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

Seb Francis 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...

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
>>
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>>     
>
>
> Harry Bissell & Nora Abdullah 4eva
>
>
>   




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