2 alternators fried; what’s going on?

[N4585K]

Good morning fellow sailors. A bit more than a week ago I noticed my 2nd alternator, a 90A Mastervolt, not charging my 3 year old house bank consisting of 4 VMF Sportline 12V 140Ah batteries. I had an electrician look at my system and he took the alternator to a specialist and the verdict was that the alternator was history. An overhauled 105A Leece-Neville alternator was put on, connected to my Mastervolt regulator and I was sent on my way. After about 30 minutes there was a bad electrical smell and some faint smoke. I turned around and went back to where I came from. The alternator was pulled again. Now the Mastervolt regulator was the suspect. A new 90A Leece-Neville with an integrated regulator (RG82043) was put on, taking the Mastervolt regulator out of the loop. I left again, thinking things would be solved now. I motored for 2 hours during which it charged ok. But there was a light smell coming from the new alternator and it seemed very hot. Should I be worried?

My boat is an 2007 Oceanis 46 with the 75hp Yanmar 4TH4 engine.

Thanks everyone for your insights.

[Stu Jackson]

Have you confirmed that your alternator output wiring is reliable?
Interruption in the AO always fries diodes.
Good luck.

[DeepFrz]

How hot is hot? Alternators will run around 200f degrees, depending on engine room cooling and charge load. A new alternator will probably have a mild smell until it is used for a while.

[Fuss]

It’s not fixed, where did the smoke come from, this is the 3rd alternator so something burnt and that is important to know

[GrowleyMonster]

Do you have a master battery switch? And do you ever even by accident switch it to the OFF position while the engine is running?



Also are the batteries going dead while the alternator is supposed to be charging them?


Try a different electrician. That one seems to be overlooking something. A different pair of eyes might see a different thing.


Does your shore power charger charge the bank okay? Do you have an ammeter connected to a shunt on the negative terminal of the bank? You can get a digital one on fleabay for like ten bucks, with shunt.

[rgleason]

With so many alternators, perhaps as a start, you should trace out and draw a diagram for how they are wired, or describe the wiring.

[Jammer]

I doubt if there was anything wrong with your regulator. Who knows. Rebuilt alternators are sometimes defective (new ones too), and manufacturers and technicians like to blame anything else.


If your batteries are discharged, the alternator is going to get hot. A new alternator is going to smell hot. This is normal.


There are two things to watch out for.


You may have a shorted cell in one of the batteries. If this is the case, the battery bank will draw charging current but will never finish charging, and the affected battery will get hot and usually become low on electrolyte. The way you find this, is you check the electrolyte levels in all the batteries, and see if one is substantially lower. You can confirm your findings by starting the engine and letting the bank charge for 10-15 minutes or so and then check battery temperatures with an IR thermometer, to see if one is running hot. You can also use a clamp-on DC alternator, if you have one, to see if one battery is drawing considerably more charge current than the others.



A shorted cell is tough on alternators, and will keep the other batteries from charging, so that your electrical system will not work effectively.


The other thing to watch is that you may have a weak connection somewhere between the alternator and the batteries. You have to check every crimp and every bolt. An IR thermometer is again your friend here, charge the bank for 10 minutes or so and then check temperatures at all the connections. Anything hot should be disassembled, cleaned up, and re-made. Check + and ground, problems can be with either.

[Parrothedd]

Use an infrared thermometer to see how hot the new alternator really is. I agree with the other guy that it may running at Normal temp and smells a bit because it’s new.

[Cheechako]

Alt's get very hot. If you are still actually having an issue check your wiring and your master switch. Look at the back of the master switch, it may be melted or have a black spot. It's not that uncommon for them to fail.

[Elie]

I had the same problem, years ago. What i discovered is that engine compartment become very hot. I have installed a very powerfull thermostatic fan, and a smart regulator(Balmar H612 with optionnal temperature sensor attached to the alternator.
This regulator reduce output by 50% when things gets too hot for the alternator. And the big fan really extract a lot of heat. Since then, no more trouble...

[Sojourn2]

Is your second alternates mounted facing aft ie. Opposite way to the Yanmar fitted alternates.

If so, you need a straight bladed fan on the front of your alternates as it is turning in the reverse direction to which it was designed. The existing fan will be curved and will be turning the wrong way!!

It took me three alternaters to find this out.

[Mike Banks]

It sounds to me as though your ignition switch is incorrectly wired. The wire that livens up the alternator rotor when you turn the start key should disconnect the moment you release the key from the start position, because once the alternator spins it is self-sustaining and the regulator takes over control of the current in the rotor windings. If it is only your rotor windings that are cooked, this could be your problem. Of course there may be other reasons too--but I like to begin with the simplest fix and work from there.

Alternately, the wiring to the alternator may be incorrect so that the regulator is bypassed and the current to the rotor is at the maximum all of the time.

I just mention this because a friend was having trouble with his alternator, and this was the cause--it was charging to the max all of the time, and became overheated and burned out the rotor windings.

[N4585K]

Good morning again,
The past few days we were anchored in a place without internet (very refreshing sometimes!) but now we’re in Kioni, with Internet, albeit a bit spotty.

Thank you all for your replies! We motored for a bit more than 2 hours to get here. The alternator was still smelling but charging.

Stu: the alternator output wiring was tested last week and was supposedly good.

DeepFrz: not sure how hot exactly. I could touch the alternator but in less than a second I had to pull my hand off.

This Friday I’ll be back in Lefkada. My brother is flying in that day and he’s bringing an IR thermometer with him that I have ordered. So I’ll be able to come with better info re. temps.

Fuss: this is my feeling too...

GrowlyMonster: I do have master switches for my circuits. But they are behind a panel and I never switch them off. The batteries are being charged properly. I had a second electrician verify the work of the first and he didn’t see any mistakes. Shore power charges the bank ok. I’m not sure about the solar though. I have 2 flexible Solbian CP140 panels and a Fox 320 20A charge controller. There are no errors on the charge controller. It seems my bank should see a bit higher voltage after a day in the sun where my panels generate 16A around peak sun. This Friday I am having a Victron BMV installed so I should know more about how many amps are going into my bank.

rgleason: I’ll try to make a drawing this Friday together with the electrician as I do t trust myself to do it alone.

Jammer: the batteries were tested and giving a clean bill of health. My batteries are rated at 800 CCA and all 4 were measured at 670 which I was told was normal for a 3 year old bank. I will double check both the battery temps and the wiring temps with the IR thermometer on Friday.

Parrothedd: will do as described above.

Cheechako: master switch looks ok.

Elie: engine compartment temp is pretty good. The fan seems to be doing a very good job at that.

Sojourn2: both alternators are mounted the same way.

Mike Banks: the wiring of the ignition switch was never changed and the first alternator that got fried worked perfectly yfor at least 5 years (when I boat the boat). The new alternator has the regulator built in so wiring there should not be an issue.

Again, thank you all for thinking with me. I’ll post more findings after Friday when I have the Victron BMV installed and an IR thermometer to confirm temps.

[GrowleyMonster]

It's probably nothing but try isolating the solar panels and charge controller from the system for a day. I can't imagine how they could be working properly but making your alternator hot, but you seem to have checked every other detail.

[rgleason]

I think you'll find that with a battery bank that big (800-670ah) assuming flooded deep cycle batteries, that getting smaller and smaller alternators does not help. 25% acceptance rate= 200 to 150ah alternator.
The smaller internally regulated alternators with no alt or batt temp sensors might be running at full for too long, thus overheating and causing the electrical smells. I would probably want a larger alternator that was externally regulated with temp sensors.