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A BETTER BATTERY CHARGER

Part 2: Hardware and Software Implementation
by Thomas Richter

Start ý The Buck Converter ý Voltage Reference and Battery Temperature ý AT90S2333 Battery Charger ý ATtiny15 Battery Charger ý Charge Current ý Software Implementation ý User Settings ý Source Code ý INT Battery Function ý The Stable_ADC Function ý BC.H ý B_DEF.H ý Charge MethodýSLA.C ý Charge MethodýNiCd.C and NiMH.C ý Charge MethodýLilon.C ý Suggested Improvement ý Sources and PDF

CHARGE METHODýSLA.C

The fast-charge of sealed lead acid batteries uses constant voltage (see Figures 8a and 8b). Before charging begins, a simple (but surprisingly effective) method is used to determine the charge voltage. A constant current of 1 C is applied, and the corresponding battery voltage is measured.

The battery is first charged with constant voltage, fixing the voltage to that level and letting the current float. When the current drops below 0.2 C, the charge cycle has finished. The fast-charge mode is then terminated and trickle-charge mode starts (see the Charge Parameter Summary document).

Trickle-charge is a constant voltage charging at a level slightly below the fast-charge voltage. Trickle-charge can be terminated after a set time (see Figure 9).

Figure 9ýThis figure shows the principle of trickle charging for sealed lead acid batteries.

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