Battery Sizing Example

Battery Sizing Example

This example illustrates a typical calculation, assuming an opportunity to charge the batteries every three days.

 

 

 

Daily watt-hours

 

 

 

needed for this

 

(A) Power

(B) Operating

appliance

 

Appliance

Consumption

Time per Day

(= A x B)

 

 

 

 

 

 

 

 

 

TV & VCR

115 W

3 hours

345 Wh

 

 

 

 

Sewing machine

150 W

1 hour

150 Wh

 

 

 

 

 

Bread maker

600 W

1 1/2 hour

900

Wh

 

 

 

 

 

Blender

300 W

15 min = 1/4 hour

75

Wh

 

 

 

 

 

 

 

 

 

 

Total Daily watt-hours of AC load

1470

Wh

 

 

 

 

 

x Number of Days between charges

 

3

 

 

 

 

 

 

= Total watt-hours of AC load between charges

4410

Wh

 

 

Battery Ah used between charges (divide by 10)

441 Ah

 

 

 

 

Recommended Battery Bank Size in Ah (multiply by 2)

882 Ah

 

 

 

 

 

This example illustrates how quickly your battery needs can escalate. To reduce the required battery size, you can conserve energy by eliminating or reducing the use of some loads or re-charge more frequently.

When sizing your battery, resist the temptation to skip the last step of this calculation (multiplying by 2). More capacity is better since you will have more reserve capacity, be better able to handle large loads and surge loads, and your battery won't be discharged as deeply. Battery life is directly dependent on how deeply the battery is discharged. The deeper the discharge, the shorter the battery life.

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