Resistance-No Resistance wire welder

[Innocuous]

Of course it was german, and thanks. I've got a 9v 2a on order and a nice, big 20v 4.5a PS from the dead thinkpad ;-)

That's German

I haven't built it yet but I've got lots of wall warts lying around. I'm going to use a 12V 1A

 

[yo han]

I've got a 9v 2a on order

That'll do fine. 2A is overkill but of course it won't hurt either.

 

[Innocuous]

well, I was planning to explore ardweenies and 1a seemed pretty limp ;-)

 

[tobarger]

This project is really getting better every day

 

[yo han]

Consider my last schematic as final.
I've added a parts list now to make it easy for everyone (these won't stay up on eBay forever of course).
If anyone's got any questions, suggestions or comments then please post.

 

[dezyner]

got a question, if the LED display's impedance is less than 10M ohm, will the LED bleed the caps off?

 

[awsum140]

Yes, the meter will bleed the capacitors down, just very slowly. The meter I'm using supposedly has a 1meg input impedance and the voltage drops about one tenth of a volt every two seconds. It does become a game of "overshoot then weld at the right point", but it's pretty easy to do once you get the hang of it.

 

[dezyner]

from what I've read online I think that if you use an LED with an impedance greater than 10M ohm that goes away maybe? wondered if there was a possible work around for it other than finding another LED with that spec. thanks.

 

[awsum140]

Well, technically, if you were to put a 9 meg resistor in series with the meter "sense" lead, it would raise the input impedance to 10 megs but would also reduce resolution by a factor of ten on the volt meter. So all meter readings would be off by a factor of ten. If you can live with that and the associated lack of resolution, it'll work.

 

[dezyner]

lol. not digging that, thanks tho. been trying to find specs on one that has the right rating, since this isn't exactly a mainstream application it is a lot of sifting. thanks. cheers.

 

[awsum140]

Yeah, going solid state has it's disadvantages...I miss my old RCA Senior Voltohmyst that had a 10meg input impedance and use, perish the thought, vacuum tubes, LOL.

 

[Mad Scientist]

from what I've read online I think that if you use an LED with an impedance greater than 10M ohm that goes away maybe? wondered if there was a possible work around for it other than finding another LED with that spec. thanks.

You could put a unity gain op amp voltage follower before the meter. Input bias current ranges from picoamps to femtoamps, depending on what part is used (input impedance from about 250 meg ohms to the gig ohms).

 

[Glenn54]

Done

View attachment 270448

Parts list on eBay incl. US shipping costs:
(Click on part name to be taken to eBay)

F1 (10 pcs) $3.50

Holder for F1 (2 pcs) $0.99

D1 (25 pcs) $0.99

R1, R2 (10 pcs) $0.99 + $1.92 = $2.91

C1, C2, C3 (4 pcs) $5.95 + $1.75 = $7.70

XL6009 (same as LM2577) $2.18

Volt meter $2.45

Resistance meter $6.64 + $1.99 = $8.63

S1, S2 $2.35

S3 (2pcs) $2.50

S4 $4.88

Total: $39.08

Remember you will still need to buy a project case, your choice of terminals, a 510 connector (or whatever you want to use) and a connector for your DC adapter plug.

Great where can I buy one already made in the US?

 

[Innocuous]

Umm.. You buy the parts. You make the box. In the USA. Congrats.

Great where can I buy one already made in the US?

 

[yo han]

Great where can I buy one already made in the US?

This one doesn't exist yet since I've only just finished the final drawing and haven't yet received all the parts to build it.
You could ask someone who knows how to solder to build it for you.

 

[yo han]

Just watched a video about the TSAF VRD and it seems capable of doing the same but in a VERY small package.
Can't understand why this guy isn't trying to market this thing in English... click

 

[awsum140]

I'd love to know what capacitance he was using. Personally, I like a bigger box and keeping one of the wires in a clip mounted to the box rather than "free hand" the weld totally.

 

[yo han]

His voltage is pretty low. You can see him charging and it's only 31.3V even when he keeps pressing the charge button.
I agree with your preference for a bigger box and one fixed terminal. But you see his method for measuring resistance and then cutting the wire at the clip? That's exactly what I had in mind.

 

[awsum140]

That's how I do it now, measure from the clip, but my meter is an outboard DVM with zero adjust on the ohms scale, which is convenient. I saw the 31.3 volts, but still wonder what capacitance he was using. I've been getting decent welds with 2000mfd and 31-14 volts, depending on the wire gauges, but there is some overheating that leads to brittleness at the weld, read wire breaks too easily. I've got to do a video one of these days.

 

[Glenn54]

Umm.. You buy the parts. You make the box. In the USA. Congrats.

OH, OK, thanks for $30 in parts I'd pay $60 to someone so I don't have to mess with it! But that's just me.