Multiple Output Power Supplies - Page 1
Forum section: electronics / beginners

author: Rapsey
author_rank: Contributor
timestamp: February 24, 2019, 06:59:26 pm
content: I have a 3D printer which has been acting up lately. Every few hours it randomly crash-reboots during operation. This is proving quite difficult to debug so I figure I should try a process of elimination. The way I see it the two prime suspects are: a fault in the main board, or an unstable power supply. So if I can run the printer from a different power supply I should be able to rule that one out.The printer's power supply is your typical 12V/30A switching mode power supply unit. It has 3 outputs and the printer uses all 3 of the positive terminals and 2 of the negative ones.I wouldn't be drawing anywhere near 30A since most of that goes towards powering the heaters and I can reproduce this fault without using those. But as it happens I do have one other power supply which is also rated for 12V/30A: a dual output Turnigy power supply which is typically used for powering RC LiPo chargers.Since the Turnigy PSU only has a two outputs I would need to pair 2 of the printer's positive wires together. So now the question is: is this a safe thing to try? I know in simple circuits you can just share a power rail but I'm not sure what the implications are for more complex devices. The printer is essentially an Arduino with a bunch of FET's, fans, stepper motors, temperature sensors (resistors) and two heating elements (also resistors) which I won't be using in my tests.

author: Arznei
author_rank: Contributor
timestamp: February 24, 2019, 07:09:28 pm
content: There shouldn't be any problem with that. The three outputs of the printers power supply are most certainly internally connected anyways.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 24, 2019, 07:10:57 pm
content: They are already paired internally in your existing supply, so I wouldn't expect any problems from that. Other possible problems would be noise or voltage regulation. Your Turnigy supply is designed to charge batteries which don't really care about a few volts of ripple. Not likely to be a problem. If you have any kind of DVM you can at least roughly evaluate this. Couple the supply to your meter through a capacitor and compare the AC voltage you see from both supplies. If the Turnigy is not greatly larger than your original supply it is probably fine.

author: Rapsey
author_rank: Contributor
timestamp: February 24, 2019, 07:56:55 pm
content: Great, thanks! I'll give it a go.Quote from: CatalinaWOW on February 24, 2019, 07:10:57 pmI suppose I can just use an oscilloscope to check the ripple. Why would you connect the meter through a capacitor? Wouldn't that smoothen out the ripple you're trying to detect?

author: rstofer
author_rank: Super Contributor
timestamp: February 24, 2019, 08:04:56 pm
content: Quote from: Rapsey on February 24, 2019, 07:56:55 pmTo force the meter to only see the AC ripple, not the DC value. It's often hard to see a small number when it's masked by a bigger number. You can use a lower scale to measure just the ripple.Some DMMs do this when you select ACV but it's hit and miss when there is a large DC component.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 24, 2019, 08:22:19 pm
content: Quote from: rstofer on February 24, 2019, 08:04:56 pmRstofer nailed it. If you have an oscilloscope it will give you a better idea of what is going on. My answer was aimed at the lowest common denominator. I have no idea what kind of meter you may have, and what your knowledge level is.The capacitor will smooth the ripple. If you know the input impedance of your meter you can select a capacitor to set the RC constant shorter than line frequencies period and minimize the problem. 1000 picofarads should be good for most meters. If you are using meters with high enough input impedance to make that an issue we should probably be asking you questions rather than the other way around.

author: Rapsey
author_rank: Contributor
timestamp: February 24, 2019, 08:28:49 pm
content: Quote from: rstofer on February 24, 2019, 08:04:56 pmAh, I see. My oscilloscope can switch between displaying the AC and DC component so I don't think I'll need to use a capacitor.Now I just need to figure out a safe way to connect those horseshoe-ended cables to a banana plug...

author: rstofer
author_rank: Super Contributor
timestamp: February 24, 2019, 09:12:04 pm
content: Why not try an experiment first? Let the CPU run without stepping and see how it works out. From a thousand feet up, I'm just guessing that the problem starts with noise generated by the steppers. How are the motors driven? As a side issue, how is the heater driven?I wouldn't expect the problem to be in the power supply but it is easy enough to check with a scope. But it isn't power supply ripple that will trash the CPU, it's Vcc at the board. Even with a modest amount of ripple, you have plenty of headroom if you are deriving the Vcc from the 30V.OTOH, how are you deriving the CPU power?It's very likely that 30V is far too much to dump into a regulator chip.Anything getting warm?When you get down to it, we know nothing about your setup so we really can't provide much more than a shopping list of things to look at. But you probably already know what to look at...

