Yes, RAMPS has 2 inputs for voltage.
The 5A input runs the motors/hot end (D10)/switched fan (D9) outputs and your Arduino.
The 11A input runs the heated bed (D8).
The heated bed draws the most current, so if you're having issues when it's on (eg: fan slowing down), this means the voltage is dropping when it's in use. If you're using the same PSU rail for the motors, this will reduce the voltage being given to the motors, which could make them to miss steps occasionally.
Questions:
How are you getting the power out of the supply and to RAMPS (a pic might be best)?
Have you placed a load on the 5V line (eg: a 10 ohm resistor) of the PSU?
Where are you running the fan for the hot end from (D9, or constantly connected to the PSU)?
The 5A input runs the motors/hot end (D10)/switched fan (D9) outputs and your Arduino.
The 11A input runs the heated bed (D8).
The heated bed draws the most current, so if you're having issues when it's on (eg: fan slowing down), this means the voltage is dropping when it's in use. If you're using the same PSU rail for the motors, this will reduce the voltage being given to the motors, which could make them to miss steps occasionally.
Questions:
How are you getting the power out of the supply and to RAMPS (a pic might be best)?
Have you placed a load on the 5V line (eg: a 10 ohm resistor) of the PSU?
Where are you running the fan for the hot end from (D9, or constantly connected to the PSU)?