Safely powering 3D printer? - Page 1
Forum section: electronics / beginners

author: MigMic
author_rank: Contributor
timestamp: May 29, 2015, 08:48:55 am
content: Hi,Sometime lurker, first time poster here. I am a mech eng by training, so know just enough about electricity to be a danger to myself and others. I've had a look at other posts but haven't found the exact answer to my specific situation so will start a new thread.I recently bought a "Migbot" 3D printer kit (https://www.3dprintersonlinestore.com/migbot-prusa-i3-kit), and am in the process of putting it together. I am generally happy with the quality of the build, but have read of a few problems on other forums so am proceeding cautiously. So far the biggest problems I have heard of are:1) Someone getting "zapped" when touching the power supply case.2) Someone frying their controller board when using the supplied PSU.3) The PSU being under-rated for the kit and not being able to supply enough power.I would like to avoid burning down my house or blowing up the printer (not to mention avoiding electrocution), so I thought I would run some checks before I hook up the power.Problem 1:The PSU I have is a no-name unit made in China, maybe a switchmode power supply (see photos)? The details on the other person's problem were sketchy, but from my limited understanding someone should only get a zap if there is a fault AND the case is inadequately earthed. Is that correct? I have checked the resistance and continuity between each of the power terminals and the case with a DMM, and found only the earth terminal is connected (0 ohm resistance/continuity buzzer went off), so if I wire up to an Australian power lead (live, neutral and earth) I presume it should be OK (even if it develops a fault later)? I plan to run it from an overload-protected power board as well.Problem 2:The controller board is a "MKS Base" v1.3 similar to the one shown here:http://reprap.org/wiki/MKS_BASE.Unfortunately it is not open-source so the information on it is a bit sketchy. Similarly the details of how the person fried their board aren't exactly clear. Aside from reverse polarity issues, and assuming there are no manufacturing faults with the board, do I need to be concerned that the PSU could damage the board? If people are finding the psu under-rated, then I presume over-current shouldn't be an issue. Is an over-voltage something to be concerned about?Problem 3:I'll check this once I have the printer hooked up.Thanks for any advice you can offer,Michael

author: Rerouter
author_rank: Super Contributor
timestamp: May 29, 2015, 09:05:18 am
content: Its a generic switch-mode module, the zapping issue would come from the EMI filter caps between Active - Earth, and Neutral - Earth, they leak some current on most devices, enough to give you a good zap when there is no ground connected given (forms a capacitive divider at half mains)As for frying the controller, you could do that just by poking around the thing while moonwalking on carpet, if your suss, hook the thing up to your multimeter, measure the DC and see that its what you expect, then flick to AC volts, and see that its a small number, e.g. less than 0.3V, this is a very crude way to see that the output is stable, a scope would show far more, but seems like you may not own one,These types of supplies are generally built pretty cheaply, look for a fuse inside the casing, or install your own, The fact your willing to wire up a mains lead to equiptment means i should already take 3 steps back from this question, but i'll play nice,

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 29, 2015, 09:44:38 am
content: 1) if there is switch for 110V or 220V on the input, make sure you put the switch on the right position based on your mains rating before switch on.2) if your home/socket has earth wiring (3 wires cable), connect earth wire to the case by any mean. if no earth, proceed to (3) and dont touch the case if you dont feel like to get zapped, its normal as rerouter explained.3) switch it on in noncombustible area, make sure there is no big bang. if big bang, buy a new psu.4) no big bang, check with multimeter the psu output for stable 12V. if not stable, buy a new psu.5) output stable, make sure your 3dprinter board is rated to be feed with 12V supply, if no, buy new 3dprinter board or mod it.6) everything is ok? switch all off, connect them per manual direction. incl steppers, sensors everything.7) switch on the test the unit. dont touch or mess with psu sections. if big bang, buy new 3dprinter, or repair.8] what else better to be suggested? buy a $5000 printer? ymmv.

author: MigMic
author_rank: Contributor
timestamp: May 29, 2015, 09:59:39 am
content: Thanks for the quick reply Rerouter, and for playing nice. Perhaps the fact that I am asking questions indicates a degree of caution when it comes to mains electricity. As it happens I have an electrician friend who can do the wiring, but I want to do my homework first.Even though there is a hinged plastic "shield" which goes over the terminals, they are not fully insulated, which makes me nervous. How do other people power their printers? When I search for power supplies the only ones I find are either the switch-mode style, or much more expensive "bench" supply units such as Jaycar sell:http://www.jaycar.com.au/Power-Products-Electrical/Power-Supply/Laboratory-Bench/13-8-Volt-20-Amp-DC-Power-Supply/p/MP3098Thanks,M.Edit: added link.

author: MigMic
author_rank: Contributor
timestamp: May 29, 2015, 10:31:14 am
content: Quote from: Mechatrommer on May 29, 2015, 09:44:38 amThanks for the tips. Yes, you get what you pay for...

