5
|
Function description
Wieland Electric GmbH | BA001052 (Rev. A) | 11/2018
13
The battery internal resistance (Ri) is measured by draining a defined AC current through an active load
(AL) from the battery and measuring the AC voltage drop across the load terminals. The principle is rep-
resented in Figure 6.
Figure 6 Internal resistance measurement
The measured resistance is the sum of the
battery internal resistance
, the
cables resistance
and the
con-
nectors resistance
, therefore cabling problem such as loose connectors are also detected with Ri meas-
urement.
When high capacity batteries and/or small and long cables are used, R
cables
+R
con
may be > Ri.
5.1.3
Battery charger
The battery charger supports batteries such as Lead-Acid, Nickel, Lithium and Supercapacitors. The
charging algorithm for each chemistry is given below.
The battery charger automatically reduces the current to avoid exceeding the maximum input current in
case of high current load. See no. 21 in section 6.2 for more details.
The user must set the following parameters to allow the charger to perform correctly:
•
Battery type (see no. 5 in section 6.2)
•
Battery charge voltage (see no. 6 in section 6.2)
•
Battery charge current (see no. 7 in section 6.2)
•
Battery float voltage (see no. 8 in section 6.2)
The battery charge terminates in case at least one of the following conditions are satisfied:
•
Low current:
The measured battery charge current is lower than 10% of the battery charge cur-
rent while the measured voltage is at least 98% of the battery charge voltage.
•
Timer:
the charge is terminated after the battery has been charged for a predetermined amount
of time. The value is automatically calculated by the device.
For Nickel batteries only, the following conditions are also checked:
•
Temperature Cutoff (TCO):
The battery temperature if higher than the "Battery maximal temper-
ature" minus 3 °C for more than one minute. See no. 14 in section 6.2 for more details. For ex-
ample, if the maximal battery temperature is set to 60 °C, the charge terminates in case the tem-
perature is higher than 57 °C.
•
Rate of Temperature Increase (ΔT/dt):
The battery temperature is rising at a rate equal or supe-
rior to 1 °C/min. To avoid unattended end of charge do not place the system on an ambient with
rapid changes of temperature (for example exposed to direct sunlight).
AC active
load (AL)
Battery
R
i
+
R
cables
Iac
R
con
Uac
