Thermocouple Plug

Have some thermocouple wire but no plug?

This thermocouple plug allows you to make a half decent replacement for the parts you buy. It does not have a wider negative leg so if the reading goes down when you warm the end up, switch the plug around.

This plug makes use of a standard car blade "Mini Fuse" which has slightly short legs but otherwise fits perfectly in my TC meter, in fact the fuse's blade thickness is more than the plugs the meter came with so it fits more snugly.

Mini fuses cost between 5c and 50c from online suppliers if you buy quantities of 50 or more. For one fuse from your car parts supplier you'll be paying about $1.00 each for a pack of 5 or 10. You might just want to buy a complete thermocouple wire with a plug online or $4 or $5 each (set of 4 or 5 for $20)

First trick is to blow the fuse, I just picked the little bridge out with a piece of wire so that the two legs are no longer shorted out.

Second trick is to solder the TC wires to the exposed ends of the fuse (these are the contacts usually used for in circuit testing of a fuse). The fuse part will accept solder without difficulty but depending on what type of thermocouple wire you have you may not be able to solder to it. In this case you have to get creative:

• crimp a ferrule on and cut most of it off because it will be too long or
• twist the TC wire around a solid copper wire, fold the wire over to "crimp: the joint mechanically and add solder to hold it together, now solder that to the fuse. I have used a small piece of a through hole resistor's leg that was cut off.
• Use one of the pins from a molex type connector that you extract from the connector, these usually get wires crimped onto them. Fold your TC wire over once or twice and crimp it instead. Cut off the excess.
• you get the idea, find something small and solderable to crimp onto the TC wire

Print the front and back of the housing

Position the blown fuse and drill a hole through the middle for the screw, stay below 3mm 1/8th" or the screw will short the two blades and your thermocouple will only measure room temperature. #6 screw might be OK but as you can see I used a self tapping screw with 3mm OD

Assemble as in the pics, use the round strain relief pegs because the solder joint is fragile. The screw holds everything together but use hotmelt or glue if that works better for you.

Too tight, too small? I have included step files for you to modify. I suggest some grips to help pull it out, some strain relief for the thin wire, a hex recess for a nut, markings for polarity, names where it is measuring.

Print Settings

Printer Brand:

Creality

Printer: 

Ender 3

Resolution:

.2

Infill: 

20%

Filament: Amz PETG/PLA Beige

Notes:

Lay the flat side on the bed, this is the outside. I uses a brim but a glue stick will also work.

Category: Tools