I recently did a little reading and found out buck converters are used in battery chargers. Curious as i am i went to see what the output on a oscilloscope looked like, and it definitely wasnt a straight line across the screen, and so i am wondering, can a battery be charged with AC? If not, how come a buck converter can without causing the same problems?

 

The output if a buck converter is DC with some amount of ripple.If you looked at it with a scope on AC coupling you would be seeing only the ripple since the DC was blocked. Look at it with DC coupling and it will look like a straight line with some wiggles.

Bob

 

A battery is charged by cumulative energy input from a dc level across it. If the dc level varies up and down then the energy input varies accordingly.

The output of a buck converter is a dc level with an imposed smaller ac (from switching transients). The dc level charges the battery.

'AC' is measured with reference to a base voltage - if that reference is zero (no applied DC bias) then the positive and negative transitions effectively cancel out.