author: ArthurDent
author_rank: Super Contributor
timestamp: February 25, 2019, 12:03:29 am
content: Just to be clear, you don't have a 3 output supply, you have a single output supply that delivers enough current so that it has to use multiple paralleled terminals that allow you to parallel wires to handle the current, as others have said. The terminal marking on your power supply is what makes it confusing. Here is a photo of another single output high current 12 VDC 30A power supply where they made it clear that all three positive terminals are the same and all three negative terminals are the same. They use paralleled terminals that allow a common terminal strip to handle more current than one of its terminals would be designed for and use 3 paralleled smaller wires rather than one larger wire on a terminal. Where the printer uses one extra wire on positive that may mean that they separated the supply lead for the logic to further isolate it from noise, etc. Is one of the positive wires smaller than the other two?The processor and logic of your printer doesn't run on 12 VDC so the 12 VDC input to the printer has to go through regulators or other dropping/filtering circuitry to get the voltages the processor needs so these circuits are well isolated from anything happening on the 12 VDC line. Unless you are seeing something obvious with the 12 VDC line, I would look at the main board.

author: DinkyMods
author_rank: Contributor
timestamp: February 25, 2019, 02:50:00 pm
content: Just to make sure you aren’t chasing the wrong gremlin have you tried leaving your machine hooked up USB monitoring the console with Probterface (or similar serial monitor) to see if your getting any fault messages? The Arduino boards used to control most printers when working probably aren’t sensitive at all to power fluctuations as they have a wide range for Vin and onboard regulators. It would be worth probing the 5V regulator and see what your getting in the output. The jelly bean 5V regulators used are a common point of failure. The previous advise to hookup a voltmeter to the 12V output doesn’t hurt although if you were experiencing enough voltage drop to cause the board to reset you would typically be able to easily hear it by listening to the fans. That’s why I would start with the board itself looking for error messages and at the regulator. After that reflashing the firmware would be the next step. Like many here I have a considerable amount of experience with 3D printer controls so keep us posted on how the troubleshooting goes and with all our heads together you will be back printing reliably in no time.

author: Rapsey
author_rank: Contributor
timestamp: February 25, 2019, 06:57:48 pm
content: I have tried letting the printer idle for many hours and checking the serial connection debug logs for any errors or disconnects. So far it appears the issue does not happen when the machine is idle. So it might very well be EM interference from the steppers or a poorly shielded cable.I didn't really want to burden you all with the details, seeing as it would take a lot of explaining before you could properly help me debug this thing. And also because I suspect it has to be really frustrating to troubleshoot something by remotely instructing a newbie. But you're right, you can't really give me advice without knowing the specifics so I'll give it a shot.Let's start with the PSU. On the AC side we have: a yellow ground wire, a black wire labeled N and a red wire labeled L. These all go straight to the 220V mains and the red wire has the main power switch on it.Now for the DC side. There is one V+/GND pair going into the main board and one pair going into a small MOSFET board. This MOSFET is used to control the bed heater, which is by far the biggest power consumer. It's something along the lines of 200W for the bed heater and 50W for everything else. The bed heater runs on 12VDC. It is PWM-controlled and uses the big-bang approach, meaning it alternates between fully on and fully off to maintain the desired temperature. But I should stress that I am experiencing this issue even when I'm not using the bed heater so I highly doubt this has anything to do with it.Exiting this MOSFET board we have a black wire going to the bed, which leads me to conclude that the bed is PWM-controlled on the GND side. So presumably to turn off the bed heater it eliminates the voltage differential by raising the GND side to 12V, rather than lowering the positive side to GND. This would also explain why the third positive wire from the PSU goes straight to the bed heater.Now for the main board itself. The V+/GND wires from the PSU go into the screw terminal on the left side of the board.What's the red arrow you might ask? Well, one time after stopping mid-print I noticed this particular LED on the board was flashing rapidly. I have never seen this LED turn on before and I have no idea what it signals.This videoshows it happening.Unfortunately I have not been able to find a circuit diagram for this board. The closest thing I have been able to find was a diagram for an earlier version of this board. The layout has changed a little but it might still provide relevant insights so I'll include it here. The two attached PDF's show thewiring diagramand theschematicsfor this earlier version of the board.I know that somewhere on this board there is some circuitry to convert the 12V to 5V. There was actually a problem with this because the manufacturer used a capacitor with insufficient capacitance, which resulted in an unstable 5V output. This was clearly visible because the voltage instability resulted in significant fluctuations in the temperature sensor readings which could be seen on the temperature graphs. After replacing the capacitor my sensor readings have been very stable to this day.Lastly I do not believe that this problem is caused by some form of overheating. It doesn't seem to behave that way. Sometimes it will crash within 1 hour of starting a print, then when I restart the print immediately (without giving it time to cool down) it will run fine for 10+ hours. It would also be strange that it printed fine for hundreds of hours during summer, when it was 32C inside, but now in winter with 20C room temperature it starts acting up. I can't exclude overheating completely but nothing I have seen points in that direction.Thank you all for your insights!

