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The main display window always shows whether a particular channel is actively working, and which
process is being carried out. A channel LED is also located above each pair of output sockets; the
LED glows constantly when its associated channel is working actively. When the process is concluded,
the LED lights up briefly every 1.5 seconds. If the process is terminated in an emergency situation,
the LED flashes at a high rate.
5 Battery capacities, charge power, currents
Charge channels 1 and 2 are designed for use with batteries whose nominal capacity is in the range
200 mAh to 200 Ah, while charge channels 3 and 4 can work with nominal capacities of 40 mAh to
200 Ah. The essential performance data relating to the ALC 8500-2 Expert is summarised in Table 1
(Chapter 1.1), but please note that the specified performance for NC and NiMH batteries is not based
on the nominal battery voltage, but on a cell voltage of 1.5 V. A micro-controller is used to manage
the available power.
All four channels of the ALC 8500-2 Expert are capable of carrying out different processes simultane-
ously. However, if the required power exceeds the specified performance data of the ALC 8500-2
Expert, then the processing occurs sequentially. The screen then displays the message "waiting for
power", and the process does not start until another channel has ended its process, and the requisi-
te power is available again.
6 Battery Ri measurement function
When assessing the quality of rechargeable batteries, the pack's internal resistance is particularly
important in addition to its capacity. High internal resistance has a negative effect especially in high-
current applications, i.e. the voltage declines at the battery itself, and energy is converted into waste
heat. If the voltage collapses under load conditions the battery appears to be flat, although a useful
quantity of residual energy may still be present.
A battery must be at a defined state of charge if its internal resistance is to be determined, and as a
basic rule the pack should be virtually fully charged before carrying out the measurement. If you wish
to compare different cells it is especially important that they should be at the same initial state of
charge.
If abrupt voltage collapses occur when a battery is being discharged, this is a very clear indication
that there is a variation in capacity of the individual cells, or that one or more cells are already dama-
ged. If a pack in this state continues to be discharged, the result may be polarity reversal and further
damage to the affected cell or cells. In contrast, accurately selected cells always produce highly reli-
able battery packs which have a particularly long useful life.
For these reasons it is essential to use identical cells when assembling a battery; there should be no
different cells in the pack, and certainly no cells of different capacity. The more accurately you select
the cells, the better the battery pack, and the longer it will last.
It is often impossible to determine the state of ageing batteries accurately simply by measuring their
capacity; checking their internal resistance at a defined state of charge gives a much more accurate
basis for assessment. Internal resistance is certainly the most useful criterion for determining a battery's
maximum load capacity. Typical values with very high-quality sub-C cells are in the range 4 mOhm to
6 mOhm.
The battery's internal resistance is responsible for voltage losses in any battery-operated system, but
it is not the only culprit: parasitic transfer resistance, caused by cables and connectors, is always
present. These values can also deteriorate considerably in the course of time through oxidation at
connector contact surfaces or screwed electrical connections, and under heavy current loads this
additional resistance can cause considerable voltage losses at the power supply.
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