Summary

Calculating AC (alternating current) load is an activity in determining the capacity of the boat'sSecond house bank of DCDirect current (direct current) batteries. Peak load is also necessary in sizing the inverter to convert DC to AC. Over estimating the numbers to provide comfort in the individual calculations is not recommended. It is better to add spare capacity calculations directly to the inverter and house bank specifications. Do the AC load calculation first because it will provide data for the peak load. However, peak load is shown first because it is shorter, and so it won't get lost at the bottom of the page.

Peak Load

To determine the peak-load requirement divide the day into [watches] that conform to the ebb and flow of your day. Here we are using the merchant-marine watch system. You can use a finer grained system if you know that your lifestyle uses a lot of electricity at a specific time.

List the appliances and enter their power consumption in watts (WWatt) in the period when they are used. Add up each column to determine what the peak load is and when it occurs, then divide by the number of hours in the watch (4 hHour in the example) for the average. After you've identified the peak period, you might want to analyze AC usage per hour for that period to get a better assessment of the actual peak consumption.

AC Load

The AC load is based on the duty cycle of an appliance. The duty cycle is the hours it is used in a day (24 hours).

AC load is calculated thusly:

• <lesser thannumber of this appliance type>greater than * <watts rated> = <watts total>
• <hours used per day> / 24 = <duty cycle>
• <watts total> * <duty cycle> = <watts/hour>

The below table identifies many common appliances and suggests some default values. Always confirm your actuals.

Download spreadsheet

[coming soon...]