UC3906 IC ARRL HB CHP 27 FIG 66 . This charger is designed to charge the 12 VDC gel cell type batteries between 1 to 8 AHr. The circuit is designed around the UC3906 charger IC and uses a TIP42 for the pass transistor. This makes a simple charger for those gel-cell batteries. The board has positions for three outputs, each output turns on the charge current to each battery individually, and then cycles to the next battery based on a 555 timer.
Power is supplied from a wall transformer.
The output is variable and can be adjusted to charge up to 10 cells in series.