[time-nuts] The home time-lab

Brooke Clarke brooke at pacific.net
Mon Jul 25 13:29:02 EDT 2016

Hi Chris:

The APC RS1500 uses what they call modified sine wave, but I call modified square wave, i.e. it's a square wave with a 
couple of parts that are at zero volts.
Don Lancaster promoted "Magic Sinewaves" where a pulse modulated waveform drives an H-bridge.  The leading and trailing 
edges are determined using the idea of FFT so that all the harmonics up to some number (typically 9 to thirty something) 
are zero.  There were also 3-phase versions.  But he no longer sells any hardware.

PS I'm looking for a source of 3-phase 400 Hz 115 VAC to power a North Finding Gryo.

Have Fun,

Brooke Clarke
The lesser of evils is still evil.

-------- Original Message --------
> Yes, "ferroresonant" is also called CVT.  Typically rather than buying
> just the transformer you buy a box that has one in it but also some
> other components to clip spikes (some MOVs) and and LC low pass
> filter.  I know it seems a saturated core might produce a non-sine
> wave but current CVTs have very low distortion.
> The other option is an on-line UPS, one that always runs off the
> battery.  These are expensive  if you need a good sine wave output.
> The UPS has an output stage not unlike an audio amplifier.  Not nearly
> as efficient as MOSFET switches.  (question:  I'd guess that modern
> versions would be designed with class-D output stages and have decent
> power efficiency??)
> The best solution is what the phone companies did.  The telco style
> equipment, like computers and such runs off 48VDC. and batteries are
> connected in parallel from a "battery room".  If designing your own
> GPSDO, it should be built to run of 12V battery power.
> For AC the best solution is a motor generator.  Basically an iron
> flywheel rides out any small dropouts in the utility power.  They had
> one for a mainframe computer at a place I worked at a long time ago.
> But only that one output 280V at 400Hz as the computer required 400Hz
> power.
> On Mon, Jul 25, 2016 at 2:43 AM, David J Taylor
> <david-taylor at blueyonder.co.uk> wrote:
>> Chris,
>> Do you mean like these:
>>   http://www.aelgroup.co.uk/products/agt.php
>> I have an old 75W unit somewhere....

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