Alternator Issue - 13.8 Volts at the battery

[dhoisak]

My alternator fried the other day on my 98 XLT, and I replaced it with a rebuilt 95Amp model. The parts guy said this was the model for an XLT with no power seats, heated seats, rear A/C, etc. I got the alternator installed and all appeared ok. 12.62 Volts on the battery with the engine off and 14.45 Volts with the engine running.

My wife was out driving the day after, and the battery charge light would come on and the battery charge guage would drop down a bit. Seems this only happened on bumby roads. On smooth roads the idiot light would turn off.

Last night I checked the voltage with the engine running.. 13.3 to 13.7 Volts, not 14.5.. cranked up the A/C, turned the lights on, hazards flashing, music playing and it dipped to 12.9 to 13.2 volts and the idiot light came on again.

I turned everything off, disconnected the battery, reset all the connections on the alternator, checked the grounding, checked the continuaty of the 175 Amp MEGA fuse and other large fuses, all were ok. Reconnected the battery, started her up, and 13.7 to 13.8 Volts. This morning my wife's driving it and the idiot light is on all the time

Do I need the 130 Amp Alternator? What else should I check?

Thanks

 

[410Fortune]

check the wiring from the alternator and the pig tail on the voltage regulator.

Your battery cables may be the culprit.
Always replace the weakish 90 amp unit with the 135 on these trucks.
You can remove the alternator, take it back to where you bought it and have it bench tested. I believe they will tell you 13.8 with a load is acceptable

 

[ma96782]

When changing out an alt., I have always found it useful to also check the battery condition. There were times when, "I thought," it was only the alt.....but, the battery was also at fault.

Having a "fully charged battery" is important, before saying that the alt. is not doing it's job. The battery may not be able to "hold" a charge. A specific gravity test, will give you an idea of the condition of each of the cells. Testing under "load," will also be helpful to assess "condition."

Hint............when "working on these kinds of problems"..........why not, remove the alt and battery, take them both down to the auto parts store and have them both bench tested. Also, since the parts are off, check the condition of the connections.................clean up those battery cables and box. Ensure that the connections are clean and sturdy.

And, for the record, I have had a rebuilt alt, go bad w/in a week...........just took it back to the store. They bench tested...........said it was on "the low side of the range"..........but, they still exchanged it.

Also, I once had a "bad" new battery.........I suspected something was "wrong" and took it back to be bench tested..........yup, it wouldn't "hold" a charge.

Additionally, did you know that Sears has been known to sell used batteries as new? Saw it on one of those TV programs.......was it 60 Min? I have also, had the Sears techs sell me a new battery, when I really needed a new alt......after, they did their, "test of the charging system." Needless to say.........."I don't TRUST Sears Automotive."

Aloha, Mark

 

[dhoisak]

Well it turned out to be faulty rebuilt alternator that I got. I bought a brand new 95 amp alternator from another auto part store, installed it and no problems. I returned the defective alternator and got my refund without any problems. The new alternator is putting out 14.95 volts at the battery contacts with the engine running. I also cleaned all the contacts on the battery and battery connectors to ensure a proper connection.

As for Sears.. I never go there for any repairs.. If I can repair it myself, I will do it, but when there's a major problem, it goes to one of my 2 mechanics. The Ford dealership near me is not very trustworthy either as I've been taken for a ride there with a bad spark plug problem on cyl #4.

Thanks for all your help!
Dean

 

[BrooklynBay]

Why didn't you exchange the alternator for the 130 amp model like 410Fortune suggested? It will provide more current when there is a demand for it, and should make everything run smoother.

 

[BrooklynBay]

AlDive managed to get higher voltage at idle with an overdrive pulley. This is a comparison from one of his threads:

The left one is the stock pulley. The right one is the overdrive pulley.

 

[davesexplorer]

A smaller pulley gets more voltage out of the alternator?

 

[BrooklynBay]

The alternator is turning faster at idle with a smaller pulley, so it will have the same output as if you accelerate with a regular pulley. The RPM range would start from a higher number. I once saw a pulley that was like a cylinder with raised sides. That would make it spin even faster. The higher RPM range might cause the bearings, and brushes to wear out faster since it is always turning faster.

 

[davesexplorer]

But wouldn't the regulator still keep the voltage limited to a certain point? If you are actually talking about amperage, then it would make sense to me and you can ignore my posts.

 

[BrooklynBay]

The regulator is a passive, not active device. It only limits (regulates) the upper voltage threshold, not the lower threshold. In electronics terms, there is only source regulation, not sinking regulation.