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 29, 2015, 10:45:30 am
content: Quote from: MigMic on May 29, 2015, 09:59:39 amthe weight 7.8kg is about right for linear psu of this magnitude. today norm is smps, linear only lies in the region of low noise test bench stuffs. if your psu got big bang, your best bet is PC ATX SMPS PSU, easy to find and cheap and more powerfull. otoh if you can tolerate 7.8kg psu due to the elctrophobia then its your call, no harm no objection there, ymmvi also have lower version of your prusa (no lcd), i never experienced any bad things you've explained above. i guess if you are so lucky that your ticket is pulled out from the lucky draw box (1 in a million), you may become one of those who complained.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 29, 2015, 10:47:06 am
content: The specs for the printer say:Power Requirements 300 W, DC 12V / 30Aso I'm not sure your power supply will do a proper job.

author: andtfoot
author_rank: Unknown
timestamp: May 29, 2015, 11:41:21 am
content: Quote from: MigMic on May 29, 2015, 09:59:39 amI'm pretty sure those types of power supply modules are usually housed within another enclosure.In my case, I built one into the control box I put together for my CNC machine. Here's a work-in-progress shot:

author: MigMic
author_rank: Contributor
timestamp: May 29, 2015, 11:46:46 am
content: Sorry, that was just the first bench supply example I found. You are both right that it is under specified and "oversized".This one is much nicer and gets a good review from Dave. Unfortunately a bit out of my price bracket.http://www.jaycar.com.au/Power-Products-Electrical/Power-Supply/Laboratory-Bench/3V-to-15-Volt-DC-40-Amp-Regulated-Switchmode-Laboratory-Power-Supply/p/MP3090Originally I did look at an ATX PSU, but when they mentioned on the RepRap wiki (http://reprap.org/wiki/Choosing_a_Power_Supply_for_your_RepRap) that it needed to be modified I thought I'd persevere with the PSU which came with the printer (opening up a PSU seemed more risky). I should have read further, because with an extension cable there's no need to do any mods.Time to start researching ATX PSUs now! Thanks for your help!

author: MigMic
author_rank: Contributor
timestamp: May 29, 2015, 11:49:19 am
content: Quote from: andtfoot on May 29, 2015, 11:41:21 amThanks, that makes sense. Nice looking control box andtfoot!

author: MigMic
author_rank: Contributor
timestamp: May 29, 2015, 12:54:00 pm
content: This one looks like it will do the trick:http://www.msy.com.au/sa/adelaide/pc-components/14158-evga-500w-100-w1-0500-kr-500watt-80plus-power-supply-unit.htmlIt's in stock at my nearest supplier, is rated to 40A @ 12V, and has good feedback on Amazon. There's also an in-depth review here:http://www.jonnyguru.com/modules.php?name=NDReviews&file=print&reid=384A few questions:1) The review states the ripple on the 12V rail is 90mV. Is this likely to be a problem?2) The review also mentions that there is no heat sink on the bridge rectifier. Is this likely to be an issue since I won't be running it at full load (est. 30A max)?3) Should I consider putting some protection in between the PSU and the control board? If so, what?Thanks again,Michael

