Volkswagen Beetle requires 120A alternator? Why?


#1

I can’t imagine sufficient electrical load in this little car to need 120A. What’s the deal? I’ve gotten some smoke and mirrors about “smoothing out the electrical load for the computers” but that’s more about the size of the battery than the size of the alternator. What gives?


#2

The computers in modern cars are more powerful than you think. Also, because of the increase in computer controls, there are a bunch of solenoids, motors, and sensors that all demand more power than the old Beetles from the 60’s that were very primitive in their electrical needs.


#3

Isn’t 120A pretty much standard for alternators? I know there are heavy duty ones that produce up to (or maybe more than) 200A, but I don’t know off-hand of any cars that have less than 120A.


#4

Yup, it really doesn’t have anything to do with the size of the car, it has to do with the electrical loads. If the alternator does not have capacity to keep up with the maximum loads, the battery voltage will fluctuate affection the computer (and your ability to start the car).

In the “old days” (before cars became rolling video games) a 60A alternator would be more than adequate. Progress?


#5

The large alternator allows the designers to operate both the engine and the alternator at low RPM and still have plenty of output with headlights, A/C, heated seats, wipers all operating. At one time, voltage fluctuations were of little concern. Today, that can be a disaster.


#6

Diesel or gas?


#7

It’s a 2001 GLS Turbo (1.8L gas) - there apparently are three alternator options: 70a, 90a, and 120a. VW replaced the Bosch alternator with another Bosch which then also failed after about 6 months. The car seems to run ok on just battery (until it runs down) so I’m not sure about the urgent need for absolutely stable voltage. At this point I’m considering an aftermarket replacement since it comes with a lifetime warranty.


#8

Think about items in the vehicle like heated seats and heated mirrors which draw a large amount of power. Also beyond that many VW’s are heavy in options like Stability control and power moonroofs etc.


#9

If a VW dealer replaced the alternator then the part and labor has a 1yr/12,000 mile warranty.


#10

The computers in modern cars are more powerful than you think.

WHAT???..What does that have to do with how many amps they need. You’re desktop computer is far more powerfull and uses 3-4 amps…And MOST of that is for the disk drive which your car DOESN’T have.


#11

Think about items in the vehicle like heated seats and heated mirrors which draw a large amount of power. Also beyond that many VW’s are heavy in options like Stability control and power moonroofs etc.

These are the items that will eat up amps…NOT the computer as someone else posted. Also many people who put in the hugh stereo amps make it necessary for a higher output alternator.

In fact increased electronics in vehicles has become just a big concern that many manufacturers are considering using 48 volt batteries.


#12

Actually one needs to be careful about the difference between amperes and watts. The comparison between auto computers and home computers is affected by the 12v system vs. the 120v system. 3 amps at 120v is 360 watts which is 30 amps on a 12v system. But I think the comment about “more powerful computers” probably related to the computers and what they control, not just the computers themselves.

But that takes me to a related question: in the “olden days” alternators put out about 14.5v at full rated output and one that only put out 13.5v was usually suspected of having a bad diode or faulty regulator. I now have two vehicles with new alternators and they both seem to line out at about 13.8 - 14 v. Is this normal for the higher capacity, newer alternators?


#13

It’s to make up for the crappy, high resistance wiring:) J/k