I want lots of battery power!

[rusty]

Ok .... I started a thread about adding refrigeration to our sailboat.

http://www.nwboating.net/forums/showthread.php?s=&postid=558#post558

The conversation quickly turned to how to get enough juice to keep the new refrigeration working so I thought I should start a new thread on that subject. See the previous thread for the complete background.

Soooo ... I have two banks of "house" batteries and a dedicated "starting" battery. I have discovered I need to increase the capacity of the alternator and modify the overall charging process to insure the best charge possible from engine power.

Looks like I should add a battery combiner. In looking at the Xantrex site, they recommend their Pathmaker. With three batteries, the whole thing should be wired up like this diagram shows.

What else should I do?

Thanks,
Rusty

[strongsail]

I have a couple of issues with the setup you got from the Xantrex site. But I've had a long day and will be on the road the rest of the week - so I will not go into the details right now - hope you can wait til the weekend or early next week:cool:

[strongsail]

geez, a day or 2 turns into 2 weeks! How time flies when you're havin' fun...

(btw, Rusty, I had trouble logging in - kept getting a dead link after I entered username and password, but the signin worked from the homepage - howcome I had to log in? The site always found my cookie before)

Anyway...

Your start battery gets very little use, never gets deeply discharged, doesn't need a totally full top charge to produce enough grunt to start the engine - but those house banks will get deeply discharged by your refrigeration, inverter, etc. With a high-output alternator and aggressive regulation, you will be operating at 14.5V or so for an hour or more to bulk charge, and that high voltage will overcharge your start battery. Yes, I know, it won't present much load to the alternator, but the high voltage will still shorten its life, especially if it is a sealed gel or agm type.

Plus, with a dedicated start battery, you can just leave your battery switch in the "Both" position all the time, which negates the need for a battery combiner.

I have a device on my boat that uses power from the house bank to top off and float the start battery. It's made by Ample Power, which is now PowerTap. It provides for total isolation of the start battery but prevents it from being overcharged.

Also, with a high output alternator and its required large output wiring, it's a good idea to have a safety diode between the output of the alternator and the battery bank. It will prevent current from flowing backward from the batteries if the alternator fails to ground, which they often do.

If you have gotten hold of Dave Smead's book, he talks in more detail about these issues.

[rusty]

Strongsail ...

Thanks for all your info. I've got quite a bit to sort out.

I think I have most of my questions resolved now. I got the book you recommended and there is some great info in it. I've been reading all I can.

I have resolved to upgrade the alternator and the regulator. The Ample Power units look good. The only outstanding question now is whether the engine can drive a bigger alternator. Right now we have a Volvo MD7 diesel with a 35 amp alternator. I am going to call a couple of Volvo engine folks and see if I can get a consensus.

The Ample Power folks assured me it would work as long as I had their fancy regulator. "Charge big at anchor and charge small when motoring" I think is what they said.

Thanks again!

Rusty

[ctenning]

I have had good results connecting the alternator directly to the house battery and charging the start battery through a Heart Digital Echo Charge. Dockside, the house battery is charged a three-stage smart charger which also keeps the start battery charged through the Heart Echo Charge. I have posted a diagram at:

http://carlten.tripod.com/Electrical_system/electrical.html

Carl Tenning
"Q E Too"