Bad Battery = Whining Alternator?

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The alternator in my Cherokee has been whining lately. Whining as in whistling, not whining from a bad bearing.

Voltage has been around 13.5 or so running (correct) 12/11.5 off.

The battery was bought in 2008, a Napa Gold. Due to some electrical issues my Jeep had this time last year, the battery has been killed 4 or 5 times. Plus, being a 4 year old battery, it's due for replacement anyway.

The last time it randomly went dead, I installed it wrong and crushed the top of the case in and it kept leaking. It ate some plastic stuff and corroded the terminals.

Sunday night at 1130, I was at Walmart buying some stuff on my way home from a huge jeep show. Went to start to leave and I got the clickclickclickclickclickclickclickclick.

I ended up getting some baking soda and water, cleaned the terminals and got it started. Figured that was the problem.

Last night it did the same thing on me at Tractor Supply. Cleaned off the terminals in a parking lot, sanded them, best I could get was about 10 volts at the battery cable. Went to Advance to look at battery cables and it did the same thing again except I couldn't get it to do anything.

Bought a battery there (out of desparation) and put it in.

Voltage on the new battery was about 12 (it's been sitting 2 months). After driving around for a bit, I checked with the vehicle OFF and it was about 13.5 ... which I couldn't achieve any more with the old battery.

Anyway, my alternator is not whining anymore, especially after a start.
 
Plausible. Could have been a high frequency thing from the diodes/electronics like you can hear when a CRT tv is on.
 
A battery working properly is a big capacitor. When it starts to
fail, it's ability to filter the dc pulses from the alternator degrades, and audio equipment in particluar react to the less than "pure" DC. Many bits of car electronics are never really turned off, like home computers they can appear off but still draw a small amount of current. If you "lose a phase" on an alternator because a diode or winding fails, the same thing can happen. Instead of a bunch of close spaced pulses which can be easily smoothed by the battery, a lost phase leaves a "hole" in the output which is much harder to filter. It's nature's way of telling you to check the charging system, in your case that battery is TOAST.
 
Originally Posted By: eljefino
Plausible. Could have been a high frequency thing from the diodes/electronics like you can hear when a CRT tv is on.

That's usually the laminations in the High Voltage transformer. The new stuff doesn't have one.
 
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12.0 rested volts indicates a battery well under 50% charged.

Alternators are not the best battery chargers, especially when the battery is above 80% state of charge. A bunch of short trip driving will never fully charge a battery, and it will go to the grave early.

Never expect a 130 amp alternator to provide 130 amps. That number can be reproduced with a cold alternator, in a lab, at high rpm, Never in your engine compartment unless you floor your cold engine with devices asking for 130 amps.

Put your battery on a 6+ amp charger overnight and see if that changes the whining.
 
Originally Posted By: HerrStig
Originally Posted By: eljefino
Plausible. Could have been a high frequency thing from the diodes/electronics like you can hear when a CRT tv is on.

That's usually the laminations in the High Voltage transformer. The new stuff doesn't have one.


Plus the horiz frequency to drive the HV xformer is 15,734Hz(that's a std def set)...

Heavy loads or shorted rectifiers can cause a alt to whine but it isn't like a TV by any stretch of imagination...
 
Originally Posted By: Donald
At least you did not buy it a TSC, they are Excide around me.


I got an advance auto battery ... may not be any better.

Originally Posted By: mechtech2
Bad batteries can puke an alternator.
Many rebuilt alt warranties are void if the battery is not charged or is faulty.


Did not know that!

Originally Posted By: wrcsixeight
12.0 rested volts indicates a battery well under 50% charged.

Alternators are not the best battery chargers, especially when the battery is above 80% state of charge. A bunch of short trip driving will never fully charge a battery, and it will go to the grave early.

Never expect a 130 amp alternator to provide 130 amps. That number can be reproduced with a cold alternator, in a lab, at high rpm, Never in your engine compartment unless you floor your cold engine with devices asking for 130 amps.

Put your battery on a 6+ amp charger overnight and see if that changes the whining.


The last time it randomly died on me, I had it on the charger for about 24 hours straight (my electric bill showed it). It kept showing fully charged, but was only reading 12 on the multimeter before it even hit the vehidle.
 
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