Power fails after printing at high temperature for a longer time

[Helge 2]

I tried to print in Co-Polyester which requires high temperatures (nozzle 250-280°C, bed 100°C) on my UM2+.

After several tries, always resulting in warping, the printer stopped dead with a power failure while printing.

Ever since, the printer has a power failure, whenever I heat up the print bed.

I checked the wiring and the resistance of the bed heating.

The measured resistance of 3.3 Ohm seems reasonable for a heating element with about 165W at 24V.

The power supply provides 24V when switched on a while after the last failure. Power stays on until I try to raise the bed temperature above ambient temperature.

When experiencing a power failure, the output of the power supply drops close to zero. It seems as if the power supply suffers from an overload condition.

I just wonder if this is caused by a broken bed heating or if the power supply simply broke after that long print.

[gr5 2,072]

These power supplies are too smart - they have a little computer in them and will shut off (better than starting a fire of course).  Typically they only shut off for a fraction of a second but that's long enough for the UM2 computer to reboot.  There is both voltage sensing and temperature sensing and possibly current sensing.  I doubt it's the temperature.

 

The power supply should never do this during normal printing on a UM2 and these supplies are known for failing so I strongly suspect it's the power supply.

 

You have a few choices.  One is to spend approx 90 euros/dollars for a new supply.  There are 2 supplies sold with UM2 printers:

GST220A24-R7B
GS220A24-R7B

 

The "T" one is newer and safer and MUCH more likely to shut down on you.  I'm guessing you have the "T" one.  The non "T" supply can put out significantly more power (maybe 10 or 20% more).

 

A much cheaper option is to use firmware to limit the current.  This also can be used to diagnose if you are right on the edge of failure (in other words lower power usage by 10% and if it never fails then you were previously near the limit of the supply and it wasn't a short circuit or anything like that but just normal use).

 

Incidentally the bed uses less power at 100C because the hotter it is the higher the resistance (lower the wattage).  Overall the bed uses more but if the bed is at 100% power temporarily it will use less power if it is hotter.  Some people try to reduce these failures by setting the bed to a lower temp and the problem just gets worse.

 

So the software you want to install is the latest tinkerMarlin found here:

https://github.com/TinkerGnome/Ultimaker2Marlin/releases

 

Make sure you get the right version (um2+ has feeder rotating backwards from um2).

 

In this version of Marlin is a power budget system.  Set the bed to 150W (that's what it's supposed to be I think) and set the nozzle to 25W (if you have 3rd party nozzle such as 3dsolex then set this to what is truth - what nozzle actually is).

 

Then if you set the budget to 175W (150+25) the power budget won't do anything and the printer will work normal.  If you lower the budget to 150W then the power budget will lower the power to the bed when the nozzle is on.  This changes many times per second (adjustments of power to nozzle).  All the remaining power goes to the bed if the bed wants it.

 

So for example if you use 150/25/150 as I mention above and the nozzle is on at 50% (12.5 watts) then the bed will only be allowed 12.5 watts below budget (150-12.5 is 137.5 watts) and so the bed will never exceed 92% power at that time.  This changes 20 times per second (nozzle asking for more then less power, bed occasionally restricted a little bit).

 

[Helge 2]

Thanks for the quick response. Since I got my UM2 when it was quite new, I got the older power supply (GS220A24-R7B).

My printer did about 3400 hours of perfect printing before the issue.

The failure is permanent, so it doesn't just switch off for a fraction of a second but stays off until I unplug it and reconnect to mains.

It happened first time when printing at very high temperatures (which I usually don't do) so I suspect this to be the initial cause for the failure.

Right now, I can't get to a state where resistance increases because of higher temperature. I turn the wheel just one degree above ambient and the power fails.

I will install the software you mentioned and see if this will fix the issue.

[Helge 2]

Great, seems to be solved!

After updating the firmware and setting the power budget, the printer is able to heat up the build plate again.

LEDs flicker (they did this already, starting a while ago when printing), so I think it's the power supply that is broken in some way.

Heating slows down, but at least I am able to print until I get a new power supply.

[gr5 2,072]

Excellent.  Out of curiosity what did you set the power budget levels to?

 

[Helge 2]

With a total of 150W I am able to heat up the bed. It looked quite promising and I started the first print. When all axis are active and heating is on, the power fails again (when homing, raising the build plate and heating).

At a total of 115W a bit of movement is possible but the power blacks out after the head is in front position.

I even lowered to a total of 100W, but it seems that peaks during stepper movement are now even too much for the power supply. I see the LEDs flickering so I think that this is a sign of power instability. Switching them off didn't help either.

All together, I'm stuck with only one of the functions possible at a time.

I'll get a new power supply and will report if it worked. I'm quite positive, that it's the power supply.

[gr5 2,072]

It could be some kind of short in the wiring.  I'd give it a 10% chance. 

 

The LED flickering is normal even on a perfect power supply but maybe your flickering is worse than normal.   Supplies to indeed go bad.  It could be a damaged capacitor maybe?  A non-working capacitor would cause excess flickering of the lights (bigger voltage drops) and also why the supply would choose to turn itself off.

 

Please keep us informed.  This information is great for other people with the same problem.

 

[Helge 2]

Since all functions (nozzle heating, bed heating, bed movement, print-head movement) are working fine when executed alone, I think that there is no short-circuit in the wiring within the printer. I checked the heating coils of both bed and nozzle and they show reasonable resistance values.

Could be a degraded or broken capacitor in the power supply but there are metal shields glued on in a way that makes accessing components in the power supply nearly impossible.

I ordered a replacement already and will have a look at the broken one later on.

LED flickering got worse recently so I suspect degraded components as a cause for the issue.

I will keep you informed.

[Helge 2]

I received a replacement for the power supply today. It's a GST220A24-R7B and so I set the power budget back to:

• Total: 200W
• Buildplate: 160W
• Extruder: 35W

The UM2 now prints again like a charm. Did a few test prints with excellent results.

The previously clearly visible flickering of the LEDs is reduced beyond recognition.

It seems, as if strong visible flickering of the LEDs may be taken as a sign for a dying power supply.

[gr5 2,072]

11 hours ago, Helge said:

It seems, as if strong visible flickering of the LEDs may be taken as a sign for a dying power supply.

That would make sense, yes.

 

Great news!