Marquette Hellige GmbH
MicroSmart V 2.xx
Page 12
Servicing Instructions 227 470 35 B - 97.12
Battery charge
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Uin
GND
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Uout
Battery charge
Current query
X501
T500
The battery is charged by means of a special charging IC (UC3906) for lead batteries. The circuitry
monitors the charging current and the charge voltage. The charging IC has the same "temperature
coefficient" as a lead battery, with the effect that the battery charge is optimized over the specified
temperature range. The circuit operates as a "DUAL LEVEL FLOAT CHARGER", with three
distinct charging states:
- high current bulk charge state
- over-charge state
- float state
A charging cycle begins with "high current bulk charge state". In this state the battery is charged
with a constant current ( Imax ) while the battery voltage is monitored. The "over-charge state" sets
in as soon as a certain voltage value ( U12 ) is reached. In this state the battery voltage is kept at
a certain value ( UOC ), while the charging current is monitored. If the charging current drops to
a certain value ( IOC ), the "float state" sets in. At this point in time the battery capacity has risen
to almost 100%. In the "float state" the battery voltage is regulated to a precise value ( UF ).
The following values for voltage and current are selected when charging the 12V lead battery:
Imax = 250mA
U12 = 13.5V
UOC = 14.2V
IOC =
25mA
UF
= 13.7V
