Heating causes printer disconnect

Hi All,

This is my first post, and, therefore is a 'help, I'm stumped' post.

I've been working on a reprap Clonedel printer for a while. I've had surprisingly little trouble so far, probably due to good documentation and lots of good stuff in forums, but, I've finally hit a snag. All the hardware is assembled and working. I'm running RAMPS 1.4 on a Arduino Mega powered with a 12v 6A brick. I've loaded the Sprinter firmware with some modification to use it on the 1.0 Arduino software and to remove the SD card support (it always kept it from compiling well). I have the Marlin firmware and have successfully loaded it, but, in checking if the problem I'm having is firmware, I've flipped back and forth between Marlin and Sprinter.

So, on to the problem. I can connect to the printer using Pronterface. I can move with the software buttons. I can move the printer using downloaded g-code. But, I lose connection with the printer when I turn on the hotend. Specifically, it gives me the error message "Can't write to printer. (Disconnected?)". Once I've turned on the hotend it gets up to temperature and melts PLA, but it won't move. This happens if I send the printer g-code or if I try to set the temperature of the hotend through Pronterface. Sending an M105 command locks up Pronterface. Unplugging the printer and restarting Pronterface resets this, but it all happens again if I try heating again. The same thing occurs in Windows and Linux, and Sprinter and Marlin. Well, not exactly: in Windows 7 it locks up before moving at all when I send it g-code. In Linux it will move through a layer or two before it locks up.

I've checked the thermistor and it changes resistance with temperature. The hotend heats well. Everything seems to work individually. Nothing on the board is unduly hot. My first thought (well, third, after bad wiring and bad firmware), is that the board is underpowered and booting up the hotend takes power away from USB communication, but everything I've read says that a 12v 6A power supply should be fine for printing without a heated bed or fan.

Any suggestions would be greatly appreciated,

greg

Quote
insectdreams
...but everything I've read says that a 12v 6A power supply should be fine for printing without a heated bed or fan.

YES, this is correct!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Maybe the output of the power brick gets noisy when you draw more current. Particularly the ground line. Try measuring the voltage to see if it drops. Also try measuring between the 0V or your RAMPS and the chassis of your PC to see if there a significant difference.

The problem with power bricks is they tend to have a long output cable which is grounded at the brick. When you draw 6A at the far end there will be some voltage drop in the cable. The ground at the RAMPS is then not ground so current flows down the USB cable to the ground of your PC upsetting the comms.

If that is the problem then shortening the cable might help.

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[www.hydraraptor.blogspot.com]

Thanks Bob and nophead.

Nophead, I think you're on to something. I'm working with a 30 year old analog multimeter (the voltmeter on my digital one is shot, the replacement should arrive tomorrow), so I'm unsure of the accuracy of the readings, but, there is a 2-4 volt drop when I power on the hotend, with a corresponding 2-3 volt increase between the ground on the RAMPS and the PC chassis. I'll try shortening the cable and let you know how that works out.

Is this something I would find in all power bricks, or is it something that would be more common in cheap bricks bought off of ebay such as the one I have?

That did it. For reference, I clipped about 18 inches off of a 48 inch cord. With a 30 inch cord there is no drop in voltage when I start up the hotend.

Thanks again for you help.

All power bricks with switch mode power supplies rather than simple transformers that I have encountered have this problem, so all laptops do when plugged in. Fine if you only use USB powered devices like mice but as soon as you connect to something grounded elsewhere you get problems.

If I designed power bricks then they wouldn't have this problem. I would use an output cable with a screen plus two conductors. I would ground the screen and connect it to 0V at the plug end of the cable. That way the equipment would always be at ground potential as there would be no current flowing in the screen. Not sure if any exist like this though.

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[www.hydraraptor.blogspot.com]

Hello , I have a Gen 6 ramps board in an evolution , (not a very well built machine and hopeless technical help)
So I am here , reading this post I have similar issue,

Hot end reaches target temperature and as soon as i do anything else via the PC, start a print , or run the extruder; the hot end temperature drops the temp moniter freezes.

I have shortened the output chord to 25 inchs on the new 5amp 12 volt supply and even tested a new supply, No change

I am using redsnapper but will try a different program . I use replicatorG on my makerbot but it does not support the gen6 board
by the looks of it .

After reading this post , I tried disablinng the temp moniter and all seems ok, but not sure if there is an issue with the gen 6 board ??

I would appreciate some advise on this if anyone's experianced this ?

Regards Paul

Have you checked if there is a voltage drop when you power up the hotend and a voltage increase between the ground on the RAMPS board and the computer chassis? That seemed to be indicative of the grounding problem in power bricks that nophead described. If you are not seeing the voltage jump between the RAMPS board and the PC, you likely have a different problem. I can't even begin to guess what that problem may be, though. This is my first reprap, and I'm still not quite printing with it yet.

I would doubt that it's a problem with the RAMPS board in general as mine is working fine now, and there don't seem to be a large number of people having this problem.