fried my arduino mega, well two of them in 2 minutes

Hi

I'm building a delta 3D printer.
Electronics are 2 kits from gadgets3d.com bought on ebay.(arduino mega, ramps 1.4, sdramps, G3D drivers.....)
Power supply is 12V 30A, switching...

I tested tested the motors couple of weeks ago, everything fine.
[www.youtube.com]

So I guess, this far everything was connected correctly.

On saturday evening, I put everything in the printer, connected ramps to power outlet and tried to connect USB cable to arduino, and as I just touched USB port on arduino SMOKE from arduino
Only the motors and endstops(two wires only) where connected.
SMD element just above the USB port blew. (diode !?, or what is it ?)

Tried the second board, with only the motors connected and same thing happend.

Next day I tried the first board again, without anything connected and now it's not detected by windows anymore, before I could still upload firmware to first board.

Second board has still demo firmware on it, is detected by windows, but I can't update firmware.
It works in demo mode, but that's it.
[www.youtube.com]

As I have AVR ISP for programming my quadcopters, I will try to program arduino this way, just for fun of it.....

I have two Arduino MEGA's on order, but would hate to do the same mistake again.

Can anyone more experienced tell me where did I go wrong, please ?

well its got to do with the way the ground is connected. this problem has surfaced before.

to explain this, lets name the supplies like this :

PC USB has a supply : USB +5v (we call this +USB ), USB GND (we call this -USB )

arduino/ramps supply : +V (we call this VSS), negative return -V (we call this GND)

due to the 2 seperately floating supplies, which have 2 different isolated return voltages (or even if only 1 is isolated). one of the power rails is sitting at a higher potential then the other, making the ground of 1 short through the arduino to the lower potential ground.

to find out, use a volt meter, measure the ground to ground voltage -USB to GND. where there is a voltage difference, it is effectively shorting 1 power supply to the other when you "short" or connect the 2 "grounds" together via the USB.

most likely, the VSS supply is not a real positive rail, it is made as a zero ground. the GND instead was made to be -ve voltage rail. so it still performs as a +12 or watever you purchased it as, but when you connect -12v to the -USB ... you create a high current short, shorting the -12v rail to zero volts of the USB "chasis" ground. gawd knows how many amps is going thru that. either that or reverse the scenario, the PC PSU is negatively regulated, and the short happens the other way around.

i hope you catch what is the fault based on the above.

Edited 2 time(s). Last edit at 05/27/2013 07:25PM by redreprap.

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______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

Quote

connected ramps to power outlet

Provide picture please of your power supply and how it is connected to the RAMPS board.

Quote

endstops(two wires only) where connected.

Picture of these plugged in as well please.

redreprap Wrote:
-------------------------------------------------------

> to find out, use a volt meter, measure the ground
> to ground voltage -USB to GND. where there is a
> voltage difference, it is effectively shorting 1
> power supply to the other when you "short" or
> connect the 2 "grounds" together via the USB.
>
> most likely, the VSS supply is not a real positive
> rail, it is made as a zero ground. the GND instead
> was made to be -ve voltage rail. so it still
> performs as a +12 or watever you purchased it as,
> but when you connect -12v to the -USB ... you
> create a high current short, shorting the -12v
> rail to zero volts of the USB "chasis" ground.
> gawd knows how many amps is going thru that.
> either that or reverse the scenario, the PC PSU is
> negatively regulated, and the short happens the
> other way around.
>
> i hope you catch what is the fault based on the
> above.

Thanks for your reply.
I measured the voltage between computers -USB and GND on ramps and it is zero.
I also measured voltage between -USB on computer and -USB on Arduino and it is also zero.
I'm really lost here, everythig was working couple of days ago and suddenly
Can I try anything else ?

ShadowRam Wrote:
-------------------------------------------------------
> connected ramps to power outlet
>
> Provide picture please of your power supply and
> how it is connected to the RAMPS board.
>
> endstops(two wires only) where connected.
>
> Picture of these plugged in as well please.

