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Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End

Posted by mrShrimp 
Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 10, 2013 12:02AM

I've been having power problems with my school's RepRapPro Mono Mendel recently, but I am puzzled as to what exactly is the problem. I haven't done too much probing for fear of damaging our controller board, which is a Melzi, but I think I have narrowed down the probable causes of the issue somewhat. The issue is that whenever we try to heat up the heated bed or the hot end in pronterface, the power supply (the second one we have tried) to the printer shuts down, presumably through some protection circuit, and oftentimes pronterface disconnects at the same time, although we have had instances where the Melzi continues to function after the PSU cuts out (the Melzi is powered via UScool smiley.

These issues arose a week ago with our first power supply, which is the same supply as seen on the RepRapPro Wiki. The printer was printing a part, and something happened while we were away that caused pronterface to disconnect and the print to stop, even though we were printing from SD. After running some tests on this power supply, I discovered that the voltage was dropping very low when we tried to power on the bed and the hot end at the same time, bottoming out at nearly 8 volts. This power supply continued to supply the 8 volts even after pronterface disconnected, so presumably it didn't have the protection circuit that was being set off in the second power supply we tried, which simply shuts off when we power the bed or the hot end. This is the second power supply we tried: http://www.thermaltake.com/products-model.aspx?id=C_00001655. From reading all the RepRap Wiki's entries on using ATX 2.0 power supplies, this one should definitely work, and it does. We can move all of the axes without a problem, the thermistors work, and the USB connection to the computer through which we start prints does not seem to be an issue. I have searched for shorts, though not with a multimeter yet (I will try this tomorrow), but I have not seen any in the power wires, heated bed wires, or hot end wires. At first, I thought the original power supply was the problem, but now I'm not sure what could possibly happening other than a short.

I would greatly appreciate any help!
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 10, 2013 12:14AM
Another thing you may want to look at is how many things are on that circut. I had a few light bulbs, my printer, and a vacuum, and blew a 15 amp breaker.
You also have to definitely check the heat bed with a multimeter. I don't know the specs, but I am sure there are some ohm specs for what you are using. Either way a dead short would show up.
Check all you electrical connections, as a fraid wire, or lose connection can cause that too.
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 10, 2013 12:22AM
Try disconnecting the heater at the board and see what happens when you switch on the heater in Pronterface.. Do the same for the heat bed circuit.

Waitaki 3D Printer
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 10, 2013 01:35AM
Thanks, I will try those out! I think the splitter we are using is connected to another splitter with a ton of plugs in it, so that could very well be our problem. The MK2 bed we have has 1.3 ohms of resistance. It has never quite made it past 70 degrees Celsius, but we print in PLA mostly, and I was hoping to see if the different power supply might remedy that issue.
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 10, 2013 06:13PM
I checked the power, hot end, and heated bed lines for a short with a multimeter, and there are no signs of one. As it happens, the power strip we had connected the power supply to was connected to another power strip that was filled with plugs connecting to various computers, not all of which are turned on though. We switched it to a wall outlet, but the problem persisted without any change. I disconnected the heated bed and hot end wires and turned them on via pronterface, and the board supplied a constant 11.5 volts to each without a problem. The power supply did not switch into standby and pronterface did not experience any disconnects. With either the heated bed or the hot end plugged in, however, the power supply still switches into standby, which I assume must mean one of its protection circuits gets turned on. It has over current, under current, over voltage, under voltage, and short circuit protection. I don't think a short circuit is the problem, so how might I test for which of these is the problem?

Thanks for all the help so far!
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 11, 2013 04:27AM
Hi, I have exactly the same problem,

I want to try to connect another bed and see what happen
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 11, 2013 12:20PM
You could try measuring the current drawn when you turn on the heated bed or hotend although with only a multimeter it may turn off too fast for that

BTW, I don't know that much about using ATX2.0 PSUs with RepRaps. But one thing I'm not totally clear about your set-up, are you totally sure it's not a PSU problem? I presume the PSU is known to be working with a computer or similar and it seems a decent PSU. But even with an ATX2.0 PSU many still don't like having the 12V heavily loaded and the 3.3V/5V completely unloaded. If you're only using the 12V then this is what your setup is like. Perhaps trying attaching something the the 5V or 3.3V line. It probably doesn't have to be much, even 3A may be enough. Worst case you could get a suitable resistor.

