spot welder for nichrome wire

[Jantoven]

I need to make a 120 volt, 300 watt heater using 32 gauge nichrome wire (10.5 ohms per ft)and have a need to make reliable electrical connection from the nichrome wire to the 16 gauge copper lead wires. I tried silver soldering (oxy acetylene with stainless flux) but the silver solder wire I had was too big and I melted the fine nichrome wire. I have read a capacitive discharge spot welder may just be the ticket. Anyone know approx how many micro farads in electrolytic capacitors I need and what voltage I should be charging it to for a good weld?

 

[Compositepro]

Welding dissimilar metals has many complications. A more common approach would be to twist the nichrome wire to a a double or triple ply for a few inches and then screw clamp it to your copper wire. This reduces the resistance of the nichrome near the termination and therefore the heat generated near the termination. This will lower the heat loss down the copper.

Melting the nichrome while silver soldering, however, is simply a problem with your technique. Using a smaller torch tip and directing the heat mainly on the copper wire should work.

 

[roydm]

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.
Regards
Roy

 

[itsmoked]

A more typical method is to use crimp terminals that are designed for connecting Nichrome to copper. Then the nichrome is terminated to larger copper wire that can conduct away the heat coming down the Nichrome.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DanEE]

We have on occasion made our own 48volt DC battery plant load testers made from nichrome wire bought in bulk..

I'd agree on the (suitable) terminal block approach above to tie the copper to the nichrome and, to provide a thermal barrier (enough bulk in the terminal block to provide heat sinking) at the connection.