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Weird pulsing Issue with RAMPS 1.4 - pots on motor drivers are turned all of the way down and heat sink stays cool

Posted by voodoomagicman 
I have finished assembling my first RepRap (woohoo!), but am having a weird issue when I
connect power. I have instealled sprinter firmware, and can connect to the arduino w/

The motors move when I tell them, but when they are not moving, the x
and y motors will sort of pulse or tick (it doesn't seem to happen in
the Z motors).. they do not turn, but it is like the motor is starting
a step and then snapping back before finishing. It pulses about two
times a second, and the frequency goes up when I turn the pot on the
Polulu driver. The motors pulse in sync w/ each other and the red
light on the RAMPS and red and green LEDs on the arduino flash in sync w/ the
motors as well. When the motors are moving, the motion starts and
stops with the same pulsing pattern.

Even when the arduino is unhooked from USB, the motors make a tick
sound, but much softer. I am thinking maybe the power supply is
cutting on and off? I have the wires connected exactly as follows:

2 x yellow 12v and 2 x black ground from 4 pin ATX + 2 x yellow 12v
and 2 x black ground from the 2 4 pin molex peripheral connectors are
connected to the power inputs on the RAMPS, w/ two wires going to each
connector. Then the grey and green wires from the ATX 20 pin molex
are connected to each other. I dont think that the power supply I am
using has any voltage sensing wires, and I didn't connect any other wires.

I found a few threads: {[forums.reprap.org] },
and {[forums.reprap.org]} which suggest that
pulsing problems could have been caused by the polulu drivers
overheating. I have tried turning the pots all of the way down
(counterclockwise) on the drivers and can't make the pulsing stop. Also, I
can hold my finger on the heat sinks, and the ticking still happens
even while they stay cool to the touch.

I know that is kind of a long read, but I am not sure what is going wrong,
so have tried to be as specific as possible about everything. If you made it this far,
thanks for sticking w/ it smileys with beer... Any ideas what could be going wrong?

If the Pololus are cool to the touch, then the over-temperature protection isn't causing the pulsing.

The LEDs blinking in sync with the pulsing sounds like power cutting out to me. Maybe try a different supply?
Have you put a dummy load on the 5V rail? PC PSUs don't behave well without one.

DaveX - I think you are right that it must be the power supply. I completely disconnected the power supply from the RAMPS, and when i power it on, I can hear the fan starting and stopping w/ the same pulsing.

Nophead - I have not put a dummy load on the 5V rail.. I am hoping this is what is wrong because then I won't have to buy a new power supply. I found a little bit about that here, which I had missed before - {[reprap.org]}, and {[reprap.org]}. Can this be connected to any of the 5v connections? I have some already opened from cutting off the 4 pin molexes.. or would it need to be a 5v wire from the 20 pin molex?

Also, I was eventually planning on measuring and trying to find ways to minimize the power consumption of my RepRap. I am curious how the energy cost of 3d printing compares to the cost of mass producing it and then shipping it through the supply chain.. obviously connecting extra lightbulbs won't help w/ that. My goal right now is just to get things working well, but eventually this seems like a really easy place for me to start trying to make improvements. What do you use for your power supply / do you know any pc power supplies or hobby/lab 12v power supplies that work really well?
You must have a load on the 5V. I have never come across a PC PSU that would work properly without one.

It can be any of the red 5V wires, they are all connected inside.

The energy cost is negligible compared to the plastic cost.

So, I got a 12v halogen light bulb and hooked it up to the one of the 5v wires. The lightbulb pulses the same way the motors did! Here is a video: {[www.youtube.com]}.. I am thinking this has to be due to a faulty power supply..

I am thinking of ordering this one to replace it, does anyone have any experience w/ it: {[www.lulzbot.com]}?
ATX power supplies have a 3.3V sense wire that needs connecting to the 3.3V. They are next to each other on the big connector. Some work without it connected but some need it.

You could also try a load on the 3.3V rail.

Also, have you connected the green enable wire to one of the black wires? I could imagine if you connected it to one of the outputs instead it could turn itself off and so pulse.

Connecting the green enable wire to ground worked! No more pulsing from the power supply. I had connected green PS ON to grey PWR OK to each other instead of ground after misinterpreting some instructions. Thanks for the help smileys with beer
Yes that would certainly make it pulse! Power good is an output that is low until the PSU has fully powered up.

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