Engine: 2.5: battery light - alternator, or something else?

[chow]

Originally Posted by sonic-1

whoa chill !!!!!!!! you do have a point though lifting the concetions off battry while running can cause a spike which could damage the ecu
mmmmmm chow its how yer tell it !!!!!!!!!!!!!!!!!!

it also will wipe out the diodes in the alternator

[chow]

Originally Posted by glock19

I've removed the battery leads before with the engine running to check alternator problems (like I mentioned) and I've even change the whole battery with the engine running (not to loose the radio codes). So from where I stand (on planet earth to be exact). I'm speaking from experience and if you feel uneasy with such procedure, then leave it to the workshops.

Who knows, with your back turned, some might even be replicating what I did.

its not often im lost for words but after reading that i certainly am, all i can say is, kids dont copy this buffoon and do this at home
http://www.engadineautoelectrics.com...intenance.html

[glock19]

Chow,
Back off on the name calling will ya ? What are you professionally or lack off ?

What I did - can and has been done albeit frowned upon by some (obviously) but hey guys, it's not that I don't know the recommended procedure but then it's my car, my (calculated) risk. I won't to go into too much details as I can see it's certainly not worth it (to some) but then show me statistics (or incidents) to prove me wrong and I'll be convinced - again I believe someone will shoot their mouths off on this.

Stinky, back to your question, see below for the text-book procedure to troubleshoot the alternator if you're more comfortable with it. Beware of engine moving parts and hot parts.

VOLTAGE DROP TEST - POSITIVE SIDE
1) Connect a voltmeter between positive battery terminal and generator B+ terminal. Start engine and run at 2000 RPM. Turn onheadlights, rear window defogger and heater blower.
2) If voltage drop is more than .2 volt, check circuit between generator B+ terminal and starter for corroded or loose connections. Also, check circuit between starter and battery positive terminal.

VOLTAGE DROP TEST - GROUND SIDE
1) Connect a voltmeter between negative battery terminal and generator housing. Start engine, and run it at 2000 RPM. Turn on headlights, rear window defogger and heater blower.
2) If voltage drop is more than .2 volt, check battery terminals, chassis grounds and engine grounds for corroded or loose connections.

OUTPUT TEST
1) Ensure connections at battery, generator, and starter are clean and tight. Ensure generator, engine and body are properly grounded. Ensure generator drive belt is tight and in good condition.
2) Connect ammeter following manufacturer’s instructions. Connect voltmeter leads to battery terminals. Run engine to 2000 RPM. Adjust carbon pile on tester until voltmeter reads 12 volts. Generator output should be 49-55 amps. (55-amp generator), 63-70 amps (70-amp generator), 31-80 amps (80-amp generator), 81-90 amps (90-amp generator). If generator output is low, replace generator.

[foggyjames]

I'd be interested to hear the logic behind why running without a battery is a bad thing...assuming you're not drawing more current than the alternator is rated to supply, of course...

cheers

James

[sonic-1]

Originally Posted by foggyjames

I'd be interested to hear the logic behind why running without a battery is a bad thing...assuming you're not drawing more current than the alternator is rated to supply, of course...

cheers

James

well first off yer have the chance of the + battry lead touching some part of the car shorting it out !!!!!! realy not good for alternator
then there is the risk of more current being drawn than being produced which will cause the alt to run over its designed output
on the other hand if yer not useing the current where has it to go ??? no where so it ends up as heat in the alt
i must admit in the past iv removed battry with running engine to save radio codes , but my mate did same thing on his bmw 525 was puttin new battry on as conneted the - lead had slight spark n it cut out not to start again till new ecu was got for it
on some old car with no ecu elec stuff yer might get away with it but now i play it safe as cant risk expence

[jeff terry]

Originally Posted by foggyjames

I'd be interested to hear the logic behind why running without a battery is a bad thing...assuming you're not drawing more current than the alternator is rated to supply, of course...

cheers

James

Im not a very technically minded person by any means James but i did recently change my battery and in the volvo owners handbook there is a dire warning about that very point, along the lines of serious damage can occur if the battery is disconnected with the engine running, why that is i know not, im afraid

[Chris_Rogers]

The reasons; the alternator voltage control scheme is designed to work into a low impedance electrical system. The low impedance is provided by the battery. Put another way, the voltage control is quite crude and relies on the battery to dump excess power generated by the alternator for a few 1/10ths of seconds until the alternator voltage control has managed to reduce the system volage by reducing the field current to the alternator.
During these 1/10ths of seconds system voltage to rise to levels that the electonics in the car cannot stand.

Even connecting a second battery to a ME7 equipped car to jump start it can damage the engine management ECU if the connection is made with the ignition switch at position II.
Repairing this damage may cost more than the car is worth. A multimeter to diagnose the fault properly costs a fraction of the potential repair cost.

[jeff terry]

Originally Posted by Chris_Rogers

The reasons; the alternator voltage control scheme is designed to work into a low impedance electrical system. The low impedance is provided by the battery. Put another way, the voltage control is quite crude and relies on the battery to dump excess power generated by the alternator for a few 1/10ths of seconds until the alternator voltage control has managed to reduce the system volage by reducing the field current to the alternator.
During these 1/10ths of seconds system voltage to rise to levels that the electonics in the car cannot stand.

Even connecting a second battery to a ME7 equipped car to jump start it can damage the engine management ECU if the connection is made with the ignition switch at position II.
Repairing this damage may cost more than the car is worth. A multimeter to diagnose the fault properly costs a fraction of the potential repair cost.

Thanks chris well explained, it appears as if mr chow was right!, very serious damage can indeed occur

[foggyjames]

Bump...I went away for Christmas! That all makes a lot of sense, thanks Soinc & Chris.

I'm always very careful not to succumb to the 'basic' mistakes like shorting the +ve connection or letting current demand exceeding the alternator rating while pulling this trick. The detail I was missing was the design of the regulator being fairly basic. I'm used to working with low-current high-accuracy (and high cost!) voltage regulators...but I guess the same level is precision simply isn't required for a car charging system, hence money is saved...

I'm always only too happy to swallow my words if a convincing argument is made, and that's very useful into to commit to memory. Thanks for an informative thread, folks

cheers

James