I am not the electrical engineer that you are looking for, but I have read your article and the web link several times and this is how I see it:
The phase charger relay is energised/switched when the two wire connection to the alternator lights up, indicating that the car battery is charged. The connection between the car battery and the boat motor battery is then made (a bit like jump leads between batteries).
This then starts to drain your car battery until the charged wire of the alternator switches off and de-energises the relay, thus breaking the connection. So the relay will switch on and off, until both batteries are charged.
Placing an additional phase switch between the main boat battery and the trolling motor battery will work and switch the connection on and off relative to the car batteries state of charge, NOT the main boat battery, it is all about the connection to the alternator, which is monitoring the car battery.
BUT, after reading this link: http://www.carbatter...information.php
then maybe the whole idea is not such a good one, as I suspect that unless the motors were of a similar size as the car battery, then they would be subject to overcharging, which would result in overheating, evapouration of electrolyte and buckling of the lead plates.
Like I said, I am not an electrical engineer and you should seek expert advice before trying these ideas.
Edited by Vodkaman, 27 July 2009 - 08:55 AM.