ElectricalCapacityAC


Calculating ACAlternating current Electrical Capacity

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.

AAmpere (amp), SI unit of electrical current link to a #spreadsheet is provided.

See also ElectricalCapacityDC.

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.

The peak load period might be a good time to run the generator to recharge the house bank.

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 — or, you might want to analyze AC usage per hour for that period to get a better assessment of the actual peak consumption.

Watch Period:0000 - 0004 (w)0004 - 0008 (w)0008 - 1200 (w)1200 - 1600 (w)1600 - 2000 (w)2000 - 0000 (w)
       
e.ggram., Toaster 1500  1500 
       
Total:      

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. OK Solar also has some typical energy consumption for different devices. Always confirm your actuals.

ITEM NUMBER WATTS WATTS
TOTAL
HOURS
PER DAY
DUTY
CYCLE
WATTS
PER HOUR
LIGHTING & SMALL APPLIANCES
Blender 1 300 300 2.0 0.08 25
Breadmaker 1 600 600 6.0 0.25 150
Coffepot 0 200 0 3.0 0.13 0
CoffeeMaker 1 800 800 3.0 0.13 100
Computer
Laptop computer 0 50 0 6.0 0.25 0
Desktop computer 0 250 0 6.0 0.25 0
Printer 0 100 0 0.5 0.02 0
Electric frying pan 0 1200 0 1.0 0.04 0
Waffle Iron 0 1200 0 0.4 0.02 0
Drill 1/2" 0 750 0 0.00 0
Drill 1" 0 1000 0 0.00 0
Circular saw 8-1/4" 0 1400 0 0.00 0
CD Player 0 35 0 0.00 0
Hot plate 0 1200 0 0.00 0
Deep fryer 0 1500 0 0.00 0
Pressure cooker 0 1000 0 0.00 0
Curling Iron 1 50 50 1.0 0.04 2
Hair Dryer 1 1250 1250 1.0 0.04 52
Shaver 0 15 0 0.3 0.01 0
Kettle 1 1500 1500 3.0 0.13 188
Microwave 1 1500 1500 5.0 0.21 313
Toaster 1 1200 1200 3.0 0.13 150
Outlets
Engine Room 1 1500 1500 1.0 0.04 63
Pilot House 1 1500 1500 1.0 0.04 63
Heads - GFC 2 1500 3000 2.0 0.08 250
Port Berth 1 1500 1500 1.0 0.04 63
Starboard Berth 1 1500 1500 1.0 0.04 63
Galley 4 1500 6000 1.0 0.04 250
Dinette 1 1500 1500 1.0 0.04 63
Salon 4 1500 6000 1.0 0.04 250
Aft Cabin 3 1500 4500 1.0 0.04 188
SubTotal 1954
MOTORS & HEATERS
Air Compressor 0 0 0 0.0 0.00 0
Battery Charger 0 0 0 0.0 0.00 0
Exhaust & Supply Fans 0 0 0 0.0 0.00 0
Air Conditioners 0 0 0 0.0 0.00 0
Water Heater 1 4000 4000 4.0 0.17 667
Electric, gas or oil Heaters 0 0 0 0.0 0.00 0
25%percent of Largest Motor 1 0 0 0.0 0.00 0
SubTotal 667
BUILT-IN APPLIANCES
Clothes
Clothes Dryer 0 1300 0 3.0 0.13 0
Clothes Washer 0 500 0 3.0 0.13 0
Clothes Dryer/Washer Combo 1 1300 1300 3.0 0.13 163
Dishwasher 1 1500 1500 3.0 0.13 188
Disposal 0 450 0 0.00 0
Freezer 0 0 0 0.00 0
Vacuum cleaner 0 700 0 0.00 0
Ice Maker 0 200 0 0.00 0
Oven 0 0 0 0.00 0
Refrigerator 0 750 0 8.0 0.33 0
Stove Top
Induction 1 2600 2600 4.0 0.17 433
Halogen 0 0 0.00 0
Coils 0 0 0.00 0
Solid Disc 0 0 0.00 0
Towel Rail 5 100 500 0.50 250
Trash Compactor 0 0 0 0.00 0
TVTelevision 1 1500 1500 0.25 375
Vacuum System 0 0 0 0.00 0
Other 0 0 0 0.00 0
SubTotal 875
FREESTANDING RANGE
Load Watts 0 0 0 0.00 0
SubTotal 0
TOTAL 3496