### How to Calculate Heat Generation from Controllers/Drivers

Posted:

**Wed Mar 21, 2012 6:10 pm**Q: I'm trying to size an enclosure for your step motor drivers and controllers. I looked through your literature, and I cannot find anything regarding heat generation of your drivers and controllers. How can I calculate this?

A: You are correct that we do not show this specification in our literature. We do show, in our manuals, installation instructions for the space requirements of the driver, and we recommend natural ventilation as the cooling method. This means we would suggest a ventilated enclosure that's big enough to house our drivers and their space requirements, and that you have the option to provide forced ventilation with a fan if needed. This would be difficult to calculate because it's specific to the application's motor current setting, motor operating speed, and duty cycle.

We would suggest that you take the difference between input power and output power in order to estimate the heat generation in watts.

For the input power, you'll need to find the input voltage and input current for your motor and driver. The input voltage for our drivers and controllers are listed in our specifications. For the input current, I would suggest that you look at the speed-torque curves for the motor because input current is affected by the operating speed of the motor. For most of our products, an input current curve is also included in the speed-torque graph which will tell you how much current the motor will draw from the power supply at specific speeds. You would estimate this value at your specific operating speed, then multiply it by the input voltage of the driver or controller to calculate your input power in watts.

From the same speed-torque graph, you will also need to estimate the torque generated by the motor at your specific operating speed. You will need this for your output power calculation.

For the output power, I would refer to the following formulas:

HORSEPOWER = TORQUE (oz-in at motor operating speed) X SPEED (motor's operating speed in RPS) / 16800

1HP = 746 WATTS

So, WATTS = TORQUE X SPEED / 16800 X 746

INPUT POWER - OUTPUT POWER = POWER LOSS (watts)

A: You are correct that we do not show this specification in our literature. We do show, in our manuals, installation instructions for the space requirements of the driver, and we recommend natural ventilation as the cooling method. This means we would suggest a ventilated enclosure that's big enough to house our drivers and their space requirements, and that you have the option to provide forced ventilation with a fan if needed. This would be difficult to calculate because it's specific to the application's motor current setting, motor operating speed, and duty cycle.

We would suggest that you take the difference between input power and output power in order to estimate the heat generation in watts.

For the input power, you'll need to find the input voltage and input current for your motor and driver. The input voltage for our drivers and controllers are listed in our specifications. For the input current, I would suggest that you look at the speed-torque curves for the motor because input current is affected by the operating speed of the motor. For most of our products, an input current curve is also included in the speed-torque graph which will tell you how much current the motor will draw from the power supply at specific speeds. You would estimate this value at your specific operating speed, then multiply it by the input voltage of the driver or controller to calculate your input power in watts.

From the same speed-torque graph, you will also need to estimate the torque generated by the motor at your specific operating speed. You will need this for your output power calculation.

For the output power, I would refer to the following formulas:

HORSEPOWER = TORQUE (oz-in at motor operating speed) X SPEED (motor's operating speed in RPS) / 16800

1HP = 746 WATTS

So, WATTS = TORQUE X SPEED / 16800 X 746

INPUT POWER - OUTPUT POWER = POWER LOSS (watts)