Power cutoff

#1

I own a custom Prusa-like 3D printer. I have printed a lot over the last year. Yesterday I started having problems with the print stopping after a few layers. I noticed that at this point there is no power. Starting from a cold printer, I noticed that the LED light strips I have installed starts to flicker as soon as I turn on the heated bed. I print ABS using an extruder temperature of 245°C and a heated bed temperature of 90°C. I am suspecting the power supply but I am not sure if it’s the power supply in itself or something on the printer motherboard (or the heated bed) that is causing the power supply to shut down. At one point yesterday I smelled burning plastic (typical of burning electronics) but I could not trace down the source of the smell.

Any ideas where to start? Thanks!

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#2

Hi mdebono,

It very well could be a power supply issue, but it might also be the controller. A few questions:

  • Are you using 12V or 24V?
  • What is the maximum power output (wattage)?
  • If you wait a while, can the printer switch back on?
  • What type of controller/shield board are you using?
  • Are the LEDs connected to the same power source as the heatbed?

The flickering LEDs could be explained by pulse width modulation (PWM) of the heatbed. The controller sends short, timed bursts of energy to the heatbed. Adjustment of the timing changes the heat output. If you are close to exceeding the power supply’s output, it could affect other circuits.

-Stefan

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#3

Hi Stefan,

Thanks for your reply.

I’m using 12V on a GT2560 controller. The power supply is 180W. The LEDs are connected to the power supply directly, not to the controller board. They never used to flicker before (or they flickered very fast such that the flicker was not noticeable); it’s only yesterday that they started to do so. They also flicker if I switch off the heatbed completely. If I wait a bit, I can print again but soon the failure reoccurs.

Regards,
Mark

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#4

Hi Mark,

I looked up your controller: it has two circuits 10A and 15A, both protected by fuses. A mk42 heatbed (I’m making the assumption you have something similar) can draw up to 150W (when they are working properly!)

150 watts/12 volts = 12.5 amps (the bed is usually connected to the higher current output on the controller)

So, I wouldn’t think that the draw on the controller is causing a shutdown. But, as indicated above, a bed could draw 150W (though usually less). This would only leave 30W for the hot end, steppers, controller, etc. AND this is assuming that the power supply is working to specifications.

My first, best guess, is that you are overwhelming the power supply.

Two suggestions. First, lower the bed heat to 60C or less and see if the shutdowns stop (Not the best solution with ABS, I know.) Second, replace the power supply with at least 200 watts.

-Stefan

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#5

Hi again Stefan,

At 60°C the shutdowns do not occur but as soon as the extruder heats up and the printing starts, the printer turns off. What is worrying me is the smell of burnt electronics but I just cannot find where it’s coming from. Could it be any component? The stepper drivers feel cool, as well as the heatbed and extruder fuses. The heatbed MOSFET is rather hot though, and I can see that the solder around its legs has left a yellowish mark on the controller PCB.

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#6

Hi Mark,

I would imagine that the fuse on the controller would have popped before the MOSFET blew out (they do get quite hot, so that could explain the discoloration on the board). If you can, check the resistance on the heatbed. Also, can you get the printer to operate with the heatbed off? It still seems like your machine is over drawing the power supply, so let’s see if we can isolate the cause.

-Stefan

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#7

Hi Stefan,

I will check the resistance of the heatbed later. If I’m not mistaken it needs to be above 1 ohm, correct? As to operating the printer without the heatbed, I tried it for a brief period of time, but the extreme flicker (it’s very visible, similar to the rate of strobe lights if you know what I mean) in the lights indicate that there’s something wrong even with this arrangement.

Mark

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#8

Hi again Stefan. I measured the resistance of the heatbed. It’s 1.4 ohm.

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#9

Ok, 1.4 ohms is spot on. With the flickering LEDs connected directly to the power supply and the heatbed resistance where it should be, I still think your issue is with the power supply. 180W is probably too light duty for the printer.

-Stefan

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#10

OHi again Stefan,

I tend to agree with you as it was also my initial suspicion. What I still fail to explain is the fact that with the heatbed switched on (that is only the extruder and the motors), the lights still flicker a lot - something I never used to see before - and the printer still stopped.

I have a 12V 400W computer tower PSU lying around. Can it be used to power the printer or does it need to have anything special?

Regards,
Mark

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#11

Hi Mark,

Even electronics have a life cycle: so it’s possible the heavy draw on the PSU has finally tipped the scales and something has given out. Once the supply was damaged, you started getting strange behaviors. Best way to know for sure is to replace the part and see what happens.

I’m a bit out of my wheelhouse about your other question regarding the computer power supply. I know it has been done by others, but I don’t know if there are special considerations. Look around, I suspect someone out there has the answers for you.

Keep us posted!
-Stefan

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#12

Hi Stefan,

I did some research and it is clear that PC ATX power supplies with minor modifications are perfectly adequate for 3D printers, so I’ll give it a shot next week. Will keep you posted.

Regards,
Mark

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