Low voltage issue

[CarlPalmer]

I am experiencing a battery charge that works well enough to start the truck between drives, but if there is any kind of draw on it, I can not start the car an hour or so later. So I took my truck to OReilys and they told me that rhe battery is fine (should be, it is brand new) but that It is charging at less than 30 amps.

What should it be? I think that the idle on the truck is too low. It seems on the verge of dying. How do I adjust this? I read somewhere that could be the problem. Anything else to check?

 

[imp]

I am experiencing a battery charge that works well enough to start the truck between drives, but if there is any kind of draw on it, I can not start the car an hour or so later. So I took my truck to OReilys and they told me that rhe battery is fine (should be, it is brand new) but that It is charging at less than 30 amps.

What should it be? I think that the idle on the truck is too low. It seems on the verge of dying. How do I adjust this? I read somewhere that could be the problem. Anything else to check?

If idle speed is too low, alternator output voltage may not be high enough to MATCH battery voltage, much less charge the battery. In that case, the battery is discharging whenever the engine is idling. With accessories "on", like A/C (blower), headlights, etc., that discharge rate is even greater.

While driving, (engine speed well above idle), if the battery no longer discharges under those conditions, the alternator is OK. Thing to do is, MEASURE the voltage at the battery terminals with engine idling and a few power-gobbling accessories "on" (headlights are good). Note voltage. Then have someone speed up engine (in neutral) to about 1200 rpm or so, and read voltage. If first reading is below about 12.5 volts, and reading at speed is about 13.5, or more, the idle speed is your problem.

Idle speed adjustment on some vehicles is no longer an easy affair. The Ford Shop Manual details how adjustment is done, if it is possible. imp

 

[hjerrett]

Just had this problem with my '95 XLT. I was showing low volt at idle, very low if I turned on the blower/defroster. If I was driving the voltage would return to normal. I thought it was my battery and had it tested, it tested ok so I shifted to suspecting the alternator. The next day I drove it to work and there was a loud pop noise that left my ears ringing for over an hour...turns out my alternator was bad, pop noise was the battery that tested good the day before exploding from the bad alternator apparently. Replaced both, working good now.

 

[CarlPalmer]

Took battery and had it bench tested. It tests good.
Took the alternator and had it bench tested. It tests good.
:-/

I used a multi meter on the battery with nothing but the hood light on, and the engine off. It tested 12.1 volts. From what I read, that is low.

With the engine running, I tested the battery, and it came back at something like 13.1 volts.

I am guessing that the problem is my wiring, but I dont know what/where to test for resistance. Any one got any info for more testing?

Where do you take an automobile to have the electrical looked at? Likely they will give you a free estimate, or do you have to pay just to look at it?

 

[CarlPalmer]

Ok, so after some more paying attention to it. It seems that when the truck is sitting and idling, the battery guage drops significantly. When the truck is driving, everything looks pretty good.

Any thoughts as to why this may happen?

 

[budwich]

"drops significantly".... as you have done, you need to "quantify" this with an actually measurement BUT it sounds like your alternator isn't really up to "snuff". Although you indicated that it was tested, that is "bench tested" which is kind of a "baseline" for overall component issues (dead diode, etc), it doesn't really test the actual performance of the unit.

 

[koda2000]

your alternator is most likely the problem. i've also had new batteries that test good but won't hold a charge, but based on your voltage readings (13.1v is still low) i'd replace the alternator. at anything above 1200 rpm i'd expect to see 13.6v-14.3v.

 

[yavapaires]

Took battery and had it bench tested. It tests good.
Took the alternator and had it bench tested. It tests good.
:-/

I used a multi meter on the battery with nothing but the hood light on, and the engine off. It tested 12.1 volts. From what I read, that is low.

With the engine running, I tested the battery, and it came back at something like 13.1 volts.

I am guessing that the problem is my wiring, but I dont know what/where to test for resistance. Any one got any info for more testing?

Where do you take an automobile to have the electrical looked at? Likely they will give you a free estimate, or do you have to pay just to look at it?

12.1 with engine off isn't cause for concern, what is, is the 13.1 with engine running. Running voltage should be near 13.6 or even 14. Check your battery cables, and clean the ends. Don't forget the ground ends at the body and frame. If the alternator is not putting out at least 13.5 volts, there is a problem.

 

[orbach]

An auto parts store will run a free check for you. I had a similar problem and two mechanics kept ruling out the alternator. One said bad battery, the other said probable wiring problem. Had it checked at Autozone for free and they found a bad diode on the alternator. Replaced it and problem fixed.

 

[hjerrett]

As I said in my above post I had the low volt at idle/normal while driving symptom and delayed changing my alternator, which ended up costing me a battery along with the alt in the end. I would change that alt out.

 

[CarlPalmer]

Alrighty, I will definitely try the alternator. I figured the bench test would tell me if it were bad, but I have seen enough intermittent problems in my life to not marry myself to the idea that the bench test is 100%.

At worst, I will return it if it doesn't solve the problem.

I have a voltage meter comming to measure the voltage while you are driving, but it isn't here yet. If changing the alternator doesn't fix it, I will be able to post some real numbers soon.

Thanks!

 

[budwich]

I suspect that the likely culprit for your problem is the brushes in your alternator... either "well worn" or not "seated" or the contact rings have an issue.

 

[my98nnj]

Don't rule out a slipping belt. Seen that cause charging issues even after everything else was replaced, which was indeed a complete waste of $$$

 

[CarlPalmer]

I looked at the belts, but I will probably get a new Serp belt while I am in there anyway.

 

[koda2000]

bench tests are okay but they spin the alt at one constant speed and it's pretty fast, faster than an idle for sure. I've seen Auto Zone type tests say "low voltage" and that's a sure sign of an alt problem, but it depends on their test equipment and who's using it. I still think it's the alternator. Belts and tensioners play their part, but don't usually cause a problem at idle unless there's a big load on the alternator.

 

[imp]

Slipping belts are far less often encountered nowadays. Years back, before the serpentine constant-tensioning method, belt "stretch", and temperature changes affected belt performance.

Today, a failed belt tensioner, other than too long a belt installed (beyond useable tensioner range), can cause belt slippage. imp

 

[CarlPalmer]

Well I bought a new alternator. I am gonna let it run with it a couple days and check my voltages again. I feel a lot better, at a stop light, the volt guage isn't dropping nearly as much. We will see when do some quantifiable testing.