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How hot should alternators get???

62K views 5 replies 5 participants last post by  Frank Messina 
#1 ·
I am a little worried about how hot my alternator gets, if you let the engine run for a bit it gets hot enough to burn you, is this normal???

I am worried that maybe my belt is too tight and it's overloading the bearings or something is wrong with the bearings anyhow.

There shouldn't be much electrical load on it as the optima battery is nearly full with 11.5 volts or so and nothing else running off it except the ignition. What are your thoughts?
 
#3 ·
The battery is new, only a few months old. Its at 14 volts when running, I was referring to the charge on the battery itself, disconnected. So, even if the battery was low, would the alternator get REALLY hot when charging???
 
#4 ·
I think alternators can get pretty hot when called on to charge a low battery.

A FULLY charged 12v automotive battery runs around 13.6v (most battery tender type automatic chargers will trickle charge if battery drops below this voltage). 11.5v is low. The alternator is working to bring it back up to full voltage.

If you have underdrive pullies, it may lose some charging efficiency near idle as well as alternator cooling efficiency in terms of the alternator fan.

Sean
 
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#5 ·
If I understand your post correctly, your Optima battery has a voltage between + and - terminals of approx 11.5v with the ignition off ... correct? If so, you have a dead battery. See this link for info on what volt profile means for Optima battery: http://mk3build.com/manual/doku.php?id=battery_final

However, if your battery is dead, I don't understand how you can start the engine. So first, check your voltmeter and make sure you have an accurate voltage read on the battery.

If, after running the Roadster for a while, you have a battery voltage - after you shut off the ignition switch - under 12.9 to 13.0v, the battery is not recharging properly. This could be due to a defective battery (partially shorted out or otherwise damaged) or to a problem with alternator/related circuit.

As I understand it, you are getting 14v at the alternator when the engine is running. If so, this is within the typical 13.5-14.8v range output.

Optima batteries have previously had high initial failure rates -- don't know if this is still an issue - so first thing to do is completely check out the battery itself.

If the alternator dumps a lot of amps into the battery in an attempt to recharge it but the battery cannot hold the inflowing charge, the alternator can get pretty hot. In fact, it may continue to rise in temperature until is just burns out.
 
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#6 ·
To answer your question, yes they do get hot. Even if you forget and leave the key in the run position and walk away it will get hot just form the juice flowing through it. Most often though when we lift the hood on a car after being run, we expect everything under the hood to be the hood to be hot and don't get too concerned. But yes they do get hot, that's why they have fans in them.
Frank
 
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