Full wave rectifier math analysis
Your circuit can not be described as you think because a true voltage source would maintain the voltage and sink current as well as supplying it.

A better approximation would be.







simulate this circuit &ndash; Schematic created using CircuitLab

This circuit has two diodes since when the bridge rectifier is conducting there are two diode drops.

\$ V_1 = |V_{pk} \cdot \sin(2 \pi f t)|\$ where \$ V_{pk} \$ is the peak voltage of the input AC, \$ \sqrt{2} \cdot V_{rms} \$

The time constant \$ \tau = R_1 \cdot C_1 \$ when the diodes are not conducting.  Taking the peak voltage on C1 to be the peak voltage on V1 minus two diode drops and calculating the droop using half the period for the input AC will give you a slightly pessimistic estimate of the output ripple.

You can get a better estimate if you compare the voltage on V1 in more detail but the quick method is usually good enough for design purposes.