Three phase full wave bridge rectifier

Hi,
I was asked in school, if I have 480vac going in and 630vdc coming out, how would I come up with this dc figure. I was not given any other values, and I'm comoing up with around 678vdc. There would be some voltage drop associated with the diodes but that is minimal. Around 4.2v. So I know thats not the reason for the drop of around 48v. This is not a test or homework, but just something my instructor asked at the end of class.

CJ

Are we talking about r.m.s. effective D.C. ? There is ripple associated with three phase full wave rectified D.C. The rms D.C. would not equal peak value of AC unless there is a filter cap on output to keep the peak.

Doesn't this have something to do with the phase angle difference from each leg?

Okay, you forced me to do the calculation.

Ignoring rectified voltage drop.

480 vac rms three phase full wave rectified

Peak = 678.82 vdc.

Minimum = 587.88 vdc

Ripple = 90.94 vpk-pk

D.C. rms = 648.62 vdc.