I lost my altenator this last week end and I replaced it on Sunday. I have worked on cars a whole lot and so I have a couple of questions. When I replaced the altenator on Sunday, I took off to town and all seemed ok. Then I turned on my lights after about a half hour and I noticed the voltage start to DROP. I turned the lights off and started for home. The voltage was slowly starting to rise again and about 20 min. later I started to smell electrical components burning. I stopped real quick, opened the hood and the back of the altenator was smoking at the lower connector of the wiring harness. I unplugged it and went on home. I took the altenator back to the sore and they replaced it. I put the new one in last night and drove to work this morning. I stopped and checked it several times on my way to work and by the time I got to work, the altenator was pretty warm(hot). I have never felt one of these before when running. Is it normal to be hot? I wasn't using lights or anything. The voltage on the battery is around 13.5-13.9v. Is that a little low? The truck is a 1992 F150 with 300 I6. I have only owned it for about a month now. Any ideas would be greatly appreciated. Thanks.

 

What happened with the late 80's early 90 model alternators was the Rectifier plug & the Regulator plug pins would work loose & heat would build up to the point where fires were possible & a lot of times probable . The new alternator you got was likely fine , the problem is both those plugs will have to be replaced . Ford sells them & I think both plugs will run you about $40 . I recently had to replace my alternator & the Recitifier plug showed signs of excessive heat so I replaced it . Simply cut the old plug off & splice in the new plug using the proper connectors & use some shrink wrap & wrap that it some high heat type electrical tape like 3M Super 88 , dont use the jap wrap type tape because heat will destroy it in no time . Also use some dieelectric grease on the new rectifier plug before you connect it to the alternator .

 

first off, take that no-good alternator back and get a good one. then check your wiring.

Wayne

 

I did replace the Rectifier plug and did use the Dielectric paste that came with the Altenator. What else could be causing the altenator to work to hard? It would seem if I had a short somewhere, the battery would discharge. Thanks for the replies!

 

13.xx is an OK voltage for a battery that is not under load.

The alternator will be warm(Warm is relative) just from being under the hood. I would feel the connectors and wires while it is running(Watch your fingers BTW), should not be hot to the touch. Smell for smoke, any smoke or really hot wires means you should make your tests quickly or shut down right away. Check the voltage across the battery while A) engine off; B) Engine on, no accessories; C) engine on with accessories, one at a time until everything is on.

The battery should read more than 12v in condition A. It should read maybe a volt or two higher in condition B but not more than say 16 volts. It should also read higher than A in condition C but may drop a little(relative to B) as more stuff is turned on. Depending on your load it should not drop below condition A while the engine is running at fast idle, if it does, you may have a weak alternator or a bad one, or there is something loading it down too much.

I have had mixed results with rebuilt alternators from unknown shops. Some alternators are fine others are crapola. Sometimes you get the "one size fits all" that may be underated for your truck. I prefer to rebuild my own, it is easy to do, no magic involved.

Jim Henderson

 

Could corroded battery connectors and posts cause the altenator to get hot because it is trying to charge the battery but can't do it very well so it is over working the altenator? I'm trying to learn.

 

Electricity chooses the path of least resistance. When comes to a corroded battery connection, it will see higher than normal resistance causing a voltage drop (or loss), letting the battery run down. But a corroded battery connection will give more noticable problems when trying to crank the engine since this operation requires huge amounts of current and voltage drop is dependent on how much current is being used. If your connection is good enough to crank, it's good enough to charge.

 

Sounds like you had a bad electrical connection at the alternators output connections.
Using push on lugs on an alternators output connection was insane by Ford. In addition they used 2 AWG 10 or AWG 12 wires connected in parallel which makes the scenario worse because current sharing becomes an issue. The 2 conductors typically will not conduct equal current, causing one to run hotter.
Replacing the connector with a new one is smart. I also use a product called "Copper shield" on the lugs before connecting them. It is a copper based grease substance which prevents corrosion and lowers contact resistance. The resistance is what causes heat (power) dissipation.
Poor connections at the battery will not make an alternator run hot or work hard, it might make the connections at the battery hot though. What it will do is limit the current through the battery preventing it from being charged adequately.
The regulator inside the alternator is of the constant voltage type circuitry with a current limit circuit set near the alternators output current rating. What it does is sense the battery voltage and adjust the current to keep the battery voltage constant at around 13.5 to about 15 volts depending on load and temperature. Under heavy load it may operate in constant current mode at the alternators output current rating. Lead acid batteries like to be charged at 13.8 - 14.4 volts. More than this and they will begin to "gas" losing their electrolyte. Lower, and they will not accumulate enough amp-hours of charge during short distance driving.
Last but not least "Powermaster" makes an alternator upgrade for these vehicles. It produces about 80 amps at idle and 140 amps maximum. It has an output stud which will not overheat and burn like the stock Ford. See www.powermastermotorsports.com
Hope this helps, sorry so long.
Mark