How hot does your Melzi get ?

Hi,

I've just replaced a screw terminal on by Melzi due to the heated bed connector burning out. I thought this was my fault - perhaps not wiring the heated bed power wires more securely. I've replaced the connector, checked the voltage and resistance of the bed (11.8 and 1.4 ohms) and the bed now heats up but the board is getting very hot near the connected. Too hot to keep a finger on the back of the pcb.

Is this normal ?!

Rob

I don't have a Melzi, but it sounds like either the pcb either needs to use bigger traces or have them fabricated with higher copper weight. Unfortunately neither of these things can be done to your board after the fact. If you keep having problems, you could try looking for places to solder on copper wire in parallel with the traces.

I have never noticed my Melzi getting hot. There must be something going on? Drawing a blank here though, have you checked for bits or metal or something possibly causing a short? Maybe right between the two terminals? With the melzi on i get 1.7Ω, was your measurement with or without the melzi? If with the melzi it is a lot lower, it might be a short somewhere. For instance a stray strand of copper from those wires.(lets hope in the future we'll use more plugs)

Maybe a 2Ω short could hide in the measurement error but still produce 12V*12V/2Ω = 70W (that seems awfully high) you can check by disconnecting the heated bed, and measuring across the melzi again, the resistance should then be pretty high. That said, i dont want to touch those terminals unless i need to myself, so maybe wait for someone who knows better what the issue is.

I have a melzi on a huxley.

When you say the heated bed connectors, mine just has a signal wire going to the bed. The bed doesn't pull power through the melzi.
Are you sure you have it wired correctedly ?

Mind you, I have nothing connected to the "bed" terminals. My huxley is wired as per the instructions on the reprappro site.
I have a FET on the bed, the bed wired direct to a power supply and a signal wire from the melzi to turn the bed on and off.

(hope that makes sense)

Are those bed terminals (if indeed that is what you are using) a high current path ?

cheers,

Dave

I got the same issue later on but it is much less now. It seems like the screw terminal was the issue, one wire in it seemed 'dirty'. It barely fit the screw terminal too.

So i basically re-did that wire making a new end to go into the screw terminal, that fixed the issue. Apparently it could create too much resistance in there.(this is all my case of course)