I'm just trying to determine if the alternator on my 1996 STi Ra is working as it should be.
Is it only newage cars that have the 'smart' alternators?

The voltage at the battery when the car is running without load is fine ~13.8 - 14.0 volts and with load it doesn't drop below ~13.6 - 13.7 volts.
The current to the battery is only ~0.8 Amps with no loads, but as more things are turned on (headlights, radio, blower level 1) the current rises to the 5 or 6 Amps that I would expect to see. Battery charge level makes no difference.

Is this about right?

 

The way I normally tell is the voltage at rest ie 12.4ish(no engine running) and see what it goes up to 13.4-13.7 with engine running, anything over 13.8 is over charging AFAIK
Hope that sheds some light on it.
Brett

 

Yes, I know the voltage is OK. It's just the way it delivers the current I wasn't sure about.
Any automotive electrical engineers about?

 

no smart charging on classics

 

whats smart charging?

 

Fitted on the later models, the alternator does not charge unless it senses a current being drained IIRC ie stop start driving with no lights or other elecs being on will drian the battery because of the cranking so best to drive with side light on full time. That make sense??????????

 

I have a PSI Data monitor thing fitted in my car and the battery voltage doesnt change with or without having any lights on????? is this right???
Also noticing latetly that the voltage has been between 12.7v-14.7v.
My battery on last a few days without dying so its either not properly charging or there is a massive drain somewhere.

 

Sorry mate aint got a clue when it comes to electrics Give mechanics any day. Again sorry i cant help

 

No worries lol

Just a general question open to all

 

That's OK, the voltage should stay just about constant. It's the current that varies with the load.
It's not as easy to measure the current flow, it needs more specialist equipment, like a digital inductive ammeter.

When is your car showing 12.7v? Engine on or off?
What age of car is it?

 

It was showing 12.7v when idling with lights on.

An 02 WRX

 

The alternator is not charging in that case. You need about 1 volt higher to put charge into the battery.

 

I'm not sure what you mean by smart alternators.
Early alternators had all the control electronics mounted on them. They have either 2 or 3 connections. All have an ignition feed, normally via the ign lamp on the dash. There's the big current carrying lead that goes to the battery and a sense lead that also goes straight to the battery. The reason for the sense lead is to sense the actual battery voltage and not be affected by voltage drop in the power lead.
Later alternators have the control electronics incorporated into the ECU. Personally I would call the early type "smart" and the later type dumb.
AFAIK, all alternator systems are designed to maintain a constant voltage at the battery terminals.

John

 

The 'smart' alternator term is as you say, having the alternator controlled by the ecu. I know the 'newage' cars have them but I wasn't sure about the 'classic' cars. You read alot of 'newage' cars batteries going flat because of the so called 'smart' alternators not charging.
I agree, not that smart if you ask me.