0
\$\begingroup\$

I have an automotive (3-phase) alternator with peak rated output of 150A at 14V (after rectification, of course). How can I determine phase (AC) currents in this situation?

\$\endgroup\$
  • \$\begingroup\$ You measure them? \$\endgroup\$ – PlasmaHH Dec 5 '15 at 17:22
  • \$\begingroup\$ Of course, but I need to choose some components (MOSFETs), so I need to know approximate phase current value. \$\endgroup\$ – jurij Dec 6 '15 at 15:54
1
\$\begingroup\$

Determine the current in one leg of a three phase generator based upon DC output after 3 phase rectifier. (Assuming current in each phase is the same).

Disregarding losses in the rectifier diodes : The power that goes in must equal the power that comes out.

Power in from 3 phase alternator =\$\sqrt3* Vph * Iph\$ where \$Iph\$ is current in one leg (phase).

Power out of DC rectifier = \$.95*\sqrt2 * Vph * Idc\$

Use the .95 for now because Peak voltage = \$Vdc = \sqrt2 *Vph\$ . Has to do with ripple and other things in the DC output.

Equating the power in and power out (equal to each other), and solving for \$Iph\$

\$Iph = .775 * Idc\$

So your "peak rated output of 150A" becomes \$Iph = 116.25\$ amps.

Not an exact solution but very very close hopefully for your needs.

EDIT : corrected minor math error in final Iph and mulitiplication

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ So at 14V/150A output, it means that through each phase there is a current of approx 116A flowing? \$\endgroup\$ – jurij Dec 6 '15 at 15:56
  • \$\begingroup\$ Yes. Normally you should expect each of the three (AC) lines to carry MAXIMUM 116A \$\endgroup\$ – Marla Dec 6 '15 at 15:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.