PSU Cable Question
I’m working on my Lack Enclosure and thought that having connectors for the PSU would make maintenance on my MK3S much easier since it will be mounted outside the enclosure. I bought some Amass XT60 connectors for the power and some XT30 for the power panic cable.
Is there any issue with tying the positive and negative cables together so I only need one connector for power? As in, do both of the positive wires come off the same rail of the PSU? I’m guessing Prusa used two sets of wires since a smaller gauge could be used and they need to go to two separate connections on the eintsy board anyway, but just wanted to be sure. The XT60 connector is rated at 60a, so I would still only be using under 20% of the connector’s design current with one connector. FWIW, I have the black Delta PSU. I've also attached an image of what I'm looking at doing.
RE: PSU Cable Question
I would not. one of the rails is for the bed, which is a high current load. As that cycles on and off I could see it causing voltage sags/spikes, or just generally introducing noise in the power line. Not something you want on the same rails as what is controlling your printer (Einsy etc).
RE: PSU Cable Question
I would not. one of the rails is for the bed, which is a high current load. As that cycles on and off I could see it causing voltage sags/spikes, or just generally introducing noise in the power line. Not something you want on the same rails as what is controlling your printer (Einsy etc).
There seems to be continuity between both positive terminals on the PSU and both negative terminals on the PSU though when I put my DMM on it. Wouldn't this mean there is a common rail, or is there possibly some sort of other filtering going on there to prevent voltage spikes? I'm an ME not an EE, so I don't know. I can certainly use two separate XT60's to err on the side of caution though. I just thought it would be much more streamlined to have one connector there.
RE: PSU Cable Question
I'm not an EE either, I just know enough to be dangerous... 🙂 so I can't really give you a detailed answer apart from saying that having the additional wire length between that internal tie point in the PSU and the einsy changes the dynamics of the system a bit, for the worse.
In all reality, it'll *probably* be OK most of the time. But when it's not or components are marginal, you can expect all kinds of weird issues due to the high frequency nature of the bed PWM and its large current load. So I'd say better not to risk it.
RE: PSU Cable Question
From all reports I have seen, the Prusa PSU is a single rail design. All Positive terminals are connected together internally.
Same for the negative. And there is apparently no chassis ground. UL waiver for low voltage devices and all that.
RE: PSU Cable Question
What we're essentially discussing now is the risks of changing the wiring layout, from, for example, star wiring to something else I don't know the correct term for. The main point I am trying to make is that there *are* EE design considerations in how you run supply rails from a point supply to all of the end points (loads) that need that rail.
RE: PSU Cable Question
Thanks everyone. I think I'll just ditch this little modification idea - loosening a few screw terminals at the PSU isn't difficult, but I'll just have to move my Lack enclosure away from the wall to access them. Was trying to avoid this, but I suppose it's better not to introduce any more failure points.
RE: PSU Cable Question
Hi!
This will work flawless. As robert-rmm200 mentioned, the two positive and negative terminals are connected in the PSU. Just be careful to use a good quality of XT60. Otherwise your connector will burn after some time.
I used a 4-pin Molex Megafit as I had them laying around and with one pin per cable you have less mess connecting them.
RE: PSU Cable Question
What you might experience is IR drop across the cabling. The PS end has regulation that responds to load changes, keeping the voltage at the two screw tabs stable. The pair of wires from the PS to the new connector adds resistance that when the bed heater energizes, may cause a voltage change in the 12V that is not sensed, therefore adding ripple to the "electronics" side of things. In reality, you already have some of this on the ground side, since these wires are connected in parallel.
In a perfect world, you'd want to use four pins. But, in this case as long as the two connector pins you use are rated for 10 amps or more, you probably won't have any ill-effects.