On 6/18/2014 6:48 PM, Tony Hwang wrote:
snip...
Hi,
I think that shown is block diagram(simplified version) Full wave rectifier
bridge does not produce pure DC, it has to be further filtered. There must
be a filtering caps in the mower too. NO?

For this sort of application all that is required is that the voltage be
DC. Having no filtering simply means that the motor is given a hefty kick
120 times per second rather than the more consistent, but smaller, push
that a filtered supply would provide. In this case the inertia of the the
rotating motor and blade are their own filter.