Starting Watts vs Running Watts — Why Does It Matter?

Sizing for Peak Power Consumption

When sizing a generator for off-grid backup, it’s essential to consider the peak power consumption of your devices, particularly those with high starting watts. A well pump, for example, may require 5-10 times more power to start than to run, so a generator that can only provide its running watts may not be enough to get the pump started when it’s needed most. To ensure reliable operation, you should size your generator based on the starting watts of the highest-wattage device in your system, plus 10-20% for safety.

Understanding Running Watts

Running watts, on the other hand, refer to the steady-state power consumption of a device once it’s up and running. This is typically lower than the starting watts, as the device doesn’t require as much power to maintain operation. For example, a power tool might require 1,500 starting watts to get it going, but only 500 running watts to keep it running. When sizing a generator, it’s essential to consider both the starting and running watts of your devices to ensure you have enough capacity to meet peak power demands.

Calculating Total Watts Required

To calculate the total watts required for your off-grid backup system, add the starting watts of the highest-wattage device (plus 10-20% for safety) to the running watts of all other devices. For a well pump that requires 5,000 starting watts and a power tool that requires 1,500 starting watts, plus 500 running watts for a refrigerator, you would need to size your generator to at least 5,000 + (5,000 x 1.2) = 14,000 starting watts to meet peak power demands, plus 500 running watts for the refrigerator. This ensures reliable operation of your off-grid backup system and prevents unnecessary generator wear and tear.