battery light at high rpm

[Mike Endrizzi]

Noticed today leaving wotk that at wot 4000+rpm the battery light comes on... as rpm drops, the light goes out



tried with all accessories on, and no accessories on.. the volt guage doesnt move much, stays about half...





Doing a google search I read that it might be either a voltage regulator or the alternator itself





Does this truck (2005) have anything else hooked up to that light??? or am i going to be buying an alternator in my near future???



i guess for now i can drive normally and be fine,, i just dont like any light to come on when i stomp on it...

 

[Jerry Gerner 2]

First guess would be the alternator. If you have an Advance Auto around you, you can take it there and they'll test the whole charging system without taking anything out of the truck. Keep us posted with the cause and cure for future reference.

 

[Bill Barber]

bad tensioner, bad belt, belt slip?

 

[Todd Z]

I was thinking the same as bill that the belt was slipping...



The right thing is to get a volt meter on it and test it first...



Todd Z

 

[Mitch Spiegel]

I just had this happen. it was the alternator going bad.

Ford replaced it problem solved.

 

[Denis Bourque]

Sounds like belt or alternator to me also.

 

[Gavin Allan]

Brushes/slip rings floating at high RPMs in the alternator. Very common Ford problem when they get a few miles on them. Replace the alternator. Fixed the problem on my '03 Adrenalin.



My alternator failed at 47,000 miles. It went from light on occasionally to on nearly full time in less than a week.



A lady I work with had the same thing on her Taurus. She put up with the light for about two weeks before the battery went totally dead. She had a 45-min commute each way, so maybe it charged just enough to keep it going in that long of a commute.



The rebuilt alternator from AutoZone cost me $150 after returning the core. Took me 10 minutes to install it.

 

[EddieS'04]

How many miles on your trac? Being an '05 I dont suspect brushes, unless alot of miles. I would think slipping belt or voltage regulator failing. Have it checked for free at some parts stores, while on the trac. Belt is an easy fix. If you have any experiance with altenator disasembly. Regulators and brushes are easy to replace. Save your self, $100 or more. Providing the altenator checks ok.



Only altenators I replace are if the windings or armature are burnt or shorted. Not sure about the trac but some bearings can be dificult. It is getting harder to find parts stores, that sell repair parts. They make more selling the whole thing. Especialy the discount parts stores.



For some stores rebuilt means they only, cleaned and replaced the bad parts. Remanufactured gets a complete do over and a better warranty.

 

[Mitch Spiegel]

Mine had 45K miles on it. The problem gets worse over time. Mine started acting up when the engine speed was above 3500 rpm in the course of a weeks time the light would come on 2500 to 3000 rpm. I thought about rebuilding the alternator myself (parts from ebay ~$60), my truck is still under warrantee. It only cost me an hour of my time for a brand new remanufactured unit installed.

 

[ProjectSparta]

My eclipse had the same problem, replaced the altenator, and bam problem fixed!

 

[Richard L]

It sounds more like the belt is slipping at higher speeds, than any alternator problem. (brushes are spring loaded and cannot/will not float even at the highest rpm the engine can produce.



The practical solution is to replace the belt first. That will be the cheapest and most logical item to replace first. If the problem persist, then you pretty much know by the process of elimination that the alternator has a problem, but that does not mean you need a whole new alternator. Alterantors can be easily tested with a simple multimeeter/volt-ohm meter and individual diodes , brushes, voltage regulators, etc can be individually replaced if they test bad. The cost to replace parts is much cheaper than a whole new alternator.



If you do not have the knowledge or tools to test your alternator, you can go to places like Autozone that will do the testing for you. If you can remove and replace the alternator yourself, you can take it to a shop and have them make the internal repairs and you can put it back on the vehicle.



Since the belt is the likely culprit and is the cheapest and easy to replace, I would start there.



...Rich

 

[Les]

(brushes are spring loaded and cannot/will not float even at the highest rpm the engine can produce.

