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[aprssig] backup pwr systems

Robert Bruninga bruninga at usna.edu
Sun Dec 10 19:06:24 UTC 2006

What I want, and no-one makes,

Is a 400 watt DC-to-Line synchronous inverter that can back feed
into my house power to save me a few pennies on the electric
bill.  It is a whole lot of trouble to configure part of the
house load to run on DC because then you need a battery, and
then you have to charge it during the day, when no one is home
and you don't need any DC, and they run it at night after
switching over to inverter.  All of this takes work, effort,
life style changes, and none of it is worth the trouble for just
a few hundres Watts of excess green power.

But if there was a synchronous 400W inverter with just a line
cord that you could plug into any outlet in the house and if you
had up to 400W of free DC power available (wind or solar), then
just plug this thing in, and it would backfeed your existing

Of course it would be man-safe, and would only provide boost
current only if there was line voltage alreaady there.  If there
was no 60 Hz AC, then it would do nothing.

What it WOULD do is reduce my electric bill during the PEAK
summer rates (time of use metering charges almosst 17 cents per
KWH duing the summer day).  And it would do this with minimal
effort, because the total interface is just plugging it in.  And
I woiuldnt lose the battery charge/discharge inefficiencies nor
would I be wearing out my batteries every day by cycling for
this minimal power.

Think of it this way.  There are dozens of stupid little
"wall-warts" haniging throughout my house that provide a
constant drain on my electric meter.  The 5W of heat that each
one is consuming is just not worth re-wiring the house for DC,
but the total of them adds up to probably a few hundred watts 24
hours a day.  By injecting my solar power during the midle of
the day when I get the most, into my mains, it would be like
paying myself 17 cents for every KWH I put in.

Again, do not confuse this with grid-tie inverters that are
desigend to run your meter backwards and which require Electric
Company and all kinds of approvals and all kinds of safety
issues.  This is just a small device to help "reduce" my
electric demand.

Anyway, it would be a dun design project for powering my 24/7
APRS system and any spare power I have.


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