On Wed, 24 Jun 2009 16:15:09 +0700, Bruce In Bangkok
wrote:

We have a pair of 250 amp alternators. They won't charge the
batteries in 5 minutes, but at half power they will drive a 2500 watt
inverter at full output.

http://www.alternatorparts.com/Extreme%20Duty%20Dual%20Rectifier%20CS-144%20type.htm

Without a battery that would be in the region of 200 amps, not
considering system loss.

Yes, and there are losses, even with big cables and heavy duty lugs.