T
.No don't do that. The voltage is produced by electron migration between the two dissimilar metals. If you solder them you add an alloy between them. It will still produce a voltage but it will be unpredictable. The wires have to be spot welded or fused together with no intermediate material.
You need either special stainless steel solder or phosphoric acid as flux.
You get welded wire thermo elements with connector for < 10 EUR at catalog distributors.cant afford to buy thermocouples where they are already spot welded.
I've read this, but it's not true according to my understanding of thermoelectric effect. Placing a third metal between the two thermo element wires doesn't change the voltage as long both junctions have the same temperature.As we discussed, soldering is not optimal for joining them (wont make the thermocouple junction).
And do you have an answer for our contractor who insists on just resting thermocouple junctions against a D2PAK drain tab, rather than glueing it?.....?
Thanks sorry i meant Loctite 382. The point is, that if the thermocouple junction is just resting against the metal drain tab, (instead of being glued to it), then there may be air currents flowing over the thermocouple junction which will slightly cool it and give a slightly inaccurate reading. As such, a small spot of glue is needed around the thermocouple end to attach the thermocouple end to the metal drain tab.?"Loctite 368" is no active Loctite product, typo?
TIf glue is not used, then you have just a point contact of the thermocouple end to the metal drain tab, and the air that is slightly flowing around the rest of the thermocouple junction will act to cool it, and give inaccuracy in reading
I must admit, we are looking for the cheapest superglue, and the cheapest activator which will immediately (within a few 10’s of seconds) cure it….but the entire Loctite website does not allow you to find what this combination is….Do you know it?
https://www.loctiteproducts.com/epoxies.shtml#multi-purpose
We must have the glue and the activator in separate tubes/bottles because otherwise you just end up with the applicator nozzle getting jammed.
Thanks, and do you have any thoughts on using a dot of glue to glue the thermocouple to the metal drain tab,....
Thanks, we intend to use Loctite 382 with 7455, and it sets in seconds. We can hold the thermocouple against the metal drain tab, and it will set like that.Most epoxy glue takes hours to set but the time can be reduced if you increase the hardener proportion (double the amount and it will set in 15-20 mins with reduced strength).
Thanks, I thought we could just use standard electronics 60/40 Sn/Pb solder and phosphoric acid flux?If you still want to solder the thermocouple end, electroplate the weld point with copper or tin (only the tip) and then you can solder it as usual
Our contractors don’t want to use glue to fix the thermocouple end to the metal drain tab, they say its allright to just rest the thermocouple end against the metal drain tab. What are your thoughts on this?
It works for me. You can also consider to crimp the thermo couple tip into a small wire-end sleeve and solder the latter.Thanks, I thought we could just use standard electronics 60/40 Sn/Pb solder and phosphoric acid flux?
The FET is a linear regulator FET in an offline linear regulator which feeds from the rectified DC bus, which doesnt have a capacitor on it.....The drain tab can go up to 373V.You didn't yet comment on the high voltage capability of your thermo couple measurement circuit. Most people will prefer an isolated thermo couple mount.
Our contractors don’t want to use glue to fix the thermocouple end to the metal drain tab, they say its allright to just rest the thermocouple end against the metal drain tab. What are your thoughts on this?
Thanks, but if the thermocouple end is not glued to the metal drain tab of the FET, then might there be air currents around the thermocouple end which will cool it down and give a falsely low temperature reading?QU: Our contractors don’t want to use glue to fix the thermocouple end to the metal drain tab, they say its allright to just rest the thermocouple end against the metal drain tab. What are your thoughts on this?
ANS: For metals, both electricity and heat are conducted by electrons (mostly) and if the electrical connection is good, the thermal connection should also be.
As such, my question is.....is it acceptable to merely rest the thermocouple end against the metal drain tab of the fet when doing a temperature measurement? (as opposed to actually glueing the thermocouple end to the metal drain tab)
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