Alternator charging issues

[Devin]

According to this post by sdpatt the battery should show ~13.8 volts at idle. I charged my battery from dead for over 8 hours at 12V 6A. At idle I was showing ~12.08 volts. When we took it out for a test drive today the battery light came on about the middle of the drive and it died at a stop. We got it on a roll and once the RPMs dropped after the compression start it died again. The battery is new as of a few months ago, and the alternator as well. Could the alternator be bad?

 

[Storm-Chaser]

You're mis-interpreting what sdpatt posted. He was referring to the system voltage - which is a measure of alternator output and the ability of the voltage regulator to maintain that output within a specified range. You simply check the alternator's voltage output at the battery terminals, to ensure it's high enough to effectively charge the battery.

The voltage range is 13.5 to 14.5 volts. Voltage output below 13.5 is usually an alternator problem, above 14.5 is a voltage regulator problem.

 

[Devin]

But if I'm seeing 12.x at the terminals at idle, or any RPM range, then most likely I'm seeing an alternator issue?

 

[frosho]

That would be my conclusion.

 

[Devin]

I'll rig up some wires into the car from the battery terminals to the voltmeter and see what I get through several RPM ranges in motion.

 

[Storm-Chaser]

It is most likely a bad alternator, as long as the harness and battery cables are in good working order.


If you end-up buying a remanufactured alternator and can afford it, I would [personally] purchase a Ford reman.

If you'll search the forum, you will find quite a few posts on out-of-the-box problems with many remanufactured alternators and starters. Unless you're buying an OEM or other high-quality remanufactured alternator, most "less-expensive" rebuilds do not completely rebuild the faulty alternator starter. Instead, they only rebuild/replace those internal components of the alternator/starter that fail their nomnal testing procedures (hence how they undercut a Ford remanufactured unit which is completely overhauled). Many of the "less-expensive" rebuilds simply clean-up and rebuild the alternator and starters using the remaining used parts that do pass testing, thus exposing the next-weaker-link which fails relatively shortly after the install, or within a very short period of time (do a search using the keywords "alternator" or "remanufacture", combined with another term such as failed or failure).

 

[Devin]

Mine is Hecho in Mexico so that might have something to do with it.

Problem solved?

I took it to Schucks (CSK) and they tested it fine. All while my voltmeter was saying 12.x volts. I purchased the HD silver colored terminal clamps since the normal car clamps I purchased before didn't fit over the cables correctly. I cleaned up the POS and NEG cables and the little 12 gauge or so wires that went with each one and clamped 'em in. I was getting about 13-14 volts from just the battery to the car's chassis, and 12.8 or so when I got it all hooked up.

I took it for a drive and it shot up to 15 then 16 volts. It bounced around topping out around 16.3 and settled in at 15.8 for the first 20 minutes of highway and sidestreet time. Coming back it slunk down to 15.4. I kept driving and about 50 minutes into it I was seeing 14.8. About 65 minutes into it I was seeing 14.3. I got home and killed it (my fault) U-turning into my drive way and started it up at 13.9. It hit about 14 when I parked. I'll keep driving it around this weekend and see if it levels out.

 

[Bizzy]

Was the battery a maintenance free type battery? If so, those were not meant to be completely discharged. A complete discharge can damage them to where they don't charge properly. Why the battery discharged in the first place is a separate issue.

I'm not an expert on what voltages should be present while driving etc. but I would be leaning toward a faulty alternator as the root of the discharge. You might want to replace the battery if it is a maintenance free type.

 

[Storm-Chaser]

Devin,
In the last paragraph where you're talking about the voltage while driving around, are you talking about the voltage output you're seeing on a gauge, did you wire-up the voltmeter to read inside the car while driving, or were you periodically stopping and measuring the voltage?

Yes, bad battery terminals, bad connections, or bad cables will all affect the voltage output at the battery, which in turn prevents the battery from charging if the condition is bad enough.

Glad to see you got it figured out, because over time it would have damaged both the battery and alternator.

 

[Devin]

So after that drive I took it out the next day and the voltage I read was 11.8 the entire ride, which was about half an hour's worth on the highway. It fluctuated rarely down to .7 and up to .9. Just to be safe I got home and hooked up my old Actron analyzer and it read the same voltage.

I took the alt out today and brought it to Napa and it failed. I returned it under warranty to the store and they are going to give me a newer one tomorrow. I'm going to have the battery tested as well since it was on the receiving end of the bad alt.