Makergear M2: Heated Build Platform Cable

The power + thermistor cable for the M2 Heated Build Platform attaches to the Z axis stage at the Y axis motor, with the conductors encased in a fairly stiff braided loom. The cable flexes from fully retracted to fully extended as the HBP moves along the Y axis. Here’s a view at about mid-travel:

M2 HBP cables - wire loom
M2 HBP cables – wire loom

Unfortunately, there’s no provision for strain relief at the HBP or around the connectors. The silicone heating pad firmly anchors the two pairs of power wires to the aluminum plate, but that simply means they flex sharply at the edge of the pad:

M2 HBP connections
M2 HBP connections

I removed the loom between the motor mount and the connectors, but that still doesn’t provide nearly enough flexibility:

M2 HBP cables - loom removed
M2 HBP cables – loom removed

The wires still flex sharply at the outboard side of the connector and at the HBP pad; this can’t possibly survive more than a few thousand long cycles before something expensive breaks. The Thing-O-Matic HBP connector debacle suggests that I may need to attach a strut to the Y axis stage that rigidly supports the connectors, with a much longer loop of wire soaking up the strain to the fixed end.

The 18 AWG wires carrying the 10+ A of HBP current get unpleasantly warm, suggesting that new loop will require heavier wire. In round numbers from that table, 18 AWG stranded wire runs 6.5 mΩ/ft, so the (roughly) four feet of wire pair between the electronics case and the HBP will drop 250+ mV and dissipate 2.5 W. I suspect it’s worse than that, but haven’t made any measurements to back up that suspicion.

10 thoughts on “Makergear M2: Heated Build Platform Cable

  1. On a trailer inverter application, I used marine 12 gauge wire on a 250W outlet. Better for dissipation, but the insulation isn’t great. A thought would be the silicone wire used in electric RC airplanes. Rooting around the Tower Hobbies site shows Acer Racing 10 ga silicone wires (one pair 5′ each length) for a mere [cough] $14.99. They also have decent connectors. (The wire is available 16ga to 10ga from Tower, but it seems to be 2 x 5′ for all…) For larger quantities, Allied Wire and cable has a wide range…

    1. silicone wire used in electric RC airplanes

      That’s a great idea: super-flexy and tough. Thanks for the tip!

      Five feet might be about right, as the power supply and SSR won’t be inside the chassis…

  2. What is the total cross-sectional area of a ribbon cable? Something like a floppy drive cable from an old PC?

    Does the heater run constantly or only for the first several layers?

    1. That’s an interesting idea: mount a tray on the Z stage with a U-folded ribbon cable to the Y stage. It would flex in a controlled way around the stablized connectors on each end, somewhat like the cable in a flatbed scanner.

      Paralleling ten 24 AWG ribbon cable conductors would give you the equivalent of a single 14 AWG wire, which seems reasonable. The resistance is 0.0025 ohm/ft, about 0.01 ohm for 4 ft: half that of the 18 AWG wires. A 20 conductor ribbon cable (equivalent to two 14 AWG wires) would be 2 inches wide, which could be a difficult fit; stacking a pair of ribbons might warm them up a bit.

      So far, I’ve kept the heater on for the complete build: I read that holding the bottom layers near / above the plastic’s glass transition temperature produces less warping. That’s on the list of things to examine…

    2. The biggest ribbon cable I’ve seen is about 26AWG, which is 323 cmils per conductor. You’d need 9 conductors to get up to the equivalent of 16ga, and it comes in crappy PVC insulation and only flexes one direction…

      1. A quick Digikey search shows 20 AWG and 22 AWG cable, but priced for a different buyer and not in stock. Probably PVC jacketed, too, although that’s not conspicuous.

        I like the general idea, though…

        1. I mostly just wanted an excuse to use my second-favorite unit of area. :)

  3. Some cables are intended for repeated flexing, like extension cords. Some are not (like floppy connector ribbon cables).
    Generally, the more strands, the more flexible (the smaller wires in the high-strand-count take longer to break).
    The fewer the strands, the more current carrying capability.

    Thumbs-up for the RC wire, it is usually very good for repeated flexing (as you remove and replace motors and batteries), but I would add a strain relief to the HBP in the form of some silicon or zip ties. Spreading the flex along a couple inches of wire will last much longer than concentrating the flex in one spot. I used 3 layers to heat shrink over the wires and a popsicle stick that was taped to the HBP.

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