Overheating alternator

[Tomek23582]

Last weekend I noticed that my alternator is running quite hot, surface temp definitely exceeded 100°C (212°F). I noticed a smell like burnt rubber, which alerted me to check on the engine. I just bought the boat this spring so I have little experience what is normal and what is not. I did not notice this problem in 2 or 3 few short trips I made since the purchase. I think the smell came from some (not excessive) amount of rubber dust from the v-belt that landed on the alternator. The rest of the engine seemed normally hot, the cooling water was running fine all the time.

Is such high temperature still in acceptable range? What is acceptable maximum?

Details: I have a Hunter 33 (2006) with Yanmar 29hp. Alternator is 60A. I have 3 batteries in 2 banks (1 starter and 2 in house). They are all the same deep cycle maintenance free, do not know exact Ah but by the looks they are probably about 110 Ah each.
During this last weekend's trip I have discharged the batteries a bit (good wind, little motoring) and among other things I used the windlass several times in 50Ft anchorage (dropping and hauling 100 ft of chain plus some line).
Would low charge of the batteries force the alternator to work extremely hard? I thought the alternator would have a current regulator that would prevent overcurrent. Is there any changeable setting on the regulator?

Any help will be appreciated,
Tomek

 

[Rich Stidger]

If your alternator is stock you may have maxed out it's output trying to charge very low batteries. A hot alternator would be an indicator of that situation.

The only regulation for a standard internal regulator that I know of is for voltage. The max current is limited by the capacity of the alternator. The max current you can get out of a stock 60A alternator is about 42A when it is cold and maybe 36-38A when it is hot.

If you have AGM batteries, I understand that they will accept much higher currents than flooded batteries when discharged. I have heard that AGM batteries can stress a standard alternator to failure. I HAVE NO DIRECT EXPERIENCE WITH AGM.

To answer your question, if you have an external regulator, then you probably have a current limiting setting. If it is the stock internal regulator, you do not have such a setting.

 

[Tomek23582]

Thank you Rich.
This generally confirms my suspicions. I will try to confirm it further next weekend after the batteries are fully charged from shore power. If the alternator runs cool(er) then the problem is diagnosed.
Now, how do I check whether the alternator or regulator is not damaged? Is there a simple voltage or current measurement I could do? It would be tricky, I guess, to measure current above 10A, even more so at 30-60A.

 

[Rich Stidger]

A quick and easy test to see if the alternator or regulator has been damaged or died-

With the batteries pretty much charged, start the engine and measure the voltage at the alternator. It should be 13.4V or greater. If it is not, run the engine speed up to 1500-1800 rpm and measure again. If it is still below 13.4V, something is wrong.

If the voltage is at 13.4 or greater, then speed the engine to about 2000 rpm and turn on every electrical load you have. Lights, refrigerator, instruments, everything. Measure the alternator voltage again. If it is over 13.4V then all is good. If the voltage drops under 13.4V, there is a problem.

The simple checks above won't define where the problem lies- it could be either the alternator or the regulator. But at this point you can remove the alternator and take it to any electrical automotive shop and ask it to be tested further.

I do assume that all of the loads that you can turn on total to less than 42A or the total capacity of your alternator.

BTW, I would not advise connecting or modifying your alternator to accept an external regulator. They can provide a high level of drive to your alternator and cause the alternator to run at it;s limit. Stock alternators are not designed for this type of service. For an external regulator you need a heavy duty hi-output alternator with dual cooling fans, bigger bearings, and heaver windings. Many cruisers don't need this type of system.

 

[Tomek23582]

My previous reply from yesterday got lost i cyberspace so here it goes again.

Thank you Rich again for your detailed answer, I will check that on the weekend.
I was not planning to add an external regulator, but wondered if there are any adjustments on the built-in one.
One additional thought: if I set the batterry switch to only one of the banks, the alternator should charge only that one, right. Would it lower the current demand to 2/3 or even 1/3 (1+2 batteries in the banks)?

 

[Maine Sail]

My previous reply from yesterday got lost i cyberspace so here it goes again.

Thank you Rich again for your detailed answer, I will check that on the weekend.
I was not planning to add an external regulator, but wondered if there are any adjustments on the built-in one.
One additional thought: if I set the batterry switch to only one of the banks, the alternator should charge only that one, right. Would it lower the current demand to 2/3 or even 1/3 (1+2 batteries in the banks)?

There are no adjustments on the internal regulator. They are simply set for 14.4V +/-0.3v. Until your batteries come up to the regulated voltage set point your alternator is simply full fielded or wide open. I have customers with these alts, the LR-160, and regularly see them putting out mid 50's for amps with the bank depleted. If you have the factory wiring harness that may limit you a little bit but will still allow the alt to get quite hot.

If your bank is heavily depleted then you'll definitely see your alt get quite hot. If the bank is too big you may even cook the alt but I see this more with AGM than with wets unless the wet bank is huge.

If your batteries are standard wet cells they'll take roughly 20-25% of the Ah capacity during bulk charge. With approx 330 Ah's of battery that means your alt is smaller than what the batteries can technically accept so you will see it get hot as it won't hit acceptance limiting until about 80% state of charge.. The trick is to not discharge below about 50% of your banks capacity then you won't be running the alt at max for as long a period of time.

So if your bank is 330Ah / 50% = 165 Ah's usable

Getting from 50% SOC to 80% SOC requires you only replacing 99 Ah's before the batteries begin limiting what they will accept. That is still 2 hours plus/minus of your alt running wide open.. If you can take a bank off line, like the start battery, that can help or reduce the engine rpm until you see the amps drop. This will allow your alt to run slightly cooler yet still charge though you do need an ammeter or battery monitor to see this..

I just realized that your house bank may only be 220 Ah's. So 50% capacity would be 110 Ah's used. Going from 50% SOC back to 80% SOC would mean replacing 66 Ah's which should not be to much of a work out for the LR-160.

 

[Tomek23582]

Thank you Maine Sail. A lot of useful information.
Just one more question: what temperature is too hot? (I can borrow remote IR thermometer to check).