Replaced alternator with used one 3 years go. Sometime when is cold battery light would turn on for minute or so and would disappear. But battery voltage gauge would stay steady. Past Friday after driving for 50 miles battery gauge evidently start falling down and till I come home it was just above red and evidently pickup was sluggish. Battery light was on. When I come home I recharged battery that was empty as it get 7 hours to do it.
https://static.cargurus.com/images/s...936.1546728101 - Battery gauge is one in upper right corner in picture. Since than alternator sometime charge sometime not. When is battery light on alternator do not charge at all as I checked with voltmeter. When is battery light off alternator do charge but voltage is not steady than change like 20 times per second and go from like 13,5 to 14,7 volts. I did voltage drop test at both side of battery to alternator connections and voltage drop is 0,02V at both side, that is 10 times below limit. Serpentine belt is old but do its job. Should I replace alternator as it work most of time?

 

If it was a used alternator it's possible the armature slip rings are worn through in spots, just from age-mileage so it's giving erratic voltage. If you take the alternator off and remove the voltage regulator/brush assy you can check the slip rings.

 

How long do you think your going on a used alternator to begin with?
Time to replace it with a new or rebuilt and have the hassle over with.
The charge light comes on when the alternator has no output.
That is one of the functions of the regulator to indicate that.
Unless your going to tear the alternator apart and/or replace the brushes, it's time to replace it.
Would be better off with another used alternator to go again and have trouble later again.
Old saying.....if you do what you always do, you get what you always got. Moral of this line is don't do the same all over again and get the same result again.
Good luck.

 

^^^ Thanks. So consensus is bad alternator. Sadly I brought already another from Upull for 20$. It is stronger than me, can not resist.

 

Well if you insist on buying used junk then it might be a wise idea to buy two or three and carry the tools needed to swap it out on the road.

Or maybe you'd be better off joining an Emergency road service

 

Interdasting 4,5 years go deal with same thing - https://www.ford-trucks.com/forums/1...grounds-2.html . Actually make me think what is this life all about. Not about alternators for sure.

 

just pointing out that an alternator has an AVERAGE life of about 150,000 miles... When it fails and you buy a new one, you SHOULD be good for another 10 years... If you buy USED, then did it have 100K or 130 K miles ? ......... that's what happens when you buy USED electrical equip with a finite life........... that's all the guys are saying.

 

^^^ This "new" used one lasted me only 25K as I use pickup only for work. Btw someone comment at another forum. Interdasting that exactly same fuse fool me a couple time in 2014.
"I had the exact same symptoms at almost the exact same time and was considering the afterlife until I checked fuse #11 for the 5th time. It looked great, it looked clean on the contacts and for some strange reason I thought I'd just check continuity since I had the meter there. It was open, I looked at it again and it looked perfect, almost. Along the one side there was a hairline crack. When I twisted the fuse in my hand the thing opened up. I invested $3 dollars in a whole bunch of fuses and one of them did more than the new alternator I bought, the new serpentine belt, the witch doctor...."

 

So I did replaced alternator with "new" one from U-pull at Monday and so far so good. Voltage drop with alternator working is steady 14,7. Interdasting that in 2014 I had to bring 3 alternators from U-pull and only 3. was, at best, good enough. Now from first I brought good one. Something in bad alternator feel detached as I'm capable with lightly turning pulley make 10 circles at pulley and with same force I can make only 2 at "new" one. For alternators from now on I will buy them at part store. Do not worth effort bring ones from U-pull. It is electricity part and obviously it do not like be exposed to rain etc.

EDIT after 3 weeks or so -
Watch what this guy is talking from 10:20 for minute or two. It explain free movement of shaft in bad alternator.

 

What did he just say in last reply?

 

Whew....Now that's some bad grammar..... My take on it is, he bought a bunch of alternators from a junk yard that didn't work, then stumbled on one that's riduculiously close to an over charge scenario. Now he's decided to take the advice given in this thread to buy a new alternator from a parts house.

@ bbsitum....Just think of the time and money you wasted screwing around with junk yard parts. Junk yards are ok for somethings like body and interior parts but alternators, water pumps and so many other things it's just smarter and in the long run cheaper to buy the good parts the first time. Now if you have one of those junkyard alternators laying around you can take that to a shop and have it rebuilt cheaper than you can buy one at the parts house. One more piece of advice..... Don't buy the cheapest parts at the parts house either..... that's a crap shoot just like buying at a junk yard.

 

In post nr #6 i put link to my old tread from 2014 where I had to bring 3 alternators from U-pull only to have last one be just good enough to use. Today 2019 I brought just one and it worked well from first. In 2014 I brought 3 and all 3 was bad (with last one just barely good enough to drive around with red battery light coming on in cold weather). Hence I was all time (5 years) suspicious that something is wrong with alternator circuit, not just alternator. Hence in 2019 I started everything with voltage drop and since it say that circuit is good at both sides I brought alternator.
Alternator that was bad in 2019 look like shaft is broken in it as alternator pulley turn completely freely.

 

The pulley turns freely while the shaft doesn't turn?

 

Brushes at old alternator are worn out.

 

No shaft turn too. Probably just brushes worn. Will save alternator for future and just buy brushes. Aye inspect slip rings, look good enough to me. However can be wrong, as I didn't know slip rings exist before 2 weeks.
Well upon farther investigation it is obvious that rear bearing of old alternator shaft is noisy. So do not worth put new brushes in it. Just will keep regulator for future if will need and return old alternator to U-pull for 5$. Nice to know that you need to check brushes and slip rings in alternator if you pull it out.