Alternator question

[1800guy]

My wife complained that her ALT light had been flashing briefly, maybe once or twice a day.  I did all the usual checks and everything seemed fine, but when I checked AC voltage I got a reading of .15 volts.  I swapped in another unit that I thought was good and was still getting AC voltage, but now it was down to .07.  I tried two different regulators in that alternator with the same results.  Checking with a friend that knows everything (he always tells me) he said that there was no permissable amount.  I checked on my own car and found that I also had .07 volts AC, but my car never has any electrical issues.  Logic is trying to tell me that if two cars (Volvo 245's) are doing the same thing with no apparent problem it must be okay.  
So, the short-form question is:  Is there a permissable amount of AC voltage that a Bosch alternator can tolerate?

[wayne petty]

245's have rubber bushing mounted alternators as i recall..


with your volt meter can you spend a few minutes and run a few tests.

engine running..  headlights on..

digital volt meter set to 20 volts DC...

1. battery positive post to battery negative post.. 14.1 to 14.6. volts DC..

2. battery negative post to the engine block.. 0.04 volts max

3. battery negative post to the body...        0.02 volts max

4. engine block to the body..                      0.02 volts max..


5. alternator housing to the engine block   you are going to get more than 0.02 volts.. not not much..  

6.. alternator output terminal to the battery positive..  this is again going to have more that 0.04 volts..  

if you get 0.00 on any of the tests.. usually 2, 3, 4..  reset the meter to 2 volt scale and retest.. ..

please post results by number..

you might also want to closely examine the wiring harness on the 245.  early 80's models were known to have wiring insulation that would fall off causing problems..   so much so.. the local dealer would keep three of them in stock at 600 bucks each..

[wayne petty]

an article on alternator testing

http://www.underhoodservice.com/Article/75217/diagnostic_solutions_alternator_testing_tips.aspx

alternator ripple article..  5 page PDF

http://www.pvv.org/~syljua/merc/TooSeptST07.pdf

wave forms

http://www.picoauto.com/tutorials/sensors-actuators.html

http://www.motor.com/article.asp?article_ID=1504

http://www.aeswave.com/TechNotes/index1.htm

could it be a fluke that fluke mentions 0.5 volts as a max AC reading for alternator health..

http://assets.fluke.com/appnotes/automotive/beatbook.pdf

This is probably the most informative article i have found.. its 41 pages in PDF form..

start reading with the link below first.. i should just erase the above.. but..

http://www.fordtechservice.dealerconnection.com/vdirs/servicetips/pdf/Generator_Ripple_Waveforms(2).pdf

http://www.fordtechservice.dealerconnection.com/vdirs/servicetips/pdf/Generator_Ripple_Waveforms(2).pdf

you will have to copy and paste the link above into a new window.. and remove the space between the G and the enerator  in Generator then hit return..

[1800guy]

Thanks for the Fluke link - it answered all my questions, and then some.  I moved that whole pdf right into my Save Forever file.  I had run all the voltage drop tests and everything was better than the minimum standards.  Plus I learned some things about the meter that I didn't know before.

[Mikej]

But did you find out why the light is coming on?

[1800guy]

Well, that's a good question.  What I do know is that the alternator that is now on the car is fine, verified with the meter and by the wife.  What I'm not sure about is what was going on with the original alternator - I now wish I had checked it more before taking it off.  What I worry about is accidently fixing something that I didn't know about - the results are okay, but no education occurs.  The link to the Fluke pdf that Wayne Petty was worth the price of admission, so to speak - thanks again, Wayne.

