Alternator Fail - 1 week old

biscuit

Member +
Hi all,

need some help, recently had a problem with my OE 15 year old alternator (it happens), so replaced with a refurb/new item from Camskill as well as a new battery, a week later the battery/cat light comes on (after working fine for a week).

I checked it with multimeter, 11.3v and dropping with lights/fans etc on, so this new alternator is goosed.

Do you think there could be some other issue causing this? or is it I am just unlucky?

Cheers
 

Texx

Super Moderator
There could be a break or high resistance/poor connection in the wiring between the alternator output terminal and the battery positive terminal.

Have you checked the voltage output at the alternator with the engine running?
 

Texx

Super Moderator
Check the voltage at terminal B first without grounding terminal F. If the voltage is less than 13.7v then ground terminal F and check the voltage at terminal B again.

Grounding terminal F bypasses the voltage regulator circuit which will help to identify if it's the regulator or generator that's at fault. Do not rev the engine above 2000rpm with terminal F grounded as the output voltage of the alternator may exceed the voltage tolerance of the cars systems and circuits.

alternatorcheck.png
 

rosso321

Member +
Alright man possibility it could be loose battery connection, also happened to me they only take up to 6600rpm I was told when mine was refurbished.
 

biscuit

Member +
Ok, I tested the following:

Battery points (car off) - 11.9
Battery points (car on) - 11.5
Battery points (car on, lights/fans on) - 11.4, dropping to 11.3 over the space of 1-2 minutes

Battery ground / alternator main (car on) - 11.9
Battery ground / alternator main (car/fan/lights on) - 11.5

What is strange is that it has been fine for a week, I reversed it out of the garage Friday, no problem, turned engine off, closed garage door. On restarting the car the cat/battery light were on.

Could something have come loose on the alternator, or has it just stopped working?
 

biscuit

Member +
Yeah, there is a large 100amp fuse that did blow originally when the alternator first went. This has been replaced and is still fine. I remove and check the connection with an 80amp, both still fine.

100amp (correct for EP91) has been replaced, still to no avail...

I wonder if I have just been unlucky, Camskill are sending me a replacement for free, but I don't want it to happen again.
 

Texx

Super Moderator
There should also be a normal blade fuse for the alternator in the under bonnet fuse box, possibly a 5amp.
 

Texx

Super Moderator
Regardless of what the diagrams say, have you checked the 5amp fuse under the bonnet?
 

biscuit

Member +
I checked through most of them yesterday. The fuse box cover doesn't say anything else relates to the alt. The blades shown in those photos are DOME, Horn etc

I'll go get a photo of the layout
 

Texx

Super Moderator
You can check the voltage drop between the alternator and battery, however so far it does appear that the alternator is not generating any electricity.

Before testing the engine needs to be ran up to temperature to avoid any unwanted additional electrical load on the charging system.

Use a multimeter set to 2v DC, connect the red probe to the B (output) terminal of the alternator and the black probe to the positive terminal of the battery, then start the engine and run it at 2000rpm. Check the reading on the meter, it should be 0.2v or less, if the meter goes out of range switch it to 20v DC and then check the voltage reading again.

Now do the same again but connect the red probe to the negative terminal of the battery and the black probe to the body of the alternator. You should expect a voltage reading of 0.2v or less.

If you get a reading that's more than 0.2v when checking either of the above, then there could be a wiring or connection issue between the B terminal and positive battery terminal or the body of the alternator and the negative battery terminal.
 

BMTMS

Fresh Recruit
I guesse I'm a little late to this thread lol. Im a beginner at diagnosing auto electrical & I've got a bit of a cluster**** going trying to figure out why my battery light is on. Batt terminals were a little corroded & loose: cleaned & wire brushed them & wrenched them tight with pads & anti corrosion spray. Charged battery too. Getting low voltage at batt when car is running (about 11.5v) then put multimeter neg pointer on battery neg & the positive on the alternator B terminal (threaded post) while vehicle running & got same low voltage about 11.5v. ODD THING: at about 22-2300 rpms the battery light in dash shuts off- ?? I checked the 3 alternator fuses (two 5amp with test probe then one big one around 100amp or more, the big one only visual inspection: it has clear top cover). I did NOT test any relays yet. Removed alternator & had it tested at O'Reillys and it Passed! Double U Tee Eff?? I'm checking the factory manual & see the test where terminal F is grounded manually with hand tool but it's vague how. Is that just a test probe held in the terminal F hole? Where is the probe clamped to? Then also a multimeter(mm); so is mm negative on the battery negative or where?? Thanks in advance!!
 
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