Boxcar wrote:I have an ORD Bot Hadron on pre order.
Me too! It'll be my second 3D printer... after the Hadron I'm finishing now!
Boxcar wrote:I'm going to be using the dual extruder with with 2x40W heater cartridges from the current Kick Starter campaign, Ramps 1.4 with Arduino Mega 2560, and A4988 stepper drivers. I haven't decided on a PSU or heat bed yet... Could someone please tell me what size power supply I'll need?
I mostly laid it out in my previous posts in this thread. Here are the likely maximum wattages and currents.
120W 10A Heated build platform
80W 6.67A Two 40W QU-BD extruder heaters
36W 3A Two QU-BD extruder stepper motors
72W 6A Three axes of stepper motors
12W 2A Worst case guess (too lazy to search) at the Arduino & RAMPS controller stack
320W 26.7A Total
The Z axis has two motors, but they're wired together, and if they're driven by one stepper driver, both of them together won't draw more than 2A.
The control electronics probably pulls less than an amp. Most of it is very low power, but the stepper drivers do run a bit warm, so that should be a conservative estimate as well.
The motors on the BOM provided by Automation Technologies are rated at 1.68A, so you'll need to set the stepper motor drivers below this current. Counting them at 2A each is a conservative estimate.
The big deal is the heated build platform. I'd expect it to be on less than half of the time once it's warmed up, so that should be 60W or less on average, not 120W.
I'd say a 12V @ 25A power supply should do it. That's a 300 watt power supply if you're buying a dedicated 12V only power supply. Realistically, 20A should be fine given all of the erring on the conservative side when sizing each load.
Note that a PC power supply will be rated for total wattage as well as maximum current for each voltage. Using only the 12V part of a PC supply, you're unlikely to be able to extract the full rated power of the power supply, so don't size a PC power supply by watts. Look instead at the current rating (amps) for only the 12VDC portion of the supply.
The math is actually very simple. Add up the amps for every load and buy a power supply capable of continuously supplying that many amps or more. To convert between watts and amps, use the following formula.
Watts = Volts X Amps
Example: 300 Watts = 12 Volts X 25 Amps
I'm at the point where I just spent 20 minutes moving my modified PC power supply all around the Hadron. It doesn't fit well anywhere. I'll probably mount it about halfway up the back of the right Z axis piece of Makerslide. It really screws up the aesthetics, but I can't find a better place. I saw where someone used a Yaesu ham radio 12VDC supply for their ORD Bot. It was short and flat, and it fit nicely under the Y axis Makerslide in the front, where the power switch was easily accessible. That was a nice touch. A 350W PC power supply might be short enough to mount in the back, on the bottom, and have the Y axis platform pass over top, although it looks like most PC power supplies are 3.4" to 3.5" tall regardless of power output. My 650W power supply was about half an inch too tall. Maybe I should make new feet that are 3/4" taller to accommodate PC power supplies mounted just below the Y axis platform? I think it'd be better to have the weight of the power supply down low, for stability and to avoid shaking the frame if the extruder carriage is moving back and forth at some resonant frequency. Or maybe I should buy a dedicated power supply that's shorter and mount it low in the back?http://www.ebay.com/itm/110904173777