ST voltage question for grid tied inverter

[bschwartz]

Could the harmonic winding be taken out of the picture and an adjustable voltage power supply be used instead?
I was thinking of using my ST head output rectified to DC to power a grid tied inverter.  48V 4KW inverters seem fairly common.
If the ST were run at standard 1800 RPM could I lower the field voltage to produce 48 volts, rectify to DC and directly power the grid tied inverter without any other mods?
What would happen to current output?  How much power would be a reasonable expectation from a 6/1 normally putting out 3.3 KW at normal 120/240V?
Thoughts/Ideas?

-Brett

[BruceM]

Sure, the simple AVR (PCB) I made would regulate at 48V, but the ST head would be limited to whatever it's rated current is, regardless of voltage.

If you do such a thing, you really need a monster choke for inductive filtering of the DC.  It's rude to the batteries (according to manufacturers)  to have much ripple.   On my 12 amp charger (nominal 120V battery bank, charging to 156V in cold weather), I use an 1100 watt toroid transformer primary for a choke.  It didn't saturate!

I haven't looked- but why wouldn't you just buy a good, smart AC charger?

[bschwartz]

I don't plan on having any batteries to charge.  How much do you think a 48v charger that puts out 75 amps continuous duty would run?  Are they readily available?  That might be the way to go.

[BruceM]

I didn't see any 48V battery chargers with enough amps, and commercial supplies are pretty spendy.  You'd get  better efficiency if you can find an inverter with AC input, but I don't know of one.

[bschwartz]

I may need to go with a high voltage unit like an SMA windy boy.
Rectify the 240V AC to 336V DC.  Hmmmmm how would I filter that?  I'm thinking the windy boy over some of the other high voltage DC inverters because they list the DC ripple at 10% as opposed to the sunny boy at I think 3% ripple.

[bschwartz]

This is what I was using for comparing the two.
Sunny Boy is listed at <5% ripple, Windy Boy is listed at <10%

http://www.dcpower-systems.com/product_detail.aspx?gid=447&pid=11799
http://www.dcpower-systems.com/product_detail.aspx?gid=31&pid=11796

Am I reading something wrong into this?  I've been known to do that before.

[BruceM]

A choke filter for your linear supply (straight rectified 220VAC) would be better- PF of 1, and at that voltage, the current won't be so bad, so choke isn't so big.

I've been using toroidal transformers (surplus) as chokes with good success. As a choke, pick a winding and wire it in series.  If it saturates (not much filtering) on the primary, you can use a secondary winding (lower volts, less turns).

[bschwartz]

would one of the windings on a 480/240 buck boost transformer work for that?

[BruceM]

Yes. A reminder- using an inductor for a filter will result in a DC voltage of about 240 if that's your AC volts.