13.3 Lead-Acid (Pb) Batteries - ROBBE POWER PEAK ULTIMATE 2 Manual De Uso

No.
Operating instructions
8470
POWER PEAK ULTIMATE 2

13.3 LEAD-ACID (PB) BATTERIES

In the world of modelling, lead-acid batteries have been increasingly superseded by
nickel-cadmium batteries, which are lighter and capable of being fast-charged. However,
as starter batteries, power sources for mobile 12-Volt battery chargers, glider winches
and drive batteries in model boats they are still indispensable.
The charge process required for lead-acid batteries is completely different to that for NC
/ NiMH batteries, as they have to be charged using constant voltage. This method of
charging is very similar to that used with Lithium batteries (see Chapter 13.4).
CHARGE RATES
Since lead-acid batteries generally have a high capacity and high internal resistance, a
method of charge limiting is only seldom necessary: it is usually possible to set the maxi-
mum charge current available. When the battery reaches its maximum voltage the char-
ge current declines, and should be halted at around 0.01 - 0.02C to avoid the battery
"gassing" (producing bubbles of gas)
CHARGING
Fast-charging lead-acid batteries is problematic, as the process raises the charge volta-
ge to 2.4 Volts per cell; this coincides with the gassing threshold, and also varies greatly
according to the ambient temperature.
CHARGE VOLTAGE
For normal discharge / charge cycling the final charge voltage can be set to 2.35 Volts per
cell at an ambient temperature of 20°C.
BATTERY POSITION
Lead-acid batteries with a gel electrolyte can usually be charged in any attitude, but lead-
acid batteries with fluid electrolytes must be kept upright when being charged.
SELF-DISCHARGE
The rate of self-discharge of lead-acid batteries is fairly low at around 0.2 ... 0.5% per day
at 20°C. This means that a fully charged battery will be completely flat after being stored
for 300 days, without it ever being placed under load. Lead-acid batteries should there-
fore be recharged every 10 - 12 months.
STORAGE
Lead-acid batteries are not critical about storage conditions; they will survive at tempe-
ratures of -15 to +40°C. It is essential to charge lead-acid batteries before storing them,
as they will be ruined if left uncharged.
USEFUL LIFE
Lead-acid batteries have a useful life of around 500 ... 1000 charge / discharge cycles,
depending on their application and the charging methods employed. After this the batte-
ry must be considered exhausted, and should be disposed of in the appropriate way.
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