[time-nuts] The home time-lab

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Jul 24 20:51:36 EDT 2016

The PFC stage needs a line frequency sinewave reference, if this is produced by attenuating the line input, then it may not function well with badly distorted line input waveforms (modified sine, square wave etc).Phase locking a sinewave to the line input may be a better approach.

    On Monday, 25 July 2016 11:44 AM, David <davidwhess at gmail.com> wrote:

 On Sun, 24 Jul 2016 14:45:02 -0700, you wrote:

>Hi Bob:
>The Sola 500 VA transformer is specified to hole up the line voltage for 3 ms.  (but not a half cycle of the line 
>I've connected the Sola CVS transformer to the output of the APC RS1500 backup UPS.  (needed to replace the 2 batteries 
>in the main unit and probably within a year the 4 batteries in the optional battery pack.
>The Sola transformer is connected to the output of the RS1500.  This will clean up any spikes or narrow drop outs on the 
>AC line since when the AC line is active the UPS does nothing.
>My hope was that the transformer would clean up the modified square wave output of the UPS, but that does not happen.
>Video of APC self test showing waveform on scope:https://youtu.be/DLE0mzAt7KY <https://youtu.be/DLE0mzAt7KY>

Was the Sola transformer under load when you ran the test?  I thought
a minimum load was a requirement for proper operation.  Maybe it is
time to get an online UPS or power conditioner but then you would not
need the constant voltage transformer.

Was the peak voltage still 170 volts?  If so then maybe it does not
matter.  Capacitive input loads and PFC power supplies should not

>I think the modified square wave killed my HP 6200 flat bed scanner.  The best scanner I've used and no longer made.

Ouch.  That is not suppose to happen but apparently some switching
power supplies have problems with modified sine outputs even though
they should not.

I have been told a couple of times that PFC power supplies are even
more likely to have problems with modified sine inverters but I have
yet to find an in depth discussion of the problem.  The PFC stage
should work with any input wave shape.
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