Powering Ramps1.4 with MEGA 2560 and LCD - using PS_ON?

Hi, I am in the process of upgrading my reprap prusa to use the above combo, but I'm having trouble configuring the power. I have an old ATX power supply that I want to use for the purpose. Firstly, am I correct in thinking that I need to connect BOTH power inputs on the RAMPS board to COM and +12V (they are labelled 5A and 11A)? I think these are rated 12V to 35V so I'm guessing the 12V output from the PSU should be fine - with current to spare.

Second, I would like the option of printing either via a USB cable (e.g. using Printrun) or else of using the SD card on the LCD board - is this possible? I've seen mention of adding/removing diodes, but I'm not keen on this, unless it's essential.

Third, and finally - I would like to use the PS_ON option of my ATX PSU so that the card could switch the ATX PSU off, when it completes. At the moment, I seem to have to force the PS_ON line to low, by connecting to COM, and the connector on the RAMPS card seems open circuit - does this depend on connecting the power as mentioned in in my first point?

I appreciate that these may be really dumb questions, bu I'm new to this game!

Yes you probably need both plugs

11amp is heated bed only (but if you don't have a heated bed, you don't need this)
5amp is everything else. hotends, steppers, fans and normally the mega

The inputs on a standard ramps are 12v only.. you need to modify the board for a higher voltage.

you absolutely need to remove the D1 diode

To use ps-on the ramps has 5v power from the power supply 5v standby wire, The ramps/mega 5v side is always on.
Only the The 12v get turned on and off.
Normally some of the 12v is converted to 5v via D1 to the vin pin to power the mega. But providing two different 5v power supplies signals will just fight each other... don't do this.
Thus you NEED to remove D1

Yes this causes issues with USB as it also provides 5v power. Use a USB cable that has the 5v line cut. Alternatively Don't use the the 5v standby power and always power the 5v from USB

NB using Vin pin or the dc jack and the usb power is ok, as the board is designed to do this. But when you put 5v into the 5v pin your not using the dual power supply protection circuit.

This might be useful


Edited 2 time(s). Last edit at 08/21/2019 09:49AM by Dust.

Hi, thanks for getting back to me :-)

I have now removed the diode D1 (at least I think I have). It's definitely a diode and in roughly the place that you indicated, as shown below:



Surprisingly, having it in didn't blow my board up, although it did lead to some weird stuff on the LCD. Fortunately, this was one of the few devices that weren't surface-mounted, so it wasn't too difficult to remove.

I have also connected my 5V standby from the PSU to the 5V pin on the board, and the PS_ON to the corresponding input to my PSU. Unfortunately, I am still having to manually force the PS_ON input to ground - i.e. the PS_ON signal from the RAMPS card seems to be floating.

I have also connected both 12V inputs to the corresponding oututs from my PSU (COM and +V)

Now, when I power the PSU on, after forcing the PS_ON low, I get a nice clear LCD display and can use the LCD control panel to move steppers.

The two things I am now missing (sorry for this):

• I would like the PS_ON signal to be set correctly from the RAMPS board. I guess this could be a firmware issue, but everything else seems to be OK, so I think this is unlikely.
• I would (ideally) like to be able to connect my laptop via USB, while the 'main' PSU is connected (to provide the high current stuff) so that I could print directly from my laptop.

I worry that I may be asking the impossible on the second point, so I may just have to live with it.

Edited 1 time(s). Last edit at 08/22/2019 02:07PM by AndyD.

Right, I am officially an idiot - it was the firmware. I had foolishly failed to specify the PSU type (i.e. ATX) hence PS_ON had no meaning.

The relevant lines appear around line 234 in Configuration.h (Marlin firmware V1.1.9). The corrected form is as shown below:

/**
 * Select your power supply here. Use 0 if you haven't connected the PS_ON_PIN
 *
 * 0 = No Power Switch
 * 1 = ATX
 * 2 = X-Box 360 203Watts (the blue wire connected to PS_ON and the red wire to VCC)
 *
 * :{ 0:'No power switch', 1:'ATX', 2:'X-Box 360' }
 */
#define POWER_SUPPLY 1

With this fix, PS_ON is being set correctly by the RAMPS card. The only (only!) issue now remaining is to work out how I could use both the ATX power or the USB power interchangeably, without too much fiddling with cables etc.

Any ideas welcome, otherwise I'll just let you know how I get on!

Well, I don't know if I'm just being lucky (I need to re-read your explanation to try and understand it)
but the combination seems to be working pretty good for me, at the moment!

I have enabled the AUTO_POWER_CONTROL facility in the firmware (just for the hell of it) and connected my laptop - this
requires the ATX PSU to be powered off (using the switch by the mains inlet).

If I then switch the PSU back on I seem the get the best of both worlds, in that I can:

• Issue the M81/M80 commands to switch the PSU on and off. From this I suspect/hope that I can send builds to the printer.
• If I switch the PSU off using M80 and then try to move the steppers from Printrun then it automagically switches the PSU on.

It keeps crashing due to heater errors - which is hardly surprising since I haven't connected any yet, but it's good enough for starters.

With thanks for all your help!