Hi

I've got a 1.3 petrol skoda felicia from 2000. Theres something dodgy with the alternator and i wanted to ask if anyone had any advice.

I dont really have any experience with repairing cars but work with electronics a lot so understand a bit about circuits.

The first issue started about 10 days ago when the battery light came on and all the electrics seemed to be getting overpowered when the engine revved higher. Most of the lights, both interior and exterior would glow brighter, the windscreen wipers would move faster and the radio would switch itself off if the revs went above 1500.

It seemed to me like everything was getting too high voltage so I read through lots of posts on the forum here and got that most likely it was the voltage regulator had gone and the alternator was connected directly to the main car power circuit. I ended up ordering a whole alternator off ebay for £25 as it included a regulator. I thought that my battery might have taken a hammering from the over charging.

The next day when i was driving the symptoms stopped. I thought it might be a loose connection that i should be looking for instead but the main risk was over. The day after that though i went to start the car and it had a flat battery. Got a jump start and it only lasted 5 minutes before the car lost power and the engine cut out. Fitted a new battery to drive it home which was ok.

I didn't measure the exact voltage while the circuit seemed high voltage but i measured it with the flat as being about 10.5v. I fitted the new battery which was at about 12.8V. I then measured the engine voltage whilst revving and it stayed constant at 12.8V. The 6 mile drive home took it down to 12.4V.

It seems that the alternator isnt doing anything. Now i get that the regulator packing up would give the high voltage that correlated with the rev speed, but am not sure why there's nothing coming from the alternator. Could i have blown a fuse somewhere? The car seems to run OK on just the battery. Only the airbag light is on which i read can be due to an undervoltage situation, which it is currently in.

Added to my frustration the alternator showed up with a bent shaft so doesn't rotate properly.

The only thing i could think of is that the regulator failed and created a short between the alternator output and the regulator output (main power circuit). This then caused something else to blow in the regulator that disconnected the alternator output from the main power circuit.

Is there any way of testing the alternator while the engine is running? Are there any fuses that go somewhere between the alternator output and the main power circuit that could have blown? I can't see anything on the fuse schematics online.

I've also read that it's unusual for the winding in the alternator to go but the rectifier diodes can go. Not sure why this would stop any power getting to the main circuit but could see that it would damage the regulator citcuitry.

Sorry for the rambling message. Any help greatly appreciated.

Thanks

Laurence

Welcome to the forum!

Let's see how to put things in order. I will start with the mistakes for future reference to other members.

• for somebody having electronics knowledge, you didn't diagnose properly the issue (thou shalt measure the voltage)
• you bought a new alternator without evidence of fault
• you didn't test the battery on load

Now, from your description the symptoms point towards a bad voltage regulator BUT that could be an effect of a faulty battery. I would suspect the battery in the first place (both the old one and the replacement one). A bad battery makes the alternator inoperable too.

 

12 hours ago, Lawmate said:

The only thing i could think of is that the regulator failed and created a short between the alternator output and the regulator output (main power circuit). This then caused something else to blow in the regulator that disconnected the alternator output from the main power circuit.

Totally wrong. You should read about how a voltage regulator works in an alternator.

12 hours ago, Lawmate said:

Added to my frustration the alternator showed up with a bent shaft so doesn't rotate properly.

A bent shaft means a big mechanical shock during shipping. It's a big no-no to install or keep such alternator both from mechanical and electrical point of view.

12 hours ago, Lawmate said:

Is there any way of testing the alternator while the engine is running?

Of course. You should measure 13.5 - 14.2 Volts on battery at 2000 rpm.

12 hours ago, Lawmate said:

Are there any fuses that go somewhere between the alternator output and the main power circuit that could have blown?

No.