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Small grid-tie inverters? - Page 12

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Posted by daestrom on July 2, 2008, 1:02 am
BobG wrote:

If you're using 250 watts or more, then *yes*.  Your unit will supply 250
watts of that load and the grid will supply 250 watts less than it would
otherwise.  That means over a four hour period, you'll use 1 kWh less of
grid supplied power than you would have otherwise (your meter will register
1 kWh less too).

Every little bit helps ;-)

Just don't expect to save the neighborhood during a power outage :-)


Posted by Don Kelly on July 2, 2008, 3:11 am

The data is questionable  as to whether there is meaningful accuracy of the
meter at low currents and low power factors as would be the case for
exciting this  transformer  (unity pf at 100V??? and 94VA at 120V,0.89A,
but the conclusion that the inverter isn't going to do much  is correct.
However, having excited the transformer, there will be potential on the high
side and sufficient reserve capacity of the inverter  to deliver a
noticeable (not nothing),  but  not normally lethal, shock to anyone in
contact with the high side. Of course if the linesman follows proper
procedure, he wouldn't get a shock but the inverter could be toast.

Don Kelly dhky@shawcross.ca
remove the X to answer

Posted by Cydrome Leader on July 2, 2008, 5:15 am
The PF at 100 volts is strange, and why I even bothered to post it here. I
wonder if it has to do with the possibly high capacitance of the primary
winding and some automatic power factor correction because of this.

Considering a 14.4kV 200kVAR power factor correction cap is only about
2.6uF or something close to that, it doesn't seem that unlikely that x nF
of parasitic capacitance in the primary winding/tank/insulators can
correct a couple dozen (if even) VA.

Posted by Neon John on July 2, 2008, 2:38 pm

Not really.  AT that low excitation level, hysteresis in the core or plain old
dissipation in the high voltage dielectric could account for the high pf.  I'd
lean toward dielectric dissipation.

Nah, the inverter will simply shut down, like it does when presented with any
other short.  But you touch on another are where the safety idiots are running
on blind ignorance.

First a little math.

250 watts at 14,400 volts (a common distribution voltage) is 0.017 amps or 17
ma.  That's assuming that the pig is 100% efficient and that the inverter can
actually power up the pig, two things that we know are not true.  But let's

Consider 17ma.  Automotive ignition systems produce more current than that.
Oil burner ignition transformers are typically 20 ma.  Neon sign transformers
are commonly 30, 60 or 120 ma at up to 15,000 volts.  Literally thousands of
people a day get zapped from all of these sources and have little to show for
it other than a sheepish grin and maybe wet underwear.  As a neonist, I've had
my share of "illuminating" experiences at the hands of neon transformers.  I'd
rather not experience that ever again but OTOH, I'm not going to cower in the
corner in fear of a few ma of high voltage current.

<we shall now pause for a moment for the safety panty wetters to quote how
much current through the heart it takes to kill, yada yada yada.  Then we take
another moment to observe that the current has to get to the heart before it
can do anything.  There's a reason why defibrillators dump 400 joules or more
of energy and literally amps of current into the paddles and it ain't to help
send big capacitor manufacturers' kids through college.>

This whole thread was born of ignorance and perpetuated by the petty
authoritarians who don't actually have any technical learning but who want to
tell others what to do anyway.  Such a waste of time.


John De Armond
See my website for my current email address
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
Unable to locate Coffee -- Operator Halted!

Posted by Bruce Harvey on June 23, 2008, 3:11 am
On Jun 20, 8:36 am, maur...@tpg.com.au (Mauried) wrote:

Oh Poo. Its 250 watts fer gods sake. Its just a little trickle. No one
will know its there. No need to ask for approval. Its easy to tell
when the rest of the world turns off... the output current limits on
the next cycle. Its the 'normal' case thats sort of hard to
That's why they have laws to stop people like you connecting to the grid so
that you don't black out your whole area. You seem to forget that your end
might only be 250W but at the other end of that line is a base load
generator or 2 (Or a lot more) putting out Gigawatts of power. Those
generators are all synchronized together for a reason. your 250 watts is
probably gust enough to bring down the whole grid. Wake up to yourself and
learn a bit more about electricity. I don't know much but I know that you
are only going to cause trouble if you put unsynchronized power into the
grid. Anyway if you do try you might find yourself eligible for a Darwin
award at least.

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