Bench testing the alternator

[prolecs]

Hi, Help required please!
2003 Astra G with Z22SE. Low volts from the alternator, like 11.5V at the battery but maybe up to 13.5V driving. But regardless the current is not sufficient to keep the charge in the battery so it slowly goes flat after a few days driving, and although a new battery, it needs regular charge from the mains.
Tested the diode packs and they seem like normal diode function. I swapped out the alternator with a spare that used to work ok, but same issue.
Bought a new regulator and replaced that but want to bench test before going through the hell of swapping it out. Auto electrician just shook his head and said it can't be tested on the bench as it's electronic - I assume he means the alternator is controlled by the ECU or some other device in the car?? Anyone know the details and/or a bench test method??
What sort of signal comes down the little auxiliary blue/white to control the alternator output? PWM? Voltage?
Also I notice there are two little square pad "terminals" on the back of the alternator, that look like test points. They are connected electrically so maybe I can bypass the regulator to test the full output.
Thanks

 

[ob one]

it might not be the alternator you might have a parasitic drain on the battery

 

[evocarlos]

he's not a very good auto electrician
https://z22se.co.uk/resources/z22se-alternator-repair.84/

 

[prolecs]

Thanks Evocarlos. I could not believe it was not possible to bench test, however, one tends to treat these guys as the experts.
Can you please explain what the connections to the two auxiliary terminals are when under bench test? I can't see from the picture although it appears to be a loop connecting the two terminals?
In the car, there is only one aux terminal used, which I guessed would be for the indication on the dash.
My trial with similar bench test did not produce any increase in voltage, although I only tried a lamp in series with 12V+ to the aux terminal that is used in the car.
Regards

 

[prolecs]

And I will test for drain on the battery thanks OB ONE, but the engine is out at the moment to replace the dreaded rear crankshaft seal. I hope that fixes the oil leak, and it's not blowby and excessive sump pressurisation which this old engine suffers from.

 

[evocarlos]

its been a long time since i did this and if you just spin the alternator it wont charge think i had to connect the exciter wire to the b+

 

[prolecs]

Well I'm giving up on this. Went to another auto electrician and he also said it's a regulator that is controlled by the ECU and can't be bench tested by normal means. I said it's 2002 model not 2018 - I know a lot of the latest cars are ECU controlled alternators (for fuel economy they say, but I'm sure to keep dummies like us from playing); anyway, he said don't expect 14V; if the voltage is around 13 loaded or unloaded, it's probably ok.
Maybe the basics can be tested by bypassing the regulator but seems it's a bolt on job to get a full test.