Can a low battery cause damage to an alternator?

[KeithG]

My intuition tells me that running a car that has a quite drained battery does not affect how quickly the alternator wears out. I.e. a low battery can't 'break' a newer alternator.

I was told the opposite recently by a non-reputable source. But, it got me thinking a bit. I certainly have a lot to learn about electronics.

Thanks for any thoughts & theories.

KG

 

[Quest]

low battery as in what? partially discharged and in need for recharging?

If the battery isn't damaged due to prolonged state of partial discharge then so long as you are able to keep your engine running above 1600rpm or more and over an extended period of time (say, 1hr), then it should have very little impact on the alternator.

Otherwise, trying to recharge a discharged battery esp. during cold weather or when during idling, this will impose a lot of wear on the alternator (and heat generation) so much so that repeating this act will bring premature death to an otherwise functional/healthy alternator.

(*and for recharging a partially-discharged battery, home AC charger is preferred*)
Q.

 

[BarkerMan]

Quest +1

There is nothing helpful about continuing to drive with a battery that won't charge for what ever the reason. In modern vehicles the electrical system is very important.

In my first job as a mechanic I wrote on an RO that the battery was low and would not take a charge, had two dead cells, and damage could result from continued use. The customer refused to let me replace the battery. That next weekend his car caught on fire. The battery had enough punch to engage the Bendix drive but not enough to spin the engine and could not disengage. That is a direct short to ground and in this car no fuse or link in the circuit. He took us to court and that RO was our ticket out of that mess. That incident always comes to mind with I see an electrical problem even though modern cars are better protected.

 

[eljefino]

The theory was born when one would drive around a couple days on a dead alternator then put a new one in. The brushes for the field control wouldn't have seated yet and would burn up delivering near 100% power off the bat.

So, says the theory, one should throw a charger on their battery when putting a new alternator in, to negate this.

Naturally one should expect parts to run out of the box without special care.

 

[KeithG]

Originally Posted By: Quest
low battery as in what? partially discharged and in need for recharging?



Correct. A battery that has no bad cells and shows no symptoms in normal operation other than perhaps a slightly slower that normal starter reving. (Also, assume a constant temp of 50 degress F for this discussion.)


Very interesting comments, Quest. Thank you.

 

[Schmoe]

On newer model cars, even if you check the battery and it's not showing that it's really drained, none of the electronics will come on because they need a substancial amount of juice just to power up. Kind of like the old Batman series "atomic batteries up to power."

 

[Quest]

To further comment on Schmoe's observation:

6-yrs into it's original factory(OEM'ed from local NA supplier)battery on my dad's 7th gen civic went in a very odd way (mind you though: we are talking about OBD-II system up da ying-yang): it would start a car no problem (when cold) but when you put it in reverse (A/T) and back out of the car port, the car would stall when you brake. Shift it back to neutral and then restart the cold engine and then put it in Drive, everything would work just fine. We tested it up to 250A using carbon pile tester and everything seems ok and ditto with the original factory charger. This happened during spring time for 3 mnths and it was so perplexing that nothing seemed to work. One day it stuck me as something electrical so I bought another battery and install it and voila! That solved the problem.

To this day, I still have that battery with me and unless I'm willing to cut it open to investigate, otherwise, I still could't figure out why it would stall....

Q.

 

[George7941]

I think a low battery can fry a good alternator.

A 100A alternator can deliver the full 100 Amps but it is not rated for continous duty at 100 Amps. Eventually, the heat build up will burn up the stator windings. This is the reason why replacement alternators always come with instructions to charge up your battery first before running the engine with the new alternator.

If you look at the stator windings of a 100A alternator, you will notice that the wire used is quite thin, maybe 12 ga. 100 amps passing thru this relatively thin wire will cause heat to build up and not all of this heat is going to be dissipated by the built-in alternator fan. You end up with a fried alternator with a very pungent aroma.

 

[severach]

Alternators are 3 or 4 phase. At 100 amps each phase would be providing around 30 amps. 12 gauge wire cooled can handle that.

 

[George7941]

Because there is a phase angle involved (120 degrees) in 3-phase circuits, the current thru each individual phase is not 100/3 = 33 1/3. The factor involved is the square root of 3, which is 1.732. Thus the current thru each phase would be 100/1.732, roughly 58 amps. Not 30 amps.

The cooling fan does a good job of cooling the outer layers of the stator windings, but heat from the inside layers have to pass, by conduction, thru the outer layers before it can be dissipated.

