thermocouple welder ideas - Page 1
Forum section: electronics / projects

author: croyleje
author_rank: Regular Contributor
timestamp: October 28, 2014, 03:37:12 am
content: hi everyone,i have been looking at a few thermocouple welders it appears most of them are mostly CD welders and even the commercial unit don't all use shielding gas so i thought it might be fairly easy to make one. the only one i could get detailed specs on lists it as 18300 MFD with a peak operating voltage of 144 volts at highest setting / 3-90 watt seconds. i have also seen a few models that appear to be using simple step down transformers rated at 48 volts and adjustable to 40 amps these unit are labeled as thermocouple/fine wire welders. all the units are using a simple carbon electrode my question boils down to any ideas pro or cons of each? i have a battery tab spot welder was thinking about writing some new code to increase pulse time but it only runs at 16 volts. well any ideas would be greatly appreciated.thank youjason

author: Teledog
author_rank: Regular Contributor
timestamp: October 28, 2014, 04:13:18 am
content: Not sure what kind of thermocouple weld you are trying to make,but I've made type K thermocouple wire beads with an acetylene torch - for use in kilns.It sometimes takes a few tries..the bead has to be small and symmetrical, then tested.Never had a spot weld work reliably on the thermocouple wire..Twisting the hell out of the end sometimes works, but doesn't seem to last (and not as accurate readings as a bead weld).My 2 cents anyway..

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 28, 2014, 04:16:27 am
content: I would just give your spot welder a try with some heavy copper electrodes. It's resistive welding so all you're really doing is putting energy enough to melt the wires into it, and if you're doing little instrument thermocouples it's not going to take much energy. How it gets there doesn't matter; it's the watt-seconds you need.OTOH, you can join them by silver soldering. All that's required is the silver solder (real stuff, something you buy by the troy ounce), flux and a propane or even butane torch. Pair of scrap pliers to act as a heat sink to keep the insulation from melting. I use a TIG welder now that I have one just because it's faster.

author: richard.cs
author_rank: Super Contributor
timestamp: October 28, 2014, 09:18:13 am
content: They're pretty easy to do, the last one I made I twisted the ends and then spot welded with two carbon rods and a car battery. I would think both capacitor discharge and transformer welders would be fine but I would stick with carbon electrodes. Even a weak bond to a copper electrode (which wouldn't matter in normal sheet metal spot welding) might be hard to unstick without breaking the wire.

author: croyleje
author_rank: Regular Contributor
timestamp: October 28, 2014, 09:11:35 pm
content: thank you for the input i also thought about just using a torch to melt and make the bead. i will be making type k thermocouples. if i use an acetylene torch is there any issues with oxidation of the molten bead? that was the only worry i had about doing it that way.jason

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 29, 2014, 03:44:51 pm
content: The Ewald I've used is pretty simple. They charge up a couple hundred uF cap to about 300VDC and then discharge it through a big transformer with a 1-2 turn secondary winding. They used a mercury relay. A Variac controls the max voltage of the cap so the power can be adjusted. The electrodes are copper. There's a particular alloy preferred for this, but I don't remember which one. Building one would be easy, but a torch is faster if that will get the job done for you.

author: croyleje
author_rank: Regular Contributor
timestamp: October 29, 2014, 10:28:50 pm
content: well i guess ill just use my old arc welder and make some carbon electrodes for it. now how about controlling the amperage is there easy way to control the amperage? it would be nice to use a variac on the primary but would prefer not to spend that much. would a simple triac dimmer be ok or would the chopped waveform cause issues with the secondary?Jason

author: DmitryL
author_rank: Regular Contributor
timestamp: October 29, 2014, 10:47:42 pm
content: Hmmm. To me it looks like overengineering.When a K-type thermocouple that came with my multimeter broke (2 wires fell apart, they probably were badly welded), I just made a graphite electrode from a pencil core (length about 2-3cm), took a decent transformer that gave me ~10-20V and about 3-5A, twisted those wires, connected them to the transformer with a crocodile clip, and welded them with the electrode in another crocodile. Now the thermocoulple is as good as new.I read that borax makes a very good flux for such cases, but it wasn't necessary.... probably not suitable for mass production though

author: TopLoser
author_rank: Unknown
timestamp: October 29, 2014, 10:54:28 pm
content: http://www.farnell.com/datasheets/1848456.pdfFound one of these under my desk, along with a box of high-end thermocouple calibration and precision temperature measurent kit.

author: mzzj
author_rank: Super Contributor
timestamp: October 29, 2014, 11:08:44 pm
content: Thin k-type is easy! I use lab power supply and carbon brush from angle grinder motor. 30 volts and 5 amps works well for me.Anyone got success with T-type thermocouple welding??