Thread: alternator issues

Tweet

Does anyone know why my 3 wire bosch alternator stops charging when it gets hot.
The car is fine when I first start driving and then the charge light comes on.
Not sure if it's when the thermo fan comes on. The alternator has only done about 1500 kms

I sounds to me like your alternator output capacity is too small for the load, and when the electric fan comes on it's not able to meet the demand, so you're pulling power from the battery. Many electric fans pull up to 30 amps under load, and some installations have dual fans. You may need to increase the size of your alternator. Look at your fuse block and add up the fuse capacities for a quick idea of your load, and compare to your alternator rating.

Idiot lights usually show if the alternator is charging, not if the whole system is gaining or losing power. For that you need a gauge. I would check the alternator and regulator.

This is about the quickest test you can do at home;

Quick Test: Faulty Alternators - Hot Rod Magazine

Or, you can take the alternator out and take it to the local parts store and have t checked. You indicate the alternator is fairly new. What issues led to the replacement of the old one? Did this alternator ever run without the idiot light coming on?

.

Originally Posted by R Pope

Idiot lights usually show if the alternator is charging, not if the whole system is gaining or losing power. For that you need a gauge. I would check the alternator and regulator.

I have a guage and it drops to 12 volts

Originally Posted by R Pope

Idiot lights usually show if the alternator is charging, not if the whole system is gaining or losing power. For that you need a gauge. I would check the alternator and regulator.

I'm reasonably sure the alternator is good for 90 amps so it should be fine.Mind you perhaps it is,nt providing the output

Weak diode(s), cold solder. Is it under warranty?

this was a brand new build,so It was the first alternator bought for the car

IMO, as you drive the vehicle the alternator warms up and causes the idiot light to come on and you say with a gauge it is only putting out 12 volts when hot and that indicates to me that there is either a cold solder joint in the regulator or on one of the diode legs or one of the diodes is weak,
There are other possibilities as Roger pointed out, the alternator could be too small for the load and there could be a short in the system, though that should show up hot or cold.

Originally Posted by roadster

I have a guage and it drops to 12 volts

Assuming the gauge is good, its time for a new alternator. The voltage (with car running) should never be 12 volts. You are running on only the battery at that point.

There are many videos online showing how to replace the diodes / voltage regulator. I saved my chrome alternator doing this for about $30.00 Its not hard to do.

I have seen many alternators work perfect when cold and give up when hot.
With that being said Bosch is the worst electrical product purchase that you can make. Most professional shops will not install Bosch products. Sure, they have a lifetime warranty and its a good thing in most cases.

Hey!! How are your grounds?? Negative side of battery to back of engine block?? Ground wire from back of Alternator to ground at block? Grounds all sanded and clean? http://www.madelectrical.com/electri...hreewire.shtml A good read!! Pete

We just chased a similar problem....barely 12 volts on gauge. Charge battery, start car. Voltage would slowly sink from 14+ to just barely 12. Alternator was suspect but checked grounds and all first. Then, swapped for another new alternator...nothing changed. Finally found that the bearing in the electric fan going bad, fan was drawing excessive current. You might look for an excessive current draw to make sure it isnt an alternator problem.

Originally Posted by prpmmp

Hey!! How are your grounds?? Negative side of battery to back of engine block?? Ground wire from back of Alternator to ground at block? Grounds all sanded and clean? Catalog A good read!! Pete

Pete, you are my hero. As I was scrolling down through this thread, I was thinking that I was going to post about grounds, motor to frame, frame to body.

.

[QUOTE=techinspector1;539676]Pete, you are my hero. As I was scrolling down through this thread, I was thinking that I was going to post about grounds, motor to frame, frame to body. Ditto!! With all your tech infro all these years some of it sunk in You taught us well!!! Pete