Do Classics have 'Smart' Alternators?
01 February 2009, 05:13 PM
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Do Classics have 'Smart' Alternators?
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?
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?
01 February 2009, 05:32 PM
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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
Hope that sheds some light on it.
Brett
08 February 2009, 12:01 PM
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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?
Any automotive electrical engineers about?
09 February 2009, 06:16 PM
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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??????????
09 February 2009, 07:46 PM
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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??????????
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.
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Give mechanics any day. Again sorry i cant help 
10 February 2009, 10:50 AM
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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?
11 February 2009, 08:03 PM
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The alternator is not charging in that case. You need about 1 volt higher to put charge into the battery.
13 February 2009, 04:20 PM
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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
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
15 February 2009, 05:29 PM
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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.
I agree, not that smart if you ask me.
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