22 replies to this topic

[whoof]

Thats the theory for traditional resistive spot welding though.
I cant help thinking that cd operates so fast that something else may be happening such as arcing

I have seen this done using a 6 v la battery and transistor switch fed from a 555 monostable.

Some form of current ballast is needed though.

Edited by whoof, 07 September 2014 - 01:22 PM.

[Crazy Cat]

So further info I forgot to post.

http://www.nickel-al...ome_alloys.html

soldering to nichrome wire. http://www.electroni...ome-wire.69407/

Welding Nichrome wire. http://www.sciencema...d.php?tid=12982

I have a bottle of copper II chloride which I typically use as a regenerating etchant, but I used it to sort of etch/plate the nichrome.
I took a AA battery and put a braid of 28ga wire on one end and a strand of 28ga on the other. I held the nichrome to the strand and let a thick black layer of oxide build up on it.
Then I wiped that oxide layer right through the solder bead on the tip of my little 15 watt iron and presto! it stuck!

http://www.vapersfor...hrome-soldering

I once built a spot welder for welding thermocouple wires to pipe. I used 10,000 microfarads charged to about 70 volts. The trick is to discharge quickly, just touching it on won't work. Make good contact then discharge the capacitor through an SCR. I think for a one off Compositepro has the answer you are looking for or you could crimp it.

http://www.eng-tips.....cfm?qid=218705

[Arthur Brown]

The critical part of spot welding is to get the pressure on the joint first then ramp up the current quickly. Usually a pressure sensor on the electrode determines when to put the power on.

[dave]

that sounds spot on Arthur

 

excuse the pun
 

[danilo]

dave, it’s a fairly simple electronic circuit but it is important to note here that this cannot be done without actually discharging the capacitor a little bit. If you want a small LED blink when the capacitor is charged, it could be done with a small timer and it won’t affect the charged capacitor as much. As you can see the charging circuit of the flash of a camera mentioned in an above post, shows that the LED will be switched on as soon as the voltage divider acquired the required voltage but since there is always a resistance connected across the capacitor, it provides a path for the charges to discharge. 

 

quick-turn pcb assembly

Edited by danilo, 12 August 2015 - 07:52 PM.

[Niall]

Wouldn't a simple transistorised latch circuit do it? Capacitor charges, resistance is higher than an alternative route, alternative route latches relay and LED takes the supply voltage cutting the capacitor feed from the supply and charge waits at the discharge curcuit? Discharge pops the transistor to unlatch the relay.....

Not sure how simple you want it. I will have a think too. But it looks like there are better versed folk here than me.

Edited by Niall, 11 March 2015 - 03:07 AM.

[Arthur Brown]

I have seen a spot welder on ebay, that was designed for welding the lugs on Li-ion batteries prior to assembling laptop replacements. I think you can do well with a rewound microwave oven transformer and a timer.

 

eg ebay 381105843926

Edited by Arthur Brown, 11 March 2015 - 11:57 PM.

[Niall]

I'll try and draw a picture..... Unless you have your answer?