I have a reoccurring problem with my ramps board overheating when driving a heater bed.
I have a 12V 30A power supply and the resistance across my heater bed and leads is about 4.8 ohms. I buy the ramps boards off ebay: [www.ebay.com]
The problem Im having is that I keep burning up the MOSFET on the ramps board that supplies the heater bed. I see in the configuration.h file that there is a way to limit either the duty cycle to the bed and or the total current aloud to be sent to the heater bed (1-255 fashion).
So does anyone have this happening as well? I have tried restricting the current and raising the duty cycle, but then the bed wont get up to 100C or will take forever to get there. Ive tried working my way up to values that reach the appropriate temp without burning up the mosfet, but this is a pretty frustratingly slow process of trial and error. I have done the auto tune for heater bed PID constants but I believe these also depend on the duty cycle and max current constants chosen, which I haven't decided on.
Any preference to PID vs. Bang BanG?? PID seems smarter to me, but I suppose they could be essentially the same if your messing around with the duty cycle and max current constants.
also, shouldn't the fuse have tripped before the mosfet gets so hot it melts everything around it??
as you might have guessed, this is getting frustrating and expensive,
any insight would be appreciated.
thanks and merry christmas!
I have a 12V 30A power supply and the resistance across my heater bed and leads is about 4.8 ohms. I buy the ramps boards off ebay: [www.ebay.com]
The problem Im having is that I keep burning up the MOSFET on the ramps board that supplies the heater bed. I see in the configuration.h file that there is a way to limit either the duty cycle to the bed and or the total current aloud to be sent to the heater bed (1-255 fashion).
So does anyone have this happening as well? I have tried restricting the current and raising the duty cycle, but then the bed wont get up to 100C or will take forever to get there. Ive tried working my way up to values that reach the appropriate temp without burning up the mosfet, but this is a pretty frustratingly slow process of trial and error. I have done the auto tune for heater bed PID constants but I believe these also depend on the duty cycle and max current constants chosen, which I haven't decided on.
Any preference to PID vs. Bang BanG?? PID seems smarter to me, but I suppose they could be essentially the same if your messing around with the duty cycle and max current constants.
also, shouldn't the fuse have tripped before the mosfet gets so hot it melts everything around it??
as you might have guessed, this is getting frustrating and expensive,
any insight would be appreciated.
thanks and merry christmas!