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charlie68
Looking at the Ramps 1.4 schematic [reprap.org] , the MOSFETS for the bed, hotend and fan switch to ground, so if I ignore the RAMPS + terminal and instead wire my fan + to (a fused) 12V, and fan - to RAMPS D9 then my fan is running at 12v with PWM control right?

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Kayjay
I realise this is an old thread but as my question is very close to the topic of this thread I thought I would ask here.

I use a Bigbox bought a few years back from E3D-Online but recently I have had a possible problem with the Duet 2 board I use in it so it's currently away being tested (the board not the Bigbox). In the meantime I'd like to use my RAMPS board from my old Mendel to drive the Bigbox. Now then herein lies the problem/question, the Bigbox runs on 24v, so it's all set up for that, bed, hotend, fans everything .... I was thinking that I would update the capacitors on the RAMPS board to 35v so the existing 16v ones don't pop nasty electrolyte all over my lovely printer, easy enough to do. I next would link out the fuses with heavy wire and put inline fuses in the input lines from my 24v supply.

Would this be sufficient or would I need to do any more changes to the RAMPS board, like,say, D1, should I take it out and power the Arduino from my PC via the USB?

Anyone have any solid answers for me?

Thanks guys
Keith

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imqqmi
Please take a look at the schematic of the arduino atmega2560. There's a 5V regulator MC33269ST-5.0T3 or MC33269D-5.0 (I suspect the same regulator but a different package).
If you put 5V on one of the 5V output you put 5V on the output of the regulator. Since the output of any regulator is low impedance, effectively giving it a short circuit. Hopefully the thermal protection kicks in and it still works. You'll need to unsolder the regulator as well but I suggest you use the pwrin (adapter power input) input instead. Just use a buck converter from 24 to 7 to 12V and all should be ok.

Another thing you can try if you're feeling adventurous, you could try replacing the MC33269 regulator to one that can take 24V. That would eliminate the need for a step down converter and simplify the design.

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imqqmi
You are using the 12v as the negative terminal and the pwm output as positive terminal. Make sure 0V of each power output is connected, and don't make assumptions by looking at markings and colors. Use a voltmeter to find each psu polarity, then use a continuity or ohm meter to make sure the 0V is connected properly. Also measure the ramps board, make sure which terminal is 0V. Use the schematic to make sure you're connecting to the right terminal.

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Khaled
Hi,
I know I'm 3 years late with this question but I'd be grateful if you could elaborate a bit on this part of your answer

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Cefiar
You can run the 11A input on 24V and the 5A on 12V if you have either two power supplies or one that produces both voltages. If you are using two power supplies, they will be tied together via the RAMPS board on the ground pin. In 99.9% of cases this should be fine, as long as the PSU have independent grounds (some cheap knock-offs do not). You can also do the reverse if you remove the diode D1, assuming other components are rated appropriately.

I do have 2 power supplies and I'm thinking of using the 24V one for the heatedbed. As far as I can understand I should connect the 24V PS to the 11A input of the ramps and the 12V PS to the 5A. What I don't understand is how to tie them together on the RAMPS board on the ground pin.

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Khaled
I do have 2 power supplies and I'm thinking of using the 24V one for the heatedbed. As far as I can understand I should connect the 24V PS to the 11A input of the ramps and the 12V PS to the 5A. What I don't understand is how to tie them together on the RAMPS board on the ground pin.