Alternator Wiring Help

[Contraman]

I'm replacing my battery isolator with a Blue Sea ACR. After reading advice here and elsewhere, I'm wiring my alternator output directly to the house battery. I've disconnected an orange #8 wire that went to my amp meter and then to the isolator and replacing it with a red #2 wire going directly to house battery.

Here's a picture illustrating what I'm doing? Is this correct? Any thing else I should be looking out for?

Thanks,
Herb

[HappyMdRSailor]

From my experience... Low voltage current will not jump a gap that large... Even if it did, it's going to be inconvenient having somebody hold the wire all of the time...

Actually... Your request is a bit vague to me.... (could just be me...) What's the question you're asking?

[Contraman]

Here's a clarification of my question... have I put the red wire on the right alternator terminal to run directly to my house battery to operate my new ACR set up? I'm looking for hand-holding reassurance.

[Stu Jackson]

Among things on the internet that are impossible to help with are sounds, smells and electrical questions without wiring diagrams and only pictures.

There are hundreds if not thousands of posts about wiring AO to the house bank.

Here are two of them:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

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)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

If you can help us with that information, we can help you, a LOT more.

Good luck.

[skipmac]

If the orange wire you removed was the one that carried the main alternator output to charge your batteries (which is what I understand from your description) then yes, put the red wire on the same terminal and run it directly to the batteries BUT, I would put a fuse in the line.

Anything that chaffs through the insulation on the red wire will short your full battery capacity straight to whatever it touches. Best option in my opinion is a Blue Sea MRBF terminal fuse block.

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

[HappyMdRSailor]

"Skip and Stu.... to the rescue"

[djmarchand]

Skipmac is correct, but put the fuse near the battery, not the alternator.

I am a bit surprised that you went with #2 wire. That looks like an OEM Westerbeke (because it is red) alternator and I wouldn't expect it to put out more than 50 or so amps. #8 should have been ok for that. But bigger is like chicken soup for your sniffles.

David

[Contraman]

Originally Posted by skipmac

If the orange wire you removed was the one that carried the main alternator output to charge your batteries (which is what I understand from your description) then yes, put the red wire on the same terminal and run it directly to the batteries BUT, I would put a fuse in the line.

Anything that chaffs through the insulation on the red wire will short your full battery capacity straight to whatever it touches. Best option in my opinion is a Blue Sea MRBF terminal fuse block.

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

I've already read the info that Stu provided and also pretty much everything written by Mainesail. Their ideas are the basis for my present plan. You guys are the best.

I believe Skip has answered my question which was really just to confirm that I've put my new red wire on the right alternator terminal(there are a bunch of terminals on the back of this thing) to run the charge directly to the house battery as suggested in Stu's "option 1".

I've already ordered my Blue Sea MRBF terminal fuse block and am following other suggestions outlined by Stu and Mainesail.

So, I'm set with my alternator connection?

[twinboat]

I have found a source for MRBF`s at a great price. Waytekwire.com

Sent from my VS840 4G using Cruisers Sailing Forum mobile app

[DeepFrz]

Contraman, I see no reference to the ground wire. The ground wire should go from the alternator to the neg. side of your batteries/bus bar/shunt and should be the same size as the positive wire.

[skipmac]

Originally Posted by djmarchand

Skipmac is correct, but put the fuse near the battery, not the alternator.

Yes absolutely.

[skipmac]

Originally Posted by Contraman

I've already read the info that Stu provided and also pretty much everything written by Mainesail. Their ideas are the basis for my present plan. You guys are the best.

I believe Skip has answered my question which was really just to confirm that I've put my new red wire on the right alternator terminal(there are a bunch of terminals on the back of this thing) to run the charge directly to the house battery as suggested in Stu's "option 1".

I've already ordered my Blue Sea MRBF terminal fuse block and am following other suggestions outlined by Stu and Mainesail.

So, I'm set with my alternator connection?

From what I (we?) can tell from the information at hand, yes. But as Deepfrz mentioned, you do have a ground wire too, yes?

[Contraman]

Originally Posted by DeepFrz

Contraman, I see no reference to the ground wire. The ground wire should go from the alternator to the neg. side of your batteries/bus bar/shunt and should be the same size as the positive wire.

The snow storm kept me busy, but I'm back to get clarification of my alternator ground wire. The only other wire that comes off my alternator is the red/yellow splotched wire pictured below(it's a sidewise photo) that goes to a fuse which splits to a purple wire(to the temp gauge) and a black wire that goes to the engine and then returns to the negative bus bar. I'm assuming that this is the negative ground from the alternator, right? It looks to be a small 12 gauge wire at best. I don't see a terminal on the alternator to connect a #2 wire equal to my proposed new positive charge wire coming off the battery. So what do I need to do to make this negative side equal to my positive side?

Here's the sideways image with the yellow painted red wire that goes to the fuse(not in the picture). Sorry that the picture is not better but it was 7 degrees out there!

[Dsanduril]

A quite common wiring detail in boats of a certain age was to run the battery negative connection to the engine block (because this is usually required for the starter to work) and then use the mounting bolts as the main negative path for the alternator (because the alternator case is usually negative).

This is a carryover from the auto industry, cars are usually wired the same way. With a small frame default alternator it (IMO) works fine. If you are running a larger alternator, high output for a long period, etc., then it is generally better to add a dedicated cable from the alternator negative to the negative bus. If there is no terminal for that then you can find a bolt on the case to which you can attach the cable. For your case with a small, standard alternator I wouldn't bother, but I'm sure there are others here who will vehemently disagree and will say so.

[westwinds]

Originally Posted by Contraman

I've disconnected an orange #8 wire that went to my amp meter and then to the isolator and replacing it with a red #2 wire going directly to house battery.

Your amp meter will now show only discharges. You will not be able to see if the alternator is charging at a rate to keep up with the current load. What I would do is get a full sweep sensitive voltmeter. That's where the needle swings from the center of the gauge across almost a full arc. These cost a little more than $100, but are worth it. Get one that shows voltage from about 8 volts to 18 volts. You can also get a digital voltmeter that is cheaper. You can use this to monitor the output of the alternator. The volt meter needs to be sensitive enough to detect a voltage that is low because one of the diodes has opened up on the alternator. The voltage will be about half a volt low, not much of a change. With a bad diode, enough voltage may be there to seem like the battery is being charged if not much current is needed for electronics. What will happen is the battery or batteries will slowly discharge because of the low voltage and become sulfated. You will need new batteries. If you want to stay with an amp meter, get a shunt and put it where the amp meter is with your #2 wire going to the shunt and then another #2 going to the house battery from the opposite terminal on the shunt. The opposite side of the shunt then goes to all of the electrical loads. The starter is on a separate wiring system so it is not included in the electrical loads. Ignore the fact that I mentioned the starter, it just confuses things. The new amp meter then hooks across the two terminals on the shunt. Or, you can also keep the old amp meter and just wire it like the shunt. The nice thing about a shunt is you can locate it near the battery or alternator, not where the amp meter is.

By the way, you batteries may be sulfated. If you have a place to add water to the batteries (not sealed batteries) get a hydrometer and check for state of discharge. Do not get a hydrometer with little plastic balls, or with an arm that swings back and forth, get one with a glass float and a little arm that sticks up with numbers on it. State of discharge can also be determined with a sensitive voltmeter while measuring the battery voltage after everything has been shut off for at least 6 hours. This is called the resting voltage. There should be a graph on the internet showing resting voltage vs. state of charge.