[Closed] Melted Terminal Block for Heater Bed  

Re: Melted Terminal Block for Heater Bed

My heatbed connector also melted. is this just due to the connector not being rated high enough or is it something more serious than just buying another connector.

cheers!

Re: Melted Terminal Block for Heater Bed

I was just having a chat to the people on #reprap and the problem is most likely that I didn't screw the terminal down tight enough (oops).

Re: Melted Terminal Block for Heater Bed

It may be but I am not sure about that. I screw that type of stuff down well. In fact the connector wires were still screwed into the connector after I removed it. The connector itself is friction based so perhaps the portion of the circuit was not tight enough. During printing you can feel that connector to see if is getting hot or not. I have ordered a new connector from Prusa Reseach and we will see if it happens again. Something to look out for and monitor otherwise your shop may burn to the ground. 🙁

Re: Melted Terminal Block for Heater Bed

What #reprap people were you chatting with? Google+ or was it somewhere else. I would like to see that thread. Also, where did you get a replacement connector or did you jimmy something else?

Re: Melted Terminal Block for Heater Bed

Hi guys, it is caused by not tightening the set screw enough. If there is not enough contact, the contact point will heatup. No worries, if you place an order with us, just contact the support and they will throw a new one in for free. 💡

OR if you are in the states, you can buy a replacement from Ulti directly 🙂 https://ultimachine.com/content/pluggable-terminal-block-2-contacts-508mm-black

There is another solution though, you can solder the heatbed wires to the PCB from the backside. We used to do that back in the day when we didn't have the electronics cover.

Re: Melted Terminal Block for Heater Bed

I just received a new terminal block and tightened the wires to it securely. I then set the Bed temp to 110 degrees C to and put my finger on the terminal as the temp rose higher. With my finger I can feel heat there at the terminal block but am not sure if that is normal.

@Prusa,
Is this normal?
Do your machines have heat at the terminal blocks of the Robomini?
I am no electrician but It seems to me the head should be focused on the be and not on the motherboard.

Thanks for any help you can provide

Re: Melted Terminal Block for Heater Bed

I just burnt up my replacement connector.

Here is a photo of the first connector which burnt up. The plastic was so burn it was crispy and just fell off exposing nothing but the metal connector.

Re: Melted Terminal Block for Heater Bed

Here are photos of what I found today. It is not as burnt as the first one but still burnt and now it won't seat properly on the motherboard.

Re: Melted Terminal Block for Heater Bed

If it helps any I noticed that the LED on my head bed no longer works so perhaps that is shorting something out or indicative of the overall problem with the bed.

Re: Melted Terminal Block for Heater Bed

To make matters worse the inside of the terminal block on the motherboard is also melted.

Re: Melted Terminal Block for Heater Bed

The conectors are rated fro 18A and 300V and are original MOLEX, basically best what you can get.

Most common cause for this is, terminals not tight enough, connector not plugged in all the way or not securing the cable to electronics cover and heatbed wiggles the connector all the time.

Best long term solution if you have problems with this, and the part on the PCB is bit "crispy", is to solder the heatbed cables directly on the back of the rambo 💡

Please not that the connectors and cables are self extinguishing, so there is no risk of fire.

You can check the connector here http://www.molex.com/molex/products/datasheet.jsp?part=active/0395300002_TERMINAL_BLOCKS.xml

If you have multimeter, can you please measure the resistance of the heated bed?

If you are in the states, you can always buy spare connectors from the manufacturer of the RAMBo mini, Ultimachine, https://ultimachine.com/content/pluggable-terminal-block-2-contacts-508mm-black they are great helpful guys 😉

Re: Melted Terminal Block for Heater Bed

What are the specs for the AMPS going those wires? Because too many AMPS are generating heat.
Also, what are the specs for resistance of the heatbed.

Re: Melted Terminal Block for Heater Bed

Heatbed resistance should be from 1 to 1,1 ohm and should take between 11 and 12Amps 🙂 So we have 6 amps spare on the connector. Connectors are one of the things I would never ever try to save money on..

Re: Melted Terminal Block for Heater Bed

I am not saying you were trying to save money on the connectors. I am trying to understand the root cause of what is causing the heat. I can rule out loose wire connectors becuase after the first one melted I was very sure to tighten those down securly. The other possibility you mentioned was that the plug may have wiggled out which it may have since the inside of the terminal block is now melted and won't seat properly and thus caused this incident. I will re-solder that joint and put the wire directly onto the board as a test. What is the current rating of the actual wire? It looks thick enough to handle it but I want to make sure.

Thanks

Re: Melted Terminal Block for Heater Bed

Today, my heated bed seems to work intermittently. It turned off during mid-print until the print job finishes. It didn't even heat up when I set the temperature manually through the settings.

Observing this strange behavior, I started to do a visual check around the printer. Then, I smelled burning rubber (around the Rambo unit). To prevent any damage, I cut the power and examined for any visible damage.

I opened up the Rambo housing and found the cable showed a sign of melted insulator near the connection to the Rambo board.

Here is a picture of the problem. NOTE: I loosened the cable to see the extend of the damage to the terminal block. Fortunately, no damage to the Rambo unit.

Re: Melted Terminal Block for Heater Bed

Yup that is my experience only the wire did not melt the terminal block did. I also experienced the intermittent behavior before discovering the melt-down. A local shop which sells the Rambo mini said he has seen the melting before on the larger board and his remedy was to get a thicker gauge wire to accommodate the load. This is why I want an answer about the Amps and if the wire provided is adequate.

Re: Melted Terminal Block for Heater Bed

I am measuring 1.3 ohms resistance on my heat bed. Is that within tolerance?

What is the amp rating for the wires?

Thanks

Re: Melted Terminal Block for Heater Bed

I just replaced the melted male terminal and cleaned out the mess in the female connector. Keeping my finders pressed against the terminal block and setting the bed temp I can defiantly feel that the terminal block is heating up as well as the bed. The block is gets too hot to the touch. It seems something is wrong. Please advise.

Thanks

Re: Melted Terminal Block for Heater Bed

I cross posted this thread on the RepRap forum.

http://forums.reprap.org/read.php?13,572157