Hybrid Car – More Fun with Less Gas

12Vdc Inverter for grain mill - Page 3

register ::  Login Password  :: Lost Password?
Posted by harry on January 12, 2010, 5:55 pm

All rotating electric motors like a pure sine wave.  This is very
difficult to achieve with electronic devices.  (But square waves are
easy). Hence cheap inverters tend to square or squarish wave forms.
The further one departs from the sine wave the more the motor has to
be derated, the worst case being a square wave.  Without knowing the
precise wave form it's hard to be specific.   However, if there's lots
of sparking at the brushes (I assume it's a "universal motor", ie with
commutator & brushes),  desist, you will f**k it up in a very short
Not only will the brushes/commutator burn out, the motor will
overheat, especially if run at full load.
It's possible to modify a square wave to more like a sine wave with a
"pi" network of capacitors and inductors but hardly economic unless
you get them for free.

Posted by Jim on January 13, 2010, 7:40 am

Would that be a "low pass filter"?  If so, what cutoff frequency
should you
design it for?

On Tue, 12 Jan 2010 09:55:58 -0800 (PST), harry

Posted by harry on January 13, 2010, 3:37 pm

Well frequency would not be an issue as it runs at the frequency the
inverter  provides.  It would consist of a capacitor in parallel with
the load followed by an inductor in series, then another capacitor in
parallel.  (Hence the term pi network)

This Thread
Bookmark this thread:
  • Subject
  • Author
  • Date
please rate this thread