Thanks for your reply,

this is how it is connected.
[shrani.si]
[shrani.si]

I don't have the switches connected anymore, but it was from COM to - and NC to S ( If I remeber correctly), only two wires and only with
first board.
Second board didn't have end stops connected and same thing happened.
Any ideas ?

the 2 yellow parts behind the connector are fuses, see if they are blown.

you should be able to slowly seperate the arduino board from the ramps board. after that ... plug the arduino to USB and see if it is still alive.

btw the PSU, any fuse blown?

Edited 2 time(s). Last edit at 05/28/2013 01:11PM by redreprap.

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______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

They are both blown, one fell off and I desoldered second one, if we think of the same thing. (both are small black SMD elements, so badly damaged, I can't read anything of them)
Here's the photo of where the damaged parts were.
[shrani.si]

On first controller that is totaly dead, even the printed circuit board on Arduino got damaged (on second try, the next day, without the fuse), I think more than couple of amps went through, it looks like it was glowing.
What kind of fuse is it, can I replace it with something simple ?
Check out the photo:
[shrani.si]

The second board can't be updated, ramps on or off.
I really "don't care" about 2 arduinos, 50€ and it's solved, I put far more money in to it, so it's battle damage for now, but it scares the hell out of me just thinking of plugging the USB to powered board, burning them again and waiting again and 50€ again without a real solution.

Error trying to update..

Binary sketch size: 47,068 bytes (of a 258,048 byte maximum)
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer

Edited 2 time(s). Last edit at 05/28/2013 01:44PM by madmito.

ouch ... that is a USB ground pin.

well you can use normal fuses as far as i know. you can prolly jump it with something thin like 1A for safety test first.

have you tried to measure the voltage between the -USB direct to your -ve PSU? since fuses are fried, it could be a "trap" there somewhere. try measure if the PSU earth and your PSU DC -ve is connected or floating. then try and see if any of these -ve/earth is conected to your -USB or +5v USB (looking at your photo, fried track is pin 1, the pin under it is +USB 5v)


*edit* the small SMD appear to be 0.08ohm (i just measure this off hand... it could be a zero ohm) safety component, made to be blown. it is connecting the ground of the USB port it seems. so if you can temp wire it up and USB power the arduino, that would be a good test i think.

Edited 5 time(s). Last edit at 05/28/2013 02:04PM by redreprap.

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______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

What do you mean USB ground pin ? As far as I know, where the fuse was blown is where USB ground touches USB on Arduino ?

This is what I measured: (all of it)
[shrani.si]
[shrani.si]
[shrani.si]

Should I measure anything else ?

If it is about zero ohm, can I just use a very thin wire ?

BTW really thank you for all your help, I'm an architect, so I'm really not knowledgable about electronics

Edited 2 time(s). Last edit at 05/28/2013 02:12PM by madmito.

*double post*

Edited 1 time(s). Last edit at 05/28/2013 03:32PM by redreprap.

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______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

madmito Wrote:
-------------------------------------------------------
> What do you mean USB ground pin ? As far as I
> know, where the fuse was blown is where USB ground
> touches USB on Arduino ?
>
> This is what I measured: (all of it)
> [shrani.si]
> .jpg
> [shrani.si]
> 7.jpg
> [shrani.si]
> 4.jpg
>
> Should I measure anything else ?
>
> If it is about zero ohm, can I just use a very
> thin wire ?
>
> BTW really thank you for all your help, I'm an
> architect, so I'm really not knowledgable about
> electronics


lol ... the exact zero value looks very strange to me ... i cant think/recall of what is so strangely familiar about it hahaha. i think there is suppose to be a float of a few mV or something.

TBH im not a real expert on arduino, its just i fiddled with it quite abit.

i think you should try and establish power via USB into arduino w/o the ramps board so that you know the CPU is still alive. n doing so w/o using the PSU to power it, use the USB power. so yes i think you should repair that SMD or jump it with a screw driver touching just to try. i didnt see the arduino PCB diagram. heck you might as well check your USB port to see if the computer USB is fried too.

there was once i made the mistake of plugging in the stepsticks in the wrong pin sockets ... but nothing was harmed ...

you should get some kinda chopstick and wedge from multiple sides and remove the ramps from the arduino

Edited 1 time(s). Last edit at 05/28/2013 02:37PM by redreprap.

