Print bed wire melted RAMPS board, what happened?

Hey guys,
Fairly new to printing (6 months) but have been able to print very nice stuff, learning a lot. My Prusa i3 kit has had me on my toes, especially this problem. Second time this has happened: the Red (positive) wire from my print bed has melted my RAMPS board where it inserts into receptacle (see picture). Both of the boards I melted were cheap ones from China, although now same problem twice, I most likely have a wiring issue. I doubled checked my wiring, seems correct. Only other thing I can think of is I'm using an 550W ATX PSU from an old computer, although I followed a diy diagram from a reliable blog explaining how to use ATX PSU for RAMPS/Atmega 2560. Plus, everything else

I don't own a multimeter because, frankly, I don't know how to use one... is this something I should purchase and learn how to use in order to figure out this problem?

I was about to order a new RAMPS board from a more reputable dealer her in the US, but thought I might post this in hopes someone might know what is going on. Plus, I might just end up frying another board, or worse!

Thanks for any help,
Richi

Prusa i3 kit (Replekio)
Repetiere Host V1.6.1
Arduino 1.6.5

ello pixel,
get a multimeter its handy to have around,
It could well be just a bad wiring moment , do you have a soldering iron, tin the ends of the wires, stop any stray threads. another culprit is the heatbed PID enabled but not configured.

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jinx
It could well be just a bad wiring moment , do you have a soldering iron, tin the ends of the wires, stop any stray threads. another culprit is the heatbed PID enabled but not configured.

Tinning the wire ends is bad advice and more or less guaranteed to cause problems. The heat due to the bed current causes the solder to creep, which makes the connection loose, son it gets hotter and burns out. The proper way to connect stranded core wire to terminal.blocks is to crimp ferrules on the ends.

If you don't use ferrules, you need to tighten the screws in the terminal blocks regularly until the creep stops.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks jinx,

I'll order a new RAMPS and start learning multimeter basics. Will also research PID since I've never paid attention to that. Here's a screenshot of my firmware settings for heated bed. Couldn't find the line to enable/turn off PID, lemme know if you see anything crazy here, i think it's all default except maxtemp.

Much appreciated,
Richi

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DC42
Tinning the wire ends is bad advice and more or less guaranteed to cause problems.

cant say I had/have any issue with tinning the ends, but I aint using massive amounts of solder either, still their no excuse for not doing a proper job either which ferrules would you suggest for those ramps connector.

Is it a normal mk2 pcb 200x200mm or something bigger?

yes, it's a general mk2 pcb 200x200mm

The simplest solution is to avoid taking the +V line for the heat bed through the ramps. It's only there to go through the poly fuse and to my mind the benefits don't merit the heating issues. I'd recommend getting an inline fuse (for example) and running a power line directly from the power supply, via the fuse, to the heatbed. Switching remains on the -V line on the ramps. Keep the -V connections from the psu to both connectors on the ramps, that helps distribute the return current over the pcb tracks and carry the current back to the psu. With this arrangement the ramps runs much cooler.

Edited 2 time(s). Last edit at 04/11/2016 08:23AM by JamesK.

What size wire were you using for the bed? You are running a computer power supply, so at 12V you were pushing at least 10A through those wires. I'm betting you had too small of wire and a bad connection. You don't just melt two sets of the same component and blame it on the boards.

While testing with my printer to find out why my thermals where being weird I had disabled thermal runaway protection, (I WAS KEEPING AN EYE ON IT DO NOT RECOMMEND) and had been running fine with for about an hour, when suddenly the flashing indicator light for the hotend went solid, and sure enough the temp rose fast and dramatically reaching 300C in no time. i quickly shut down the printer. Upon closer inspection on of the solder points on the mofset for the hotend had failed. I re soldered the mofset and has been working well for a couple moths

TLDR; check the mofset solder points

Thanks James,
that does seem like a simple solution, although I don't know what the "poly fuse" is... but if this method results in a cooler running board, I'm all for it. I'm very new to electronics, so I'm taking a bit of a chance I suppose, but I like the fact that there's a fuse on these so I'll give it a shot.

MrBaz-
I'm not sure what size of the wire, but it came with the bed, and it's 3.2mm dia... 8 gauge then?

polyfuse
those flat yellow squares on your ramps are fuses.

RAMPS required reading for new owners of RAMPS pixel,

Quote
JamesK
The simplest solution is to avoid taking the +V line for the heat bed through the ramps. It's only there to go through the poly fuse and to my mind the benefits don't merit the heating issues. I'd recommend getting an inline fuse (for example) and running a power line directly from the power supply, via the fuse, to the heatbed. Switching remains on the -V line on the ramps. Keep the -V connections from the psu to both connectors on the ramps, that helps distribute the return current over the pcb tracks and carry the current back to the psu. With this arrangement the ramps runs much cooler.

Thank you again, James. I looked a bit more online and it seems like your solution should work. Could you be so kind as to tell me how to find the proper wire coming out of my PSU? There are tons of wire, not sure which would be the best. I suppose this is where a "multimeter" will be needed, if so, what voltage am I looking for, 12V? Or, is it amps I should be looking for?
Thanks.
And appreciate all the help.
- Richi

Hi Richi,

Yes, it's a 12V wire you want, on an ATX supply these are usually the yellow ones. At the moment you should have two sets of 12V wires connected to the ramps, one to the 5A input which runs the stepper motors and hotend heater, and the other to the 11A input which is only used for the heated bed. You can remove the one that is connected to the 11A input and use that to connect to the inline fuse and then the bed. The 11A connector is the one further from the edge (they are labelled on the pcb). With an ATX supply it's generally best to use two of the yellow wires to power the bed to cope with the high current.

Awesome. So, that made sense up until you mentioned "use two yellow wires..." Does that mean I should just 'cut' an unused yel wire from the PSU, then take those two yel wires and attach to the single red Heated Bed wire? (and the blk to blk, of course)

What is currently connected to the 11A input of the RAMPS - was it just a single yellow wire? If so, then yes, take that one and add another from your unused ones. Connect both of those to the fuse, and then the fuse to the red heated bed wire. The black is going to stay connected to the ramps so that it can control the heat bed.

beautiful. Yea, just a single yel wire (had 4 ATX wires connected to PCB via connector plug).
Think i'll check out NAPA Auto Parts down the road, they might have the in-line fuse, if not I'll go online.
Thank you so much, James. I'll let you know how it turns out!

James-
your solution works great... can't beat a $5 fix. I used your dbl-yel wire idea, seems fine.

Thank you!
and thanks to others' who helped me too.

Glad it's working. Keep an eye on the fuse, they can get quite hot if the bed is running flat out, so you don't want to bury it under a pile of stuff.

Can the hotend also be wired direct from psu, returning to Ramps?

Yes, it's the same circuit so the same applies. The currents are lower so there's less need but it will still help reduce heating in the ramps. The in-line fuse would still be a good idea, a 7.5A would be about right for the hotend.

Cheers James, I have some blade holders so will get a smaller fuse for it, also found an old auto relay 12v 40A 4pin, when I scrapped my car all I got was this relay...so it makes it an expensive little bugger, I must squeeze some use out of it for sentimental reasons. I have another which is 12v 20A much larger? and many more pins(8) wonder if there's any point in using a relay with hotend(i guess not).