Ramps v1.4 unable to powered without usb and lcd flickers without showing anything

Dear all,

I have build my own 3d printer and it works. But it wont work when it is unplugged from pc. It has voltage output still but the lcd screen wont power up. I have changed the arduino mega into another one. This time, it powers up the lcd without needing to connect to usb but the lcd shows nothing with pulses of dim light flickering. I am not sure what is my problem. The ramps have d1 d2 diodes in place. The overcurrent protection of the mega's dont heat up quickly. Is there anyway to troubleshoot the arduino mega? I have tested with a fully working mega of my friend's and it works fine.

Please help !! Thank you.

First mega has a dead voltage regulator, it takes 12v from ramps and make 5v for the mega.

On both megas I would check it has +5v and +3.3 volts on the appropriate pins with just a dc power jack plugged in.

This isn't a fault with your Mega, it's a design flaw in the Arduino/RAMPS/LCD ecosystem. The Arduino can only provide enough 5V power to drive small LCDS with modest backlight current requirements. Likewise it can't provide enough power to drive a servo. Workaround is to provide external 5V power, or use an Arduino variant that can provide more 5V power.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The mega2560 regulator is meant to be a NCP1117ST50T3G, its meant to be good for 1A

If they have a servo, I would agree with you as they are current hungry, but they don’t seem to.

And the fact that it works on a mates mega, indicates that its not a lack of current due to the design limitations...

Quote
Dust
The mega2560 regulator is meant to be a NCP1117ST50T3G, its meant to be good for 1A

If you were an electronic design engineer, you would know that the regulator doesn't just have current rating, it has a power dissipation rating too, which depends on how well it is cooled (not very well on Arduinos). So the 1A rating is irrelevant. The practical limit is around 200mA with a 12V supply, and the Mega itself already takes quite a lot of that (130mA AFAIR). That's why the Ardiuino folks say that although the maximum input voltage is 20V, using more than 12V is not advised.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'm well aware of power dissipation ratings... But I presume the designer had some sense and has designed it somewhat sanely

I doubt the current is that low...

If your an engineer, please do the tests for real, not just continue the speculation...

What I do know from real world practical experience is that there are thousands of people happily running standard 20x4 and 128x64 on the ramps, with no power issues. (including myself)
But that’s its limits, adding a servo does seem to take it over the top.

More speculation:
Google tells me "The limit on the typical voltage regulator used on the Arduino to convert the external supply to +5V is 800 mA (and it’s going to be quite hot at 800 mA)" But well it's the internet, full of lies and half truths... But is more what I would expect.

Edited 1 time(s). Last edit at 01/21/2016 06:44PM by Dust.

Dust, I did some tests on heat generation in the voltage regulator about a year go. I ran an Arduino Mega + RAMPS board, running Marlin firmware, from a variable voltage power supply. I didn't measure the temperature of the voltage regulator with professional measuring equipment, I put my finger on the regulator and the surrounding parts of the board to get an idea of how hot it was getting.

With 12V input, the regulator already got hot, but not excessively so. With 15V input, it got as hot as I would be happy for it to run - and too hot to keep my finger on it for more than a few seconds. I also measured the current draw, which I recall was about 130mA.

Allowing for 0.8V drop in the diode, at 15V input the regulator is dropping 9V @ 130mA so it is dissipating 1.2W. That sounds reasonable for a regulator of that size that is mounted on only a small area of PCB as a heatsink. With 12V input, the same power dissipation will occur at 193mA.

I conclude that connecting a 20x4 test display (backlight current about 40mA) is OK, but connecting a 12864-based LCD (backlight current varies with module, but up to 100mA) is pushing it too far. This is with 12V input; some users turn up the power supply voltage to overcome the inadequate heating power provided by many PCB bed heaters

If you read these forums as much as I do, you will observe that this problem comes up very frequently.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
Dust
What I do know from real world practical experience is that there are thousands of people happily running standard 20x4 and 128x64 on the ramps, with no power issues. (including myself)
But that’s its limits, adding a servo does seem to take it over the top.

Yes, I do have no problem connecting 20x4 LCD on the ramps with other Arduino Mega. That is why i concluded that my these two Megas were faulty. I have no idea on how to troubleshoot the Mega's voltage regulator. The second Mega has no problem powering up the LCD but it doesn't light up the LCD but just some backlight flickering.

Quote
dc42
This isn't a fault with your Mega, it's a design flaw in the Arduino/RAMPS/LCD ecosystem. The Arduino can only provide enough 5V power to drive small LCDS with modest backlight current requirements. Likewise it can't provide enough power to drive a servo. Workaround is to provide external 5V power, or use an Arduino variant that can provide more 5V power.

Old post I know but still.

You say provide external 5v power, is that straight to the lcd on pins ?

Cheers Johan