Alternator hot with engine off for days

[svJasmine]

diodes in alternator not working. batteries are trying to charge the alternator.

[john007]

So much information. Batteries connected in parallel. Solar panels in parallel connected to regulator. Solar regulator to batteries. The regulator should stop any feed back to the engine wiring

[Montanan]

Originally Posted by jsbartley

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!

In this regard, you were given wrong advice. This is a VERY common mistake when battery banks are wired. Reference the link below to learn about the tremendous imbalancing of charge and discharge that will arise from wiring both your positive and your negative leads [be they your load leads or your charging leads] to just one battery at the end of a parallel circuit of batteries.

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

I strongly recommend you utilize the illustrated perfectly balanced circuitry for wiring your inverter / charger to the battery bank.
I am suspecting that your solar power system is connected to your alternator somehow because if your alternator continues to be hot when the alternator is disconnected from the battery bank [i.e., the positive cable of the alternator is disconnected from the positive cable of the battery] than an alternate current source is still feeding into your alternator. I can't perceive a circuit requiring your solar power system to be connected to your alternator.

If you have this fundamental error in your wiring of a parallel battery bank, I suspect that you also may have other errors in your wiring. Your "experts" should know better, since they apparently don't, I wouldn't consider them to be experts.

[Montanan]

Originally Posted by mitiempo

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.

[David Mathis]

Try disconnecting the field wire for a day. Is the alternator still hot? Whether it's hot or not, you've started troubleshooting.

[Jlp0217]

Voltage checks tell you nothing but that connections exist. It takes current to produce heat. Check all wires to the Alt with a clamp on ammeter. There should be no significant current on any wire when the engine is not running, and only on the B+ and Ground wires when it is running. Besides B+ and Ground, there may or may not be an idiot light connection, a tach connection, and an ignition wire connection. Those should all have high resistance, thus little current, and no current when the ignition is off. For the Alternator to get hot requires some sort of internal failure if it is internally regulated, so advise to remove it and have it tested and fixed is good advise.

[GrowleyMonster]

Originally Posted by rslifkin

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.

THIS. You would not believe how common this is. Luckily it is a fairly cheap DIY fix unless you toast the batteries by driving them down to literally zero volts.



And BTW, FYI, one common way to cause this condition is to switch batteries OFF or disconnect them while the engine is running. It is okay to switch to both banks or to the other bank, if you have multiple banks, with a modern battery switch, but do not place the switch in the "OFF" position. Or disconnect any "sense" wire to the regulator while the engine is running. So, don't do that. Sometimes diodes just fail, though, for no particular reason.

[Cadence]

I'd go back to a shorted diode in the alternator. It acts as part of a bridge rectifier but as a blocking diode then not turning the alternator. How is your alternator output?

[jsbartley]

Dear fellow sailors... thanks for generous input to the problems I posted a few days back. I have refrained from filling this thread with individual or partial responses, and did some follow up of recommendations including dismounting alternator, replacing diodes, and testing. I was told alternator is fine.

I re-installed and found alternator was still heating up (with ignition off), and even if solar panel controller was offline. However, the alternator stopped heating up when I unplugged the two small red wires from the alternator (see attached photo), even with everything else connected. Any input on why these wires might be causing power to feed back to alternator would be appreciated.

FYI The heating of alternator is not affected by solar panels/controller (now connected to each end of house bank chain).

Looking forward to finally sorting this out, and thanks again for your help! Best.

[Montanan]

What is the make and model of the alternator?

Please provide information as to where each of the wires leading from the alternator connect to. One needs to be able to discern the complete circuit not just the leads to the contacts of the alternator to be able to assess the current pathways.

[ronstory]

The next step is figuring which or both of the red wires is hot with with ignition off.

Also, do you know the model of the alternator?

[ronstory]

It looks Hitachi to me.

[kenbo]

Bad ignition switch, that's based on that alternator bring fully checked and found to be fine. Check the voltage at both small wires when the ignition switch is off. Should read 0 vdc.

[ronstory]

Yep, it's a Hitachi and looks to be internally regulated.

Looking at the connector:

_ = sense line
| = Field/Indicator Light

Sense should be connected directly to the battery you are charging only

The field wire should be attached to a switched source, normally in series with an indicator light. When the internal reg fails it's there's a voltage difference and the light goes on, alerting you to problem.

[ronstory]

Oops... premature send

If the Field wire is hot with the ignition off... something is not wired correctly or the ignition switch is bad. So check that first.

If that is not the issue, for testing... just disconnect sense wire and jump the sense connector directly to alternator output and see if the case still gets warm.