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Old 13-10-2019, 06:55   #1
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Question Alternator hot with engine off for days

I have a 1996 Beneteau Oceanis 400 with a Yanmar. I have recently added 4x100W solar panels, connected thru regulator to one of batteries on house bank, which keeps them topped off as I do not have shore power. Went to boat after one week since last outing, and found the alternator to be hot (uncomfortable to touch). I thought somehow the solar input was "feeding back" to the alternator and causing it to heat up, however, I disconnected panels and two hours later, alternator still hot. Had to disconnect alternator. Any clues as to what could cause the alternator to heat up on a cold, and unused engine? Thanks for your advice for an "electrical neophite"...
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Old 13-10-2019, 07:00   #2
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Re: Alternator hot with engine off for days

We could guess but you would be better served by measuring voltages with a simple voltmeter at the alternator with the engine off and panels on
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Old 13-10-2019, 07:09   #3
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Re: Alternator hot with engine off for days

Generally this would be a symptom of a failing rectifier diode on the alternator. If one of the diodes starts to allow current to back-feed, the alternator can draw power while not running and turn into a heater.
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Old 13-10-2019, 08:21   #4
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Re: Alternator hot with engine off for days

Remove your alternator and take it to an alternator/starter repairshop and have it checked out. Thx-Ace
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Old 13-10-2019, 08:36   #5
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Re: Alternator hot with engine off for days

Thanks for quick feedback. Will test voltage as suggested and pursue the diode theory. Will report back! Thanks again.
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Old 13-10-2019, 08:45   #6
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Re: Alternator hot with engine off for days

Leaving ypur ignition key on. Alternator has an electromagnet in it for field. No rotation equals no cooling.
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Old 13-10-2019, 09:53   #7
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Re: Alternator hot with engine off for days

You likely have field current going to your alternator. Probably drawing around 5 amps or more. Any chance you accidentally connected the field wire to a +12v source? I should only be connected to the regulator.
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Old 13-10-2019, 10:23   #8
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Re: Alternator hot with engine off for days

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Originally Posted by jsbartley View Post
I have a 1996 Beneteau Oceanis 400 with a Yanmar. I have recently added 4x100W solar panels, connected thru regulator to one of batteries on house bank, which keeps them topped off as I do not have shore power. Went to boat after one week since last outing, and found the alternator to be hot (uncomfortable to touch). I thought somehow the solar input was "feeding back" to the alternator and causing it to heat up, however, I disconnected panels and two hours later, alternator still hot. Had to disconnect alternator. Any clues as to what could cause the alternator to heat up on a cold, and unused engine? Thanks for your advice for an "electrical neophite"...
Unrelated to your hot alternator issue which is drawing considerable current, but I noted that you stated the 4 solar panels are connected "to ONE of" the batteries of the house bank. The charger from the solar power circuit should not be connected to just ONE battery in a bank as that would lead to significant imbalances and inefficiencies in the charging and the discharging of the batteries and premature degradation of the bank.

Not sure if your bank is a parallel or a series bank or a paralleled series of batteries but it may be wise to see if your battery bank is properly wired.

Some references of images of circuits listed below showing commonly incorrectly wired and more appropriately wired battery banks.


https://www.impactbattery.com/blog/t...s-in-parallel/

https://www.mobile-solarpower.com/20...ar-system.html
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Old 13-10-2019, 10:40   #9
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Re: Alternator hot with engine off for days

Yep, likely the diode. If you take the belt off it may run/turn like a motor.
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Old 13-10-2019, 10:59   #10
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Re: Alternator hot with engine off for days

I second mvmojoís response. Your field voltage is likely still on. If you have an external regulator, it should be tied to a source that gets shut off (often ignition). If you donít have an external regulator, itís probably the built in voltage regulator and send the alternator to a shop.
A good test for field is to put a screwdriver on the hub of the alternator. If itís magnetic, your field voltage is on, and it shouldnít be with the engine/ignition off.
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Old 13-10-2019, 11:48   #11
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Re: Alternator hot with engine off for days

Hello friends, thanks for the multiple inputs. I just ran a few tests as best as I could. FYI, these tests were with engine off and ignition switch fully off.

1. When I got to boat, even with alternator's positive terminal disconnected (and solar panels connected), alternator was still hot.
2. Voltage reading at (connected) alternator was 14V with panels connected, and 13V with panels disconnected.
3. I've hired two different (presumably) electrical experts, and the boat's previous owner had a boat electronics company, so was supposedly set up by "experts".
4. The alternator is relatively new (I replaced), and I was told the alternator controller is internal. It was removed in July and taken to a shop for testing, and came back OK.
5. Regarding point about panels being connected to one battery on the bank, that is what I was advised to do... so, I have all four panels joined in parallel (using Renogy MC4 connectors), going to one Coleman regulator rated for 32 amps. So, don't see how I can split the flow into the house bank unless I install additional wiring from each panel to individual regulators, which I understand is bad because regulators may conflict.
6. FYI, I have a Xantrex inverter charger in the configuration.

Sorry for so much detail, but if anything obvious pops up, happy to hear it, though at this stage, I think I will have to try to find another boat electrical guy in South Florida to handle this, hopefully more reliable than previous ones.... I'm planning a cruise to Exumas after New Years and need to have this sorted out before departure.

Thanks again for your input!
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Old 13-10-2019, 12:04   #12
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Re: Alternator hot with engine off for days

Check for voltage at the field terminal with ignition switch on and off as suggested above.
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Old 13-10-2019, 12:14   #13
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Re: Alternator hot with engine off for days

Quote:
Originally Posted by jsbartley View Post
I have a 1996 Beneteau Oceanis 400 with a Yanmar. I have recently added 4x100W solar panels, connected thru regulator to one of batteries on house bank, which keeps them topped off as I do not have shore power. Went to boat after one week since last outing, and found the alternator to be hot (uncomfortable to touch). I thought somehow the solar input was "feeding back" to the alternator and causing it to heat up, however, I disconnected panels and two hours later, alternator still hot. Had to disconnect alternator. Any clues as to what could cause the alternator to heat up on a cold, and unused engine? Thanks for your advice for an "electrical neophite"...
My WAG is a diode is shorted in your alternator.
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Old 13-10-2019, 12:42   #14
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Re: Alternator hot with engine off for days

Quote:
Originally Posted by jsbartley View Post
5. Regarding point about panels being connected to one battery on the bank, that is what I was advised to do... so, I have all four panels joined in parallel (using Renogy MC4 connectors), going to one Coleman regulator rated for 32 amps. So, don't see how I can split the flow into the house bank unless I install additional wiring from each panel to individual regulators, which I understand is bad because regulators may conflict.
In a parallel bank the negative should be connected to the battery at one end of the string and the positive to the battery on the other end. This applies to any other connections to the bank as well. If all wiring is on one battery it will see the most use, use more water if a flooded battery, and live a shorter life than the others.
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Old 13-10-2019, 12:51   #15
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Re: Alternator hot with engine off for days

I don't understand why you would have your panel power run through yor regulator. Why not panel to controller to batteries. No alternator/regulator involved
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