Heatbed gets too warm.

Hi!

I have just completed bulding my huxley an everything works fine exept for the heatbed. As soon as I connect the power supply the heatbed begins to heat without me sending a "heat" command in pronterface or repetier. It just keeps going hotter and hotter, The temp is correctly reported in both pronterface and repetier ( I have used a thermometer to check) so my first thought was to install a new firmware, that did not help. Also the LED on the bed does not light up.. Any ideas?
Thanks.
//Tobias

Looks like you mis-wired it. Apparently the bed gets juice as soon as the PSU is turned on. It should get juice only through the MOSFET.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thanks! I had apperently reversed the polarity :/ (bows down in shame)

Hi,

I have a mk2a heatbed @ a sanguinololu 1,3 a. I've the same problem as described above. There is Power running trough the MOSFET. Anyone an idee what this can be? Steppers and heatend work just fine

Tom

Have you made sure that the polarity on the heatbed is correct? Otherwise the heatbed will get full power all the time.

Hmm. So far I considered heatbeds to be a simple resistor, so I don't see how polarity makes a difference. The mk2a layout file in the wiki shows up without traces, though, so I can't be sure.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Don't you have a small mosfet on the heatbed?

I have a similar problem, my heatbed AND hotend just start heating as soon as the power is turned on and don't stop. The temperature rise is reported in pronterface but seems to lag behind the real temperature (that i measure with a multimeter). It goes straight past whatever temperature I try to set it at, only stops heating when I unplug the power supply. I tested the voltage on the Mosfet pin and it says 4.15V. The polarity of the power leads to the heated bed is correct as far as I can tell. The light comes on on the bed when the bed is heating.

Another problem is the y-motor doesn't respond to commands, the motor works when plugged into the other sockets... probably unrelated.