Section 7: Batteries

HOURS. This can then be easily converted to an estimate of the battery amp-hours that the appliance requires:

BATTERY AMP-HOURS USED = AC WATT-HOURS / 10 (for a 12-volt battery), or

BATTERY AMP-HOURS USED = AC WATT-HOURS / 20 (for a 24-volt battery)

For example, a 100W light bulb that is used for 4 hours will use 400 watt-hours (Wh) and the inverter will consume approximately 40Ah from a 12V battery, or 20Ah from a 24V battery.

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 start-up demand.

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 Example

Appliance

(A)

(B)

Daily watt-

 

 

 

hours needed

 

Power

Operating Time per

for this

 

Consumption

day

appliance

 

 

 

( = A x B )

 

 

 

 

TV & VCR

200 W

2 hours

400 Wh

Small microwave oven

800 W

15 mins = 1/4 hour

200 Wh

 

 

 

 

3 lamps, 60W each

180 W

4 hours

720 Wh

 

 

 

 

Coffee maker

600 W

15 mins = 1/4 hour

150 Wh

 

 

 

 

Hair dryer

1500W

6 mins = 1/10 hour

150 Wh

 

 

Total Daily Watt hours of AC load:

1620 Wh

x Number of Days between charges:

3

 

 

= Total Watt hours of AC load between charges:

4860 Wh

 

 

Battery Ah used between charges

486 Ah

(divide by 10 for 12V system, divide by 20 for 24V system)

 

 

 

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

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