Re: alternators for 3 phase power...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, September 01, 2003 7:39 PM
Subject: Re: alternators for 3 phase power...


 > Original poster: Harvey Norris <harvich-at-yahoo-dot-com>
 >
 >
 > --- Tesla list <tesla-at-pupman-dot-com> wrote:
 >  >  > Most alternators can do 60 amps..  12V x 60 = 720
 >  > watts.  I would think
 >  >  > your alternator would run cool!!
 >  >
 >  > What's the rotating speed of the alternator (i.e. is
 >  > it a 2 or 4 pole
 >  > device...)...
 > 7 pole face rotor on each side equates to 7
 > cycles/alternator field rotation.

Whoa... that's some alternator... judging from the "alternator whine" in my
radio (say,500- 1 kHz at 3000 RPM engine speed), I was going to guess that
the run of the mill alternator was a 4 pole device (3000 RPM-> 50 rev/second
* 6 bumps/rev for 2 pole = 300 Hz, so a 4 pole would be 600 Hz). Time to go
look at that fine product of Hitachi out in the garage...  7 poles seems a
lot (and, is not a multiple of 2, to boot...)

 > The 60 Amp output from the alternator
 >  > is typically with the
 >  > engine running at >3000 RPM, and the alternator is
 >  > "geared" (actually
 >  > "belted") to run somewhat faster than the engine.  I
 >  > assume that you're
 >  > measuring the voltage with a significant load (i.e.
 >  > to draw that 9 Amps at
 >  > 40 V)..
 > I cited loads of 12.5 ohms here, and of course this
 > equates to the tripling of the cited current when we
 > count all three phases, and of course a three phase
 > rectification into DC would give a much higher cited
 > amperage output from the alternator.
 >
 >
 > > Yes people may not realize that an alternator can
 > overheat when no load is placed on the outputs! The
 > stator windings are connected in wye, and internal
 > amperage ciculation will occur depending on the amount
 > of energized field being employed.

Wye windings can have NO circulating current.. There's no loop for the
current to circulate in.  Perhaps you're thinking of delta connection?  In
any case, the alternator on my 280Z is definitely Y connected, and I suspect
this is essentially standard for automotive applications.  No circulating
currents... With no load connected, the only means for overheat would be in
the field (which, by the way, is fairly fine wire, and can be overheated
without too much trouble...(i.e. by connecting to 12V with no regulator and
alternator not turning... first hand empirical knowledge here...)