V40: Alternator Questions

[cheshired5]

Originally Posted by UK180skill

Looks like the alternator is not putting out anywhere near the voltage it should.

True.
It would also suggest that it isn't receiving enough voltage from the small wire too which may cause the low DC output.

Have you tried an AC voltage test on the alternator B+ post?
Also do the diode test.
Disconnect the battery negative lead.
Set meter to diode.
Touch the red lead on the alternator B+ and black lead on the alternator metal casing and take the reading.
Then reverse the leads so black on B+ red on casing and take that reading too then report back.

[UK180skill]

Measured at the battery terminals as before at 2000 rpm reads 11.68V

[UK180skill]

cheshired5 thanks for helping the readings as follows

AC test 0.01 to 0.02 at battery terminals

With battery negative disconnected
black on B+ red on case 0.443V
red on B+ and black on case 1.672V

[cheshired5]

Originally Posted by UK180skill

cheshired5 thanks for helping the readings as follows

AC test 0.01 to 0.02 at battery terminals

With battery negative disconnected
black on B+ red on case 0.443V
red on B+ and black on case 1.672V

With red on B+ and black on the casing you should have no reading as working diodes prevent reverse voltage flow back into the alternator so from that I would say that your diode pack has failed.
There are 6 diodes so if one fails you'll lose approximately one sixth of the DC voltage which seems to be born out by your earlier DC voltage readings.

If you want further proof.....
Close everything on the car. Key out of the ignition.
Set the meter to DC Amps, put the leads in the correct meter sockets for this too, remove battery negative lead then put the red meter lead on the battery negative lead and the black meter lead on the battery negative post then wait for about 20 minutes. Meter lead clamps make this much easier as you need a secure connection which can be left.
Then view the Amp draw on the meter.

You should see an excessive parasitic drain flowing back through the alternator which will kill the battery prematurely.

Don't activate anything electrical on the car with the meter in this state as you could blow the meter.

You can replace the diode pack but a new alternator may be the better option.

[UK180skill]

cheshired5 thank you very much, although I am not sure how to set the meter up for this, I have left the black lead in the common socket and moved the red lead into the 250mA socket on the meter.
Connected as you suggest and am immediately seeing between 14 and 16 mA on the meter.
The cost for a diode pack is in the order of £50 for my alternator and a new one, albeit a different make, is between £100 and £160.
I am reluctant to risk £50 that may not solve the problem but also not looking forward to the huge amount of work involved in replacing the alternator.

[cheshired5]

Black is always COM socket and if you have a choice, always use the 10A socket for the red lead.

My video here shows how to set up the meter for a test at around 3 minutes in.

[UK180skill]

Big thanks for your help, I have bitten the bullet and ordered a new alternator from a family run company in Manchester, advertised as a new Valeo unit for £129 including dhl delivery, and not an exchange unit.
Just for info Volvo quoted me £220 plus VAT for an exchange unit plus a surcharge of £120 refunded when you take your old one back.

[UK180skill]

Final update, fitted the new alternator today with the help of a friend that has his own small workshop.
What a bit of a nightmare of a job, having unbolted a module that sits on the left and moved it out of the way, unbolted the steering pump and moved it out of the way, unbolted the alternator but there was no way at all of getting it out.
Not enough room to the left and the air conditioning pipe in the way to the right.
Removed the plastic engine pan at the front to get access to the lower two bolts and unbolted the air conditioning compressor and moved it to the right to create just enough space to wangle the alternator out with a lot of twisting and turning.
Put new alternator in and bolted it up, put the steering pump back and bolted it up, put the air conditioning compressor back and tightened it up.
Then the task of putting the serpentine belt back, then the module, then the plastic engine tray.
Finally reconnect the battery and test, all good, over 14V at the battery and no red battery light on the dash.
The job would have been extremely difficult without the use of the car lift, we must have had it up and down eight times, somethings accessible from above others from below.

[cyanv40dog]

On a V40 2002 there is a clip at the top of the alternator, how many wires should be going into it? Had battery problems since I changed my oil filter and fear I may have damaged something when changing it. Sorry to hijack the thread op.