[sdiy] 12VDC to 12VAC converter [OT]
seb at burnit.co.uk
Tue Sep 4 18:22:09 CEST 2007
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...
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:
>>> 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!
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> Harry Bissell & Nora Abdullah 4eva
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