| email@example.com wrote:
|> So: AC -> DC -> 20 kHz AC -> step-up -> high V 20 kHz AC -> high V DC ->
|> 50/60 Hz AC
|> Is that right?
| Almost. I'd suggest:
| The first bit would be-
| AC -> DC -> 20 kHz AC -> step-DOWN -> Very LOW voltage 20 kHz AC -> Very
| LOW V DC ->
How well filtered would the first AC -> DC part need to be? I would think
it might not matter, much.
| This produces the very low voltage DC needed to (1) charge/maintain the
| battery voltage and (2) provide power for the output inverter when mains
| is available.
| All the above is, is a SMPSU, not very different to the one in any
| desktop computer.
| The second bit would be-
| Very LOW V DC -> 20 kHz AC -> step-up -> "high" V 20 kHz AC -> "high" V
| DC -> 50/60 HZ AC
| Which is just what you would find in most boats/RVs etc, to provide a
| mains supply from one or more deep-discharge batteries.
Ultimately this can be encapsulated:
AC at supply voltage/frequency -> [first bit] -> DC at battery voltage
Appropriate parallel/switched operation with batter
DC at battery voltage -> [second bit] -> AC at utlization voltage/frequency
Now, back to my original issue, with these "encapsulated" modules doing the
AC (supply) -> DC (battery) -> AC (utilization)
My concern is the practicality of a universal UPS that works on an AC power
supply in the 50..60 Hz range, with any one of these systems:
1. Two wire 200..240 V grounded at wire A.
2. Two wire 200..240 V grounded half way between wire A and wire B
3. Two wire 200..240 V grounded at wire B.
With the _possibility_
that it can also at least supply output power like:
4. Two wire 100..120 V grounded at wire A.
5. Two wire 100..120 V grounded at wire B.
The design with 20 kHz AC step-down and step-up stages doesn't seem to apply
to dealing with the utiliztion voltage systems here, EXCEPT that it could be
a semi-split design, where the inverter is a single unit up to the point where
the final "high" V DC is converted to the final 50/60 Hz AC. If the latter is
split into two parts, along with that final DC voltage being chosen for this,
it could still produce TWO isolated 100..120 V AC outputs that could be used
to produce system #2 above, as well as #4 and #5.
There are other issues. For example if the UPS has domestic outlets, there
will be an issue of which conductor is allowed to be grounded. With outlets
of the style used in Argentina, Britain, France, India, and USA (for 120V,
not for 240V), a specific conductor must be the grounded one (let's call it
wire A). If the UPS were to output any other system of power, it would be
operating in an unsafe way with respect to the expectations in that country.
However, if a correctly wired AC supply were given, it could "learn" what the
correct way is and output exactly the same. I don't know if that would enough
for the appropriate equipment safety listings.
Consider the case of Argentina and Australia. They use the same outlet/plug
design, but have the current carrying conductor that is to be grounded in the
opposite configuration. Consider a UPS constructed with this kind of plug
and outlet. It could learn which conductor is grounded and do the same for
its outlet. That's case #1 and #3 above. From an engineering perspective,
how hard would it be to make it safe under the conditions that someone does
in fact, actually plug it in to a live outlet in the host country (as opposed
to plugging it in one, then taking it to the other and operating it standalone
using its charged battery power, or plugging it into an incorrectly wired
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