Need Help With Alternator Battery Charge Question

Don S/V ILLusion · Jul 4, 2016

Got an isolator between them? That would give you the voltage drop.

Gunni · Jul 4, 2016

If your house battery doesn't have the juice to start your engine you most certainly do not have 13.4 volts resting. You need to check your house battery after resting overnight, that will give you the true house voltage, and I suspect it is dead. (<12vdc). There is no way that hitachi truck alternator is going to give you 80 amps.

Stu Jackson · Jul 4, 2016

Mine Sail has posted this a number of times before and on other boating forums. I just copied it because it comes up so often:

Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. The battery simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com/showthread.php?t=125392

and these, too:

http://www.cruisersforum.com/forums...d-smart-regulator-instal-question-125843.html

http://www.cruisersforum.com/forums/f14/most-practical-way-to-upgrade-yanmar-alternator-142083.html

Bill Roosa · Jul 4, 2016

Your set up may have the starter battery set up to start the engine and the house battery to run the house loads. The starter may not be able to drive the house loads and the house may not be able to start the engine. Kinda dumb but I've seen this set up before. pretty idiot proof if you don't loose the starter battery (which will happen when you are away from the slip BTW and probably when you really need to start the engine fast to get out of the way of that 300' container ship). check the alternator + cable to see if it goes into a box that has three cables on it. (alternator +, house + and starter +). That box is the isolator that Don is talking about and it will keep the batteries isolated from each other and their respective loads also. There would need to be a switch between the house + and starter + terminals on the isolator to connect the two banks and get the house to start the engine.
Good luck.

smokey73 · Jul 5, 2016

Rick486 said:
Hi all:
Well, I own a Hunter 44DS and we are on a several week cruise and my generator (you know which one) is down hard. Inconvenient but not the end of the world for sure. So I am charging the batts with the main engine alternator. The engine is a Yanmar 4JH4E and I believe the alternator is 80 amp by Hitachi(?). In charging the batts running at around 1200 RPM on the hook, the charging voltage as indicated on the DC breaker panel on the start batt is 14.2 or so but only 13.4 on the house bank, where I need the charge. I have tried turning off the Start barrel switch to start the engine on the house bank but I find the starter will not turn over. Could someone please explain to me why the charge voltage on the house bank is only 13.4?
Thanks in advance
Rick

Rick, Do you have one barrel switch for the House Battery and a separate barrel switch for the Start Battery? The set up Bill describved is what I have on my boat. My Hunter 40.5 is wired that way and you cannot start the engine from the house battery. It will only start from the Start Battery. (And you can't run house loads from the start battery in an emergency) If yours is wired that way then you won't get the engine starting from the House. And, by the way, even with the Start Battery in the off position, it still charges from the engine through an Automatic Charge Relay (ACR) so turning the barrel switch to off will have no effect on what goes to the House Battery and what goes to the Start Battery.

By the way, I don't like that setup and have consulted Mainesail and he has provided a way to add a third barrel switch with a wiring diagram to allow the House to start the engine or the Start Battery to supply emergency power to the rest of the boat for things like the VHF radio, etc.

Stu Jackson · Jul 5, 2016

smokey73 said:
By the way, I don't like that setup and have consulted Mainesail and he has provided a way to add a third barrel switch with a wiring diagram to allow the House to start the engine or the Start Battery to supply emergency power to the rest of the boat for things like the VHF radio, etc.

Maine Sail is great to consult with. He's also posted those wiring diagrams for easy access, if you can't get a hold of him 'cuz he's busy working on OPBs.

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

The Short Version of the 1-2-B Switch Stuff: http://c34.org/bbs/index.php/topic,5977.msg38552.html#msg38552 This is a link to the Electrical Systems 101 Topic, reply #2

What are ACRs, Combiners & Echo Chargers? (by Maine Sail)
http://forums.catalina.sailboatowners.com/showthread.php?p=742417