Subject: Re: serial port control
To: None <current-users@NetBSD.ORG>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: current-users
Date: 02/18/1998 14:41:45
> Its not clear to me yet that sine wave output wins.  Square wave
> should be more efficient since you don't have the big dead-time
> between, the two peaks.

Of course, it depends on what you're feeding; I certainly wouldn't want
to drive a normal incandescent lightbulb, since the effective RMS
voltage will be well above what such a bulb is designed to handle.  I
don't think trying to run a room light off the UPS is unreasonable;
perhaps you disagree. :-)

> If the load is your typical PC switching power supply then it would
> really prefer to have the full ~170v peak voltage applied all the
> time.

This all *sounds* very reasonable.

However, just recently I had occasion to inspect two power supplies
taken from disk enclosures.  They didn't have killer transformers on
them, but they also weren't multiple-hundred-watt power supplies.  I
followed the etch runs (single-sided pc board, y'know, piece of cake to
trace) and line voltage fed directly into *something* inductive.  I
didn't take an ohmmeter to it to determine whether it was a normal
transformer or co-inductive chokes in series with each wire...but
either way, feeding it anything with sharp edges is not going to keep
it happy-as-designed.

If you're really that sure what you're feeding is as you describe, why
not just feed it 170VDC and be done with it?

> It just doesn't pay to round the corners of the wave unless one is
> running a motor or transformer or something like it that will get
> very upset at the high dv/dt of the square waves.

...or something like an incandescent light bulb that will get upset at
the higher V RMS even though the V P-P is the same as line voltage.

No, I want at least approximately sine-wave output for anything I can
just plug regular line cords into.  (If it's closely coupled with the
machine's power supply, sure, do anything that's convenient.)

Of course, I also want continuous conversion, not cutover. :-(

					der Mouse

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