[phat46]

I'll have to take the time to check Waynes links. My wife told me her "battery light" was staying on for a minute or so after starting the car. I changed the  five year old battery, started the car and no light, and then the light stayed on for several minutes the next day after a 60 mile drive....then today no light on at all...'07 Saturn Vue,

[wayne petty]

for the saturn... i have a trick i would like you to try...

disconnect the battery...   stick the ignition key in and turn it 50 or 100 times..

gm starting somewhere in the early 90's started using music box type of ignition switches..  where the tube rotates with stubby pins on the outside...  the stubby pins hold the multiple switch contacts OPEN.. when you turn the key.. the contacts are closed by spring pressure..

working the switch with the battery disconnected.. ENGINE OFF. of course..  allows the switch contacts to close many times without power causing additional arcing..  this will many times cure the problem..  but also will let you know that the ignition switch is coming to the end of its service life...  warning.. late model GM cars have TINY External torx that are probably an E4 or E5 size...

harbor fright used to have these..  now discontinued..
http://www.harborfreight.com/6-piece-14-drive-e-socket-set-68017.html
Sizes: E4, E5, E6, E7, E8 and E10
Drive: 1/4"

[Arnold]

What is with these similar problems? Not to hijack the thread but I did post that I am going through the same thing. I have not had time to do the tests that Wayne recommended in his response..Thanks!..but I did put a digital volt meter with an adaptor in the cigarette lighter socket. My case the light comes on/goes off..and the voltage does not changet at all.

Thanks..Arnold..

[wayne petty]

but what was the voltage measured???

14.1 to 14.8 is expected on most cars...


loose ground wires between the engine and the body will make the alternator light flicker..

the tests i have outlined above.. only take a few minutes ..  try it on a car that works properly...  try it on several cars..

how alternator lights work on MOST Cars.....

the alternator light is hooked on the car side usually to the ignition switch ign 2.. so it gets 12 volts positive power when the key is turned on..  the alternator side is hooked to the voltage regulator..

when the alternator is NOT charging..  the voltage from the regulator will be less than the voltage from the ignition switch.. so the electrons will flow through the bulb and light it up...

once the alternator starts charging .. the voltage from the regulator equals the voltage from the ignition.. this equalizing of voltage stops the flow of electrons and the bulb goes dark..


now... there is usually just one wire from the dash to the alternator..  

the other side is the ground..   if the engine ground connections come loose or fail... the engine could have MORE voltage on it than is in the ignition circuit..  this would make the bulb light up again...

the reason for the voltage drop test at the top is it will almost always find the loose ground...

engine running.. head lights on..

set digital volt meter to 20 volts DC scale..

1.   positive battery post to the negative battery post..  14.1 to 14.8 volts..

2.  negative battery post to the engine block...  0.04 volts is expected

3.  negative battery post to the body...     0.02 volts is expected..

4.. engine block to the body..   0.02 volts is expected..

if you can reach the alternator output wire..  test that and the other end on the battery positive...  depending on the car... less than 0.08 volts..

you are actually testing the restriction in the circuit..  

since volt meters measure the difference in voltage where you touch the probes to..   with power flowing through the circuit to an electrical load..    the voltage will be slightly less than where it started from do to the slight resistance in copper wire...   circuit wire thickness is designed for a small voltage drop.. this is the most effective way to build cars..  

this test actually tests how good the FLOW is through the entire circuit...

[Arnold]

Thank you Wayne!..
 We have had nasty weather..on/off for a  while here. Seems whenever I might have time to do those quick tests..the weather is bad. Of course lol..my shop is full haha. Oh well.

 My car..little glitch has not changed at all for a few weeks now. It requires a cumulative amount of time before the light comes on. If I drive it a really short distance..run it for a short time..it just takes x amount of running time before the light comes on. Really short running times..may take several days before the light comes on. I swear this thing is on a timer haha. It then comes on for a little while..then goes off. Stays off until the car has not run for x amount of time.

 All I have been able to do so far is get an adapter for the cigarette lighter socket to my digital volt meter. I stick it in when the car is off. The voltage is 12.6..or very,very close. I turn the key on..the voltage of course drops a tiny bit..the alternator light comes on. I start the car it goes up to 14.5 the light goes out. After enough time has passed the alternator light comes back on..the voltage does not change. The light stays on for a minute or so..goes back to sleep haha..again the voltage does not change.
 There are no codes. I actually did take it in for someone to take a quick look at it..qnd  with what they said was a sophisticated machine. Did not cost much. Of course the light did not come on and they could not find anything wrong haha. Oh well.
 I will do those tests when I can.

  Thanks again Wayne

  Arnold..