Hot altrenator

[cdory25]

I got this new IR temperature gun and boy is this thing fun. After I got finished aiming it at all the girls I shot my alternator. 300 degrees is a little hot it seems. Charges normal and batteries are good. Anyone want to tell me if this is normal?

Thanks!
John

[Interested]

[Sea Wolf]

Hi!

I'm no expert here, but I do know the diodes themselves get quite hot doing their work of rectifying the AC output of the alternator. Somewhere between 200 and 300 or even a bit more degrees wouldn't surprise me at all.

The diodes use the aluminum body of the alternator as a heat sink, and the whole unit is cooled by air circulation from the built in fan unit.

Under hood/shroud temperatures themselves can be 200 degrees or more, so who's to tell the diodes they're overheating for being 100 or so degrees above the ambient temperature they're being fanned with?

I tried to research this, but can't seem to find a quick quantitative (numerical) answer, at least, so far.

Were you pointing the IR gun at the alternator as a whole, or specifically at the diode groupings (usually two groups of 3 diodes)? Bearings should be pretty warm, too. of course!

Idea: try the gun on one of your other vehicles (car), and see what you get, by comparison.

Keep your cool!

(And, BTW, watch that image! (And those girls!) You know what they were saying here a few days ago about "old" guys with sports cars, Harleys, jet skis, etc,, etc……..Ha!)

Joe.

[thataway]

Sounds hot to me…I have run big alternators (150 amp) on my cruising sail boats before the IR thermometer was readily available and could touch them without burning my hand.

Balmar sets the termal cut off on their high output alternators at upper limit of 115* C or about 240* F. This fits with the max temp of many automotive alternators. One of the problems with smaller alternators, which are rewound, and have diodes changed to double the output is overheating and burning the windings. Joe's ideas about your just picking up the diodes is a possibility...

Is there any possibility you are reading a temp off the exhaust manifold (not sure where your alternator is located on the motor).

[potter water]

you do need to be careful about the "field of view" of your IR thermo. The cheap ones look very wide. The more expensive ones have a good lens that looks at a square inch or two. So, anything hot in the close vicinity of your sensor could be giving you a false reading. For trailer bearing temps, I do want a fairly wide field of view. Of course, the field of view changes a lot depending on how close you are. I keep my sensor about 3 to six inches away and use the laser dot for targeting.

[Robert H. Wilkinson]

The temp. of an alternator is dependant on the amps it is producing in relation to its capacity and the speed it is being turned. As well as the quality of its construction and the ambient temp. of the engine compartment.

Some sailboats(as Bob mentioned) and diesel trawlers have a special built high output 2 or 3 phase alt. installed. $$$$$

Normal off the shelf alternators are not designed to charge batteries. If you attempt to run an alt. anywhere near its rated capacity for any length of time it will either ramp down or burn itself out. The rated capacity is NOT continuous duty.

As the alt. is cooled by its internal fan the amps to rpm ratio is also an important factor. They do attempt to regulate their amps to speed ratio somewhat by way of the field current - however - Attempting to charge dead batteries at an idle may save you a few cents in fuel but you risk overheating the alt. It will attempt to put out a lot of amps - producing a lot of heat but the fan is still only running at a slow rpm. An alternator under load will require 4-5 horsepower from the engine which may slow its normal idle speed - slowing its water pump - further compounding the problem.

Much like your anchor - bigger is better! If you are replacing your alt. get the biggest one you can fit. If you anchor out a lot, depleting your batteries - it may be worthwhile getting something built by a shop that will do the job day in day out. This is one area where an inboard is more adaptable. As for outboards I believe the Evinrude has the highest amps available for battery charging but it doesn't use an alternator.

If your batteries are depleted and need a charge you are better off going for a ride, raising the idle speed or using some kind of auxiliary fan to keep that alt. cool.

Regards, Rob