Heated bed troubles

I have a MendelMax 1.5 that is having issues. When I begin a print the heated bed responds correctly. As it is heating up, it shuts off before the proper temperature is reached. The temperature reported in the display is correct. So the thermister should be functioning properly. I have checked all of the wiring and it is fine. Could there be a problem with the Ramps or the Arduino? It almost never reaches the proper temperature before shutting off. I am confused. Any help, please. By the way, it has been working just fine for the last 12 months or so.

Milt

Edited 1 time(s). Last edit at 05/27/2014 03:28PM by mondo50m.

Every time it is stopping at a standar temperature? What temp you set, and what is it stopping temp? Try to set at a temp, that was before stoped, what happent

If I set the temp, to say, 40C it goes to 40C with no trouble. After a few minutes it will stop heating and the temp starts to drop. Sometimes it will come back on and sometimes not. I just tried to get it up to 90C, it did that just fine this time, but it would not stop heating and just kept going up, so I shut it off before it got too hot. It is as if whatever is controlling the temp, is not working correctly. It is not a problem with the bed as it heats just fine. I just feel that the problem lies in whatever is controlling it. I have another Ramps board, but, I would rather not pull everything apart until I know I need to.

Milt

In your situation , i would swap thermistor hot end, with thermistor bed, just unplug from hotend pin and plug it to bed thermnistor pins. Maybe miss operating thermistor or some connection cables.
After that, try to upload the firmware, without vhange anything and test your bed.. But maybe is miss operating atmega.

I close circuit inputs thermistors with 12 volts, and working everything fine except those two inputs!

I will give this a try in the morning, thanks for helping

Milt

Your MOSFET is probably fried, did you have a heatsink and fan on it? The one that runs the bed on ramps isn't really up to it. Mine got so hot it basically melted and then wouldn't shut down without turning off the psu. I read through a load of posts by other people who had the same problem and bought one that can handle the load and doesn't even get warm now. Try getting one of these IRLB8743PBF MOSFET, N CH, 30V, 78A, TO220

Edited 1 time(s). Last edit at 06/03/2014 05:07PM by Brainscan.

i have the same problem, it wont reach 60 C. the closest i got was 51 C and that was by starting off with 30 C then 40 C then 50 C however if i tried 60 C it wont go that high. its not a power issue as i have measured the voltage at the supply to be over 12 V. ive yet to find a way to fix it

Quote
aboyd
i have the same problem, it wont reach 60 C. the closest i got was 51 C and that was by starting off with 30 C then 40 C then 50 C however if i tried 60 C it wont go that high. its not a power issue as i have measured the voltage at the supply to be over 12 V. ive yet to find a way to fix it

How hot does your MOSFET get? If you're still using the standard one it's probably overheating and tripping the yellow fuse. Have you tried reducing the current from 255 to about 180 and add a heatsink and fan over the MOSFET and fuses. If it is getting very hot change it for the one I've mentioned above.