Hot Alternator

[Juliet 15]

Hi all. Last weekend I took my boat out for its first spring trial run and to make sure everything I did over the winter worked. Once every hour I go into the engine room and do a temperature check with a laser thermometer. I've tracked all the temperatures for a year now, so I can tell when there is a change occurring. One of the things I'veChecked has been the temperatures of my three alternators. I have 2 x 32V alternators (one per main engine), and 1x 12V alternator on one main engine that charges My 12 V system.

Over the winter I replaced the belt on the 12 V alternator. I also noticed the original installation had placed the alternator out of plane with the drive pulley, so there was some twist to the belt. I adjusted this and set it up so there was no twist and the alternator appeared to be in plane. On this last outing, The alternator temperature was about 128 Fahrenheit on the trip out. After spending two days on the hook using the 12V system, we headed home. About an hour underway I checked the temp on the 12v alternator and found it to be 220°F. Does anyone know the normal temperature of a 12 V alternator? Is this common when charging at maximum capacity? It's a Presto light/Leece Neville 51 amp alternator. It charges 2 x 8D batteries and the bow thruster batteries. Am I killing this alternator by using it to charge too large of a load?

 

[Larry M]

Temperatures can run up to 240 or higher based on ambient temps and loading. What you are seeing is with low batteries, the alternators working hard so the temperature goes up. I wouldn’t be worried.

 

[DavidM]

I think that your alternator is reacting as expected to a very large load suddenly put on it. A 51 amp alternator is pretty small, so it will take quite a while to pull up two 8D batteries.


As Larry notes 220 F is high but not that high. The problem is that the large load is going to be on it for a long time, several hours at least, until it gets the batteries charged up and the load diminishes.


Leece-Neville makes lots of battery types and sizes. Can you find a heavier one to replace it with?


David

 

[FlyWright]

[STRIKE]IIRC, I think I was told by CMS that the max Balmar alt temp should be ~135*F and my alt temp circuit on the Balmar ext reg is set to cut off at 135*. (I'll check my numbers next time I'm aboard.) [/STRIKE]Ultimately, I needed to add a cooling blower to keep the temp within specs. When I smoked my Balmar, it was indicating 350*F after the smoke cleared.

Sounds like you might have lost a bearing from the sideload. The alternator will continue to work until it won't any longer. Then you might lose the function of a water pump like I did on my lil' Perkins. Might as well look into it on your schedule and pull it. It's worth pulling and looking into, just in case.

EDIT: The proper temps are posted below by David Frye

 

[AKDoug]

I have a temperature sensor on my Balmar 100 amp alternator, and when I am charging hard it gets quite hot (not 220 degrees F hot, but 80+ degrees C) and cools off after it drops out of bulk into accumulate and float modes. I have come to accept that as the normal cycle.

My bank is just over 400 AH on two 4D Lifeline's, so it usually tops out of bulk in less than an hour when I start running. I have no genset, so everything runs off the house bank when the engine is shut down.

 

[fryedaze]

Balmar Series 6 Alternator specs attached.
Normal Operating Temperature: 180 °F / 82° C

Max Operating Temperature: 225° F / 108° CView attachment PDS-60-100-DV(1).pdf

 

[O C Diver]

Does the alternator have an external 4 stage regulator?

Ted

 

[rsn48]

Check out this regulator info from Jeff Cote:

Also a longer video from Jeff on the external regulator:

 

[C lectric]

I Agree about check the alternator bearings. That would also give a shop time to check the windings for any trouble. Any problems internally may also heat the unit.

Any air flow restriction from dust/dirt will heat the alternator. Tried blowing it out both ways, fwd & rvs?

Are you positive that the belt is not slipping as that can surely heat an alternator? The slippage will heat the sheave and the heat can travel the shaft to heat the internals.

It's also possible the batteries were discharged deeper than you realize so the alt. was running in bulk longer than you realize.

You might consider a larger alt. so the bulk charge is passed through a lot quicker.

