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Old 19-04-2018, 08:29   #1
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Alternator wiring question

My Yanmar 2GMF20 is being rebuilt. I decided to upgrade the fuel and electrical systems while that is being done. The old Yanmar panel and wiring harness were not the correct ones for the motor so I decided to build my own panel, harness and connections.

FYI, my engine start battery and my house bank do not connect to each other. The house bank is solar charged only. The SLA start battery will be charged by the alternator when the engine is running, and kept topped off by a 40w solar panel with it's own charge controller when not.

The question is the alternator wiring. I am replacing the alternator with another Hitachi style unit. Pictures are attached. I found this info:

E = ground (DC negative) I will connect to my negative bus bar
B+ = Battery (DC Positive) I will connect to my battery directly
P = tachometer send

Question 1 is: do I need to also connect the Green and Yellow wires from the T style connector, or no?

Question 2: do you see any other issues I should be aware of?

I am sending pics of all the new stuff so you can see how I am doing this, absent all the other wires used by the original Yanmar harness.
(FYi, the engine alarm components are not yet installed)

Thanks,

Bob
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Old 19-04-2018, 11:34   #2
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Re: Alternator wiring question

On the Bosch alternators I use the T connection is for voltage sensing and the charge warning light.
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Old 19-04-2018, 13:08   #3
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Re: Alternator wiring question

Have a look at this Yanmar wiring diagram, it will help you figure out the connections. Stock Yanmar 2GM20 does not have continuous pressure and temp sensor outputs. The sensors are just on/off switches. You can either install additional sensors to feed your gauges or remove the gauges and install warning light. I think warning lights are simpler and more efficient.

One other idea is to create a much smaller panel. You only need the tach and three warning lights around the tach. I have been thinking about installing a chartplotter in the space for the instrument panel and moving the tach/warning lights elsewhere. You also need a buzzer which is much more important than the warning lights in my opinion.

SV Pizzazz
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Old 19-04-2018, 14:27   #4
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Re: Alternator wiring question

Don't know for sure. looks like you have a 12288N alternator, found this online





which seems to indicate that the yellow wire is a regulating wire and should be hooked to the charging terminal, while the green should be hooked to the voltmeter.

How far is your start battery from the alternator?

Typically the charge wire is hooked to the main starter cable at the starter, and charges back through that cable, which eliminates the need for an extra, long 6 gauge or so wire from the charging terminal to the battery; simpler and less expensive.
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Old 19-04-2018, 15:18   #5
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Re: Alternator wiring question

All: Thanks for the useful info, esp. the drawings. I will study them more tomorrow, but I believe they will answer my questions.
Pizzazz: I have always liked having gauges, just a thing with me. The old set up included a temp and oil pressure gauge. I have the correct sensors for the new ones. I am going to reuse or replace the old on/off sensors to activate a new buzzer, the old one did not work. As for warning lights, maybe, for triple redundancy, we will see. The location in the cockpit of the old panel meant when seated on the port side of the boat (it has a tiller, not a wheel) you could not see them, so a new location would have to be determined to make them useful.
Jim: the battery is about 4 feet away. I was going to run the B+ wire to the new fuse panel on the engine bay wall, but going to the starter main cable post makes more sense, and in looking at the old harness I think that is how it was done.
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Old 19-04-2018, 15:23   #6
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Re: Alternator wiring question

On second thought, there's some more, conflicting information here

Hitachi (Yanmar) alternator - machine sensed, or battery sensed?

I would ask either someone at the place you got it from, or if you don't trust them, call or go to a good alternator repair shop and ask them. If I couldn't get some information I trusted, I would hook up just the charge wire, run it and see what happens. As long as you have a place for the power to go, i.e. a positive cable to the battery, you won't pop the diodes. While the engine's running, test the output terminal for more that 13.5 volts and then check the voltage on the green and yellow wires.

If the alternator isn't putting out, it is likely that one of the wires is an excite wire, and should be hooked into an on/off switch in some manner, usually incorporated into the starter switch.
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Old 19-04-2018, 15:32   #7
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Re: Alternator wiring question

Quote:
Originally Posted by Stillwater1 View Post
..........

The question is the alternator wiring. I am replacing the alternator with another Hitachi style unit. Pictures are attached. I found this info:

E = ground (DC negative) I will connect to my negative bus bar
B+ = Battery (DC Positive) I will connect to my battery directly
P = tachometer send

Question 1 is: do I need to also connect the Green and Yellow wires from the T style connector, or no?

.....
Thanks,

Bob
Yes, one of those wires will need to be connected otherwise the alternator will not deliver any volts. I think it is the yellow one but right now I am only going on memory...

It may be connected direct to the B+ (like JimB suggested) which means the alternator will be operating any time it is spinning or it maybe connected via the engine off/on/start switch (to the "on" terminal) which means the alternator will operate only when the switch is "on". FWIW This is also the way the Yanmar panel works.

The other wire (presumably green) need not be connected if you are foregoing the alternator "charge" light.
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Old 20-04-2018, 13:37   #8
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Re: Alternator wiring question

"Yes, one of those wires will need to be connected otherwise the alternator will not deliver any volts. I think it is the yellow one but right now I am only going on memory...

....The other wire (presumably green) need not be connected if you are foregoing the alternator "charge" light."

I think not. The diagram shows the green wire can have an optional "charge" indicator bulb--but that is in parallel with a resistor. In typical automotive systems, they just use a light bulb as the resistor (which is problematic if the bulb burns out). The idea is that the resistor (or bulb) allows some power to be on this line IF THE KEY IS ON. So the alternator is only turned on when the engine is running, that's why it shows a connection to a "run hot" which we could call "ignition hot" in the US. A line that gets power any time the ignition/engine is in the "RUN" position.

(And no, I haven't tried to look over the whole thing, just saw that one right up.)
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Old 20-04-2018, 23:37   #9
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Re: Alternator wiring question

The Y/W lead is the voltage sensing connection to the regulator and it is used to sense the voltage level at the battery terminal. If you sense the voltage level at the alternator output and have resistance in the charging lead between alternator output and battery terminal it will result in the regulator tapering down the charging current before the battery is fully charged and you will only get a lesser charging current.

The LG/R lead provides a small current to the regulator to allow it to sufficiently activate the field coil on the rotor to provide a small level of magnetization to the field rotor in order for current generation to commence. Once a current is generated in the main coils the regulator takes it's current source through the W/BK connection.

The resister is there in case the indicator light goes open circuit.
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