I was thinking about adding a battery combiner to my boat's electrical
system, but I may have to rethink this.

Present System
------------------
Bank 1 - Starting battery
Bank 2 - House - 2x6V Trojans (225AH)
Shore power charger - 2 bank Truecharge 10 charger connected direct to
batteries with fused leads
Alternator - 55Amp on Yanmar 2QM15.

Presently, my alternator charges back via the starter motor cable. It leads
to the common terminal of the "red" 1-2-All switch. The batteries are
connected to the other two terminals in the usual way. So, I can chose to
charge either battery or both. House load also connects to common terminal
but also has it's own breaker switch.

1. Using Combiner
----------------------
I have looked at using the New Zealand made BEP VSR (Voltage Sensitive
Relay) as the combiner. But, in reading their website, they warn against
using such devices if the alternator and batteries are not matched. They say
that for the combiner to work, the alternator must be larger (80-90A) or the
batteries smaller (100-130AH). Otherwise, the unit will oscillate and not
work properly.
http://www.bepmarine.com/showproduct.cfm?productid=12
http://www.bepmarine.com/products/inst-710-100a-vsr(web).pdf

Another supplier - Sure Power talks of same problem but says that time delay
avoids chattering - But they don't provide details - Perhaps if alternator
is connected to house battery, it may work better?
http://www.surepower.com/separator.html

West Marine do not mention this problem in my older catalogue.

2. Echo-Charge
-------------------
Another possibility is to use a Xantrex Echo-Charge.
http://www.xantrex.com/web/id/103/p/.../5/product.asp

Seems alternator is connected to House bank. Then when voltage reaches 13v
this unit actuates and then charges starting battery. No mention of cycling
with undersize alternator. When unit kicks in, wouldn't voltage likely drop?

3. Diode isolator
--------------------
Would work, but voltage drop would likely reduce battery capacity and life.

4. Manual switching
-------------------------
That's what we do now! We have zap-Stop to protect alternator. But, it is
easy to forget to switch the batteries.

5. New Alternator
---------------------
Installing a larger alternator (say 120A) would be an option, but with
single belt and a real HP output of less than 10HP at normal rpm, this could
diminish engine output and perhaps put loads on engine that 'it's not
designed for. (The 55A is the optional alt. - normal is 35A!). Seems
overkill just to allow easier switching, but this would allow quicker
recharging of house batteries.

6. Portable Generator
--------------------------
This has passed my mind - Use a portable Honda to charge the house
batteries. But at 10A, this would require a long run!

Ideas, comments or condolences welcomed

GM