 

[FF]

"Are you positive that the belt is not slipping as that can surely heat an alternator? The slippage will heat the sheave and the heat can travel the shaft to heat the internals."

YES!

A slipping belt can heat the heavily loaded bearing enough to melt out its lubricant , then the alt really heats up.

The "best" solution a really quality large frame alt with dual belts driving it.

Leece Neville 135A under $150 at truck parts house.Fan (right direction) extra , dual belt pulley extra , V regulator 3-4 stage extra .

Once installed nothing extra for a decade or two.

 

[Juliet 15]

Thanks for the input. I know the belt isn't slipping, but I hadn't considered some of these other points. The batteries are pretty big for that little alternator. No, it doesn't have an external regulator. Great idea, though. I will get a shop to look at it and see if the breading is still ok, but I bet you're right - it's probably too small for The bank size, and it'll have a short life. I'll look for a larger one. Interesting, I haven't found a 150A that cheap, so maybe I'm looking in the wrong places.

 

[DDW]

Alternators are quite inefficient, around 60% is all you can expect. That means 40% or more of the power input heats the alternator frame. 50A output at 12.8V is over 400 watts in heat in a small piece of metal.

If you look online you can find LN or Delco alternators in the 160 - 200A range for around $200 - $250, for example try alternatorservice.com.

 

[Juliet 15]

It looks like my alternator is just undersized. I'll get another larger one. I've Been avoiding it since it's almost impossible to tell if a replacement will fit my mounting system, or to know whether the pulley will fit on the new alternator. Is there a way to tell that?

 

[C lectric]

Most alt. mfgrs. show dimensions on their site. As you zero in on a unit look from those dwgs. You will need to study them and also measure what you have.

I measured the shaft and the new unit used the same diameter shaft.

Most larger alternators use a J180 mount. You might have that in which case the fitting will only be to allow for the extra alt. case size. That was the case with my 60A alt. so It just went all together.

Your engine mfgr or dealer may be able to tell you which mount you have.

Many smaller alternator use one of several other mounts. IF the J180 is not what you have then maybe the J180 is available for your engine.

If not then you will need to determine what you do have.

GOt some GOOD photos?

You may not want to go 150 unless you can drive it with two belts. A one belt drive should be limited to about 100A. You could go the 150 but then control it with an aftermarket regulator which almost always incorporate the the ability to turn the alternator output down. That would not be a bad idea as the alt. could run far longer at that lower output yet still double what you have now. To boot they will actually recharge faster than the internal ones almost always used in off the shelf units.

Someone mentioned that L.N. offers a regulator that is three stage. Take a look. That would be a good way to go.

 

[Juliet 15]

Thank you. That is super helpful. I looked up J180 mounts and got the info about the long ones and the short ones and the measurements of each. I'll measure mine and see what I have. It's a small Prestolite. I also appreciate the info about 150 being too much for a single pulley. You're right of course. Even a 100A will double what I'm putting out.

 

[FF]

"Even a 100A will double what I'm putting out."


IF 100a is the hot rating.

 

[EngNate]

2 x 8D's at 50% charge will easily demand 100 amps if available. The alternator is undersize for the application and a reduced service life can be expected. The temp observed under these conditions is in the expected range. 100-140A is what you need.

 

[Comodave]

Check out marinehowto.com for a lot of great info on alternators.

 

[Juliet 15]

I just got in the mail my (COVID-19 and gluten-free) brand new 105 amp alternator which is a direct swap out. This should largely fix the high temp issue, I hope. I could have gone bigger, but I didn't feel the hassle of adding a 2nd pulley and building a new mount system was worth it.

Looking back I think it was dumb of me not to figure out that demand was the issue. I spent a number of hours fine tuning and tweaking the alignment and tension while ignoring the obvious. Lesson learned... Plus, I'm really good at aligning and tensioning alternators now. Bonus!

 

[Comodave]

What brand did you get?