10
20hr rating, C20 = 100Ah (rated capacity)
→
t2 = 20hr
→
I2 = 100Ah/20hr = 5A
Peukert exponent n =
5
log
15
log
5
log
20
log
−
−
=
1,26
(1)
Please note that the rated battery capacity can also be defined as
the 10hr or even 5hr discharge rate.
(2)
The 5hr discharge rate in this example is just arbitrary. Make sure
that besides the C20 rating (low discharge current) you choose a
second rating with a substantially higher discharge current.
When no ratings are given at all, you can measure your battery using a
‘constant load bank’. In this way a second rating can be obtained,
besides the 20hr rating which represents the rated battery capacity in
most cases
(1)
. This second rating can be defined by discharging a fully
charged battery with a constant current, until the battery reaches 1.75V
per cell (is 10.5V for a 12V battery or 21V for a 24V battery). a
calculation example is shown below :
A 200Ah battery is discharged with a constant current of 20A and after
8.5 hours 1.75V/cell is reached.
So,
→
t1 = 8.5hr
→
I1 = 20A
20hr rating, C20 = 200Ah
→
t2 = 20hr
→
I2 = 200Ah/20hr = 10A
Peukert exponent n =
10
log
20
log
5
.
8
log
20
log
−
−
=
1,23
To calculate the Peukert exponent with the specifications above, you can
also use the Peukert calculator which can be downloaded from our
website at www.victronenergy.com, or is part of the optional PC-link
interface kit software. (see page 23 for article number)