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 29, 2015, 01:45:15 pm
content: Did the kit come with a power supply? Your description is confusing.The specs on the web page says: "AC Input 100v - 240v"And also: "Power Requirements 300 W, DC 12V / 30A"That would appear to imply that a properly-rated DC power supply was included with the printer kit.The power supplies you have shown in the photographs are INTERNAL modules. They are not intended to be used "standalone" outside a proper enclosure.Using a PC power supply seems rather "dodgy" to my thinking.A proper 12V 30A power supply would seem like the straightforward solution.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 29, 2015, 02:49:34 pm
content: Quote from: MigMic on May 29, 2015, 11:46:46 amno need research, no need rocket science modification. you just take care of black and yellow wires (12V), parallel each color (black to black, yellow to yellow) as many as you can for greater amperage capability, each of it are connected to a single point inside the PSU anyway. and lastly you connect green wire to chassis, there is only one green wire there so dont get scary, the rest of colors? you can throw them away... but...when i said about using atx psu as replacement, thats only when your existing psu goes big bang or you need higher amperage, ie not needing the existing 20A unit shown above. but what you got to lose? i say use that existing underrated psu until it dies. the 30A max is probably if all steppers, heaters are ON at the same time which is very unlikely during normal printing, the psu should survive for sometime i believe.and why i did advice for it? in case the existing one breaks? because its readily available and cheaper than the specialized smps psu like that, depending on your location, its likely you need reorder from china, like my location.

author: sleemanj
author_rank: Super Contributor
timestamp: May 29, 2015, 03:01:18 pm
content: Most 3d printers from china come with that style of psu, including my own.It works fine (but of course 2 psus that look the same may be entirely different), the only things i did were1. Throw away the 2 prong power cord and instead sacrifice a nice moulded earthed iec cord for it2. Crimp ring terminals onto said cord to properly attach to the screw terminals instead of just jamming the wire under them3. Double check the voltage selector switch which is just visible through the housing4. Plug in and check output voltage was correct before connecting the control boardYes, it's really not supposed to be used where people could touch the live terminals, so, don't touch the live terminals! You could always print a better safety cover ;-)

author: MigMic
author_rank: Contributor
timestamp: May 30, 2015, 12:10:46 am
content: Quote from: Richard Crowley on May 29, 2015, 01:45:15 pmSorry for the confusion. The photos in the first post are of the power supply actually provided with the 3D printer kit. The stated power requirements are 30A @ 12V, but the power supply provided is only rated to 21A @ 12V.Yes, I now understand that the supplied PSU is meant to go inside another enclosure. Since safety is important to me I am considering finding a suitable enclosure or going with another power supply.Is using a PC power supply any more "dodgy" that using the internal module without another enclosure? It seems to be common practice for 3D printers. I'm not saying that "common practice" is either safe or ideal, but at least a PC power supply has the mains power inside the enclosure. Drawing DC power out of standard ATX connectors for use in the 3D printer should be no different to powering a PC, or am I missing something?Just trying to understand so I can make an informed decision. Thanks for your input!

author: MigMic
author_rank: Contributor
timestamp: May 30, 2015, 12:20:29 am
content: Quote from: Mechatrommer on May 29, 2015, 02:49:34 pmYour advice made perfect sense. I bought the printer mainly as a way to learn more about electronics, so I'm happy to research alternatives to improve my general understanding. I also bought a cheap printer expecting that I would have to replace or upgrade some bits, so don't mind replacing the power supply if I need to.

author: MigMic
author_rank: Contributor
timestamp: May 30, 2015, 12:23:10 am
content: Quote from: sleemanj on May 29, 2015, 03:01:18 pmVery true. In fact I found some designs on Thingiverse especially for this application.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 30, 2015, 01:00:09 am
content: Quote from: MigMic on May 30, 2015, 12:10:46 amI would NOT a priori decide that the provided PSU is inadequate without at least measuring the ACTUAL current draw from the gadget. 30A seems like a remarkably humongous current for a little 3d Printer. For that matter, 20 amps seems rather more than I would expect.QuoteIME, using a PC power supply is rather "dodgy" because PC supplies are designed for a very specific kind of load. They are expecting a substantial current draw at the primary (and secondary) logic voltages, while 12V is a secondary output for peripheral devices. Drawing all the current from the 12V output is well outside the design parameters of PC power supplies.Now, some premium PC power supplies might be designed well enough to thrive on that kind of mis-application. But it really seems presumptuous to just assume the the provided PSU is "inadequate" and run out and buy something that wasn't designed for the job. YMMV, but it wouldn't be my first choice.

