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Old 04-04-2017, 08:58 AM   #1
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Wires to alternator

I have a 2006 30' Main ship rumrunner. 315HP Yanmar motor. For those of you that have the 315 HP Yanmar could you tell me the following.
How many wires do you have going to your alternator? 1 or 2? If you have 2 where do they go to, isolator and then to battery? I have an issue with the way mine is wired and I wanted to check with other 315hp Yanmar owners.
Thanks Jeff.
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Old 04-04-2017, 09:58 AM   #2
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Different alternators are set up differently and some have even one more for a tachometer.

Need to know what you have.
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Old 04-04-2017, 10:44 AM   #3
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All Yanmar engines use Hitachi alternators and AFAIK they also have more than 1 or 2 wires. Typically they have a heavy Pos output, a heavy negative, and a regulator start connection and a charging light connection.

Whether a diode type isolator is used is dependent on the boat builder. My 2006 Mainship 34T did have an isolator. The alternator pos output was connected to it and one of the isolator's outputs was connected to the common side of the 1,2,all switch and the other output was connected to the bow thruster battery.

All of the above may be irrelvant to what you are trying to know/do. Can you tell us what you are really trying to do?

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Old 04-04-2017, 11:27 AM   #4
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Ok,
I'll try and explain.
A while back I had a post asking what would cause charring or melting of the end of a cable on my battery isolator. I have a Guest model 2501 70 amp dual battery isolator device. The general answer was loose wires. I just got a chance over the weekend to start working on the boat before we launch. In fact the wires on the burnt cable were loose.
I searched for a replacement and they no longer sell that Guest 2501 model. Promarine? did suggest a replacement model . So I purchased the new one and went to take it off and trace out the cables and found the following. Two of the wires go to the alternator, Hot and ground?. One other wire goes to a battery switch that controls the start batteries for the gen and engine. The odd part was they had a wire 10 gauge? jumped out at the isolator going from the hot on the alternator to the other terminal which should have been for a battery. I showed it to the yard mechanic at the marina and right away he stated is was jury rigged. Now I did check the instructions and the one terminal is hot and the other two were supposed to go to the batteries. I didn't question him but I have not had any issue with the boat while running. The only thing was I saw this charring on one of the cables and that's why I questioned it. Now I'm wondering if it was jury rigged or can the device be wired this way? I can only assume they did this instead of running new cables? I don't know?
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Old 04-04-2017, 11:45 AM   #5
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I'm trying to upload attachment to make this easier. This is the device and how the wires run.
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File Type: pdf Battery isolator - wire hook up.pdf (339.6 KB, 38 views)
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Old 04-04-2017, 12:23 PM   #6
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OK, I understand your question/concern and it has nothing to do with the alternator, simply the way the isolator is wired.

That jumper means that the alternator directly charges the jumped connection. There is no diode protection against discharging. That is a little weired but maybe not fatal if that battery is not critical to engine starting. What is that other battery used for?

But it really doesn't matter except for better understanding. It could be a house battery or a bow thruster battery in which case it would not likely be discharged from the other starting battery running down.

I would just wire your new isolator without the jumper and it will be just like the Mainship I described above.

Now if you want to discuss the pros and mostly cons of isolators.....;-).

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Old 04-04-2017, 02:03 PM   #7
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Since you have it, wire it according to directions. Sounds like someone was working around something that was either broken or misunderstood...?

However, I'm no fan of isolators either.

Isolators have a bad habit of prematurely killing batteries via incorrect charging, their purpose as a "one way valve" prevents the alternator/regulator from seeing the true condition "on the other side". The batteries on the other side end up undercharged.

Boats and RV's are riddled with the things... and both camps end up fooled that it is acceptable to change batteries annually or bi-annually....

Using a heavy relay to combine the batteries, as simple as switched with the ignition key, or more fancy, charging system activated, will protect the start battery from careless house loading, and let the charging system properly charge the batteries.

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Old 04-04-2017, 03:06 PM   #8
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Your isolator's rated at 70A. How big is your alternator? It's possible the toasted conductor you saw was the result of the isolator as well as the appurtenant wiring being undersized... Same with the jumper. Perhaps one of the diodes opened and the jumper was added to get that battery to charge? Either way, you need to look at the whole picture, not just a terminal on one of the connections.

First rule of troubleshooting 101: Never assume that the guy before you knew what he was doing. Presume that it's all wrong and look at it from that perspective, you'll stay out of trouble and fix more stuff right.

Second rule: If you don't what you're doing, call in someone who does.
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Old 04-04-2017, 07:54 PM   #9
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Jeff
I had issues with charging on my MS 34HT and eventually decided to eliminate the isolators in the alternator & shore powered charger.
Here's the thread w/ links to more info, diagrams, etc.
MS 34HT Charging Mods
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Old 04-04-2017, 08:11 PM   #10
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So is an Automatic Charging Relay such as the Blue Seas a better option then an isolator?
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Old 04-05-2017, 06:05 AM   #11
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Several options better than diode isolators IMHO...ACR is one of those that eliminate the V drop associated w diodes.
The Same Today lists the various alternatives w +/- and was a good place to start for me.
As I outlined I considered a couple different approaches before deciding on the Sterling unit I chose. I'm sure other options would work as well and would be better than diode isolators.
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Old 10-12-2017, 09:33 PM   #12
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