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Old 15-07-2010, 19:00   #1
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Alternator Heating Up . . . Too Much !

The alt on my Yanmar is a Delta. It is a 60amp internally regulated. recently rebuilt. It gets so hot you cannot rest your hand on it. I took it back to the outfit who rebuilt it, they put it on the bench ran it and said it was working properly.?? I don't think so. There has been much to be disired in this town of Savannah Ga in the way of marine outfits. I am not sure how to handle this at this point. The alt pulley and the main pulley are lined up. Is there something I could be missing. I do know I need to replace one of my bats and don't attempt to charge the bad one, it strains the alt. So other than that I'm not sure.
I will be happy to recieve input on this one too. You folks were great on my last question about Gallons per Hour. I am hopeful. Thank you in advance, forum.
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Old 15-07-2010, 19:02   #2
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What is the size of your house battery bank, and what type of battery (flooded, AGM, gels, etc.)??
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Old 15-07-2010, 19:16   #3
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my balmar instructions warn not to touch the alternator when it has charged at a high rate because of possible burns.

I was shooting mine with a heat gun and read just over 200 degrees when high charging. I called Balmar and they said that isn't abnormal.

When the battery is down a good amount the alternator will put out max charge (bulk phase) and get real hot. When the bulk phase is over, the temp will drop. When my bulk phase ends the temp comes down to around 140.
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Old 15-07-2010, 19:43   #4
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the house banks

are a mixed match that will be remedied on Sat. They are merely Wallmart bats. One is a group 29(good bank)...EverStart Maxx Marine, the other (bad bank) is a group 27 EverStart Marine, much smaller in all ways. I will trade out the group 27 for another group 29. Could this be my alt overheat issue? I thought it may be which is why I keep the 27off line. ?? They are flooded.
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Old 15-07-2010, 19:51   #5
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my balmar instructions warn not to touch the alternator when it has charged at a high rate because of possible burns.

I was shooting mine with a heat gun and read just over 200 degrees when high charging. I called Balmar and they said that isn't abnormal.

When the battery is down a good amount the alternator will put out max charge (bulk phase) and get real hot. When the bulk phase is over, the temp will drop. When my bulk phase ends the temp comes down to around 140.

We Shall see what my deal is once i unload the group 27 for another g29. I had no idea that it was norm for an alt to run at over 200 degrees. hmm. Well this is good info gentlemen. I thank you for the knowledge. It is comforting to know, gettinthere, that a good alternator like Balmar gets that hot...same as my Delta.
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Old 15-07-2010, 20:13   #6
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Put a clamp ammeter over the primary wire and confirm that it is indeed putting out its maximum current. No alternator is 100% efficient, therefore there will always be some waste heat.
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Old 15-07-2010, 20:13   #7
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G' day

Most high output alternators run too hot to touch,is not helped by high local ambient temps.Check all connections, batts, etc to be on the safe side.
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Old 15-07-2010, 20:18   #8
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"Hot" is a subjective concept. The question is, what temperature is your particular alternator rated for continuous duty?

Airflow in a boat engine compartment is much less than under the hood of a car, so a marine alternator is going to get hot. It might be equipped with one fan (front or rear) or two fans, which usually keep it cooler. Or you might need to duct some air flow over it.

If your alternator has an external regulator which is keeping it putting out a full charge--that will overheat it compared to the typical internal automotive regular, which puts out a full charge very briefly and then ramps way down, fast. Likewise if your batteries are hungry and sucking up a full charge, the alternator will be heating up more and faster.

But it comes back to what that particular alternator was designed to accomodate. And in any case, solid state electronics (the alternator diodes and the regulator) will last much much longer if they can run cooler, so it pays to get the temperature down to something bearable, no matter what it is rated for as a maximum.
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Old 15-07-2010, 20:19   #9
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Originally Posted by nico105 View Post
We Shall see what my deal is once i unload the group 27 for another g29. I had no idea that it was norm for an alt to run at over 200 degrees. hmm. Well this is good info gentlemen. I thank you for the knowledge. It is comforting to know, gettinthere, that a good alternator like Balmar gets that hot...same as my Delta.
If you want to see it get really hot throw in some AGM's or a large bank of wet cells and then discharge them deeply. Alts get hot when run hard. If you don't regularly discharge your bank below about 50% capacity, and the bank is not to over sized for your alternator, you should be fine even though it is "hot" unless of course it is unrealistically hot.

An infrared thermometer is a good investment as it will give you more specific information about the actual running temps then these can be compared to the alts "rated" temperatures.Longer alt life begins with cooler temps if you can finagle that.
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Old 15-07-2010, 20:28   #10
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we have learned, Nico105, that you are a brave man.
welcome to the forum.

Next time, you may want to check in here BEFORE laying hands on hot engine parts.
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Old 15-07-2010, 20:48   #11
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Alternators can also get very hot from a slipping fan belt.
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Old 15-07-2010, 22:20   #12
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Bosch has a high efficency alternator at 70%. At 70% (at best) the engine has to be feeding the alternator 60 amps plus another 30% to make up for the inefficiency which is 18 amps. So 60 amps plus another 18 amps is 78 amps. 18 amps times a typical charging voltage of 13.8 is 248 watts that must be dissipated as waste heat. It could be that you are feeling those 248 watts (plus with a less efficient alternator) of waste heat.
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Old 15-07-2010, 22:37   #13
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So 60 amps plus another 18 amps is 78 amps. 18 amps times a typical charging voltage of 13.8 is 248 watts that must be dissipated as waste heat.
Actually it's 355W of waste heat and noise by your numbers.

(1-1/.7)*60A*13.8V
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Old 16-07-2010, 00:13   #14
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Just found the same problem with mine. Then I noticed a little arcing at the output stud on the back, my amp gauge was jumping around too. Turns out the nut holding the output wire had vibrated loose just a bit, causing a bad connecction. Tightened it up and all is good. Check the simple things first.
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Old 16-07-2010, 01:42   #15
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Wait a minute, guys. We don't even know how hot it is. We don't have any basic data.

OP, I think the very first thing to do, in my opinion, is buy one of those infrared thermometer guns and measure what we're talking about.

It is perfectly normal for an alternator to get hot enough to fry an egg, when it's putting out near maximum current.

Then check the temperature against the manufacturers specs.

THEN we'll know whether there is any question or not, and whether it is necessary to start working through the other issues.
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