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______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

I tried to establish contact between arudino and the computer, without ramps connected.
1. board dead (I guess, USB controller is completly dead, ATmega alive, but no help)
2. board, can be found by windows, but no programing of ATmega.(I guess it can be helped)

gonna try and solder a very thin wire instead of a fuse and see what happens, just wanna prevent fatal injuries to my soon to arrive new Arduinos, not "reanimate" anything
I'll update in an hour, after testing......

Thin wires soldered, connected ramps to 12V, connected arduino to USB,
nothing happened, no smoke no whatever.....
Gonna wait for new Arduino's and test again.

madmito Wrote:
-------------------------------------------------------
>
> this is how it is connected.
> [shrani.si]
> .jpg
> [shrani.si]
> 8.jpg
>

The interesting thing is that in your 2nd picture you apparently have live and neutral swapped on the mains connection. I can't see the other end, but that is how it looks.

I say it is interesting, because one of our guys had problems blowing the USB port on a self-powered device, turned out the problem was the USB device was plugged into a power strip that was mis-wired, his PC to a different power socket that was wired correctly.

Hi Bobc,

as far as I know, it doesn't matter with AC current.
You can have live and neutral connected anyway you want (you can plug it in turned 180°) as long as ground is connected to ground.
My power sockets aren't misswired, I power computer and everything else from same power outlet multiplier.
Thing is, it worked with the same power outlet, then it didn't work and now it "works" again (at least no more smoke from damaged arduinos).
Very confusing time for me

hmmm im not so sure about that L/N connection the way u said it lol. where it is indicated it should be followed because it is build such that the neutral line is a designated power return. by reversing, you might be energizing the ground or even some chasis by mistake though it is rare modern equips are chasis neutral. the L line definitely needs to go through some filters for PWM, and by reversing it is not happening LOL ...

---

______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

Hi,

I have fried one arduino just similar way. I soldered broken USB CPU of and replaced it with separate USB to TTL converter board buyed from eBay for about $3 Uou can try to replace that broken bpart with awire but I quess that the USB processor is damaged anyway.

But I think I do know what happened:

I live in European country, where mains live and neutral swapping means nothing.
I think that all countries which uses 3-phase end user distribution works the same way.
Although our N line is real zero and L line is "hot" there is no reason for polarized mains plugs and all device manufacturers are making their equipments for tolerating that swap. They mark the AC inputs L and N only for such countries which uses polarized mains plugs (for example UK)

And here is the most propably reason to firing that USB ground protection component (it is an RF inductor AFAIK).
BOTH L and N lines have capacitors connected to mains plug protection eathing line (marked yellow-green or PE)
PE must allways be connected to all of equipment metallic parts.

From L and N lines point of view, those capacitors forms an voltage divider, which causes that devices PE metallic parts to have AC potential of half the mains voltage. It is an AC voltage. So it's DC average value is zero!
These capacitors are allowed to cause max 0.5 mA AC current floating to earth. If not earthed that equipment have half the mains voltage being in its PE line. That continuous AC current is not dangerous level.

BUT that curent is coming from hundred volts charged and about 0.1nF sized protection capacitors and those caps may cause very high curent spike then discharged.
THAT current and energy definitely IS dangerous for electric parts

If ALL eguipments are connected to same mains ground or same extension distribution box with 3 pin cable, the all earths are the same and no problem arises. All RF protection caps finds their way to earth and earth leakage current path does not flow via your USB eath pin.

But for example most LCD displays and laptop power supplies have EURO type 2 plug connector only. And there is still a capacitor from mains (live) side to touch proof insulated secondary side due the RF interferece norms.

All these makes the potential risk of getting some equipment of real earthed and some other having half of mains AC on its ground terminal.

You can test that current by touching something which is really grounded (television antenna cable) and the ground of your system under test.
Maybe your fingertip skin is not sensitive enough, but other parts of hand may sense that current.
Knucle (opposite side of hand than palm) is more sensitive.

