Hello,

Whether X-switches (relays) or isolators (diodes) are used, the problem 
remains the same.  The alternator's voltage capability is high enough not to 
be of a concern.  The key consideration is that the voltage is sensed (using 
a separate non-current carrying wire) at the main battery's terminals, and 
not at the auxiliary battery.  Thus, to best split the alternator's output, 
the resistance of the charging path from the main battery to the auxiliary 
battery must be kept very low.  This means increase the size and shorten the 
wire to the auxiliary battery as much as practical.

In addition, using an X-switch (very low resistance) rather than an isolator 
will improve the situation.

Mike

Michael A. Radtke  -  Z74               Voice: 602-862-4897
Bull                                      FAX:         4853
13430 N. Black Canyon Hwy.
Phoenix, AZ  85029                      Email: m.radtke@bull.com