Roff said:I thought it was oscillations, but I looked at the frequency, and it is 120Hz. I also tried powering it from a 16.5V battery, and the pulsations disappeared, with the current steady at 3.86A. With no pulsation, the dissipation at the start of the charge (battery voltage=12) was about 12W. The pulsation reduces Q4 dissipation to about 2.66W, but, as noted on the plots, average current dropped to about 1.7A.
The 120Hz would be the 60Hz from the wall, doubled by the rectifier, no?