Estimating Power Requirements



Formulas and Examples for 12 & 24 Volt DC Systems

This “Rule of Thumb” is intended as a general guide for estimating the DC amps required to operate a DC to AC inverter. Since the calculations yield approximate values, an appropriate safety factor should be considered when designing and specifying system components, such as wire size and length.

12 Volt DC Systems

  • Formula: 12 volt inverters require approximately one (1) amp of DC input for each 10 watts of AC output.
    Example: How many DC amps will a Vanner 12 volt inverter require to operate three 500 watt quartz lights, or a 1500 watt electric heater?
    Answer: 1) Total watts = 1500
    2) 1500 watts/10 (from formula) = 150 amps

This is the DC current the inverter will use to operate the 1500 watt load.

Note – if this 150 amps is drawn from the battery for one hour, 150 amp hours (AH) of battery power will be used. To support 150 amp hours of battery power, 300 amp hours of battery capacity is required.

24 Volt DC Systems

  • Formula: 24 volt inverters require approximately one (1) amp of DC input for each 20 watts of AC output.
    Example: How many DC amps will a Vanner 24 volt inverter require to operate three 500 watt quartz lights, or a 1500 watt electric heater?
    Answer: 1) Total watts = 1500
    2) 1500 watts/20 (from formula) = 75 amps

This is the DC current the inverter will use to operate the 1500 watt load.

Note – if this 75 amps is drawn from the battery for one hour, 75 amp hours (AH) of battery power will be used. To support 75 amp hours of battery power, 150 amp hours of battery capacity is required.

Average Wattage Ratings of Products Operated from Vanner Inverters
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WATTAGE
TYPICAL PRODUCTSMINMAX
AIR CONDITIONING, 9000 BTU11002200
AIR CONDITIONING, 13,500 BTU
18003500
AIR CONDITIONING, 16,000 BTU22004500
BLENDER200800
BROILER12001800
CARVING KNIFE95
CAN OPENER100150
Clock
2
CLOTHES DRYER4900
CLOTHES WASHER5255000
COFFEE MAKER5001500
CORN POPPER575
CURLING IRON40






Average Wattage Ratings of Products Operated from Vanner Inverters (Cont.)
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WATTAGE
WATTAGE
TYPICAL PRODUCTSMINMAXTYPICAL PRODUCTSMINMAX
DEEP FRYER1200KNIFE SHARPENER40
DEHUMIDIFIER650MAKEUP MIRROR20
DISHWASHER9001200MICROWAVE OVEN8001600
DISPOSAL4501500MIXER80150
DRILL2501500PERSONAL COMPUTER150350
ELECTRIC AIR CLEANER50PIPE THREADER1500
ELECTRIC BLANKET100250PLASTIC PIPE ELECTRO FUSION14003900
ELECTRIC KNIFE100RADIO25
ENGINE HEATER750RANGE12200
FAN - WINDOW200REFRIGERATOR3001625
FURNACE FAN400SHAVER3075
FLOOD LIGHTS3002000SLOW COOKER200
FREEZER450800SPACE HEATER1500
FRYING PAN10001500STEREO SYSTEM50400
GRINDER10001500TV - BLACK & WHITE50100
HAIR DRYER5001500TV - COLOR75200
HAIR ROLLERS350TOASTER10001400
HEATING PAD60TRASH COMPACTOR400800
HOT PLATE 1251500VCR3575
HOT WATER DISPENSER5001400VACUUM CLEANER - HOME400900
HUMIDIFIER200VACUUM CLEANER - SHOP8401380
ICE CUBE MAKER250300WATER HEATER4500
IMPACT WRENCH900WATER PUMP1000
IRON6251200

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INDUCTION MOTORSSTARTING WATTSRUNNING WATTSNotes:
1. The electrical power consumed by an electrical device is measured in watts. This information is essential to proper inverter selection. Wattage may be found on the appliance nameplate or by multiplying the AC voltage (120 volts) by the running current (amps).

2. The wattage required to start certain motor driven loads could be 3 to 10 times their normal running wattage. The starting watts for a motor are obtained by multiplying the locked rotor current by the AC voltage.

3. Induction Motor running watts obtained from the National Electric Code Handbook. The above power ratings should only be used as a guide.
1/4 HP750 - 1500700
1/2 HP1500 - 30001175
1 HP3000 - 60001950
2 HP4000 - 80002900

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