Not true, if the springs have been damaged by heat, they can float.

 

[Richard L]

Les,

I disagree, only because there is nothing pushing up on the brushes. The shaft of the alternator would have to be bent or out of round to exert a force against the brushes/spring. and that would not be the fault of the brushes or springs. He would need a whole new alternator, or new bearings. Without some force to push the brushes away from the alternator shaft the brushes cannot "Float"



The brush springs in alternators are not very strong to begin with because floating is not an issue and the springs are only to keep feeding the brushes and maintaining light but even contact as the brushes wear. What you may be considering as brushes floating is probably the brushes just getting stuck in their bores and losing contact with the contact ring as they wear.



...Rich

 

[Les]

I disagree, only because there is nothing pushing up on the brushes

Again, not true. A spring is used to keep tension on the brush for contact to the rotor. If it becomes damaged by heat, it may not make adequate contact during high loads or high rpms. Typically heat issues result from excessive output due to a failing battery, short, or excessive loads placed on the alternator such as high output stereos.

 

[Mike Endrizzi]

Solved.... Thanks for all the replies...



On my way to work last night (midnight shift) the battery light was on about half the trip, then went out, on lunch break it was on and didnt go out at all... On the way home I watched the battery guage go from middle to zero... by the time I pulled into my driveway there was only enough battery juice to power fuel pump and ignition... called napa, and ordered an alternator... installed it, charged the battery and boom... no light on at any speed..

 

[Jerry Gerner 2]

Great news, I knew it was the alternator. Les, Rich settle down, not work argueing over. Everythings cool now. Mike, atleast it lasted until you got home.

 

[Gavin Allan]

Yep. Another quality Ford put back on the road due to a crappy alternator!

 

[Richard L]

Les,

First off, the springs cannot be damage by heat in the alternator because the springs are created by heat treating the steel to temper them. You would have to heat the springs to nearly white hot to damage that temper. That kind of heat would melt the plastic and copper in the alternator and it would not work at all. Yes, a spring could break, but then it's not likely that the alternator would function at any speed



Secondly, Alternators do not depend on speed to generate maximum output. alternators are capabile of producing their maximum power output at speeds slightly above idle. Alternators increase power output by simply increasing the exciter voltage. This can be as little as 3 volts, but is amplified in the alternator. And while alternators are rated in Amps, the power they produce is all based on voltage senseing, and very slight changes in the exciter voltage.



If you disconnect the input battery voltage from the alternator, it will not produce any power regarless of what speed yo spin it.



I think you may be confusing the way old generators operated instead of how alternators function Generators were speed sensitive and allowed the headlights to dim at idle and brighten when the engine rpm inscreased.



With and alternator, you can run your engine at idle and operate all the accessories and keep you battery fully charged. It's all done with voltage senseing and not engine rpms.



In the end he simply replaced the alternator, so we will never really know what was wrong with the alternator?



...Rich

 

[Les]

Richard, your basic premise is correct, but you said "cannot/will not float." All I said was there are times under certain conditions when it is possible. For the most part you explaination is correct.

First off, the springs cannot be damage by heat in the alternator because the springs are created by heat treating the steel to temper them. You would have to heat the springs to nearly white hot to damage that temper.

And that is exactly how they look. These are very thin spring, much like you would see in a ball-point pin.



Just so you know, I used to own a rebuilding shop and have personally built thousands of starters and alternators. So your statement of "cannot/will not" is not true.

 

[Gavin Allan]

It doesn't appear to be worn bearings, bad stator, bad rotor, bad rectifier, or bad anything else. It appears to be a bad electrical connection at the brushes/slip rings. It could be a roughness or contamination/oxidation of the surface of the slip rings, misalignment, weak springs, etc., but whatever it is, it appears to be a lack of good electrical contact at the slip rings/ brushes. Most of the folks I talk to seem to call it "floating brushes" because the electrical contact degrades with higher speeds. Its also a well-know weakness in Ford alternators for the past 15 years or so.