Page 499 - Battery Reference Book

48/6 Taper charging of lead-acid motive power batteries
less. For example, when a 65% discharged battery of short delay is provided before the contact closes and
400 Ah capacity is connected to a 12 h Spegel charger current begins to flow. If the battery is inadvertently
for 1 h, it will receive 44 Ah of charge (Le. 11.0% of disconnected during the charging process without first
400 Ah). switching off the mains supply circuit breaker, the sup-
ply contact within the charger will open. Electrical
isolation of the exposed output terminals of the con-
48.4.1 Principles of operation of the Spegel nector is therefore provided.
charger During the switch-on delay period the open circuit
voltage of the battery is measured. The contact will
This charger operates on the well proven principle of be prevented from closing if the battery voltage lies
continuously monitoring the on-charge battery voltage outside the range of 1.8-3.4V/cell. This will avoid
and terminating the charge only when the stabilized damage if a battery of the incorrect number of cells is
conditions occurring at the top of charge are detected. connected to the charger.
The charge duration is therefore totally dictated by If the battery is not required for use it should be left
the battery and, in practice, will vary considerably connected to the charger after the main charging phase
depending on actual requirements. is complete, so that it receives periods of refreshing
The detection system employs fully solid-state charge of lOmin during every 6h to maintain its
components, and enables continuous monitoring to be condition.
achieved without interruption of the charge cycle. Spegel chargers are designed to provide a taper
The system is designed to compensate for mains characteristic, which means that the d.c. output current
voltage variation so that the battery always receives the falls as the battery voltage rises during the charge
correct amount of charge irrespective of mains supply cycle. The rated output current is delivered at a cell
fluctuation or battery condition. This is illustrated in voltage of 2.1 V at the start of charge, tapering to
Figure 48.2. 37.5% of this value at a cell voltage of 2.6V. Used
A failsafe circuit is included, which is totally in conjunction with Spegel control, this characteristic
electrically independent of the main control and pow- is suitable for all recognized makes of motive power
ered by the battery itself. This system will terminate lead-acid battery irrespective of age or condition.
charge after a fixed time from the commencement of When the charge time available has been determined
gassing at 2.35 V/cell. (7.5-1421) and the battery capacity required is known,
Following the connection of a battery and the the correct charger can be easily selected from the
switching on of the mains supply circuit breaker, a chart.

Voltage rise
constantly
monitored
Freshening
I k ~ ~ ~ ~ charge ~ ~ a g e
~
~
I h- detected at d
?
I
Battery voltage I , I topof charge y
I i I
I
I

I
I Time I I I I 1
1 White -I indicator lights 4
I
I White and flashing green '
i+ I-
Failsafe circuit '
operates indicator lights
Figure 48.2 Principle of operation of the Spegel charger (Courtesy of Chloride Batteries)