Duet 3 wiring and Power Questions



  • Hooking up my Duet 3 and have a few questions revolving around power.

    I have 14ga wire running from my Mean Well power supply to the Duet 3 VIN terminals.

    I'd like to use Out 0 to trigger the SSR for the bed which means i need to provide it with power to the Out 0 (Power In). Shall I just jumper it across using a short piece of the same wire and a couple of fork terminals or should I run it straight from the power supply?

    The SSR is a Cydom D2410, and if I'm reading the Datasheet right, it only requires 12mA maximum to turn on. There's lots of headroom with the power supply and that 14ga wiring that it should't be a problem. Would I be correct?

    Second power question goes for the Out 4-6 and Out 7-9, the documentation leads me to believe that I could provide them VIN (24VDC) or switch them over and they'd be 12v. The Duet 3 has an onboard 12v regulator? In that case I could un 12v fans without any type of buck converter?

    Next power question comes between the Duet 3 and the Pi 4. I'm wiring up the Pi with it's own 5v power supply. I would like neither of the boards to power the other. So I'll set the jumper correctly, and not connect 5v between the two. The question is, should I still provide ground between them along the 26-pin connector? They'll both be grounded to their own power supplies and then both to the same ground pin of my IEC socket.

    Last question about crimping the motor cables to the newer beefier JST Connectors, as the Wiki stated, the cables for my Nema 17 are too small (24ga), I'd rather not solder them. Can i instead strip off double the length of sheathing, twist them up, and then fold them in half, thus doubling the amount of copper in the crimp? Of course making sure there are no errant strands hanging out to short anything.



  • @blt3dp said in Duet 3 wiring and Power Questions:

    Can i instead strip off double the length of sheathing, twist them up, and then fold them in half, thus doubling the amount of copper in the crimp?

    thats what I do if I can't get terminals in the correct size and my non-ratcheting crimp tool is unable to shoe horn the smaller wire into the terminal with good results.

    to evaluate crimp just the copper and try pulling it out, if it shears in front of the crimp you're golden; if it pulls out or shears at the crimp you're too loose or too tight.



  • Keep in mind that the crimp is just one part of the equation (yes, doubling up works fine) .... the other is the current capacity of the wire. If you run higher current then you might run into limitations with the 24 ga wire. I am not saying this applies here but is something that should be looked at in a case by case basis. 24 ga wire has a resistance of approximately 26 ohms per 1000 ft which doesn't seem like much but do the math. A 5 ft run is 10 ft of cable which works out to 0.26 ohms for that run. Again it doesn't seem like much but if you are running 2A that is 0.5 volts out of 12V.
    Since the Duet3 can support what 6A for steppers, you have a potential drop of 1.5 volts out of 12V which is no longer acceptable. This does not include any contact resistance of connectors!
    Things get easier if you go to a 24V power supply and a lot of issues go away.



  • It’s 24v and the leads for the motors are a meter long. Seems to do ok on a Duet 2



  • @blt3dp said in Duet 3 wiring and Power Questions:

    Hooking up my Duet 3 and have a few questions revolving around power.

    I have 14ga wire running from my Mean Well power supply to the Duet 3 VIN terminals.

    I'd like to use Out 0 to trigger the SSR for the bed which means i need to provide it with power to the Out 0 (Power In). Shall I just jumper it across using a short piece of the same wire and a couple of fork terminals or should I run it straight from the power supply?

    Jumper is fine for triggering an SSR.

    Second power question goes for the Out 4-6 and Out 7-9, the documentation leads me to believe that I could provide them VIN (24VDC) or switch them over and they'd be 12v. The Duet 3 has an onboard 12v regulator? In that case I could un 12v fans without any type of buck converter?

    With the jumpers set to 12V, you can run fans. TOTAL of all these must be less than 800ma. (0.8 amp), so really, small brushless fans only.

    Next power question comes between the Duet 3 and the Pi 4. I'm wiring up the Pi with it's own 5v power supply. I would like neither of the boards to power the other. So I'll set the jumper correctly, and not connect 5v between the two. The question is, should I still provide ground between them along the 26-pin connector? They'll both be grounded to their own power supplies and then both to the same ground pin of my IEC socket.

    Ground - yes. Absolutely yes, for signal integrity.

    Last question about crimping the motor cables to the newer beefier JST Connectors, as the Wiki stated, the cables for my Nema 17 are too small (24ga), I'd rather not solder them. Can i instead strip off double the length of sheathing, twist them up, and then fold them in half, thus doubling the amount of copper in the crimp? Of course making sure there are no errant strands hanging out to short anything.

    Doubling is fine. With proper crimps, single is also fine.



  • @blt3dp said in Duet 3 wiring and Power Questions:

    It’s 24v and the leads for the motors are a meter long. Seems to do ok on a Duet 2

    Yes, that is fine. I only included the sermon for completeness sake lest you try to run higher power motors (that the Duet3 can drive) on a 12V system. Also as a reminder for those trying to run heaters on 24 ga and 12V which I tried to do and it sort of works but will bite you in the ass sooner or later. I am now on 24V because I got bitten.



  • To add to the "jst with small conductors" thing, as well as doubling the copper, I snip the wings that wrap around the insulator so that they are only about half the length. I've done 13 stepper motors like that (so 52 crimps) and narry a problem.



  • Unless you use a rather pricy pair of snipps that doesn't leave a sharp edge I'd much rather leave the tabs as is, and if you have a ratcheting type crimp it would only exaggerate the isse, and if you have a manual crimp the tabs will simply fold and curl into a spiral-ish shape with no sharp edges to nick the conductors which will be where it breaks when it breaks.



  • @bearer Each to there own as the saying goes. I was simply passing on the information that I found having the wings too long for the insulation size caused me problems and that reducing their length solved the problems for me. I'm not saying that I will never have a problem but the machine has done a few hundred hours without any issues so far.



  • @deckingman good for you!


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