Which UPS?

[D. Hugh Redelmeier]

| From: Scott Allen <mlxxxp-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org>

| Small point:
| 
| On 14 June 2012 12:18, D. Hugh Redelmeier <hugh-pmF8o41NoarQT0dZR+AlfA at public.gmane.org> wrote:
| > The 170VDC you are mentioning is really the function abs(sin(t)) and
| > bounces between zero and 170 volts.
| 
| I think both James and I were assuming that the 170VDC was also
| "flat", being filtered with capacitors so that it was a constant
| 170VDC with a little bit of ripple voltage (but unregulated).

I think it is an interesting point.  Thanks.  Remember: I don't really
know much about this.

If the rectified DC is flat (filtered by capacitors) would it not be
closer to 120V than 170V?  Would the filters not do some kind of
averaging (technically: mean function)?  The RMS of the
simply-rectified voltage would still be 120 (the quadratic mean).

(<http://en.wikipedia.org/wiki/Root_mean_square> explains RMS.)

My intuition: you can put a diode between the raw rectified voltage
and the capacitor.  But if you keep the capacitor at 170V, there are
only two instants in the cycle where current can flow into the
capacitor.  If the capacitor is at 120V, current can flow in in two large
portions of the cycle.  Without any diode, I imagine the charge in the
capacitor being some kind of average.

I emphasize again: I don't know what I'm talking about and would
welcome corrections.
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