Thermistor connections – screw terminals vs Molex crimping

Screw terminal strip used to parallel the two Z-motors on a Mendel Prusa

Screw terminal strip used to parallel the two Z-motors on a MakerGear Mendel Prusa

A couple of days ago I decided to smarten up my Prusa, by covering the exposed threaded rods with plastic “loom tube” (available locally from Jaycar). The 7mm variety fits nicely over the 8mm threaded rod, and also over the Z stepper motor wiring, as you can see in the photo on the left.

The red twisted plastic stuff came with the kit, and Jaycar calls it “spiral binding” and only sells it in black. I’m using it to tidy and brace the extruder motor’s wiring.

While doing this prettification, I broke one of the leads from the nozzle thermistor to its tiny Molex plug. Oops. By special request of Gary, here’s a photo showing how I fixed it.

Thermistor screw-terminal connection replacing Molex plug

Thermistor screw-terminal connection replacing Molex plug

Yes, I just pulled the remaining lead out of its crimp, and plugged both leads into my last remaining piece of screw-terminal block. Then I pulled the black and white leads out of the matching Molex connector and plugged them in opposite the thermistor leads. Problem solved.

Note that I’ve left two spare screw terminals attached, next to the thermistor leads. That is so that if/when I break a lead to the nozzle heater (the red and green wires on right of shot), I can do the same replacement with them.

In the back of my mind is a plan to redesign the extruder mount so there is some place to firmly attach the terminal block, so there is no lead flex on the thermistor or heater.

Why didn’t I just fix the original connector?

Turns out that getting the crimps out of the tiny Molex connectors used for the thermistor and heater is next to impossible without a special tool from Molex. It is not expensive, but it is not in my toolbox, either. Thanks to Sonny on the MakerGear Google Group, I now know about the tool, and how to use it, but I’m still happy to have a repair that I can do with stuff available locally.

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2 Responses to Thermistor connections – screw terminals vs Molex crimping

  1. jtktam says:

    if you need i can send you a few extra crimps.. i have hundreds

  2. BrazenArtifice says:

    Thanks for your kind offer!

    I don’t really need more crimps, they are easy enough to buy locally. I just find them very fiddly and annoying without a decent crimping tool, which I don’t have. Decent crimping tools are expensive! So I’m happy to use old-technology screw terminals that I can work on with a screwdriver. Nothing else has come unstuck in the last 11 months of using the printer.

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