HIGH DISCHARGE RATES & PEUKERT'S EQUATION

EXPONENT

The table below may be used to understand the effect of high rates of discharge on available battery capacity. It may also be used to estimate the exponent "n" for a battery after a single discharge test. The table is based on a 100 Ah battery but may be used for any capacity battery by using an appropriately scaled current. See the examples below:

PERCENTAGE OF AVAILABLE CAPACITY FROM A 100 Ah BATTERY AT DIFFERENT DISCHARGE RATES USING DIFFERENT PEUKERT'S EXPONENTS

 

 

DISCHARGE RATE IN AMPS

 

 

n

5

10 16.7

25

50

75

100

150

200

250

300

400 500

1100 100 100 100 100 100 100 100 100 100 100 100 100

1.1 100 93 88 85 79 76 74 71 69 67 66 64 63

1.2 100 87 78 72 63 58 55 51 48 46 44 42 40

1.25 100 84 74 67 56 51 47 42 40 37 36 33 32

1.3 100 81 69 62 50 44 41 36 33 31 30 27 25

1.4 100 76 61 52 40 34 30 26 23 21 20 17 16

1.5 100 71 55 45 32 26 22 18 16 14 13 11 10

Example #1: Assume you have a 200 Ah battery and discharge it at the 50 amp rate until the battery reaches

1.75V per cell (10.5 V for a 12 V bat- tery). This is equivalent to a discharge rate of 25 A for a 100 Ah battery. If the battery delivered 67% (134 Ah) the appropriate Peukert's exponent would be 1.25.

Example #2: A 100 Ah battery with a Peukert's exponent of 1.3 will deliver only 41% of its capacity when supplying a 100 A load.

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