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Are alternators supposed to run HOT?


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11 replies to this topic

#1 DiscoPete

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Posted 02 August 2005 - 08:55 PM

Hi, folks. I'm new here. I've checked out the message board and it looks good. Glad to be meeting you-all.

I replaced the alternator in my '96 Impreza LX the other day when the voltage regulator went bad. Besides water boiling out of the battery, I also noticed that the alternator was very hot, which seemed reasonable under the circumstances (output voltage of 15-18 volts).

A rebuilt alternator went in with no problem. The voltage regulation now looks right and the electrical system, warning lights and accessories are all operating fine.

But the new alternator runs about as hot as the old one - too hot to hold on to after just 3-4 minutes of operation. Is this normal?? I have about 80 miles on the new alternator and it seems fine so far. I hope that I'm not slowly cooking it.

I am concerned about this because, in my experience, most electrical parts are not supposed to get excessively hot in normal operation. Fans or heat sinks are used, if necessary, to keep down the temperature.

So what's up with this alternator? Are they made to withstand elevated temperatures? I never felt up the old one when it was working, so I don't know how hot they are supposed to get. Any insights, anyone?

#2 Midwst

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Posted 02 August 2005 - 09:06 PM

Check everything that is turned by your alternator belt. Sounds like one of your pulleys is bad or belt is super too tight. Any alternator that puts out more than 16 volts is BAD!!! 14.5 to 14.8 is pretty normal. Anything over 15....might make me nervous.

#3 nipper

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Posted 02 August 2005 - 09:27 PM

Anything that produces or uses energy will make heat. The alt makes a lot of power, and heat is a waste product.Doa voltage test on the charging system, if the voltage is ok, and you have some slack in the belt, clsoe the hood and enjoy.

#4 Cougar

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Posted 02 August 2005 - 09:28 PM

I agree with Midwst. The voltage needs to less than 15.2 volts You will cook your battery and damage the alternator if the voltage is higher. There may be a connection problem to the alternator that is causing it to put full output. If the exciter wire is grounded that will cause the output to do that. Check the voltages at the alternator connections. They all should be at around the battery voltage. Running the output at full all the time will cause a premature failure. The internal regulator may be bad also.

#5 DiscoPete

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Posted 03 August 2005 - 07:03 AM

I agree with Midwst. The voltage needs to less than 15.2 volts You will cook your battery and damage the alternator if the voltage is higher. There may be a connection problem to the alternator that is causing it to put full output. If the exciter wire is grounded that will cause the output to do that. Check the voltages at the alternator connections. They all should be at around the battery voltage. Running the output at full all the time will cause a premature failure. The internal regulator may be bad also.


I could have phrased it a better, I guess. What I was trying to say was that the BAD alternator was putting out 15 to 18 volts, making the battery boil over, and was also running very hot. So I changed it out.

My concern is that the new alternator also gets hot enough to burn the hand.

The new alternator voltage output is 13 to 14 volts, and varies downward over time, evidently in response to the level of charge on the battery. I think it is working fine. I was just wondering about the large amount heat the new alternator was generating. It seems like the alternator would have a longer life if it ran cooler.

#6 DiscoPete

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Posted 03 August 2005 - 07:22 AM

Doa voltage test on the charging system, if the voltage is ok, and you have some slack in the belt, clsoe the hood and enjoy.


That's comforting. The belt and the voltages are looking good. The alternator has over 100 miles on it and hasn't fried yet, so maybe there is no problem.

After the engine heats up, the brackets that the alternator bolts to and the surrounding engine are about the same temperature as the alternator. So it would get hot by conduction even if it wasn't making the heat itself.

Thanks.

#7 friendly_jacek

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Posted 03 August 2005 - 08:47 AM

My car is 2000 legacy, but alternator is very hot. 220 F by IR thermometer. Still works fine.

#8 frag

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Posted 03 August 2005 - 09:12 AM

It's also my experience that alternators become normally very hot fast.
It does'nt seem to cause any problem.

#9 nipper

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Posted 03 August 2005 - 05:10 PM

Just wanted to apologize for the really bad typos, since the car accident sometimes my typing really sucks.Altenators can get as high as 115 degrees c/239 f under full load. Thats why its best to by one thats "hot rated" if upgrading. Cold rating doesnt really mean anything.

nipper

#10 DiscoPete

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Posted 04 August 2005 - 08:39 AM

Thanks for all the replies.

I'm glad to hear that alternators typically get very hot, fast. My alternator is probably OK, after all. :banana:

I applied a temperature probe to it and measured 175 F .
That is well below the 220 F on that Legacy or the 239 F maximum temperature. Great!

A "hot rated" alternator? I didn't know that such a thing existed. Worth looking into next time...

#11 Leitah

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Posted 28 February 2014 - 02:00 PM

I have an alternator related question. We installed a new alternator and battery in my 1999 Subaru in August of last year. The car was running fine until I noticed a very strange pungent odor after letting the car warm up yesterday morning. I checked under the hood to see if I could see what the cause might be, didn't see anything obvious. Then today, the electrical inside the car stalled (ie. radio, internal lights) when I was stopped in a parking lot making a phone call. Again, I checked under the hood. Then when I went to start up and drive, the car died, no sound when turning the key. I waited a few minutes thinking I needed to call triple a, then started the car, and it started right up. I have a little voltage meter inside my car that is oscillating between 12 and 13 when it should be up to 14. With the combination of the smell, the low voltage reading and car dying, but starting back up, what do you think? I took the car for its oil change this morning and they think the alternator is bad but didn't see any belt issues. It looks like I will need to replace my alternator.

#12 Cougar

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Posted 01 March 2014 - 11:50 AM

It does sound like the alternator has a problem. Even though the DC voltage is slightly low the AC voltage should also be checked across the battery while the engine is running around 1,500 RPM to see if excessive AC ripple voltage is getting to the battery. This could explain the smell you noticed and may be coming from the battery. AC ripple voltage should be less than.1 volt. Have a load check done on the charging system to check the condition of the system.






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