'93 F-150 - possible alternator problem?

On Mon, 07 Feb 2011 20:56:24 -0500, Nate Nagel rearranged some electrons to say:

Your problem could have a multitude of causes. Or, it might not be a problem at all. Because you are unable to do any basic diagnostic work, it's difficult to answer your question. Report the charging voltage at the battery terminals at idle, and also at 2000 RPM or so. As long as it's above about 13.5 volts, then the alternator is doing a reasonable job. A voltage drop under load can be caused by a number of things, corroded terminals, bad wiring, bad switches, etc. Without doing some troubleshooting, and just shotgunning parts, you're wasting time and money. Of course, that is your choice.

Nate Nagel wrote in news: snipped-for-privacy@news2.newsguy.com:

Well, this is a Ford, so maybe there are issues I'm unaware of.

But to me, an alternator in good condition should be more than capable of keeping the system voltage well above 13 even with full-load, and at idle.

Remember that alternators replaced generators for the reason that generators were often unable to keep up with a loaded system with the engine at idle.

True, but my point is that the gauge may be giving you a false indication of what's actually happening. That's why I'm encouraging you to verify whether the gauge is fibbing or not.

What you are seeing is normal. I wish my 1971 chevy truck's gauge worked like that. I know that at a slow idle with all the lights and accessories turned on the voltage does drop a little, but the gauge needle stays steady as a rock (well maybe with a magnifying glass I might see it move).

The fact that you don't drive the vehicle very often or for very long also makes the voltage drop at idle more noticeable because the battery is sucking more juice than it would if it were charged longer and more often.

-jim

In message , Tegger writes

Maybe it's my age, but I can remember alternators replacing generators because (d.c.) generators didn't produce usable output below 1500rpm. The were at a much lower gearing due to the much higher centrifugal effects of the armature, compared to the magnet rotating inside on an alternator (a.c.) generator.

The regulation on the alternator (even with the old mechanical buzzer regulators) was much, much better than with the generator. You don't see headlights dimming when you come to a stop at the intersection the way you did back then.

--scott

IMO this isn't that difficult.. If your alternator isn't putting out enough voltage replace it. If your battery is 4-5 years old replace that too. Of course checking for any corrosion on the alternator & battery might help too before replacing any components.

That's the problem, all of that has already been done, and recently too.

nate

Haven't been paying attention but if the problem is that in cold weather with all accessories on you're seeing enough of a drop to dim the lights noticeably then you have a problem. The reason being that in cold weather the voltage should actually ramp up some to cover the drain caused by the accessories and the cold. Temperature compensated regulators do that by design.

m:

It is possible you have a defective part. Fully charge the battery and give it a load test. Also give us a reading on what the alternater is charging at idle. Check for any loose/dirty connections and check to see if the belt might be slipping.

Chas

I read all the replies, here is all you need. Stick in the cigarette lighter and you can determine if the alternator is doing it's job, the charge of the battery and after using it a while know get a good feeling of what's doing what. One of the handiest things to have around I know of when there are charging/battery/starting problems.

IMHO both of you are correct. Generators were somewhat current challenged (for a generator to produce 75 amps would require some massive brushes, and other components), and as well generators didn't produce good current at anything less that cruising speeds, and could not be geared up because then they'd self destruct at high engine RPMs.

I own a 1993 F-150, straight 6, 4.9L engine, 5 speed Toyo-Kogyo Mazda transmission. Battery is from 9/2008. Mileage is 118,174.

Running heater, lights, wipers, radio, in rain at 40 degrees F, the alternator seemed to sag in power, the other morning. the meter dropped to the bottom of the "Normal" range.

I think the belt slipped after going through a large puddle of water.

Automotive charging systems are dynamic in their operation, meaning that the conditions and outputs are variable, due to outside factors.

This alternator is quite satisfactory at most operational conditions, but, there will be times when the "envelope" of normal performance is exceeded.

I do clean both ends of all the battery cables, each year. I am in Central Florida. In Northern states, where salt is used, I would do this cleaning twice each year.

If the engine or battery ground (Negative) cables get a bit of corrosion, then the voltage can really take a dump!

I would clean the battery terminals, and check the positive cable at the engine solenoid on the inner fender. Check the negative cable on both ends. All my cables were all new, with the battery, in 2008, and the negative cable connects under my upper starter bolt.

But, what could I know, at 64, as a retired Air Force electronics technician on exotic aircraft which I still can't tell you about, because I'm sworn to secrecy, and, it would break national security.

WTF, a retired AF mechanic trying to use a vehicle's dash volt meter? Throw a real meter (VOM or a DVOM) on it and see what's really happening.

Well sure if your a duck you get out and splash around in the driving rain every time your truck runs through a puddle of water.

Forgot to mention, it bounced back in about 30 seconds, so, it was probably belt slip due to the splash of water.

I own a whole shelf of digital VOMs, and a couple cigarette lighter led testors, that are super cheap, from Harbor Freight Tools.

If you have corrosion on a cable end, and it results in one ohm of resistance, then, at 13.8 Volts DC you would lose 13.8 Amps of current just at that one dirty connection!

The 1993 F-150 XL, 4.9L engine, have 65 Amp alternators. Not much capacity left after the needs of the lights, heater fan, wipers, to waste on bad connections!

No matter that you can replace it with a 100 amp alternator by Bosch, for only $112, still need clean connections on all wiring!

In message , Big Red Truck writes

I read what you said you know, but this sentence gives me serious reason to doubt you.