Product Manual

33
NL FR DE ES SE IT PT
EN NL FR DE ES SE IT PT
5 MORE ABOUT PEUKERT’S FORMULA AND MIDPOINT
MONITORING
5.1 Peukert’s formula: battery capacity and discharge rate
The value which can be adjusted in Peukert’s formula is the exponent n:
see the formula below.
In the BMV Peukert’s exponent can be adjusted from 1.00 to 1.50. The
higher the Peukert exponent the faster the effective capacity ‘shrinks’
with increasing discharge rate. An ideal (theoretical) battery has a
Peukert Exponent of 1.00 and has a fixed capacity; regardless of the size
of the discharge current. The default setting for the Peukert exponent is
1.25. This is an acceptable average value for most lead acid batteries.
Peukert’s equation is stated below:
where Peukert’s exponent n =
The battery specifications needed for calculation of the Peukert exponent
are the rated battery capacity (usually the 20 h discharge rate
1
) and for
example a 5h discharge rate
2
. See below for an example of how to
calculate the Peukert exponent using these two specifications.
5h rating
1
Please note that the rated battery capacity can also be the 10h or even 5h discharge rate.
2
The 5h discharge rate in this example is just arbitrary. Make sure that besides the C20
rating (low discharge current) a second rating with a substantially higher discharge current
is chosen.
A
h
Ah
I
ht
AhC
h
15
5
75
5
75
1
1
5
==
=
=
2
1
12
loglog
loglog
II
tt
−
−
t
n
ICp ⋅=