I have fried many home stereo equipment RCA (cinch) or S-video inputs this way. Because home amplifies are true grouded via their antenna cable.
Then connecting a laptop audio speaker output to stereo amplifier line in may broke that input, because RCA connector connects it signal tip before its ground ring. 0.5 mA and 115V AC
On my home I measured antenna ground line and mains protective ground line voltage differences and that was about one volt difference.
And all my tens of equipments causes about 0.1A current together if antenna earth and PE earth are connected together. If 5kW home theatre amplifiers are online their current draw makes my house N lines (connected in PE inside house mains fuse table) more drop and leakege current is much more higher...

I think that just similar has happened to you. Do you have 2 pin EURO and 3 pin connector (PE earthed) equipment connected to same system?
IF all your equiupments were connected to same earthed mains distribution box with 3 pin cables, well, then your problem seems very weird.

That RF protection capacitor leaking current problem is dangerous because switching of the equipments means nothing.
Most cases those RF caps are on live side, before any power switch!

So unpluging the ALL connected devices from mains before USB or any signal line connection is the only way of protect youself 100% proof.


"A owner of MANY similar way (self) burned equipments...."

yep some or most equip should be reverse L/N tolerant ... but then again most PWM based equips, rectifies the AC. then the problem comes when interequipment does not share a common ground level. some hifi equips even have balanced power supplies which i find very amusing

---

______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

Hi everybody,

I had similar case with a fried arduino board. I started by checking the output Voltage of the Power Supply and it was aprox. 15.4 V !!! I put it down to 12 V now.
The question is if this 15.4 V was responsible to fry my arduino. Should I try with the 12 V or again the issue might have been as discussed above with the "ground"?

If anyone can help, I would really appreciate it.

thanks

IIRC there is an issue with RAMPS where the USB connector on the Arduino can short to the 12V on the RAMPS board above it.

---

[www.hydraraptor.blogspot.com]

so far i have ran my ramps 1.4 to 27Vdc over long periods, the regulator on the arduino gets hot and some others too get hot ... and thats about it. i think if it just shorts and burns right from the start w/o any heavy load ... either the board is made with error ... or like what some experienced a reversal in the ground of the supplies ... causing 1 PSU trying to kill each other "grounding" through the arduino/ramps board ... thus this "battleground" ... is fried ...

xerox1821 Wrote:
-------------------------------------------------------
> Hi everybody,
>
> I had similar case with a fried arduino board. I
> started by checking the output Voltage of the
> Power Supply and it was aprox. 15.4 V !!! I put it
> down to 12 V now.
> The question is if this 15.4 V was responsible to
> fry my arduino. Should I try with the 12 V or
> again the issue might have been as discussed above
> with the "ground"?
>
> If anyone can help, I would really appreciate it.
>
> thanks

---

______________________________________
__my mixed bag blog || aka --> [http] || ___ so 3D printing is everywhere ... dont worry, hospitals can now 3Dprint body parts, they will charge you $1million excluding surgical fees ... you will die paying your debts. thats their aim ___ if every patent expires tomorrow, everybody will surely get a 3dprinter and make EVERYTHING ! ____ there is a "DIY-DTG" t shirt printing forum, you can mod an EPSON printer to PRINT like a pro. ___ CNCzone? overly commercialized it seems ___ my country? they will be taxing you for every cm of road you use and track you to your grave using GPS and its government authorized, now they will fire all the traffic wardens instead.___ EEVBLOG? there is only 1 way to do things --> take it apart like a pro

How much your arduino tolerates depends entirely on the regulator. The standard reg on many arduinos and arduino clones only handles about 14V before failing. There are a number of clones that happily take 28-30V before the regulator fails, and I would not be surprised if newer arduinos will happily handle that.

Telling the difference between a clone and a real arduino can be harder than you might think. Also telling the difference between an older arduino and a newer one is just as problematic.

This is why the docs for RAMPS say that if you're going to run >12V, you should remove diode D1 and power the RAMPS board separately. This guarantees that, no matter what board you have, it will work.

I was thinking the same. Since the second arduino board was a white clone that should be able to handle more V, and this one got also real fire on some of the fuses (!!!), I am pretty sure that the problem is with the Power Supply.
When I had the arduino connected only to the Power Supply (even with this 15.4V) and I was operating it through Bluetooth connection there was no problem. When I just connected the USB, everything was on fire.

