A charger for the internal battery pack of FT-897
2 Ιουνίου, 2011 § Γράψτε ένα σχόλιο
This charger charges the homebrew internal battery pack of FT-897 with about 450 mA current (1/10 C). At this current the battery needs 12 to 14 hours for a completed charge.
The main part of the circuit is the IC LM-200. With this IC we can build a constant voltage and constant current power source. Resistor Rsc determines the charging current Io (Io=0,45/Rsc). For 450 mA current we need a 1 Ohm resistor.
Charging voltage Vo is determined from the resistors R1 and R2 (Vo=Vref(1+(R2/R1)). Vref is the voltage on pin 4 of LM-200 and it’s about 2.77 volts. According to these if we use an 820 Ohm resistor for R2, R1 must be 4.1 KOhm for an otput voltage of 16.6 volts. When Vo is 16.6 volts the charging voltage of each cell is 1.51 volts. Diode D1 prevents the discharge of the battery via the LM-200.
The charger needs a 19 volt power supply to work. You can build one with a transformer and a rectifier bridge or you can use your laptop charger. Most laptop chargers give 18 to 19.5 volts and much more current than the 500 mA we need. You can connect a LED as operation indicator and a fuse of about 0.8 Amperes.
For the FT-897 homebrew internal battery pack click HERE