author: rstofer
author_rank: Super Contributor
timestamp: February 25, 2019, 08:05:58 pm
content: Quote from: Rapsey on February 25, 2019, 06:57:48 pmLow side switching is common. We connect the load between V+ and the MOSFET drain with the MOSFET source connected to GND. Then we PWM the gate. No, the MOSFET doesn't pull up to 12V, it is either open circuit or pulling to GND.QuoteThe board input is labeled 12V-24V so you should be OKQuoteIf you don't have the manual, you can request one from the web site. I don't know that they will provide a schematic but they should describe the LED. Let's just assume it is an error signal.QuoteWell, the 12V is regulated to provide VREG-5V but that appears to go to a USB connection in the Interface section and comes back as VCC5V-M which is used all over the board. There is also a VBUS connection. It's not clear to me how this works because USB is 4 wires, not 3. +5V, Gnd, D+ and D-.I would take a look at what is happening here because it appears to be the source for all VCC5V-M. Or maybe it's just another load and I didn't really find the regulator for the logic supplyQuoteI had originally thought that the PSUs were a much higher voltage and regulators tend to get warm when the input voltage is much higher than the output voltage.You might try to email the manufacturer and find out what the LED means. It might flash in some kind of pattern to differentiate among several errors.

author: DinkyMods
author_rank: Contributor
timestamp: February 25, 2019, 08:45:47 pm
content: The one thing I still haven’t noticed you mention yet is have you flashed the firmware just ensure that there isn’t any corruption in the MCU. It’s not uncommon to have random instability show up from Firmware issues. It’s a simple thing to try before going to far down route of troubleshooting the hardware. As the to stability of the 5V rail do you have a oscilloscope to be able to see any smaller variations since that can easily be tested at the MCU as it has a know pinout.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: February 25, 2019, 11:53:56 pm
content: Quote from: Rapsey on February 24, 2019, 07:56:55 pmThe cap passes the AC component for you to measure with your DMM and blocks the DC component. If you measure a lot of AC (ripple) the charger may not be suitable, at least without some additional filtering.Sent from my SM-G900V using Tapatalk

author: Rapsey
author_rank: Contributor
timestamp: February 26, 2019, 01:17:29 pm
content: Quote from: rstofer on February 25, 2019, 08:05:58 pmAh yes of course, that makes a lot more sense.Quote from: rstofer on February 25, 2019, 08:05:58 pmI think the USB connector is the 5 pins under "USB to UART" in the schematic, not the 3-pin USB thing in the "Interface" section. You can also see 5 wires going into the connector on the board photos. No idea what the 5th pin is. It could be part of the USB OTG standard or maybe it's just unused here.The USB circuitry might be a bit weird because the 5V electronics on the board can be powered both from the internal 12V PSU and from the USB connection. So even with the PSU turned off you can interface with the printer via USB.I should note that the problem also occurs when I'm printing from the internal SD card, without having anything connected to USB. So I doubt the USB circuitry is the culprit.Quote from: rstofer on February 25, 2019, 08:05:58 pmI guess that would be the only way to find out. Will do, but it might take a while to get a reply from the Chinese manufacturer.Quote from: DinkyMods on February 25, 2019, 08:45:47 pmWhen the problem started occurring I had already been using that firmware for several months without issues. But I did consider the possibility so I compiled a new firmware version and reflashed it a couple of days ago. Sadly no change, it still crashes like it did before.

author: DinkyMods
author_rank: Contributor
timestamp: February 26, 2019, 01:31:20 pm
content: Quote from: Rapsey on February 26, 2019, 01:17:29 pmCreality is usually pretty good about quick replies as they are trying to be more involved in the community than most Chinese printer manufacturers. If you don’t get a reply directly you can also try messaging Naomi Wu (she goes by Naomi ‘SexyCyborg’ Wu on YouTube) as she works directly with Creality as a bit of a community liaison. I’ll reach out to a couple people I know here as well that have CR-10s still using the stock board and see if they know what that LED indicates.

author: Rapsey
author_rank: Contributor
timestamp: March 02, 2019, 04:21:51 pm
content: Alright so I contacted Creality and although their response times are indeed pretty good, they weren't all that helpful. I asked them what this flashing LED meant to which I got the default reply: it's probably your G-code file, here try this one. After informing them it was definitely not the G-code and once again asking about the LED they told me "the diagram is not so carefully marked". They said it was probably a fault in the board and suggested I get a replacement.Although this didn't tell me anything I didn't already know I opted to order a new board anyway. I'll report back then I have received and installed it.