Do you know how to fix this issue with the Power Supply? Can it be fixed or I should buy another one?
thanks in advance


redreprap Wrote:
-------------------------------------------------------
> so far i have ran my ramps 1.4 to 27Vdc over long
> periods, the regulator on the arduino gets hot and
> some others too get hot ... and thats about it. i
> think if it just shorts and burns right from the
> start w/o any heavy load ... either the board is
> made with error ... or like what some experienced
> a reversal in the ground of the supplies ...
> causing 1 PSU trying to kill each other
> "grounding" through the arduino/ramps board ...
> thus this "battleground" ... is fried ...
>

Hi,

I had the very same problem with my arduino(s).
The EMI filter burnt exactly the same way.

I made the same mistake of interverting neutral and live on the power supply. So I switched them back and tried with the other arduino Mega I just received.

Same shit just happened :x
I plugged in the usb cable and could see a small cloud of smoke coming out of the arduino... Now the arduino isn't recognized by windows anymore.
Nothing was plugged in exept the stepper motor drivers on the ramps. It was just PSU/ramps/arduino/usb cable/laptop

I don't really know what to do next, I'm not really planning to fry a MEGA on every try :'(
Do you think the RAMPS could be damaged from the first try and now just burned the 2nd arduino ? Could it be a problem with my house power wiring (old house, electricity redone recently but I'm not too confident about it)

I ordered another couple of mega, but it will be weeks before I receive them. Any Idea meanwhile about what's going on ?

Thanks !
Charles

Edited 1 time(s). Last edit at 04/23/2014 06:18PM by cthumerelle.

I ran further tests and it appears that there is a huge difference between the grounds of the power supply and the laptop.

When the laptop is not connected to the power supply, everything seems to be fine.
But when I plug in the laptop, i see a gap of arround 12V between the power supply V- and the laptop groung (I take this laptop ground on the usb plug ).

I bought another aduino mega. I have the feeling that I could use it safely if I don't connect my laptop to its power supply but that doesn't seem a good long term solution.

Do you have any idea about what's going on ?

Thanks for your help !
Charles

You can buy USB cables that isolate the device completely from the PC, but they're not likely to be cheap.

Can you test the following:

Disconnect your printer PSU from the wall and your laptop. Leave it for 5 minutes, then using a multimeter on the resistance scale, look for a low resistance (eg: 0-5 ohms) between the AC Earth pin to the +12 and Gnd pins on the DC side of the PSU. My guess is that the +12V pin will be connected to AC Earth somehow, possibly internally in the PSU.

Disconnect your laptop PSU from the wall and your laptop. Leave it for 5 minutes, then perform the same test from the AC Earth pin and any pin on the DC connector that goes to the laptop. Change the meter to the DC voltage scale, plug in the Laptop PSU to the wall and find the pins that provide the voltage to the laptop on the DC connector (only required if the PSU and/or laptop PSU is not marked to indicate which way it is). My guess is that the DC Ground pin will be the same pin connected to AC Earth.

I'm assuming here that your laptop has an earth pin, as most now do (using a 3 pin IEC or 3 pin Clover-leaf style connector), and this is how they get a "common ground" beyond the USB cable (it completes the circuit).

If the above suppositions turn out to be true, you need to change the link between AC Earth and +12V on the printer PSU to be between AC Earth and DC Ground. If this is internal to the PSU you're pretty much out of luck, but if it's external, (eg: there is a wire between +12V and AC Earth) you can change this to solve your problem.

Note: I have seen some PSU wiring instructions that tell you to join DC Ground on brick-style PSU's to the AC Earth. The problem is, the picture assumes that DC Ground is RIGHT NEXT to AC earth. However, in some cases it's actually right next to +12V, as there is no standard for these PSU's (and even if there was, suppliers will cut corners if it saves them a few cents). Of course, people look at the diagrams only but don't look to see if it's marked +12V or Ground, and so you can get issues like above.

PS: This may not be the case with your setup, but it's one of the things I see happen, so I thought I'd call it out.

Edited 1 time(s). Last edit at 04/24/2014 04:54AM by Cefiar.

Hi,

Thanks for your input. I justed tested my PSU and the ground is indeed wired to V+.

Is there a logical reason (except plain stupidity) to link ground to V+ instead of V-/COM ?

