Alternator

[clivvy]

chaps.

as I have weird electrical issues, I started thinking about my alternator. Firstly, is there a godo way to test it, to see if its 100% or not? I did a test using my multimeter following a guide I found on the web, and I got 13.6V underload, 13.9 at idle, which I believe is within tolerances. When under load, lights on etc, and revving, the lights go brighter, then darken as I let the pedal up. So this made me wonder about the alternator.

I understand the Alternator charges the battery, but does itdo anything else on the TDi's? Does it provide power to the car whilst charging, or is this all dealt with by the battery? I wonder if its possible that when cold or whatever, my alternator struggles to push out the required charge, thus causing weird issues liek what I am experiencing....

also, where can I get a good, cheap refurbed one??! Ebay appears VERY expensive!

 

[solarman216]

your battery is there to start the engine and provide lights when the engine is not running, once the engine is going then everything comes from the alternator including recharging the battery after starting, as long as the voltage remains above about 12.8 then nothing is being drawn from the battery, the lights will get brighter when at 13.9, Rick

 

[clivvy]

ahh right, so this is normal then?

good, one more thing to tick off my list of things to think about!

 

[rustic]

ahh right, so this is normal then?

good, one more thing to tick off my list of things to think about!

Yes and I agree with Rick, 12.8 volts is the average voltage of a fully charged battery, a lower voltage when the engine is running means there is a discharge from the battery, this can often happen whilst sitting at traffic lights, lights on, rear screen heater on, wipers on, etc. often a quick dip on the throttle often brings in the alternator, often accompanied with a squealing fan belt.

A higher voltage than 12.8 indicates a charging battery, and if the battery gets to 13.9 volts then the batttery is fully charged.

A battery showing 14.5 volts, indicates a faulty alternator, or a battery that needs replacing or both.

These voltages will also depend on the ambient temperature, but is a good rule of thumb.

Many years ago I designed the test circuit for testing refurbished alternators.
There were various resitive loads, with digital displays of voltage and current which tested the alternator at all loads etc.

This knowledge comes in handy sometimes..
Best regards, Rustic

 

[96terrano]

your battery is there to start the engine and provide lights when the engine is not running, once the engine is going then everything comes from the alternator including recharging the battery after starting, as long as the voltage remains above about 12.8 then nothing is being drawn from the battery, the lights will get brighter when at 13.9, Rick

Ahh right, I've got a voltmeter in my t2 and it sits about 13.2v idle and when I rev the engine it goes upto about 14.5v. I'm guessing this is because the alternator spinns faster thus generating more power?

 

[solarman216]

Something is very wrong if you get 14.5, as Rustic says alternator output too high or bad battery, but could be a misreading meter, so it needs checking out, Rick

 

[clivvy]

yes, Ryan, isnt your volt meter from a Fortrak though? Perhaps its misreading some how...??

 

[96terrano]

yes, Ryan, isnt your volt meter from a Fortrak though? Perhaps its misreading some how...??

It's from a Volvo something. Can't remember the model:doh

 

[96terrano]

Just rechecked it all with a multi meter and I get 12.43 idle and 14v when at 2000 rpm. Gauge is ok now Since I cleaned battery terminals :augie