RAMPS 1.4 Low Vcc

After having a ton of x and y drift problems and retightening/tensioning/checking everything mechanical, I checked the vref on my stepsticks and they were lower than I had originally set them! I set them at 350 mv and they read 2something (I forget the exact numbers). I proceeded to check Vcc on the stepsticks and it was at 3 volts!

Does the Ramps board get its Vcc from the arduino? I looked at the schematic and it appears that way but I was unsure. If so, do I need a new arduino or can I splice in a 5V source? I have a ton of extra 5V USB chargers. I did check the voltage with the arduino unplugged from the computer but I'm assuming it needs more current than the standard 500 mA.

This all happened after a 12 hour print gone bad, I left it alone and you can see the layers getting worse and eventually the x axis skipping steps (assumed loose belt, added tensioner but problem persists), since then I haven't had a successful print longer than 15 minutes (layers are perfect up until around this time), so I assume some kind of overheat damage. I tried printing again with a fan on the stepsticks but the drift is still there.

And I did do a search in this forum for low Vcc and 5v Vcc and couldn't find anything...

Yes, the 5v comes from the Arduino . . . So, two things you can do:

1) Remove whatever load on your RAMPS is dragging it down - servos, LCD, etc.
2) Add a regulator
3) A combination of the above.

A lot of folks describe the regulator on the Arduino as being bad . . . I don't accept that description myself . . . The issue is that the RAMPS design tends to overload it, and the designers of RAMPS failed to take that into consideration when RAMPS was designed, by either adding a 5V regulator to the card, or an easy way to source external 5V. At this point, short of cutting pins off the interface to the Arduino, the only 5V that can be isolated with any ease is the servo feed . . . If you have an LCD that is pulling it down, time to start cutting and making modifications . . .

- Tim

Edited 1 time(s). Last edit at 06/24/2015 04:35PM by tadawson.

Exactly what Tim wrote, adding two small points:

1. What voltage are you supplying to the RAMPS? Did you leave the D1 diode in the RAMPS? Can you measure the voltage across D1 when printing (it should be something like 0.8V)? You see, the regulator on the Arduino will work fine if you supply it with something like 7 to 12V, and the D1 diode on the RAMPS is supposed to pass approximately 11.2V to the Arduino regulator. If you have > than 11.2V, you risk overloading the Arduino regulator. Also, if your PSU does not properly regulate the +12V output for some odd reason, again you could be overloading or underloading your Arduino's voltage regulator.

2. Under normal conditions, the RAMPS + LCD does not require more than 50mA to operate, and that is easily within range for the Arduino regulator. But if you have a servo or anything using > 50mA on the RAMPS VCC, the Arduino regulator may not keep up... simply because it's not designed to.

Note: If you have an external 5V source (eg: a 5V line from a PC PSU), then you can supply RAMPS completely with this 5V source.

You need to:
1. Remove D1. This stops RAMPS supplying voltage to the on-board regulator.
2. Connect your 5V source to a 5V/VCC line on the RAMPS/Arduino. Note that there is a "second" 5V line that goes to the servos that ISN'T connected to the main 5V line by default.

Regarding the LCD comment: The issue usually is that while an LCD may only use 50mA itself, the backlight can in some cases use quite a bit more, and this causes real issues overloading the regulator.

As for RAMPS, the board covers the Arduino regulator area (preventing airflow), and the Arduino regulator is poorly laid out for efficiently disposing of excess heat. The upshot is that they can easily overheat even at 12V input and less than their rated current, due to something as simple as a bad solder joint (so the regulator doesn't lie flat on the PC or if the ambient temp is > 25 Deg C.

Quote
AndrewBCN
Exactly what Tim wrote, adding two small points:

1. What voltage are you supplying to the RAMPS? Did you leave the D1 diode in the RAMPS? Can you measure the voltage across D1 when printing (it should be something like 0.8V)? You see, the regulator on the Arduino will work fine if you supply it with something like 7 to 12V, and the D1 diode on the RAMPS is supposed to pass approximately 11.2V to the Arduino regulator. If you have > than 11.2V, you risk overloading the Arduino regulator. Also, if your PSU does not properly regulate the +12V output for some odd reason, again you could be overloading or underloading your Arduino's voltage regulator.

2. Under normal conditions, the RAMPS + LCD does not require more than 50mA to operate, and that is easily within range for the Arduino regulator. But if you have a servo or anything using > 50mA on the RAMPS VCC, the Arduino regulator may not keep up... simply because it's not designed to.

I made all my measurements under no load I.e. not printing, PSU was reading 12.42 volts. I don't have any servos or LCD on the 5v rail. I'll measure the voltage across D1 tonight.

Quote
Cefiar
Note: If you have an external 5V source (eg: a 5V line from a PC PSU), then you can supply RAMPS completely with this 5V source.

You need to:
1. Remove D1. This stops RAMPS supplying voltage to the on-board regulator.
2. Connect your 5V source to a 5V/VCC line on the RAMPS/Arduino. Note that there is a "second" 5V line that goes to the servos that ISN'T connected to the main 5V line by default.

Regarding the LCD comment: The issue usually is that while an LCD may only use 50mA itself, the backlight can in some cases use quite a bit more, and this causes real issues overloading the regulator.

As for RAMPS, the board covers the Arduino regulator area (preventing airflow), and the Arduino regulator is poorly laid out for efficiently disposing of excess heat. The upshot is that they can easily overheat even at 12V input and less than their rated current, due to something as simple as a bad solder joint (so the regulator doesn't lie flat on the PC or if the ambient temp is > 25 Deg C.

Wonderful, I will try a separate 5 volt supply tonight.

Thanks everyone for the help, hopefully this will help others as I googled x and y leaning/drift problems and scoured the results and couldn't find any suggestions of Vcc/5V going bad and changing Vref.