bed cooling

w33m4n_

hi
i want to cool my printerbed with a peltier element. is it possible to modify the firmware in such way that i can set a low temperature (for example 0°C) and the firmeware turns on the pins for the printerbed as long as it is above the target temperature?

Repetier

No, that is not supported and also makes not much sense. If you are heating you swing around target temperature. Switching between heating/cooling makes no sense here.

You could use the peltier to cool faster after print is finished to get it better of bed. For that just use the second fan feature and enable fan with M106 S255 P1. Of course a simple fan would also cool bed much faster.

w33m4n_

thank you for your answer. sorry i did not tell you about what i am trying to do. im trying to build a printer to print icecream. and i dont want to put my printer in a freezer.
i know that it is not supported. so i have to try it to change it by my self. can you tell me in which part of the firmware i can find the temperature controling of the bed?

Repetier

Bed and extruders are controlled in Extruder.cpp.

I think the easiest way is to make a own temperature curve that is inverted so that 20 is -20. So logic wants to heat for 6°C and with peltier this is freezing so temp. goes up (down in reality). So you have the same loop.

Main problem will then be that the temp. curve goes the wrong way. If the sensor is a NTC it will be the right way if we assume PTC (so that we negate this). If you use a NTC you could hijack one of the NTC curves preprogrammed so firmware works from the other side of the table.