To your question:
otherpower.com has some stuff on this, probably would lead to others.
Gratuitous rambling:
When you total up your savings don't forget to include the cost of a hitch for your bus, 'cuz your gonna need to pull around a trailer load of batteries to run that inverter more than 10 minutes or so ...
Just a little food for thought, my 700 watt inverter uses 1RT3205 switching transistors (xref's to NTE2991 at Allied Electronics, the only place I could find with a less than $100 minimum single part order), $3.52 a piece - mine has 18 of them, that's already 63 bucks, mulitply that by 6 for 4kW for a rough estimate, toss in another hundred or so to burn a custom board, yada, yada, yada ...
All you're saving is the labor and you're competing with 30 million people in China that also know how to solder, and you'll lose all that and more paying 3 or 4 prices for buying the parts in onsies and twosies .... so now you've spent 3 times as much on parts and 30 hours putting this thing together perfectly (no cold joints, solder bridges, electrolytics all going the right way, etc), plug it in and all the smoke comes out of the power transistors ... email the source for your schematic - replies "Oh yeah, all the 10 watt resistors should have been marked 20 - it's a typo, I'll email you a new one right away" - as you write that second check to Allied for a coupla hundred bucks you can enjoy the additional savings - you got TWO schematics for the price of one! I could go on with all the things that could make this very costly (not oddball things that COULD go wrong, but things that are LIKELY to go wrong) - design testing, manufacturing testing, longetivity testing, all of which has been already paid for by Xantrex or Trace or whoever, but you get the idea .... The whole thing is like building a car from a Haynes manual and the NAPA store ....
Don't know if you've consdered it, but if you don't need the 4kW to a single load, think about splitting up your circuits and running them off of individual, smaller inverters that can be had for little money on eBay and buy them as you can afford them. I got a 1200 watt Xantrex for $80 there, not much more than the cost of the switching transistors bought in small quantity.
Of course, I'd be tempted to build one for the fun of it ...
There are a few other sources for schematics, but most are selling them, not free. You'd probably need a plan also, rather than a schematic, design of the heat sinks on something like this is pretty critical ...
Tom
