Batteries
To calculate
(AC amps × 10) × 1.1 × hours of operation = DC amp hours * (AC watts ÷ 12) × 1.1 × hours of operation = DC amp hours * (AC VA ÷ 12) × 1.1 × hours of operation = DC amp hours * In all formulas, 1.1 is the factor for inverter efficiency.
*Divide amp hours by 2 for
**Batteries are frequently charged to 85% of full charge when charging with alternators without
Calculate the above for every AC appliance you intend to use on your inverter. This will give you the total number of amp hours used between recharges. Size your battery bank using this number as a guideline. A good rule to follow is to size the battery bank about two times larger than your total amp hour load requirement. Plan on recharging when 50% discharged.
Table 3-4 Typical Power Consumption
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Appliance | Wattage | 5 min | 15 min | 30 min | 1 hr. | 2 hr. | 3 hr. | 8 hr. | 24 hr. |
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13" color TV | 50 | 0.33 | 1 | 2 | 4 | 8 | 12 | 32 | 96 |
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19" color TV | 100 | 0.66 | 2 | 4 | 8 | 16 | 24 | 64 | 192 |
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VCR | 50 | 0.33 | 1 | 2 | 4 | 8 | 12 | 32 | 96 |
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Lamp | 100 | 0.66 | 2 | 4 | 8 | 16 | 24 | 64 | 192 |
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Blender | 300 | 2 | 6 | 12 |
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Curling iron | 50 | 0.33 | 1 | 2 |
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3/8" power drill | 500 | 3.3 | 10 | 20 |
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Icemaker* | 200 |
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| 2.6 | 5.2 | 10.4 | 15.6 | 41.6 | 83.2 |
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Coffee maker | 1000 | 6.6 | 20 | 40 | 80 | 160 |
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3 cu. foot refrigerator* | 150 |
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| 2 | 4 | 8 | 12 | 32 | 96 |
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20 cu. foot refrigerator* | 750 |
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| 21 | 42 | 84 | 126 | 336 | 672 |
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Compact microwave | 750 | 5 | 15 | 30 | 60 | 120 | 180 |
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1500 | 10 | 30 | 60 | 120 | 240 | 360 |
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Vacuum | 1100 | 7.3 | 22 | 44 | 88 | 176 | 264 |
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The number in each box represents the amp hours used (at 12 volts DC) based on various continuous run times.
* Note: refrigeration is typically calculated using a 1/3 duty cycle.