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.
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 | 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
Download spreadsheet: Microsoft Office xlsx | Libre/Open Office ods
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.
| 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 | 0.00 | 0 | ||||
| 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 | 1 | 1500 | 1500 | 4.0 | 0.17 | 250 |
| Induction | 1 | 0 | 3.0 | 0.13 | 0 | |
| 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 | |||||
[coming soon...]