author: MigMic
author_rank: Contributor
timestamp: May 30, 2015, 01:16:13 am
content: Quote from: Richard Crowley on May 30, 2015, 01:00:09 amI'm not presuming anything. If you have a look at my first post, I was actually asking how to safely hook up and test the supplied PSU (e.g. by adding additional over-current or over-voltage protection) while avoiding problems other people have mentioned. I was only planning to check the report that the PSU is inadequate after I got the whole printer running.While I admit the thread has gone off on a few tangents (which I don't see as a problem, since I'm learning heaps in the process), I would be happy not to spend any extra money if I can use the supplied PSU safely.If you could provide some suggestions on testing the PSU (if not yet covered in this thread) I would gratefully receive them.Cheers,Michael

author: MigMic
author_rank: Contributor
timestamp: May 30, 2015, 01:21:53 am
content: Quote from: Richard Crowley on May 30, 2015, 01:00:09 amOK, thanks. That makes sense.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 30, 2015, 01:45:46 am
content: Quote from: MigMic on May 30, 2015, 01:16:13 amI would grab an auto head-lamp (or two) and connect them to the output of your 20A PSU. That should provide a good stiff load to test what it's got.You should certainly have a DMM if you are doing things like building a 3D printer kit.If your DMM won't measure 30A (or 20A), you could rig up an appropriate current shunt to put in series between the PSU and your test load.Then you could measure the voltage across your current shunt and use Ohm/s Law to calculate the current.I would probably get one of those $5 digital panel meters from eBay that will display both the voltage AND the current. And build that into the enclosure that you make for the PSU. Like this one....http://www.ebay.com/itm/Dual-LED-DC-Digital-Display-Ammeter-Voltmeter-LCD-Panel-Amp-Volt-Meter-100V-100A-/271862702359(just the first one I found of a great many)

author: MigMic
author_rank: Contributor
timestamp: May 30, 2015, 01:58:28 am
content: Thanks. Yes, I've got a lamp somewhere I can use to load up the PSU. I was although thinking of connecting the heat bed PCB directly to the PSU to test it's actual current draw.Yes, I've got a DMM. Will check it's maximum current rating and get a shunt if necessary.I like the idea of the panel meter - will investigate as well.Cheers.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 30, 2015, 02:04:31 am
content: Honestly all those "problems on other forums" seem like free-floating anxiety expressed by people who don't really understand what they are doing.Most certainly, any power supply module like that is potentially dangerous because it was NEVER INTENDED to operate as a stand-alone box. It was designed to be built INTO some product which provides proper grounding, shielding, mechanical stability, and ventilation.Complaining about the potential dangers of an internal PSU like that sitting out on its own is like complaining about a fan with the grille removed. That is what makes me think the the people who are "complaining" don't know what they are talking about.Millions of switch-mode power supplies (SMPS) are made in China every year and used in products all over the world. The one in your photo looks pretty average for build quality. Dunno why one would just assume that it was any more dangerous to use with your gadget than any other SMPS you could buy. Again, seems like ordinary "free-floating anxiety" to me. Unless you encountered some statistically-significant string of customers who reported failures with that particular SMPS. Sorry, not a very compelling argument, IMHO.As for being "under-rated", If I had to wager one way or the other, I would bet that the "30A" specification is greatly padded. I would be quite astonished if it draws even HALF that.

author: sleemanj
author_rank: Super Contributor
timestamp: May 30, 2015, 05:33:23 am
content: Quote from: Richard Crowley on May 30, 2015, 02:04:31 amWe can make some educated guesses.A typical 3d Printer hot end runs 40W at 12v, so that's 3 AmpA stepper is going to be 2 Amps at the absolute most, because that's what the typical stepper drivers can run.A single extruder 3d printer has likely at most 5 steppers (X, Y, 2 for Z and one for the extruder). 2 * 5 = 10A for the motors.The control board, maybe a display, we'll just be generous and say they did a really bad job and took an amp for that.The heated bed however is trickier, looking around it seems that they have a resistance of about 1.5 Ohms for the 12v, so that gives us a surprising 8A for the bed if it's running flat out (~100W !)Anyway, adding that all up into a very much worst-case scenario, we get about 22A at 12v. But realistically, the bed isn't going to be running full tilt, neither is the hot end, the steppers probably drawing somewhat less than 2A, and the control etc is probably only a couple hundred mA.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 30, 2015, 05:44:49 am
content: I forgot about the heated bed! Why on earth do they use "premium" regulated and filtered DC for such a "junk" load as a resistive heater? That just seems remarkably stupid.