I'll have a look if I can do something about that but I'm not really sure :s
If I need to buy another PSU, how do I know that GROUND will indeed be connected to V- and not tu +12V ?

Thanks !
Charles

If it's a brick-style PSU, you don't.

For many systems (where it's driving a strip of LEDs, downlights, etc) this doesn't matter, so the suppliers don't really tend to give a rats arse, especially if that is what the PSU is being labelled as being used for.

If you got this as part of a kit for a 3D printer, I would definitely be letting the supplier know and asking why they buy PSU's wired like that.

Lost a Arduino Mega on my P3Steel printer 2 days ago. It was strange because it happened when it was hooked up to the PC in a configuration that's worked for a few months.

The failure mode was the ReprapDiscount LCD Display going really bright then blinking. After which the PC stopped seeing the Arduino board. This only happened when I when I was heating up the bed and hot end. I noticed the USB cable was hot but thought it was from a blown UART or something.

I replaced the mega and it was working until I powered up the hotend and bed again. Then it blew out the same failure mode.

I thought it might be related to a blown fet or since it only happened when I was heating up the bed. Granted the FETs were still working until the next blow and weren't hot. After reading this I'm wondering if either my V- on my PSU isn't at the same ground as the USB ground. I guess I'll disconnect them power up the reprap PSU and measure the voltage difference between these "gounds". I also can check if resistance from the guidance here. I also have to check that USB+5V is good from the PC.

Edited 1 time(s). Last edit at 06/09/2016 03:28PM by CTCHunter1.

Following up & I believe problem solved for me. The problem was negative terminal of the bed was shorted to AC (chassis) ground. The bed control is will a pull down fet configuration. Solution: Clear the short, make sure negative terminal of bed and V- on PSU is not at low resistance with the PSU and USB disconnected. Additionally, I bridged the V- terminal on the PSU to AC ground.

Trouble Shooting:
This is was what my failure looked like on the LCD screen. The screen was brightly illuminated with the screen fonts kind of behind it. I took out a 2nd Arduino Mega tying to fix this.Initially by power to ground bridge was running through the USB cable to wall ground killing the Arduinio.

This failure happened only after setting up turning on the bed and hot end in repetier firmware.


(Imaged attached as well if tinypic no longer works)

The usb wire between the printer and PC got warm.

I reset the system and measured the voltage between the USB ground and the V- on the power supply (DC common for the printer) with printer plugged into the PC and the power supply on. This voltage was 1.2 V when the failure happened. Before turning on the hot end this voltage is .03 V. Current it coming from the PC into the ground on the the printer during the failure.

I measured the resistance between V+, V- and AC ground on the PSU. They were all infinity = open circuits. However USB ground on the arduino and AC ground on the PSU was low resistance (closed circuit). Conclusion my USB ground is the the same as my AC ground and PSU was floating. My solution: bridge V- terminal of PSU to AC ground.

OK. Did this and got a print. However bed kept heating. I had to shut down the PSU to stop this. Resistance between source and drain on the bed FET was high with PSU off indicating the fet was still good and not shorted. However the bed FET LED was constantly illuminated with the PSU on and USB disconnected (bed + terminal also disconnected at this point).

I disconnected the negative terminal on the bed and this darked the LED. I measured the resistance of the negative terminal of the bed to V- on the PSU, now bridged to ground and found it to be low (closed circuit). I realized that one of the bulldog clips I'm using to clamp down the glass was bridging the negative terminal of the bed to the bed aluminum which is connected to chassis ground. I moved the clip and resistance between V- on the PSU and negative terminal on the heated bed went to infinity (open circuit). I turned on the arduino and the bed is no longer over heating.

Conclusion: Be careful shorting the neg terminal of a bed to chassis ground. The FET that controls the bed is in a pull down configuration. High voltage on this FET gate brings the negative terminal on the bed connector to ground while the positive terminal on that bed connector is always at the V+ on the PSU.
Hence if the negative terminal on the bed is already shorted to ground the bed will always be on. It would be better if this FET was in an pull up configruation so that it turned of the supply voltage to the bed instead of the other way around.

Edited 1 time(s). Last edit at 06/10/2016 12:27AM by CTCHunter1.