In an off the wall reply to a transmission linkage lubrication suggestion I made over on The Bird, I was challenged to supply proof for an assertion I made in an old thread here (!) regarding possible alternator damage from jump starting a car with a dead battery. As the alternator in a car is intended to function primarily as a battery maintainer, NOT a battery charger, Bosch has seen fit to include a warning label or tag with every new or remanufactured alternator they sell. I think it's reasonable to assume they have some valid reason to supply us with that warning, and to extend that wisdom to a dead battery situation leading to the necessity for a jump start.


Click to view attachment


Some folks have a long memory for things that, for whatever reason, offended them. Because I've been challenged to provide a reason for my earlier statement, which I fully stand behind, I've searched the web for an image of that warning tag. After reading the tag, the person challenging my advice is, of course, free to do exactly as he wishes. Frankly, Scarlett, I don't give a damn. If risking a new alternator, which can be priced at thousands of dollars (yup, and that's in US money!) is what he, or anyone else chooses to do, please be my guest! If this person's engineering department comes up with peer reviewed double blind test results that disprove Bosch's advice, I'd be happy to issue a public apology and review my opinion. Until that happens, I'll err on the side of caution, and do it the right way as I see it.

See, Krustiness AND politeness in the same post! Betcha you didn't see THAT coming!

The Cap'n

I accept your expert opinion always on 914s. Follow up question then. Once the altinator is installed and the battery goes dead (left the lights on). Is it then ok to jump start the battery?

No. You would be asking the alternator to do something it was never meant to do: charge a dead battery. Put it on a proper charger and do it right. Good small chargers are available online and at better auto parts and accessory stores. I've used a CTEK charger ever since my big 40 year old Silver Beauty charger bit the dust.

The Cap'n

Cap'n where are you buying a new OE Bosch Alt for our T4 (& /6's) for K's of $'s~?!!

I wasn't referring specifically about alternators for 914s or air cooled sixes. There are applications out there that are unbelievably expensive. Maybach, anyone?

The Cap'n

Cap'n Krusty is 100% right on this one!!! Alternators are designed to maintain, not charge a battery.
Tom

While I agree that charging a dead battery can pull hundreds of amps and easily stress an alternator, I have two issues:

1 - Since starting a car with a low/dead/just-jumped battery is clearly something most of us will do many times in our lives, the engineers must design the system for this eventuality.
SO if modern alternators are not designed with self-preservation in mind (current limiting regulator), then SHAME on the engineers.

2 - Look at the second statement "Remove cables from battery prior to connecting opposite ends of cable to Alternator. Failure to do so will damage the alternator"

I call 100% Horse$|-|IT on that one.
From the perspective of the alternator terminals there is absolutely no way they know if the voltage applied to them was applied directly AT them, or 5 feet away through a wire.
Now if they had actually instructed the installer what order to re-hook them in, then that might be useful.
I have a feeling they meant something different and it was lost in translation

I learned this leasson the hard way back in the late 80's with a 911E I had at the time. I was the hero for about 2 minutes until I noticed my alt light on. Never jumped another battery again without first disconnecting mine.

This arguement also means: NEVER GIVE SOMEONE A JUMP or you will be violating this rule.

While jumping anther car there is a completely different way that altternators get stressed.
When the dead car starts running then you have TWO alternators in the system.
That means two different voltage regualtors (likely with different setpoitns) fighting each other.
The stronger of the two willl win and stress the lesser of the two alts.

SO whenever I jump someone, I am always at the ready to unhook the jumpers the SECOND the dead cars starts running.

A generator can charge a dead battery.
An alternator cannot.
Jump start a car with a weak battery ?..... be careful !
Jump start a car with a dead battery ? ..... never !

We appear to have the same s*#@storm we had the last time this topic came up. Please, read the pictured tag. If you feel it doesn't apply to you, ignore it. If your engineering department is larger than Bosch's, ignore it. If you don't mind a little extra effort in replacing an alternator or properly charging a battery, the tag might be a gentle reminder to proceed in a workmanlike manner. I'm NOT justifying the warning, nor am I telling you that the sky is falling. I merely (and possibly mistakenly) posted this in response to a related (and WAY off topic) post on another forum, from a person who has broadly labeled things I have said in the past as false and unreliable. As many of you know, when convinced I have erred in my statements, I'm pretty quick to either correct or retract such posts.

Thanks for reading this!

The Cap'n

I dont see any kind of storm.
I am actually agreeing with you, I just have some issues with the wording on the tag.
It is an absolute fact that asking a stock alternator to charge a dead battery is bad and could fry an alternator if the engineers did not design overcurrent protection into it.



I can say this: The engineering dept where is work likely IS bigger than BOSCH's and any engineer that designed a system that would fail under expected circumstances, would be fired.

I have some faith in Bosch so I dont believe they would design an alternator (today) that would immediately fail if asked to charge a dead battery.
With that said ANYTHING that asks the alternator to run at maximum capacity will shorten it's life.

Seriously- No-one else sees a problem with the second statement on the tag?
If one of the statements is a flat out lie, what does that mean about the first one.

Again, I beleve they meant to say somethig different and screwed up the wording.

Probably written by the legal department ...

The Cap'n

Just to revisit this discussion:

A Bad alternator can kill a good battery.
AND a Bad Battery can kill a good Alternator.

My friend at work just went through this with his Lexus:

Car kept dying acting like battery was dead.
Dealer:
Replaces Battery - Battery still goes dead
Replaces Alternator - Battery still goes dead
Replaces Alternator - Battery goes dead
Replaces Battery - Battery goes dead
Replaces Battery AND Alternator - Car is now fine.

First time they replaced the battery, the Alternator was bad, so new battery is stressed and runs down and is damaged
Replace Alternator (with Bad Battery) Kills Alternator
Replace Alternator again ( with Bad Battery) stresses Alternator again
Replace Battery, but Alternator is now bad, drains Battery & ruins it.
Replace Battery AND Alternator at the same time - All is good.

SO here is a perfect example where installing a brand new alternator with a drained battery can ruin a good alternator.
And replacing a battery with a bad alternator can ruin a battery.

SO - Bad alternator designer!

The Cap'n is correct - do not ask an alternator to charge a dead or bad battery if it can be avoided.

WOW!! A TRS80! I havent sat in front of one of those for many years.
That's even the newer model. First I used loaded from a tape recorder.

Makes me want to play Zork!

Don't reverse the terminals either....

Venkman: Why?
RobW: It would be bad.
Venkman: I'm fuzzy on the whole good/bad thing. What do you mean, "bad"?
RobW: Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.

Venkman: Right. That's bad. Okay. All right. Important safety tip. Thanks, Rob.