home *** CD-ROM | disk | FTP | other *** search
- Newsgroups: sci.electronics
- Path: sparky!uunet!spool.mu.edu!sdd.hp.com!uakari.primate.wisc.edu!usenet.coe.montana.edu!news.u.washington.edu!milton.u.washington.edu!whit
- From: whit@milton.u.washington.edu (John Whitmore)
- Subject: Re: AC power inverter questions?
- Message-ID: <1992Sep15.235550.9873@u.washington.edu>
- Sender: news@u.washington.edu (USENET News System)
- Organization: University of Washington, Seattle
- References: <1992Sep14.210900.1@acad2.alaska.edu>
- Date: Tue, 15 Sep 1992 23:55:50 GMT
- Lines: 41
-
- In article <1992Sep14.210900.1@acad2.alaska.edu> aslt@acad2.alaska.edu writes:
-
- >Many inverters use square waveforms rather than sinusiodal waveforms.
- >Intuitively, though, it seems that significantly less energy will be
- >transferred from the primary to the secondary of the transformer using
- >square waves (input changes at discrete places in the waveform) than
- >would be transferred using sinusoidal waveforms (input continuously changing)
- >What am I missing?
-
- First, a square wave is simply a lot of different frequencies
- all lumped together; the efficiency of the transformer would have
- to be less at high frequencies for the square wave drive to
- have some disadvantage over the sine-wave drive. Some sources of
- energy loss ARE worse at high frequency (eddy current losses
- in the transformer iron) while some are improved (saturation
- losses).
-
- More to the point, the DRIVING circuit is typically running
- off a DC source, and can operate with nearly zero loss ONLY when
- switching (which produces... square waves). There are some tricks
- to generating sinusoids, but they require extra inductors or many
- taps on the transformer, and are not employed casually (nor cheaply).
-
-
- >Along the same lines, presumably the outputs of inverters are square waves
- >rather than sinusoids (I'm speculating, I don't know). It seems you could
- >do some serious damage to the motors in some devices, drills, margarita
- >blenders, refrigerators, freezers, and such. Any comments?
-
- Probably not; the series inductance in a motor results in
- the higher frequency components of the square wave being...ignored.
- If you fed an AC motor with DC, it'd damage it. Feeding it with
- too high a frequency, you'd simply lose torque (and the motor would
- not draw current). The worst case would be if it made the motor
- respond acoustically (instead of a comforting hum, your refrigerator
- would make an annoying BUZZZZZZ).
-
- John Whitmore
-
-
-
-