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alternator beef

disappoint

disappoint

Lifer
So my alternator went out last year, replaced it with a remanufactured one and it works....sort of. Replaced the battery at the same time.

When the engine rpm is low the battery voltage goes low sometimes. When the engine rpm is normal or high it has no problem.

Sometimes it seems like it's going to stall at low rpm because of the low voltage problem.

I let the battery sit for 12 hours and its at 12.9 volts engine off, so the battery seems to be ok.

Bad voltage regulator on the alternator? Or is the alternator not supposed to charge the battery at low rpm?

Basically what I'm asking is which one is responsible for holding up the voltage at low rpm, the battery or the alternator?
 
disappoint said:
So my alternator went out last year, replaced it with a remanufactured one and it works....sort of. Replaced the battery at the same time.

When the engine rpm is low the battery voltage goes low sometimes. When the engine rpm is normal or high it has no problem.

Sometimes it seems like it's going to stall at low rpm because of the low voltage problem.

I let the battery sit for 12 hours and its at 12.9 volts engine off, so the battery seems to be ok.

Bad voltage regulator on the alternator? Or is the alternator not supposed to charge the battery at low rpm?

Basically what I'm asking is which one is responsible for holding up the voltage at low rpm, the battery or the alternator?
Click to expand...

Well you can test or have the alternator tested and that will immediately tell you which one, although it's most likely the alternator. This will tell you whether or not the alternator is undercharging or not.
 
Just answer me one question.... was the usage of "alternator" and "beef" in your title on purpose...or just randomly selected to describe your temperament regarding this issue you are experiencing?
 
What type of warranty did the alternator have when you bought it? Back-in-the-day when I would buy remanu parts they usually came with a lifetime warranty. If the alternator is bad (to be determined at the parts store) have them replace it.
 
As an alternative, I can suggest chucking a brick at the truck of the gentleman who sold you the remanufactured one...?

😉
 
Do you have a multimeter?

When it's running the voltage should be ~13.8V.

What kind of car? I think most cars have the voltage regulator mounted on the alternator. A lot of Dodges & Jeeps have external regulators - sometimes in the ECU.
 
PricklyPete said:
Just answer me one question.... was the usage of "alternator" and "beef" in your title on purpose...or just randomly selected to describe your temperament regarding this issue you are experiencing?
Click to expand...

On porpoise.

dug777 said:
As an alternative, I can suggest chucking a brick at the truck of the gentleman who sold you the remanufactured one...?

😉
Click to expand...

In an alternate universe, the alternator may alternate between being an alternator and bulk beef unit.

PottedMeat said:
Do you have a multimeter?

When it's running the voltage should be ~13.8V.

What kind of car? I think most cars have the voltage regulator mounted on the alternator. A lot of Dodges & Jeeps have external regulators - sometimes in the ECU.
Click to expand...

I do have a multimeter, and yes the voltage regulator is in the alternator. When it's idling fast the voltage is good, when it's idling slow it goes down too low. I'll have actual numbers in a few minutes if that helps.
 
disappoint said:
I do have a multimeter, and yes the voltage regulator is in the alternator. When it's idling fast the voltage is good, when it's idling slow it goes down too low. I'll have actual numbers in a few minutes if that helps.
Click to expand...

Check the battery and the alternator at low RPMs, and you should find your problem, I think...?
 
Ok so engine idling in park 13.87 V, but in drive (auto trans) with the brake on, it goes down to 12.5 volts. Whereas engine off it's 12.9 V at the battery terminals.

So it's not charging the battery when its idling slowly in gear. Is this normal?
 
disappoint said:
Ok so engine idling in park 13.87 V, but in drive (auto trans) with the brake on, it goes down to 12.5 volts. Whereas engine off it's 12.9 V at the battery terminals.

So it's not charging the battery when its idling slowly in gear. Is this normal?
Click to expand...

Wow, sounds like either the alternator is not rated AMPs for your car or some accessory is sapping your power like crazy. Do you have the radio or fan or lights or anything on when doing this test or just in drive?

It doesn't sound like a bad ground or voltage regulator.
 
An Auto Zone or Advance Auto will check your charging system for free. But it sure sounds like the alternator is laying down on the job...
 
LTC8K6 said:
An Auto Zone or Advance Auto will check your charging system for free. But it sure sounds like the alternator is laying down on the job...
Click to expand...

Thanks for all your help and suggestions, looks like a trip out to AutoZone is in order. Yeah I thought it might be the alternator too.
 
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