[aprssig] backup pwr systems
bruninga at usna.edu
Mon Dec 11 22:33:21 CST 2006
>> My thought is just a sensing circuit that only fires
>> the inverter MOSFET's on the rising side of the
>> 60 cycle waveform. And then fires them for 50ms
>> or so on each cycle. If there is no waveform, then
>> the inverter transistors don't fire. Should
>> be very simple.
> You would have the power company beating down your
> door that way. Switching the MOSFETs on only a
> half cycle would introduce even more harmonics
> into the output power and get fed back into the grid.
No, that's what every light dimmer does, And if it is running a 400 watt lamp load like a dining room light then it is the same harmonics. A simple RFI filter can smooth it up so even a HAM can run on the same power.
THink about it. The load of the "grid" is something like maybe 0.01 ohm or much less. There is little that a single mosfet (or a single light dimmer) can do that would cause any discernable gliches on the waveform. All the mosfet would do would be to contribute a flea power of current, and it would never leave my house, since with only 400W going in, and my houose drawing 1 kW, then nothing leaves my system. I just reduce my current is all.
> Best to just stick with a standard UPS for each
> item (or group of items) ... or go with a
> grid-tie inverter system.
Yes, that was the orginal thread. I'm looking for a synchronous inverter (call it a grid tie system) in the 400 watt class that should be able to be built for under $100 in electronics. The cheapest grid-tie systems are in the thousands of dollars. Hence by post.
> Having something that plugs into the wall as you
> describe is a sure-fire way to electrocute a line
> worker when the power goes out (because you don't
> have an anti-islanding relay installed as would
> normally come with a grid-tie inverter).
No, you didnt read my post correctly. I said a synchronous inverter which means it cannot generate power on its own with out the presence of the 60 Hz grid in the first place.
It is inherently safe by design.
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