Bimmerfest - BMW Forums - View Single Post - new vs rebuilt alternator...cost & quality
View Single Post
Old 09-16-2010, 04:08 PM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by 16valex View Post
Bluebee, You mean rectifier converts AC to DC right!
ooops. Just corrected that. Sorry. What it does, for those who don't know diodes, on the positive part of the curve is it forward biases the diode until the junction voltage is overcome (I think that's about 0.7 volts so you lose that) and then lets the rest of the voltage pass through as a short circuit.

Then, on the negative part of the curve, the diode essentially blocks the (now) reverse-biased current such that only the first half wave gets through that diode ...

But wait ... if you add another diode, opposite the first diode, it then is forward biased and it allows that second upside down wave through and the whole thing is in a wheatstone bridge like configuration (someday they'll name a bridge after me ... ).

Or at least that's what I remember from college days ...

BTW, the danger isn't the voltage so much as the CURRENT. Over time, that heat from the current ruins the rectifiers as stated in this thread above.

Reply With Quote