Possible Short in the Power to the Heated Bed

The Molex 8981 Series Power Connector (4 pin used for HDD) are certified up to 11A (http://en.wikipedia.org/wiki/Molex_connector).

What do you suggest as an alternative?

 

I used these:
http://www.mouser.com/Search/Produc...040virtualkey53810000virtualkey538-50-84-1040
http://www.mouser.com/Search/Produc...040virtualkey53810000virtualkey538-50-84-2040

With the phosphor bronze pins/sockets.

 

OK, Digikey came through and delivered the RHEF1500CT-ND Fuse and IRLB3036 MOSFET as well as replacement harnesses. It took me about 2 hrs to replace all and the printer has successfully run a new print with the heated bed. I used WM7847-ND and WM7953-ND terminals rated to 15A since as noted above I may have a "hot" hot bed due to an apparent lower ohm reading. I wouldn't mind going higher...

After the rebuild an IR thermometer read 28 deg C on the mosfet and 25 deg C on the new fuse after 5 minutes at 100 C on the bed. Warm only to the touch. Seeing the LEDs work when power is going to the extruder and bed then cycle when maintaining temp was good to see now knowing what I know and would have helped me troubleshoot initially. You can see a very bad video of that. If for nothing else you can see the LEDs cycle (I am no videographer! Like this project, the video is my first to Youtube)



I do have a Hakko desoldering gun so getting the parts out was relatively easy, but without this, using a bulb desoldering iron, or handheld vacuum "snapper" with desoldering wicks would have been a tougher proposition. Soldering everything in was a snap. Thanks for the tinning suggestions on the ends of the wires, I did do that. The 11A power line was getting to 30 C so there is juice flowing through it but I feel much better about it now. With the above temps I do believe I could run without the fan on the board, although I didn't take it off.

The existing MOSFET and Fuse were good... but... running as cool as it is now glad I replaced and all said and done, the printer was really only down for a week which is pretty amazing. Since it is the shipping that makes these inexpensive parts worth more than a replacement ramps board I ordered 2 of each so if someone is in a jam, let me know and I'll share. I would prefer it gets someone back up and running rather than upgrade an operable printer. My attempt at paying it forward to the many great contributors here teaching me how to do this and making what could be a painful experience a journey of learning.

 

I agree Ziggy. I took your advice and tinned but looking at it I agree...not enough. I also didn't touch the connectors directly to the heat bed which should probably get it as well. Thanks for the advice, hopefully what I did tin will do the trick until I clean that up.

 

Ok, I decided to take them, but 15Amp or 30Amp?

 

ok, I order the version with 30amp ...

thanks

 

My repaired bed is on its way back! woo! I have also been reimbursed for shipping.

I'll post pics of the new plug when I get it back

 

I have changed the connectors and seems to work well ...

 

As promised, pics of repaired bed. I wish the official fix included a higher amperage and relocated plug, but I guess this was the best they could do for now. I may try and source a better plug for ease of removal.

 

Can you grab a pic of said ziptie connector? is it those 3m stick on wire holders?

 

You should check all the wire and connector first.

 

for those of you that have had the connectors melt, burn, or catch on fire, it's just not the connector. it's the type of wire itself, though the wire is the correct gauge for the Amps vs. distance it's not the correct wire for the heated bed application where motion is involved. the original harness is 18/4 (18 AWG, 4 conductor) rated for 75°C but it only has 9 strands of copper in each wire which leads to a stress fracture at the crimp or the point of greatest range in motion. for the heated bed you need to replace the harness with a 18/4 that has minimal 19 strands per wire.

for those that have just replaced the connector('s) and not the wire you will still get a failure later as it will break from a stress fracture caused by the motion.

the quick fix I used to get me going till I find a better replacement was to use trailer plugs and harness, it cost me less than $4 and a couple of hours of time, it can handle the heat and amps (these connectors are rated for 80°C to 125°C depending what you choose), has a keyed connector and can handle the motion to a point, it only has 19 strands per wire and in this application it should really be using 70+ strands per wire.

p.s.
I am not an electrical engineer, but I did stay at a Holiday Inn last night. LOL

 

I had a similar issue. Was printing a 10+ hour ABS print. All was good until the last hour when I checked on the print and I found it has separated from the bed, and the bed was cold. I checked the resistance of the bed/wire by pulling the wires off where they connect to the board. No continuity. The wire had a pretty good kink in it since new, and I think the heater wires finally fatigued and broke inside the wire bundle.

I found some good replacement wire on McMaster-Carr: http://www.mcmaster.com/#catalog/120/819/=tze277 This is the continuous flex wire designed for robotics. They have a 18Ga, 4-conductor wire for $0.76/foot (part number 8082K18). I'm planning on installing it this weekend.

I bought enough to replace the wiring on the extruder as well. Maybe another day.