Section 7: Batteries
HOURS. This can then be easily converted to an estimate of the battery
BATTERY
BATTERY
For example, a 100W light bulb that is used for 4 hours will use 400
Another useful rule of thumb is that the current drawn from the battery can be estimated from the AC output watts by using these same factors (10 for 12V systems, 20 for 24V systems). For example, when running an 800W microwave oven, the inverter will draw approximately 800 divided by 10 = 80A from a 12V battery.
Motors are normally marked with their running current rather than their starting current. Starting current may be three to six times running current. The manufacturer’s literature may provide more accurate information than the motor nameplate. If large motors will be started, you may need increase the battery size to allow for the high
Battery Bank Sizing Example & Worksheet
The following battery sizing example illustrates a typical calculation, assuming an opportunity to charge the batteries every three days:
Table 3: Battery Sizing ExampleAppliance | (A) | (B) | Daily watt- |
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| hours needed |
| Power | Operating Time per | for this |
| Consumption | day | appliance |
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| ( = A x B ) |
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TV & VCR | 200 W | 2 hours | 400 Wh |
Small microwave oven | 800 W | 15 mins = 1/4 hour | 200 Wh |
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3 lamps, 60W each | 180 W | 4 hours | 720 Wh |
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Coffee maker | 600 W | 15 mins = 1/4 hour | 150 Wh |
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Hair dryer | 1500W | 6 mins = 1/10 hour | 150 Wh |
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Total Daily Watt hours of AC load: | 1620 Wh | ||
x Number of Days between charges: | 3 | ||
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= Total Watt hours of AC load between charges: | 4860 Wh | ||
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Battery Ah used between charges | 486 Ah | ||
(divide by 10 for 12V system, divide by 20 for 24V system) |
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Recommended Battery Bank Size in Ah (multiply by 2) | 972 Ah |
This example illustrates how quickly your battery needs can escalate. To reduce the required battery bank size, you can either conserve energy by eliminating or reducing the use of some loads, or recharge more frequently.
Prosine 2.5/3.0 Installation & Operation Guide | 71 |