Actually lowering the voltage requires a larger capacitor to maintain the same % ripple.
for e.g. for three motors rated at 12A continuous, to operate all three simultaneously at rated continuous and allow for a 10v p.p ripple at that current would require a 30,000µf capacitor at your DC voltage..
It is very seldom you operate all three at the rated current so some leeway is the norm.
It depends on what % ripple you aim for and also something to keep in mind that increasing the µf value more than you need actually increases the VA requirements of the supply.