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Selecting a Fuse

Sizing a fuse is an application dependant process. Although each of our manuals do suggest a fuse, this may not be what is needed in you application. To find the correct fuse, calculate the input power needed to the drive, then divide that power by the input voltage to the drive. The process is detailed below.

Please note that the following calculations do not take into account inrush current. A time delay fuse is required for all Compumotor products, because of inrush current.

To calculate the power input needed for a rotary motor use the following equation. Note you must do this for continuous and peak for servo motors (See graph below).





To calculate the power input needed for a linear motor use the following equation. Note you must do this for continuous and peak for servo motors (See graph below).






If you are sizing a DC system, your work is nearly done. You have calculated the amount of continuous and peak power that your drive will require. To get the current for which the fuse must be sized for use the following equation.

I = P / V

Where P is the power calculated above and V is the DC voltage supplied to the drive. IT IS IMPORTANT TO SIZE A FUSE WITH A CURRENT RATING HIGHER THAN THE PEAK CURRENT REQUIREMENT.

If you are sizing an AC system, you must now convert your requirements (in units of watts) into units of volt-amps by dividing the value in watts by a power factor of 0.66. Again, you need to consider both continuous and peak requirements for all of your axes. The following equation will give the current required from the AC input line.
I = P / V / 0.66

Where P is the power calculated above and V is the DC voltage supplied to the drive. IT IS IMPORTANT TO SIZE A FUSE WITH A CURRENT RATING HIGHER THAN THE PEAK CURRENT REQUIREMENT.




Note: The points of the torque/speed curve that are circled are the maximum power points for a servo motor.

If you plan to use a power supply for more than one axis, you must perform the previous steps for each axis, and you must select a power supply that will satisfy the total continuous and peak wattage for all of your axes.