battery light random on/off

[mikeinaustin]

first, the battery light came on and after a few days the battery was too low to start vehicle (it has a fairly new battery). the alternator was replaced and after a little while the battery light went off and stayed off for a few days.

now the battery light, which i suppose means charging system status light, is coming on/off at will (i don't mean to imply flashing). the only thing i can think of is the belt is loose on the alternator. this suv has a belt tensioner which should keep that from happening, but who knows.

nevertheless, any other things can cause this? i know all the electrical wires and connections have been checked and they look good.

 

[eljefino]

What car? Sometimes the ECM or BCM controls the alt, particularly chrysler stuff.

If it were a tensioner problem you or your mechanic would have spotted it putting the belt back on the new alt. Though they can be intermittent, and rather quiet, not high pitched squealy like the old v-belts.

Any pattern? RPM? Electrical load?

You'd feel the power steering get heavy if the belt were slipping.

 

[jldcol]

If you have a volt meter you can verify the alternator functions. That tensioner may be bad/weak and allow some slippage. SLI batteries don't like deep discharges, some more than others, so I also suspect the battery, It should have been tested when alt was changed.

 

[eljefino]

Another good test is the blower motor pitch, the human ear is real sensitive to pitch changes, it'll dip when volts drop.

 

[mikeinaustin]

there is no noise, nothing that indicates the belt is slipping. vehicle is 2002 v6 ford escape. battery is less than a few weeks old so i can't believe its bad. alternator was installed this weekend.

 

[StormRider]

Did you charge the battery before installing the new alternator? I heard or read somewhere that installing an alternator with a dead battery can damage the regulator or diode or something by overheating...

 

[StevieC]

I had this problem on my VW Cabriolet. Could be sticking or worn brushes inside the Alternator or a flaking out regulator. Either way I would think your Alternator is on it's last leg. Take it to a shop and have them test it.

Also could be a bad connection depending on your charging system setup.

 

[mikeinaustin]

battery was fine when new alternator was put in.

the alternator is only a few days old (with the old alternator the battery light was on all the time).

i will measure voltages later tonight, car off, car running. any other test recommendations/procedures for me to run?

 

[StevieC]

Start the car and let it idle, then turn on all accessories and see if you can get the light to come on, or the headlights to dim this would indicate a bad connection or faulty alternator... Should be able to support all the load.

 

[Eddie]

You probably should be checking the ground leads if you had light-on issues with two alternators. Cabe ends corrode inside the covering to so check that. Ops stevieC. I didn't read yours before posting. Ed

 

[jldcol]

Car idling, thats 10 amps for ignition/computer, blower fan on high 10 amps, rear defroster 10 amps, and all lights on about 20 amps for a total of 50 amps, a decent load for alt. Then you need some for battery, below 10 amps unless really discharged. Measure volts across battery at idle 14-15 is expected, with all I mentioned turned on volts will drop but should stay above 14 hopefully.

 

[StevieC]

+1

 

[alanu]

Your alternator is bad.

 

[StevieC]

Originally Posted By: alanu
Your alternator is bad.


Even if it is new... This is what I think it is! I had one that that worked for a week in my Cabriolet and then stopped charging... Happens. Someone is asleep at the Q.A. desk!

 

[AcuraTech]

Need voltage readings at the battery. Car off, car running no electrical loads, and car running with all the electrical loads on.

Without that it's just a stab in the dark.

 

[mechtech2]

The cables and connections always look fine.
But yank them and clean them shiny brite on BOTH ends of power and ground cables.
Charge the battery - the alternator needs this.
A visual check of the drive belt and it's tensioner is a must.
Check the voltage with the car off, running at 2,000 RPM, and 2,000 with the lights on and fan on high.
About 12.5V and 14-14.5 V is good.
Use a multimeter at the battery.
Yes, this is basic, but must be done first.

 

[alanu]

Take it to a shop and get a load test.

Doing home multi meter tests are meaningless because it will never indicated diode issues in the regulator.

I would be certain its an alternator issue and regardless of rebuilt its probably defective.

 

[brianl703]

Originally Posted By: alanu

Doing home multi meter tests are meaningless because it will never indicated diode issues in the regulator.


You can put the mutimeter in AC volts mode and take a reading. I think anything over .5V is cause for concern, I'm unsure of the exact figure.

 

[mikeinaustin]

ok, turns out the problem was the belt tensioner. i replaced this weekend and the light is off and measured voltage is in the mid-14's now (was about 13.7v - with both old and new alternator).

 

[Eddie]

I assumed that something as simple as checking a belt for slippage would have been done before asking the question. My bad Ed