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6 | SAMLEX AMERICA INC.
SECTION 3 | General Information
3.1 DESCRIPTION
SunChargers SC-05 and SC-10 are portable solar panels designed for float charging of 12V
nominal rechargeable Lead Acid batteries like those used in cars, boats, RV’s, motorcycles,
All Terrain Vehicles (ATV) and Powered Water Crafts (PWC). These can also be used as DC
power sources to charge small electronic devices like cell phones, iPods, iPhones, PDAs etc.
The rechargeable batteries inside these small electronic devices are charged through their
charging adapters.
The panel float charges the battery directly through built-in Blocking Diode (Forward Voltage
Drop, V
f
= 0.55V). External Charge Controller is not necessary (see Section 5.2)
3.2 SELF DISCHARGE AND TRICKLE CHARGING OF LEAD ACID
BATTERIES UNDER STORAGE
3.2.1 Sulfation Due to Under Charging: A fully charged Lead Acid Battery comprises of
(i) Positive Plates: Lead Dioxide, (ii) Negative Plates: Sponge Lead and (iii) Electrolyte:
Mixture of 65% water and 35% Sulfuric Acid with Specific Gravity = 1.265 at 80°F. During
discharging, electro-chemical reactions lead to: (i) At Positive Plates: Conversion of Lead
Dioxide to soft Lead Sulfate crystals, (ii) At Negative Plates: Conversion of Sponge Lead to soft
Lead Sulfate crystals and (iii) In Electrolyte: Conversion of portion of Sulfuric Acid to water
leading to reduction in Specific Gravity (<1.1 for fully discharged condition). During re-
charging, electrochemical reactions are reversed leading to: (i) At Positive Plates: Conversion
of soft Lead Sulfate crystals to Lead Dioxide, (ii) At Negative Plates: Conversion of soft Lead
Sulfate crystals to Sponge Lead and (iii) In Electrolyte: Conversion of portion of water to
Sulfuric Acid leading to increase in Specific Gravity (1.265 for fully charged condition).
3.2.2 Effects of Sulfation: If Lead Acid battery remains undercharged over a long period
of time, the soft Lead Sulfate crystals of the uncharged portion will get hardened and will
be difficult to reconvert through normal charging (refer to Section 3.2.1 above regarding
charging and discharging reactions). Further, these Lead Sulfate crystals are non-conducting
and hence, introduce increased internal resistance in the battery. This increased internal
resistance introduces internal voltage drop during charging and discharging. Internal voltage
drop during charging results in overheating and undercharging and formation of more Lead
Sulfate crystals. Internal voltage drop during discharging results in overheating of the battery
and reduction in terminal voltage of the battery. Overall, this results in poor performance of
the battery.
3.2.3 Self Discharge: Self discharge of Lead Acid Battery is the electrical Ampere Hour (Ah)
capacity that is lost when the battery is not being charged and there is no load connected
to it. i.e. sits idle in storage. Self-discharge is caused by electro-chemical processes within
the battery and is equivalent to application of a small electrical load. For example, Lead Acid
battery stored at 30°C / 86°F would self-discharge at around 1% of remaining capacity every
day. Self-discharge increases with increase in temperature.
Self-discharge of the battery under long term storage will create condition equivalent to
under charging and consequently, lead to sulfation as explained at Sections 3.2.1 and 3.2.2
above. To prevent this, the battery should be “Float Charged” as explained in Section 2.2.4.