Charging system on-car testing REFECTION

  On 14/04/11 we did  an on-car assessment about testing the charging system, which including testing the battery, the alternator and some load test. Subject was a Subaru Impreza STI 2008, 2.0 Japanese Import, Single Turbo, Cam, Cold Air...None of them are important.
  When starting, the engine needs a straight away DC voltage that can only be supplied by the battery. Then, when the engine is on, the job is for the alternator to brag. That's the main idea about the charging system. Moreover, you can say that without the engine turned on, all electrical functions are authorized by the battery, until it is dried. When the engine is on, alternator takes charge charging the battery also takes care of all electrical  functions. And this practical on car test is all about that.
   Like every morning, you go to work and expect your car to start up. For doing this, you need a capable battery. And our first check is just like that, but a little bit more throughout. Visual check is always critical, because you can tell that smth is wrong when it happens to be obvious, it saves your time critically. Next, we start your technical diagnosis.
  It is always the OCV first, Open Circuit voltage is right now, how capable is your battery. So just parallel the meter to the terminals, record the reading. A starter needs a minimum of 9.5V to start, but our test requires a fully charged battery, because eventually, some implicit loads still applied when cranking, which are always monitored by ECU. Battery should be as ready as 12.7 V.
  Once the engine is on, generated voltage is regulated, and this can be measured through the battery. Just leave it under no load, the reading expected is around 14.5V, and what we got was 14.11V. This is fine because it is relatively reasonable thus a higher result than 14.5 tells me that alternator might overcharge. This could be dangerous for the circuit and fusible link. And reason we got 14.11 because when it's idling, the rpm goes up and down which affects the result.
   Still the no-load condition, now we check the current output. Specs is different from Diesel to Petrol. Diesel is form 5 to 12Amps, 10-18 for Petrol. Instead of leaving it to idle, we can rev the car up to 1500 rpm to obtain a more secured reading, but serouly it makes no different. This means that the regulator is doing a good job keeping the current output still. If the regulator is faulty, current form rectifier to this can be jeopardized, we might get no current at all or too high a current. Some other anomalies that could cause a higher reading could be stator resistance too low, or some implicit loads were applied like power steering etc...
    Underload test: Charging V under load=OCV+0.5V, so we got 13.23V. That is about the minimum amount to compensate with all loads also be able to charge the battery. If the voltage output too low, it might result in the battery getting used up, then next time you start the car, it might not be capable, because of not enough amperage. With the engine not turned on, the current drawn from the battery under load( all accesory except radio n wipers) is around 20Amps, way lower than 40-50 Amps when put on the alternator, this is simply because the battery is not charged.
    Last but not least, a charging system voltage drop test indicating the quality of charging. Although the specs for Positive side and Negative side are both 0.2V when operating, the REAL result for a good quality charger wiring should be WAYYY belong that, like 0.05 and 0.03V thats what we got. Grounding is always non-tolerable. Also, high voltage drops mean low quality wiring, bigger resistance affects the current output, affecting operation.
   So this is actually the big picture of your car's electrical supplier side. Before getting too technical, just do these simple, surface tests first, and thats about it for a regular user. If your car is ok, move on. If it is my car and smth is wrong, i'll definately dig in.