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Old 28-09-2017, 10:58   #1
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Phantom Electrical Issue - Yanmar 3HM30F

I have a 1984 Prout Snowgoose with a few electrical nuances i'm working through and think are related. Both engines are Yanmar 3HM30F.

1.) When plugged into shore power the starboard engines alternator is warm to the touch (104 deg F).
2.) Engine hour meter runs, even though the engine isn't on. I located and disconnected wire to stop it from continuously running.
3.) Warning lights stay on when the engine is off and key removed. The lights turn off once the engine has been started

The starting/ignition systems functions property otherwise, as far as starting the engines. The buzzer and warning lights function as well, recently i had a freshwater cooling pump break and the buzzer/lights went off.

The warm alternator is the issue i'm most concerned with getting squared away. I'm heading up to the boat with a multi-meter this weekend to see if i can chase down down some of these problems.

Any electrical gurus out there have ideas of what might cause that warm alternator? or suggestions of where i should start trouble shooting?

I have Type B Instrument Panel, included is a wiring diagram for a 3HM35F - which i'm guessing is similar to mine.

Thanks
Nich
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Old 28-09-2017, 11:03   #2
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Re: Phantom Electrical Issue - Yanmar 3HM30F

Sounds like you may have AC leaking into your DC. Disconnect your battery charger and see if it goes away.
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Old 29-09-2017, 05:44   #3
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Re: Phantom Electrical Issue - Yanmar 3HM30F

Greetings and welcome aboard the CF, Nich.
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Old 29-09-2017, 07:14   #4
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Re: Phantom Electrical Issue - Yanmar 3HM30F

Quote:
Originally Posted by Jarlsbergn View Post
I have a 1984 Prout Snowgoose with a few electrical nuances i'm working through and think are related. Both engines are Yanmar 3HM30F.

1.) When plugged into shore power the starboard engines alternator is warm to the touch (104 deg F).
2.) Engine hour meter runs, even though the engine isn't on. I located and disconnected wire to stop it from continuously running.
3.) Warning lights stay on when the engine is off and key removed. The lights turn off once the engine has been started

The starting/ignition systems functions property otherwise, as far as starting the engines. The buzzer and warning lights function as well, recently i had a freshwater cooling pump break and the buzzer/lights went off.

The warm alternator is the issue i'm most concerned with getting squared away. I'm heading up to the boat with a multi-meter this weekend to see if i can chase down down some of these problems.

Any electrical gurus out there have ideas of what might cause that warm alternator? or suggestions of where i should start trouble shooting?

I have Type B Instrument Panel, included is a wiring diagram for a 3HM35F - which i'm guessing is similar to mine.

Thanks
Nich
You have an electrical short circuit across your key switch.

If you are highly skilled with marine electrical systems troubleshooting and safety procedures, proceed.

If not, hire a sparky, you will be dealing with energy sources that could easily cause a fire if mishandled.

First of all, verify what has changed since last working properly. Did you or anyone mess with the wiring? If so check there first.

1. Verify that when the battery switch is off, there is 0 Vdc on the key switch 30 connection. If there is 12 Vdc, find out why.

2. With battery switch off and key switch off, verify there is 0 Vdc on the AC (unfortunate choice for identification) side of the key switch. If there is 12 Vdc find out why.

3. After confirming 1 and 2, with the battery switch on, and key switch off, verify there is 12 Vdc on the 30 side, and 0 Vdc on the AC side of the key switch. If 12 Vdc on the AC side, find out why. (Likely a short circuit to 12 Vdc on the AC side, either due to erroneous wiring, bad key switch, or bad alternator.

4. Verify the alternator is wired correctly. If so, disconnect the wires and check AC side of key switch. If it was 12 Vdc and drops to 0 Vdc, you have an alternator wiring or device fault.

5. If you still have 12 Vdc on the AC side of the key switch, verify there is no extraneous wire connection to that terminal.

6. If 5 is verified, disconnect the wires from the AC side and verify it is 0vdc with the key switch off (battery switch on).

7. If the AC side is 12 Vdc in step 6, replace the key switch.
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Old 29-09-2017, 21:43   #5
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Re: Phantom Electrical Issue - Yanmar 3HM30F

I would begin with the most obvious. Replace the ignition switch--I think it must not be turning off properly.
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Old 30-09-2017, 00:53   #6
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Re: Phantom Electrical Issue - Yanmar 3HM30F

I do not think you have a bad key switch or AC voltage leaking into your DC system.

I think your battery charger was wired to the engine instead of to the battery. It is supplying DC power directly to the engine electrics - bypassing the key switch.

Why do I think this?

AC power would not cause hour hour meter to run - it would destroy it.

Your alternator's voltage regulator is being energized and therefore the alternator is warm AC would, again, destroy it.

You say that the only time this happens is when shore power is connected. If it was a bad key switch this would be happening anytime the engine was off.

Check how your battery charger is connected. It should go directly to the batteries with appropriate circuit protection (fuse or circuit breaker).
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