Food Trucks and Generators

Generator Calculation for Mobile Applications

This page is intended to help calculate the needed power (in Watts) that a Soft Serve or Frozen Beverage machine needs when running off of a mobile generator. When running off “shore” or building power (with unlimited reserve), the LRA can usually be overlooked.

To calculate the correct power supply needed for a machine, you will need the LRA, or Lock Rotor Amperage, for the given primary compressor in the cooling system. Realistically, any other power demands (e.g. drive motors, auxiliary compressor, etc.) will either not be occurring at the same time as the primary compressor, or are too small to worry about. The primary compressor is by the far the largest power demand, and is what should be used when calculating the power supply.

When an electric motor starts spinning from a stop, it pulls significantly more power to get the rotor (output shaft) spinning quickly. Once the motor is up to full speed it will draw much less power; this is called the RLA, or Running Load Amps (or: Rated Load Amps). The running amp draw will vary with the load (demand) placed on motor, but regardless, it is a much lower power consumption overall and should not be used as the basis for this calculation.

Once you have the LRA, you simply need to multiply the Voltage rating by the LRA to get the required Watts. Most generators will be rated in Wattage (e.g. 10,000W generator) so this is what we’ll use.

Example 1: Model SM-6250H

  • Voltage rating @ 220V
  • LRA listed @ 55 Amps for primary compressor
  • 220V x 55LRA = 12,100 Watts.

It’s safe to say that 15,000W generator will be required to run this application, allowing room for overhead power consumption. A 12,000W generator would not safely work for this application.

Example 2: Model SM-6210

  • Voltage rating @ 110V
  • LRA listed @ 33 Amps for compressor
  • 110V x 33LRA = 3,630 Watts

A 5,000W generator, or 2 x 2,000W generators run in parallel, would work safely for this application.