Facotry high-output alternators put out HUGE idle current. I've personally tested them. Aftermarket units will do the same (at high cost... about $250-$500).

What does NOT work is re-winding a small stock unit to be 'high ouput', since THOSE will almost always put out less at idle, even though peak output increases. The factory units are physically much larger - you can't get that performance from the dinky stock 55-70A units.