[sdiy] 12VDC to 12VAC converter [OT]

[harrybissell at wowway.com]

The RMS is a DC equivalent heating value... so if we ignore
(ie rectify) the square wave, it would be the equivalent of
12VDC.  This is indeed equal to the 12VAC * 1.414 (also rectified)

So you are correct, and the heating equivalent into the motor might be
different. The slew rate of the voltage waveform might impose additional
stress, but for a 12V motor the insulation resistance should be more than
enough :^)

(it is an issue at industrial voltages...)

H^) harry


On Tue, 04 Sep 2007 17:22:09 +0100, Seb Francis wrote
> But isn't the p-t-p voltage of a sine 2 * 1.414 * RMS voltage
> 
> Thus a 12VAC RMS sine wave is actually 34V p-t-p
> 
> A 12VAC RMS square wave is, as you say, 12V peak or 24V p-t-p
> 
> The 2 should yield an equivalent amount of power when faced with the 
> same load, no?
> Whether a motor presents the same load to a square wave as it does 
> to a sine is a different matter though...
> 
> Seb
> 
> harrybissell at wowway.com wrote:
> > I'd say that a square wave has an RMS value (area under the curve)
> > equal to the 'peak' value. 
> >
> > So a 24V peak to peak square wave would not be equal to a 12VAC RMS
> > sine wave. Its way more imho...
> >
> > H^) harry
> >
> >
> > On Tue, 04 Sep 2007 11:21:12 +0100, Seb Francis wrote
> >   
> >> ASSI wrote:
> >>     
> >>> On Montag 03 September 2007, Seb Francis wrote:
> >>>   
> >>>       
> >>>> I need to produce a 12VAC 20VA 50Hz supply from a 12VDC input.  It's
> >>>> to run a 12VAC motor from a car battery, so the AC voltage doesn't
> >>>> have to be particularly sine-like or regulated.
> >>>>     
> >>>>         
> >>> Look for a PWM driver for appliance motors, preferrably with an 
> >>> integrated H-bridge and just feed it an unmodulated 50Hz (or whatever 
> >>> is close enough) signal.  Rolling your own is entirely possible at 
> >>> roughly 2A, but then you have to deal by yourself with controlling the 
> >>> dead-time during the switching event and with the reactance from the 
> >>> motor coils.  If you do roll your own controllers, there are ready-made 
> >>> H-bridge or half-bridge IC, both bipolar or MOSFET and with or without 
> >>> the driver circuitry from many companies.  Just the bridge drivers are 
> >>> available seperately, too.  There's a stub entry on Whackypedia that 
> >>> has a few external links that may be helpful:
> >>>
> >>> http://en.wikipedia.org/wiki/H-bridge
> >>>
> >>> Google brings a lot of useful links on that topic as well.
> >>>
> >>>
> >>>       
> >> Ah that makes a lot of sense .. it's still going to be a square wave
> >>
> >> (not sine) fed to the motor, but it will be effectively 24V peak to 
> >> peak which (being a square wave) should be equivalent to 12VAC RMS.
> >>
> >> Looks like it would be a nice simple circuit too.  Thanks!
> >>
> >> Seb
> >>
> >> _______________________________________________
> >> Synth-diy mailing list
> >> Synth-diy at dropmix.xs4all.nl
> >> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >>     
> >
> >
> > Harry Bissell & Nora Abdullah 4eva
> >
> >
> >


Harry Bissell & Nora Abdullah 4eva