author: ruffy91
author_rank: Regular Contributor
timestamp: May 30, 2015, 07:05:38 am
content: Because a "premium" regulated 240W smps goes for 20$ while a 150VA transformer goes for 30$, and you need regulated 12V nonetheless.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 30, 2015, 07:39:57 am
content: Quote from: sleemanj on May 30, 2015, 05:33:23 amfor my setup. the bed will be full tilt during print startup until the desired temp. during this time all others are OFF. when the bed reach temp, the next thing is hotend, and then printing commence, its sequential not parallel, from thereon bed and hotend will be on and off just to maintain the set temp (pulsing current). hotend maybe working hard to compensate for the leaving plastic (heat loss), but bed not so much i guess, depending on surrounding temp, if one keep it enclosed, bed heating can be relaxed to some degree.Quote from: ruffy91 on May 30, 2015, 07:05:38 amwhere do you get >360W 50/60Hz transformer (12V x 30A) for $30? thats cheap. not to mention its weight, i dont feel like moving around 3dprinter with its separated but wires connected 7kg worth of metal.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 30, 2015, 01:29:25 pm
content: Quote from: Mechatrommer on May 30, 2015, 07:39:57 amBut why do you need anything but direct mains voltage to operate a resistive heater? And it is so easy to control with Triac. We don't operate reflow ovens on regulated DC. Still doesn't make sense to me.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 30, 2015, 01:41:31 pm
content: Quote from: Richard Crowley on May 30, 2015, 01:29:25 pmi dont know, though it can be done. it depends on how the insulation will be made and the robustness of the control, because thats where the hand is working on, plus this DIY OSSW stuff can be nastyly assembled during DIY, the heating circuitry of my unit is just below the bed insulated with kapton tape or simply exposed. so i guess maybe people who developed this dont want to take the risk... + the diy is using 1.5ohm copper pcb trace around 2-3mm wide zigzaged, easy to build, no need special resistive element, but whats the odd of 160A flowing through it at an instant?

author: MigMic
author_rank: Contributor
timestamp: June 01, 2015, 12:16:24 am
content: FYI the heated bed I have is a "Mk2b" PCB:http://reprap.org/wiki/PCB_HeatbedIt measured 1.3 Ohms at RT.

author: ConnorGames
author_rank: Regular Contributor
timestamp: June 01, 2015, 01:37:37 am
content: Many newer ATX PSU's like the G-550 from Seasonic (About $60-70 'like new' from amazon warehouse deals) actually generate all rails except 12v using DC/DC converters off the main 12v rail. The days of 5V and 3.3v being the main rails on an ATX supply are long gone. A supply like this Seasonic shouldn't need any mods besides a switch between the green wire and ground, and can deliver its full rated power on the 12v rail. It can also deal with no load/low-load conditions well (this is a requirement for PSU's for Haswell and later PC's). I currently abuse an older supply that does not use the dc-dc approach for powering my printer's heated bed though, ands it works fine although regulation is terrible without a load on the minor rails (the heater doesn't care though, and I got the PSU for free!). I would recommend sticking with newer supplies if you want to use an ATX psu without any big mods though.No idea how good that supply you already have is though. It may well work just fine.

author: MigMic
author_rank: Contributor
timestamp: June 01, 2015, 01:43:59 am
content: Thanks ConnorGames. I plan to test the PSU I received with the kit and if it appears to be OK will put it into an enclosure. However, if it goes up in smoke or doesn't appear to provide a clean supply then I will certainly look at the ATX option. I might be able to score one free from the IT department, otherwise I'll look at a Haswell-compatible one (I also seem to remember reading on one of the RepRap pages that they are designed for no load/low-load conditions).Unfortunately work's busy at the moment so it may be a while before I get around to it. Still waiting on replacement mechanical parts so no real rushCheers,Michael

author: bills
author_rank: Frequent Contributor
timestamp: June 01, 2015, 02:32:18 am
content: Just buy one of these and be done with it.http://www.ebay.com/itm/400-Watt-Adj-Volts-9-15-DC-36-Amp-HAM-CB-Power-Supply-Real-USA-MegaWatt-TM-/180777043955?pt=LH_DefaultDomain_0&hash=item2a1726c7f3

author: MigMic
author_rank: Contributor
timestamp: June 01, 2015, 07:51:59 am
content: Quote from: bills on June 01, 2015, 02:32:18 amThanks.

author: Delta
author_rank: Super Contributor
timestamp: June 01, 2015, 02:12:00 pm
content: Look for a server psu on ebay. Very powerful and dirt cheap. 😀