Edited 1 time(s). Last edit at 12/11/2013 12:21PM by Nil Einne.
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 11, 2013 04:38PM
it also could be your power supply can not provide the current to power the heated bed and every other device at peek current. you can alleviate the current requirements a little by switching which connections are used to power the bed and which are used to power the rest of the machine. look at the schematic which are on the supply. does it tell you which rail has more current? the higher power rail should power the heated bed. you can also experiment. the rails are likely separated by the length of wires out of the supply. 1 set of wires will have 2 or 3 molex connectors on them.

if your supply only has one rail then you can reduce the power draw of the extruder by setting current level to less than 255. it turns on a little bit less and heats slower, but takes overall less current.
sorry if any information is repeated here.

Edited 1 time(s). Last edit at 12/11/2013 04:40PM by jamesdanielv.
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 11, 2013 05:46PM
If the machine is resetting, it's a power issue. Either there's a fault with the PSU, or a poor connection/short circuit on the power, heated bed or hot end wiring.

I sent this email to massimo earlier:

It sounds like you have a short circuit that is causing the voltage to drop, or a poor connection in the power circuit. I don't think it will be a problem with the Melzi. Test the 12V power while you turn on the hot end and/or heated bed, and see if the voltage drops. As this happens when the heaters are turned on, I would suspect that you might have a loose connection on the 12V power input - check the wires are tight in the screw terminals, and well connected.

If you feel the screw terminals, one of them may be getting hot; check particularly the 12V input screw terminals, and the heated bed screw terminals. Heat would imply a poor connection.

RepRapPro tech support
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 14, 2013 09:45PM
The board resets only when we use the PSU that came with the kit, which I do not think has protection circuits. The PC PSU that we tried in lieu of the original PSU gets shut off by one of its protection circuits, so I think it is working fine. We have tested for a short circuit on the power line going into the board with a multimeter, and there does not seem to be one. The power terminal doesn't get hot when we run the Z motor (which does not shut off the PSU), but perhaps the motor draws too little current to make a noticeable difference. The screws on the hot end and heated bed terminals are tight, so the only poor connection I can think of would be in the soldering job of the XLR receptor, but that doesn't get jostled around much.

We did have an accidental short circuit a few months back that damaged the screw terminal for the power line, but the printer continued to work after that until this most recent problem. Perhaps a strand of wire got stuck inside the screw terminal from that incident and is shorting the power out, but not entirely. We have an additional Melzi on which one of the motor controllers is defective, but the screw terminals are intact on it. I'll use that board as a control to see if the melted terminal on the working board is being shorted. Other than that, I am stumped.
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 17, 2013 04:37AM
I have disconnected both Melzi boards, and upon testing the resistance of their screw connectors have concluded that the partially melted terminal on the board with which we are having problems is not causing a short. I should have tested for a short with the wires in the board (I'll do this test and post the results tomorrow), as they are rather fat wires, but seeing as they are tinned I do not expect them to be the problem.

jamesdanielv, I'll try your solution of changing the software to make the bed draw less current. Then I can hopefully find the threshold at which it sets off the safety circuit in the power supply, and maybe get some insight into what exactly is going on. I will also try feeling the for heat on the screw terminals at certain points during this test to see if there is a short somewhere that I missed.
Re: Printer Disconnects, PSU Shuts Off When Heating Bed/Hot End
December 17, 2013 07:21PM
The problem is fixed. It turns out that a piece of insulating wire I had on one of the power leads going into the board rendered the lead too short. The connection was the problem after all.

Thanks again for all your help!
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