5.5 Evaluation function Diagnosis
The “diagnosis” menu enables an evaluation of the status of the battery in respect to
state of health (SoH, capacity) and state of charge (SoC).
The battery states are determined by indirect measurements which use the following
relations:
a) The open circuit voltage (OCV) is dependent on the state of charge (SoC)
This relation is specific to the battery technology and is stored as a internal table
in the instrument. The measured voltage is automatically transformed into the
SoC and displayed as a relative value.
b) The internal impedance (R
AC
) increases with decreasing capacity / SoH
For an estimation of the state of health (SoH) it is common to apply rules of
thumb: a 20% decrease of capacity is indicated by a doubling of the internal re-
sistance. These relations are stored in the instrument
.
The capacity (SoH) is displayed qualitatively: the longer the bar, the higher the ca-
pacity. The color of the bar indicates a rating:
green: good
yellow: usable
red: unusable
For more accurate results, individual tables can be stored in the instrument.
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