At work, we had an alternator fry its windings on a medium duty truck. This truck has two 1000AHr batteries in parallel, effectively having 2000AHr. I think the alternator burnt up after the batteries were deep-discharged (probably from leaving the interior box lights on overnight) and then the truck was taken out on the highway for sustained high rpm operation which caused too much heat buildup in the windings.

 

[George7941]

I just went and looked at a Delco 22SI 130 amp alternator and the windings are of 14ga wire!

I have no difficulty seeing the inner layers of a winding of 14ga wire, carrying 130/1.732 = 75 amps, overheating.

 

[alreadygone]

Originally Posted By: George7941
I just went and looked at a Delco 22SI 130 amp alternator and the windings are of 14ga wire!

I have no difficulty seeing the inner layers of a winding of 14ga wire, carrying 130/1.732 = 75 amps, overheating.



X-RAY vision?????

Bob

 

[George7941]

I think you misunderstood what I was saying.

When i said I have no difficulty seeing----- , what I meant was that I could understand (visualize) how the inner windings could overheat and get damaged.

 

[alreadygone]

No, understood perfectly well,, just being a

arse

Do think that any run of the mill alternator is perfectly capable of bringing any average run of the mill batery to full charge occasionally (from near dead status)without any internal damage. If not, the original supplier would spec a heavier unit. Other wise a new alt would be needed every time someone forgot their lights at the mall, etc.

Bob

 

[tom slick]

I'm curious what "extra wear" is put on the alternator from exceeding its duty cycle? I fully understand the damage from overheating but am not sure what parts experience accelerated wear.

 

[Gary Allan]

Had a hesitation in my mother's Corsica ..off idle. I just figured it was a lame design feature of the lackluster engine. While I had it at my job during plant shutdown, I put it on the charger just for the heck of it. No more hesitation. One cell in the battery had lower water than the rest (maintenance free, but removable caps).

As Quest related, just because a battery holds enough of a charge to start the vehicle, doesn't mean the battery holds the correct level of voltage. My mother's battery was never going to reach the charge level to unload the alternator. That's why she had "just off idle" hesitation ..that's why his dad's car stalled in reverse ..but had no trouble cranking the engine.

I've seen this in the later 70's. This was before PCM controlled fields. The customer reported his lights getting very bright while driving at night. Figured it was a defective internal regulator ..replaced it. It worked for a bit ..same problem. Again no problems starting the thing ..no (at that level of normal diagnostic schools of thought) hint that the battery would be the source.

 

[mechtech2]

A low battery [for whatever reason] puts a greater demand on the alternator.
More load on the bearings, more brush/commutator wear, and more heat to potentially puke things is the result.
From a little to a lot.

 

[ThirdeYe]

Yes, I believe it can. I had a bum battery in my old Altima (Interstate Battery, was probably just getting old) and it eventually started to make the bearings whine in the alternator. Replaced the battery and had the alternator rebuilt and it was good to go.

I was told by a local mechanic who worked on it, that one of the battery's coils wasn't charging properly, or something along those lines. I can't remember exactly what it was, since that was years ago.

 

[George7941]

Originally Posted By: alreadygone


Do think that any run of the mill alternator is perfectly capable of bringing any average run of the mill batery to full charge occasionally (from near dead status)without any internal damage. If not, the original supplier would spec a heavier unit. Other wise a new alt would be needed every time someone forgot their lights at the mall, etc.

Bob



You forgot one important factor -- sustained high rev operation. Most times someone leaves their lights on at the mall, the alternator gets a chance to cool off at traffic lights etc. during the subsequent drive.

Also, the damage from overheating is cumulative. Alternators will charge an occasional deep-discharged battery but if asked to do it weekly, or even once a month, will fail from overheating.

 

[meep]

It's the diodes that I suspect are the most sensitive.

As for the coils, yep, there's three of them, but remember, they pulse, so while yes each might be pushing 75 amps, it's not constant... on-off-on-off in a sine wave. The *average* by time may actually be closer to ~33 per example above.

Typical diodes lose ~0.7 volts. That loss becomes heat. Ideally they'd be adequately cooled, but they aren't. They stink bad when they let go.

Some off-grid folks tie an alternator to a small engine for days "when the sun don't shine." There's a neat writeup somewhere on homepower.com . They offer a [free] regulator design that limits current output first, voltage second, to charge properly and avoid burnout. I have a similar project at home. The alternator by itself gets surprisingly warm in the open air at 15 amps. The coils definently get warm.

RPM also plays a factor. Higher rpms means less field current needed, lower load through brushes.

Mike.