Problems with prints resetting, then found burned/melted power wires
So I've been printing without problems for several months, until a few weeks ago when I found that the printer would sometimes stop during a print. I never saw this, but it was as if the power had cut out, since the printer head was still on the print and the screen looked as if it was just turned on.
More recently, the printer started to turn off as soon as the heaters started up.
Today I decided to open it up and see what was wrong. See the attachments - the two power cable plugs on the RAMBO end were both melted/burned. What could cause something like this?
I plugged these both back in to see what would happen. It now can heat the nozzle but not the bed. Checked the connection of the bed heater to the RAMBO and was fine, but could not heat the bed.
Seems like something has gone very wrong here, and possibly in a dangerous way. What could cause the wires to get so hot that they melt the connectors?
How to fix my printer now?
Re: Problems with prints resetting, then found burned/melted power wires
Hello Jim!
I would recommend to use a multimeter and measure how many Ohms the heated bed has. I suspect a short circuit in the heated bed.
The heated bed should be in the range ca 1 to 1.1 Ohms.
You could also Ohm measure the fuses of the Rambo to see if they are broken.
If all seems well, we can take it from there.
/Henrik
Re: Problems with prints resetting, then found burned/melted power wires
Ok, thanks. I do have a multi-meter. I will measure when I am home later today. Thanks.
For the fuses, I suppose it is just a case of pulling them and measuring resistance across their terminals?
Re: Problems with prints resetting, then found burned/melted power wires
You probably won't get a sensible reading on a multimeter; the bed resistance is less than 1 Ohm; less than some multimeter leads...
It's unlikely that the bed is a problem; most likely cause is that the bed plug was not inserted correctly or there was a missing cable tie which allowed movement of the plug while printing.
Best solution is to discard the plug and solder the leads onto the underside of the RAMBo (there are plenty of posts here about doing this).
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Problems with prints resetting, then found burned/melted power wires
Ok - I agree it is unlikely with a short circuit in the heated bed. But the old make of the bed (2015) had a possibility of a short circuit from a copper trace to a screw to ground. That's why I suspected that.
I would recommend to bend the wires inside the box like the picture, to accomodate for movements that the wires themselves can induce into the box. Then the bend will act as a suspension and take some of the movements. Of course it is vital to zip tie the wires to the box. As well as to inspect the screws that are securing the wires to the connector regularly. High frequency vibrations will unscrew the screws over time, leading to arcing and high resistance in the connecor. An easy way to control the resistance over the connector is to measure the voltage over the heated bed when new and measure the voltage regularly. If the connector itself has high resistance, the voltage over the bed will decrease - say by a few 0.1 Volts.
/Henrik
Re: Problems with prints resetting, then found burned/melted power wires
The picture ... 🙂
Re: Problems with prints resetting, then found burned/melted power wires
Ok - I agree it is unlikely with a short circuit in the heated bed. But the old make of the bed (2015) had a possibility of a short circuit from a copper trace to a screw to ground. That's why I suspected that.
Whenever that happened, it would usually prevent the printer operating; basically pulling the 12V rail to earth. It was generally dependant on which way up the washers were placed; being stamped, they had a sharp edge one side which could cut through the insulation.
Purely mechanical joints will never be as stable as soldered joints. And the connector uses 2 mechanical joints + 1 soldered joint. A single soldered joint is usually much more reliable.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Problems with prints resetting, then found burned/melted power wires
This happens when there is a bad connection in the connector causing high resistance. Those connectors sometimes tend to be to cheap for higher current applications causing this issue. We run into those issues with the Led lighting as well.
Re: Problems with prints resetting, then found burned/melted power wires
I've just measured and I get about 1.5 ohms over the terminals of the print bed. I guess it could be an intermittent short, but I don't know how I would measure that.
If the connectors are low quality and that's why they melted/burned and the printer turned off, what would be the best course of action?
Basically, I just want to get a working printer again and to take the simplest path to get back to there.
Re: Problems with prints resetting, then found burned/melted power wires
So it sounds like the consensus is to solder the wires from the connector to the underside of the Rambo. That’s just about within my skill level. Anything else I should know before attempting this?
Re: Problems with prints resetting, then found burned/melted power wires
So I finally found some time to do the soldering (used some 3 core flex with the earth trimmed because it's what I had available):
Haven't run a print yet but it can at least get up to ABS temperature now without crashing out:
Re: Problems with prints resetting, then found burned/melted power wires
It looks to me as though that cable is not sufficient rating - you should be looking for 20A minimum.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Problems with prints resetting, then found burned/melted power wires
It looks to me as though that cable is not sufficient rating - you should be looking for 20A minimum.
Peter
I used 0.75mm² mains flex, which I assumed would be fine since the conductor was visually thicker than the wire that came with the printer.
Are you sure 20A? Not saying that you're wrong but that's a lot! For that I'd be using 2.5mm² cable - which here in the UK is to go-to for wiring in sockets in a house. That's much thicker than the 'speaker cable' type wire that came with the printer.
Is this because the voltage is only 12v so the current needs to be very high?
Re: Problems with prints resetting, then found burned/melted power wires
I used 0.75mm² mains flex, which I assumed would be fine since the conductor was visually thicker than the wire that came with the printer.
Are you sure 20A? Not saying that you're wrong but that's a lot! For that I'd be using 2.5mm² cable - which here in the UK is to go-to for wiring in sockets in a house. That's much thicker than the 'speaker cable' type wire that came with the printer.
Is this because the voltage is only 12v so the current needs to be very high?
House socket cabling is usually rated just over 15 Amps (ring, so 2 directions = 30A fuse). I thought 0.75mm^2 was lighting/5Amp rating?
Heated bed draws 15 Amps, give or take, so a 20 Amp rating allows a bit of overhead.
I used heavy duty speaker cable.
But you do need multicore and not solid... 😉
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Problems with prints resetting, then found burned/melted power wires
Yes, that's right, 0.75² flex that I used is around 6A. I don't really use this for lighting, unless I know for sure that only LEDs will be used. For lighting 1.5mm² is common in case some time traveller from the 90s puts a ton of incandescent bulbs in :-s
Thanks for telling me. I'll get some 2.5mm² or similar in there. When not surrounded by insulation that's usually rated for 27A - sensible for here.
I have a hard time believing the cables Prusa provided were rated so high. By eye they look pretty skinny.
Re: Problems with prints resetting, then found burned/melted power wires
Ebay coming through as usual 🙂 4 core rather than 2 lots of 2. I had 2.5mm² around but only in inflexible solid wire.
Re: Problems with prints resetting, then found burned/melted power wires
I have a hard time believing the cables Prusa provided were rated so high. By eye they look pretty skinny.
Yup, I queried that with Josef a while back. But that was with the Mk1 which used a 12 Amp bed. Seems they are still using the same cable for the Mk2.
The Mk3 uses 24V, so half the current...
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Problems with prints resetting, then found burned/melted power wires
Now with much thicker wires, and the printer has been running without problem for about 10 hours of a test print. Thanks for all your help! Still seems like the connectors that come on the RAMBO are poorly chosen for the job.
Re: Problems with prints resetting, then found burned/melted power wires
So in US, any flexible, solid core 15a capable wire should do?