Electronic – soldering nichrome wire


I am trying to build a heater based on Nickel-chromium 80%/20% wire (nichrome) to heat tubes of solutions for an electrophysiology research setup. The plan was to wrap a length of nichrome around each tube, then chain the tubes in series by joining each end of the nichrome to a short piece of hookup wire with a gold connector on the end.

BUT I just tried to solder a length of hookup wire to the nichrome and found that the nichrome won't accept my standard rosin-core lead solder at all. I'm using a Weller iron at around 750°F (400°C), but playing with the temp made no difference except for increasing my frustration. My suspicion is that I need to use some other kind of solder, or if the soldering technique is too cumbersome, some other way of joining the nichrome to the circuit. What are my options for getting this nichrome stuff to play nice?

UPDATE: Thanks for all the responses. I ended up using a type of gold connector we had around where I could trap the nichrome wire by filling the hole for the wire with solder. Hopefully this will hold up.

Best Answer

A crimp is usually used inside heaters for connecting nichrome wire to other metal parts or wires. Since it can get hot, you'd need a bare metal (not plastic coated) butt crimp.

bare splicing or butt crimp

Its a very reliable method if you use the right tool and a very poor method if you make-do with pliers and brute force. With the right tool, the two metals in a crimped bond are actually cold-welded together, forming a gas-tight bond. Other connection methods (including soldering without sufficient flux) may leave oxide layers or admit oxygen which can affect conduction and mechanical strength.

The "right tool" is the ratchet crimp tool recommended by the manufacturer for the particular crimp and wire. Ratchet tools ensure that the correct pressure is applied before they release (unless you use the emergency release lever which is only meant in case of trapped fingers). As opposed to a pair of pliers, which may under or overcrimp the part, not shape the crimp correctly, slip off etc. Ratchet crimp tools can and should be calibrated.