Alternator Warning Light at high rpms

Maybe the belt is starting to slip at high rpm's. The belt could have stretched a little bit. You probably would not hear it slipping at 5500 rpm since the engine will be pretty loud at that range.

300 miles seems just about the time to check tension on a new v-belt and adjust tighter if needed.

 

Yep. The belts stretch shortly after installation.

What is being presented is probably high speed slippage.

 

Take it back to who put the belt on.

If it was a shop, they should readjust it at no charge, and should have told you so.

 

It is one of two things.

Either your belt needs to be retightened - and I would do that first - or your rectifier bridge is going South.

If you have the alternator that I suspect that you do, then there is an internal rectifier made up of three diodes that together make up the bridge.

When one starts to go, the light flickers at certain times until that weak diode overloads the other diodes and your light stays on for longer periods until failure.
Very common failure. - In this case, remove the alternator and bring it to an alternator/starter rebuild shop near you.
They will be familar with it as there are only a few different types, and will rebuild it as good as new for around $150.

 

Can you test for diode failure with switching your test meter to "AC" and see if you get a reading?

ken

 

On the car? Maybe.

If you have a Support Systems Inc. model 10-647-01, which looks just like a little analog multimeter with a probe that clamps over the alternator output wire then you can hook it up and a bad diode will show up on the meter.

Any alternator shop has one, and they can check the unit on the car while it is running. Most Alt shops will do this for free.

Or, you can use an oscilloscope to check the alternator output for excessive voltage ripples or spikes caused by a bad diode.
You might hear this as noise in your radio.

You could possibly use a regular meter if you wire a a capacitor in series to the positive lead from the meter to block out the DC voltage so that only the ripple voltage gets to your meter. If you know what values are correct.

 

take the car to a parts store and have them check the voltage and amps at the battery before you take a bunch of stuff apart. they can load test the battery and see if the alternator is doing its job.

 

I would not let one of those guys near my car.

IMO, only a shop that rebuilds alternators really knows what they are doing.

 

It is pretty safe. All they do is connect to the battery + and -. The computer does all the work, running through a series of tests, then a print out of the results. The electrical shop will likely use the same exact machine.

 

yep. thats what i meant. its unwise to be conceited and think the local parts shop guys dont know a thing or two about many cars. i have frequented several Autozone and Advance Autoparts stores in my exotics and been very well treated. the machine is very simple, and will help to save time and money.


throwing parts at the car will do nothing . you need to know what to fix, and if any subsystems may be affected.

 

+1

In fact, I'll take that sentiment one step further: you want to see tests first. When you are doing your own work on your car, do the free tests first.

When you are paying to have work done on your car, have your mechanic show you the test that isolates the problem.

If the free tests aren't being done, then you are going to be "guessed to death" by a glorified parts replacer instead of properly fixed by a true mechanic.

So just replacing parts is guessing...a sign of a hack or of a hack job...you want to see or do tests to isolate your problem first.

For this thread, you'd tighten the alternator belt a little (or better yet, use a $6 cricket belt tension tool to insure proper tension) to test if the problem is a slipping belt.

If not a slipping belt per your test, then it's generally safe to say that one or more of the components for the charging system is/are going out (e.g. battery, voltage regulator, diode rectifier, etc.).

 

Unwise and conceited? That was rude!

It is your choice to let an untrained minimun wage kid hook up things to your Ferrari, but not smart to let a person who fixes this subsystem professionaly to do a similar test for free?

The local autozone kids around here are good for about nothing at all They sell parts! They don't know anything except what the manager told them to do.

In short, you do what you want with your car. Take it to the autozone professionals.
I will keep mine in the hands of the professionals who know exactly what they are doing, do the tests for free, and know how to fix any problems as well, rather than your parts guy, okay?

I suppose I could take my aircraft to the FBO aircraft parts store for testing, but no.

Conceited!