a cautionary tale

i run a printerboard
came home last night to my 4pin connector that powers my heat bed burned out, i found that the connection overheated, some jury rigging later i now have a 40mm fan mounted aimed at the HB and Extruder connections to keep extra cooled

if anyone else has seen this please spread the word unless its already known and im now a statistic...........stay calm and keep printing

I had to swap out some of the power plugs for screw terminals onmy ramps the other day, if you smell burning plastic or hot wires, check your connections.

You can also connect the + from your hot bed directly to your power supply. That way its only the ground going through your ramps ( which is the part switched by the ramps). As the ground are connected together the load is shared between 2 connections on the power plug.

Did you buy your printrboard from Printrbot? If so I would contact them and let them know what happened. They have always been super helpfull to me. I agree that you should try and connect directly to the power supply and the ground through your board. I currently use an xbox power supply the 203 watt one. It works great running everything including a 8x8 heated bed. Everything heats up quickly and it has great power protection. Ive never had my wires heat up or melt at all since ive been using it. Ive used the xbox psu on 3 or 4 builds and I highly recommend them. I also have info on my WordPress blog on how to modify it. Good luck buddy.

---

--------------| For Everything |--------------------------
Check it out here:
[reprapsquad.wordpress.com].
---------| For Everything Prototype Related |------
Now featuring comp case mods:
[RepRapLab.wordpress.com]

--------------| Find us at Twitter|------------------------
@REPRAPSQUAD (RS Main)
[mobile.twitter.com]
@REPRAPSQUADHQ (ProtoLab)
[mobile.twitter.com]

This is usually due to not enough contact area.

You need to properly crank down on the connector, and make sure you have FULL contact.

If the actual contact is only a strand or 2 of wire, the full current goes through those small wires and overheat.

I crank down on the screw, wiggle the wire a bit, and crank down on it some more. Repeat that a few times to ensure good contact.

Since the heated bed consumes rather a lot of power (10A at 12V is 120W) and the tracks (and connector) on the Printrboard seem a little bit puny to carry this sort of load, I've been wondering whether it might be a better idea to use the heat bed output on the Printrboard to switch a relay and let that carry the hefty current. The downside to this is that you'll effectively be limited to simple on/off (rather than duty-cycle) control but given the thermal lag of most heated beds this shouldn't be an issue as long as your power supply and wiring can handle the continuous current.

Connecting the bed directly to a power supply is a very bad idea as you won't be able to control the temperature and the bed will most likely heat up to the point where it catches fire or at the very least burns itself out.

I'll let you know how I get on using relay control once I get around to fitting my heated bed - right now I'm still struggling to get everything else working right

Quick update;

After readuing a few horror stories about Printrboard tracks burning out as a result of the extra current drawn by the heated bed, I decided to install a relay system as I mentioned in the above post, and it's working really well.

I used an SPST car headlamp relay rated at 40A (the heated bed draws around 10A so no there shouldn't be any issues with contact burning or anything like that). I have it wired to the heat-bed output on the Printrboard

IMPORTANT:
Don't forget to solder a rectifier diode - I used an old 1N4001 that I had in my spares box but almost and kind of power rectifier diode will work fine here - across the relay coil terminals, with the cathode end connected to the +12V connection, to soak up any back-EMF generated by the relay coil that could, in theory, damage the output MOSFET on the Printrboard. If you're not sure how to do this, then dont attempt it as getting this diode the wrong way round will likely fry the diode and the Printrboard itself.

The clicking on and off of the relay can get a bit distracting but as I'm only printing PLA at the moment I normally turn the bed off after a few layers have been laid down - it's just there to help the first couple of layers stick properly.

Another thing I did (since I'm running the printer now with a 500W ATX power supply) was to wire up a pair of Molex connectors to supply power to the relay (and thus the heated bed) directly from the PSU rather than draw it from the Printrboard. I have two seperate Molex cables from the PSU connected in parallel via these connectors to ease the current load on individual (in my opinion rather thin) cables. I know this is probably overkill but I like to over-engineer things a lot - I spend a lot of time repairing other peoples' gear but I hate having my own stuff give trouble

I also tapped off this power connection to supply power to the 40mm fans on my X, Y and E motors, as well as the one cooling the extruder assembly.