There is no way to know without.

A. Understanding more about the battery's chemistry

B. Knowing what all of the other loads in the circuit are pulling from the
alternator.

C. Knowing what RPM the alternator is spinning at and de-rating that 90
amperes to the curve above that RPM.

Tom

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
Arkady Mirvis
Sent: Thursday, April 29, 2010 5:33 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Alternator charging ability

Westy's alternator max. output is rated 90 amperes. Assuming that (3)
batteries, each rated 65 amper-hours, connected in parallel, and at 80%
state of charge, what alternator output amperage is expected to be needed to
charge the bank of 3 batteries to 100% state of charge?
Ark