Out of control heating

Running a prusa i2 with printrboard, pins that the extruder power plugs into overheated and the plastic connector melted.
Have replaced connector but now out of control heating happens even when I have extruder set to off. Thermistor still functions.

I recently upgraded from a standard jhead with resistor to e3d5 with heating cartidrige with same results.

Anyone know solution? And even a solution to the bed heater and extruder pins overheating would be nice, I have tried aiming a 40mm fan at the spot which helped but shouldn't be a permanent solution

Thanks

Edited 1 time(s). Last edit at 02/06/2014 08:03PM by jasperash.

Sounds like the mosfet that controls the extruder is toast. When they go bad they often short causing it to be 'on' all the time. Just Google your board and extruder mosfet to find which one it is and decide if you want to try and fix it or just replace the board. Just an fyi, when they go bad, they sometimes take other components with them so replacing just the mosfet may or may not fix it but they should be cheap if you are comfortable with replacing it.

thanks, i dont notice anything else overtly wrong, the 4 pin connector its associated with, 2 outside pins are a little toasty looking but still put out power, im assuming that means only the mosfet may be bad?

Well, maybe. The chip that drives the mosfet could also go bad.

OI had this issue with my Ramps 1.4 board after accidentally shorting the nozzle heater circuit at the hot end. It blew out the trace on the Ramps 1.4 board and I thought all was well after soldering in a wire jumper. I turned on the board and the nozzle heater was stuck on. I swapped out the mosfet for the fan/second nozzle mosfet and it works fine.

You blew your heater mosfet.

Thanks, bought a 10pack and waiting for delivery,

Ah 3d printers, a hole on your desk you pour money into

@umdpru:
"shorting the nozzle heater circuit at the hot end"

Would a fuse on the heater have helped, or not applicable?

I really just think it over heated and blew, the pins on the molex connectors had actually melted the connection, other than an active cooling on the molex or mosfets I don't know any other solution, I can't be the only one running a printrboard that's had this issue before

Would something like this circuit work?

[www.digikey.com]

Or how about soldering one of the leads of the thermistor onto the board, bridge, (i.e. bypass) the molex connector,
and solder the other end to the lead going to the heater cartridge.

NTC thermistors can be used as inrush-current limiting devices in power supply circuits.
We can use PTC thermistors as current-limiting devices for circuit protection, as replacements for fuses.
[www.electronicshub.org]

limiting of current surges with NTC and PTC thermistors
[www.amwei.com]

Inrush current limiter
An NTC thermistor's resistance is high at low temperatures. When the circuit is closed, the thermistor's resistance limits the initial current. After some time current flow heats the thermistor, and its resistance changes to a lower value, allowing current to flow uninterrupted. It is inherently impossible for 100% of supply voltage to appear on the protected circuit, as the thermistor must continue to dissipate power (producing heat) in order to maintain a low resistance. The resulting voltage drop from the operating resistance, and the power consumption of the thermistor must be taken into account.
[en.wikipedia.org]


[www.soselectronic.com]

Edited 2 time(s). Last edit at 02/12/2014 03:02AM by A2.

ok so an update
i got an electrician co-worker to solder in a new mosfet for the hot end, i made sure it was the same part, but am still having the same out of control heat problem

so my new question would be for my printrboard could i switch some settings around so that i use the heated bed port for the hotend, and just not have a heated bed? so the board would only be able to print pla so to speak?