as possible to keep the exposure of all components to heat as short as possible.
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#27
(02-28-2018, 10:48 AM)thanar Wrote: Do you really need a 1000A power source to use kWeld? I've been watching a couple of videos lately (namely, this one) that seems to get the job done using a 330A 12V lead-acid battery and just a solenoid relay with completely manual switching. Wouldn't kWeld automatically lengthen the duration of the weld if less current was available?

The 330A current rating of such a battery is its tolerated maximum continuous current. kWeld is operating its power source in short circuit, and any decent and fresh 65AH starter battery is capable of delivering 1000A+ in this situation.

It's like DarkRaven said, it is important to keep the pulse time as short as possible. The longer it gets, the more the heat has time to spread out into the vicinity. If the heat is no longer concentrated in one small spot, then the kWeld energy metering principle can no longer ensure a consistent welding result.

Just wanted to let you know that the capacitor module is now available for pre-orders at https://www.keenlab.de/index.php/product...or-module/ ! I expect to be able to deliver by beginning of June. The production batch size for this first round is not too big, and I expect not to be able to build up regular stock yet.
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#28
I did some experiments a year ago with spot welding with very good results ...

If I remember correctly all I use for power was one 80 p pack of 18650s .... two nails for electrodes banged through a piece of wood and out the otherside...the correctly spaced points of the nails are the welding points .The nails were wired to the pack constantly , when pressed on the strip the circuit is made , after a few tries you can judge when to pull away to end the weld .
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#29
I don't see why a fully charged 18ah agm battery (used in a jump pack) couldn't be use to power one of these welders, it should be at least comparable to a lipo pack? I been using a 28ah fullriver agm to power my spot welder with excellent results. 

But from my experience you get the best performance from using large gauge pure copper welding cable on your connections to the battery, and especially on your welding probes. I use 6 gauge wire, they are heavy and very impressive. They let you reduce the power of the welder to get good results. With lower quality copper clad probe cables, you won't get good results unless you crank up the power on the welder. The higher the power, the hotter the cables get. After 20 welds the probe cables will be too hot to hold. I see many of the probe cables from chinese mfg using copper clad audio cables (8 or 10 gauge) , you would need very high power settings to get decent results with that cable.
6 gauge pure copper welding cables for the probes would be the minimum I recommend.    


Battery I been using
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#30
Who said it couldn't be used? Any power source that can deliver high short circuit currents can be used. Some can be used, some can't, some are more suitable than others.
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