hughmanoid
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I have a 7 KW grid tied solar array that is useless when the power grid goes down.
I would like to use some off the shelf VICOR DC-DC converters that are rated to put out 400 watts when fed 200 to 400 VDC.
They put out 24 VDC and can be trimmed down to 13.6 (car battery voltage). or I can use a Newmar voltage reducer (20 to 50 vdc in , 13.8 out @ 35amps max.
From there I can use an inverter or two to get 120VAC to get emergency power in daylight.
I would hope to pull an amp or 2 from the 15 amps max the panels put out and get a kilowatt or so.
Maybe enough to run a refrigerator or charge an electric wheelchair and recharge a laptop etc...
Under load, the panels drop to maybe 385 volts but depends on season, clouds, temperature,,,.
Rewiring the panels from 4 strings of 10 (450 VCD) to 5 strings of 8 (360 VDC) is the logical solution but would probably cost a lot. Changing to a battery backup solar system would cost much more.
Another inverter, batteries and having an electrician rewire the electrical service to code ? Ouch.
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So I can burn off power a few ways but was hoping to find a SMPS that drives an external FET.
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BAD Idea 1: use incandescent light bulbs to drop 100 volts.
Oops: inrush current and low initial resistance of bulb overvoltages converters. No load on converters means less current in light bulbs and too much voltage.
Idea 2: Use three 24 volt 50 watt zeners in series to run at 1/2 power (1 amp per series) and parallel more series strings to get more current. Aim a fan at the the big heat sink and done.
Oops: when the solar voltage goes down, I am still burning a few hundred watts under load.
Idea 3: A series pass emitter or source follower (IGBT or NFET) with 375 volts worth of zeners at the gate. A crowbar to blow the input fuse if the FET(s) fail (shorted drain to source).
The source follower should drop the least voltage / power when the input voltage is below the 375 volt zener stack.
Oops: If the solar array only drops to 425VDC and I pull 2 amps, 100 watts through one or more 600 volt high current FETS may be hard to manage.
Idea 4: A buck circuit to chop the DC (discontinuous mode ?) when over 375 volts and then stay full on below 375 all the way down to 200 and eventually 0. Still will use a crowbar.
Oops: Inductors and capacitors big and bulky
I have tons of power resistors, zeners, and a few ways to get 170, 450, or 1100 VDC to test with (at very low current). I don't intend to hook up to the solar until I get something that works.
Any suggestions ?
I would like to use some off the shelf VICOR DC-DC converters that are rated to put out 400 watts when fed 200 to 400 VDC.
They put out 24 VDC and can be trimmed down to 13.6 (car battery voltage). or I can use a Newmar voltage reducer (20 to 50 vdc in , 13.8 out @ 35amps max.
From there I can use an inverter or two to get 120VAC to get emergency power in daylight.
I would hope to pull an amp or 2 from the 15 amps max the panels put out and get a kilowatt or so.
Maybe enough to run a refrigerator or charge an electric wheelchair and recharge a laptop etc...
Under load, the panels drop to maybe 385 volts but depends on season, clouds, temperature,,,.
Rewiring the panels from 4 strings of 10 (450 VCD) to 5 strings of 8 (360 VDC) is the logical solution but would probably cost a lot. Changing to a battery backup solar system would cost much more.
Another inverter, batteries and having an electrician rewire the electrical service to code ? Ouch.
--------------------------------------------------------------------------------------------
So I can burn off power a few ways but was hoping to find a SMPS that drives an external FET.
---------------------------------------------------------------------------------------------
BAD Idea 1: use incandescent light bulbs to drop 100 volts.
Oops: inrush current and low initial resistance of bulb overvoltages converters. No load on converters means less current in light bulbs and too much voltage.
Idea 2: Use three 24 volt 50 watt zeners in series to run at 1/2 power (1 amp per series) and parallel more series strings to get more current. Aim a fan at the the big heat sink and done.
Oops: when the solar voltage goes down, I am still burning a few hundred watts under load.
Idea 3: A series pass emitter or source follower (IGBT or NFET) with 375 volts worth of zeners at the gate. A crowbar to blow the input fuse if the FET(s) fail (shorted drain to source).
The source follower should drop the least voltage / power when the input voltage is below the 375 volt zener stack.
Oops: If the solar array only drops to 425VDC and I pull 2 amps, 100 watts through one or more 600 volt high current FETS may be hard to manage.
Idea 4: A buck circuit to chop the DC (discontinuous mode ?) when over 375 volts and then stay full on below 375 all the way down to 200 and eventually 0. Still will use a crowbar.
Oops: Inductors and capacitors big and bulky
I have tons of power resistors, zeners, and a few ways to get 170, 450, or 1100 VDC to test with (at very low current). I don't intend to hook up to the solar until I get something that works.
Any suggestions ?