Hello,
I am new to this forum and currently in the planning phase for a LowRider CNC. As board I have ordered a SKR V1.4 Turbo with TMC2209. Since I have scrunged a fat power supply from an old gaming computer I wonder if it could be used for the LowRider?
It seems to have two 12 volt outputs with 28 amps and 20 amps. I also wonder if it would be possible/better two wire the two 12 volt outputs in series in order to get 24 volts ?
Here are some pics:
Any thoughts?
I used a similar PC power supply to run a Prusa clone for years and it worked fine running both the extruder and the heated bed, so there shouldn’t be any problem with it providing enough power for the lowrider.
I don’t think using both 12V rails will get you 24V. You might be able to get a very small amount of 24V current running from the -12 to the +12 line, but when I experimented with that the power supply reset itself, repeatedly. I finally just settled for 12V from that supply, and purchased a 24V supply for the other machine I was working on at the time.
Thank you for your input.
I was only not sure 
if a 24 volt power supply would be better suited for the LowRider with that kind of board. But when 12 volt is ok I will go that route. 
It isn’t intuitive, but 24V gives you more speed, not more power.
The only problem we’ve seen with this kind of PSU is that some of them expect at least a little load, and the rambo/skr isn’t enough sometimes, so they will shut off, or have wild voltages. But I haven’t seen that in a while. It doesn’t take a huge power supply, so buying a new one for this purpose is not a large investment.
If you’re going to use this, find one of the dozens of online articles about turning a PC power supply into a bench power supply. They’ll explain which wires to short to get it to come on and where to add what size resistor to manage the minimum load issue.
When I used this in conjunction with a RAMPS board, you could use a software command to turn the power supply on and off, which worked for me since I always used Repetier Host to send jobs and therefore the USB connection supplied power to the controller.
Do you think more speed would be good/necessary in my case?
In this respect I found the ATX specification on Wikipedia really helpful:
If using an ATX PSU for purposes other than powering an ATX motherboard, power can be fully turned on (it is always partly on to operate “wake-up” devices) by shorting the “power-on” pin on the ATX connector (pin 16, green wire) to a black wire (ground), which is what the power button on an ATX system does. A minimum load on one or more voltages may be required (varies by model and vendor); the standard does not specify operation without a minimum load and a conforming PSU may shut down, output incorrect voltages, or otherwise malfunction, but will not be hazardous or damaged.
(ATX - Wikipedia)
Good idea! I plan to use the SKR V1.4 Turbo board with TMC2209 and control it over octoprint. It looks like octoprint has a plugin that lets you turn on any sort of device over the GPIO pins: OctoRelay
Not sure if that would work because since I never have done it but at least for me it looks promising.
24V really isn’t necessary. The one case where I would recommend it is if you had a very heavy router and wanted to use a 1 start lead screw, then you would need 24V to move the screw fast enough to be satisfied. Most of us are using this machine to break down a barrier, and we won’t be using the machine 8 hours a day. Waiting 5 more minutes on a 1:15 job is not going to make anyone upset. Pushing a machine too hard and scraping a work piece, that’s what gets people upset (at these quantities). So I prefer slow and steady.
Just beware that even if you leave your 3D printer alone, you will never leave your CNC. The 600W router and no sensors can turn that dry piece of plywood into a fireplace very fast.
Computer PSUs operate off of a common ground, so you cannot put voltage in series. You cannot get 24V from this (Nor, honestly, do you need to.)
Some of these do require a load on the 5V channel. FWIW, a Raspbery Pi is usually enough load on the 5V rail for most PC power supplies, if you wanted to run V1Pi or the like. I’ve sometimes used 5V fans as a load on the 5V rail when hacking PC supplies to get 12V.
And I’d reiterate Jeff’s comment:
(I added emphasis)
Thanks - sometimes I need that 
I think I had something in the back of my had that someone had done it but upon further researching I realized that the guy had connected 2 PSU’s in order to get 24 volt:
https://www.instructables.com/Two-ATX-PSU-One-juiced-24-V-DC-PSU/
Hello, I am using pc psu on my currently building lr2. I also have skr 1.4 turbo, 2209, double endstops and 7" LCD. Psu itself works perfect on 12v, but at least until now with that setting but I’m still not finish with firmware yet.
I just have configured and flashed the firmware of the SKR1.4 turbo board with TCM2209 drivers for sensorless homing. They seem to work as the stepper motors move as espected. I only have to build the actual CNC machine now, so that I can integrate them 
Have you build the actual CNC already?
Also the 12 volt PSU from an old PC works flawlessly up to that point …
I’m still waiting for Z lead screws and some pulley to have all the parts, so I will post some photos later today 
Cool! I am already curious how your build went! 
