Ramps 1.4 meltdown

Tonight the screw terminal for the heated bed melted down on my Ramps 1.4. I'm trying to figure out what may have happened in an effort to prevent it in the future. It was running a print at 220 C hot end, 100 C bed. These are the same temps I've used successfully many times before. If you have any thoughts on what may have gone wrong I'd love to get some ideas.

Thanks.

Vibration probably loosened the connection slightly. The contact resistance increases and then the connector overheats.

The power dissipated by the contact is I^2R, so with 10A the resistance of the connection has to remain at a few milliohms. At only10mR it would dissipate 1W, which is probably enough to overheat it.

Make sure the movement of the bed can't cause that end of the cable to move slightly. The slightest movement repeated millions of times will cause this sort of problem.

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I realize this is an old thread, but same thing just happened to me. Same exact terminal melted. Had an ABS print fail due to terrible warping and just thought I didn't put enough juice on the bed. Then I realized that the bed was cold. Then I remembered the burning smell from thirty minutes prior. Damnit!

My GND on the main power connector did that yesterday... maybe this is a design flaw? Now I need to find a new connector and plug... I wonder if my local electronic shop has this in stock - or does anybody know the Digikey part number for terminal and green plug?

Edit: I found some Digikey part numbers for 20A rated ones: ED2830-ND and ED2910-ND

Here is the info from the wiki, but these are on 15A:
WM7847-ND (CONN HEADER 4POS 5.08MM R/A TIN) & WM7953-ND (CONN TERM BLOCK 4POS 5.08MM R/A)

Edited 1 time(s). Last edit at 02/18/2013 03:44PM by alpha.

If you have a fast running printer which is fairly light weight, vibration is eventually going to start looostening things up. You might try the mildest loctite on the terminal screws to prevent this.

I'll add in my current issue, which is about the same. The leftmost power input on my RAMPS 1.4 board has only intermittent contact, but I can wiggle it a little to get the current flowing. Of course then it heats up and starts to melt the plug. This applies only with the heated bed turned on. I'm using an adjustable LED Strip PSU set to ~12V, not sure how many Amps it's putting through the circuit, but I presume only what the circuit is drawing. The D10 MOSFET is also heating up, like it's supposed to, though I can't tell if it's heating up more than it should.

I'm assuming that poor contact with the left pin is causing the overheat due to too much current flowing through a narrow point, so I'm going to first try cleaning off the power pin, and it looks like I should just replace the slightly-melted plug part. Thanks for the DigiKey parts numbers above, that helps.

If this first attempt at a fix fails, what components I should look at next for problems? I presume the traces on the RAMPS 1.4 PCB can handle this current.

Edited 1 time(s). Last edit at 11/12/2013 07:59PM by Thinkyhead.

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If you have a loose connection at any of the screw down terminals, you will eventually melt the connector. Everything needs to be *tight* and *clean*.

Unless your LED supply is a > 20A version at the constant voltage cut out point, it may be part of the issue. They are often set up to do odd constant voltage / constant current stuff that is LED specific.

The bed issue is fixed for now. Once everything was adjusted with the plug and power pin properly aligned it stopped overheating. But now... one of my stepper drivers died, and I believe the "Y section" of the RAMPS shield is messed up, so... yeah. I'm ordering some new stepper drivers, and I'll try using the E1 stepper position since I don't trust the Y circuit. That should be fun. I don't think the stepper driver meltdown is necessarily related to the bed power issue. I think there may just have been a short at some point and something on the RAMPS fried. Specifically, any stepper in the Y position would only move in one direction, with only a descending whining sound in the other direction. The Y motor moved fine from other stepper driver positions, even using the same driver board. Ipso facto the RAMPS board was implicated. And then the stepper driver board died. In fact the board won't boot with it installed, so it's dead.

Anyway, I'll get back to the bed power after I get this fixed or worked around.

Edited 1 time(s). Last edit at 11/17/2013 09:28PM by Thinkyhead.

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