Alternator voltage

[X-North]

Hi guys! I was just wondering how much voltage you got when you probe the big alternator wire and put it to the battery negative with a multimeter. In the dash which letter of the NORMAL word does the needle point. I want to know if mine is normal...the needle point at the letter O of Normal but the system give me 13.5 volts.... normally for a car it gave me around 14.2. So whats the normality for your 1991 to 1994 truck.
Thank you

 

[nssj2]

A new alternator will run 14.2-5 usually. Theyre good down till around low 13s then i recommend a replacement. the voltage is universal for all vehicles with a 12 volt battery.

 

[X-North]

Ok so only 0.7 volt drop....maybe only a slipping belt but it dont make noise so....Gonna do other tests later ...thank you.

Eric

 

[mikeinri]

The gauges are probably just a ballpark. Is it running differently than usual? Are you loading the system more? My gauge sits in a different spot, depending on what I have running. Worst case is at night (headlights), with the defroster or A/C on high, raining (wipers running), sitting at a red light (low idle). With fewer items running, the drop isn't as bad or even noticeable.

Mike

 

[BrooklynBay]

Did you test the alternator with the engine cold or hot? You will get a higher reading when it's cold since it has an internal regulator.

 

[X-North]

I tested it cold and it gave me 13.5
Sometimes the needle point as same as before but sometimes it go down ...not usual i would say.The strap is like new but maybe it slip that would cause this full reading and 13.5 reading voltage sometimes.

 

[kert0307]

Did you test the alternator with the engine cold or hot? You will get a higher reading when it's cold since it has an internal regulator.

Is that why mine reads 14.2-.4 when I first starte it up and levels off around 13.7 after it's been running for awhile?

 

[trucku]

Is that why mine reads 14.2-.4 when I first starte it up and levels off around 13.7 after it's been running for awhile?

My rebuilt replacement alternator does the same

Before that though with the stock alternator showed 14 constantly since I bought the truck used. Finally the stock one died ant only could give out 12 volts. Service tech said that voltage was supposed to change with demand and not run at 14 constant.

 

[X-North]

thats ok problem solved

 

[trucku]

thats ok problem solved

what was your solution?

 

[X-North]

i unplugged the sinlge wire output that go to the dash warning light tried to test it but i accidently shorted it on the alternator housing with my multimeter probe. It made a spark.....after that i tought i had burned something inside the alternator si i retested the alternator on the battery wire and the voltage was now OK at 14.2 volts.....dont ask me why but thats the solution.

 

[mikeinri]

That's got to be in the top ten things that are completely random and make no sense... but like they say, "If it ain't broke, don't fix it, and charge double!"

So does the gauge work?

 

[X-North]

The alternator voltage is OK now but the gauge still fluctuate a lot....random **** happens on this truck lol indicated 205 000 kms but the first 0 is not aligned so uts probably more than 225 000 kms

 

[BrooklynBay]

Is that why mine reads 14.2-.4 when I first start it up, and levels off around 13.7 after it's been running for a while?

Yes.

 

[X-North]

thats a good thread i started everyone need inos on alternator

 

[BrooklynBay]

I have a thread on alternator rebuilding in the Technician Forum section of this website if you want ot learn more about the inner workings of alternators: http://www.explorerforum.com/forums/showthread.php?goto=newpost&t=193296

 

[X-North]

Thnak you.
I used to kinow how but its been a long time now that my mechanic course is done..i did it in 1998 and never rebuilt an alternator since then so

 

[mrphiltx]

Alternator going bad?

OK, so I better be careful what threads I read...

I read this one yesterday, and then my car wouldn't start - no voltage. The alarm does the weird chirpy down staccato thing. And it would go off if I turned the ignition off. It wouldn't take the input from the key fob either to turn off. Voltage indicator was waaay low.

The weird bit was that I had just started it, drove it outside the gate at work, turned it off, and closed/locked the gate. Then it wouldn't start.

Eventually got it jumped and drove home, no worries. Voltage looked maybe a little high, but fine. (in the dash gauge).

Got home, tried cranking. No cranky. Low voltage alarm stuff going off again. Can't turn the ignition off without the alarm going off. Leave the key in the ignition, and go inside to tell my wife I'm home. Come back out, take the key out without a problem. Car even starts!

This morning, back to the no/low voltage. I put my voltmeter on the battery clamps. 1.26V. What? That's pretty low. I tried it post to post. 12.6V
Hmmm... I had recently replaced the negative terminal battery clamp. I tried negative post to positive clamp: 12.6V. Interesting. I also noticed the wires to the negative post were warm, and so was the post.

So I cleaned the mating surfaces of the negative post and clamp with sandpaper, and tried it. Ouch the alarm went off! A good sign. 12.6V clamp to clamp. Car started right up and ran. With the car running, the voltage was 14.86 (I think).

I took it by the local O'Reilly, and had them check the battery: good, almost over charged. Tested the alternator, and the voltage was still 14.6ish. He said that was pretty high and somewhat borderline. He thought my alternator was going to go out in a few months, and take the battery with it.

I drove it to work, and checked voltage when I got here, 14.4 or 14.5V I think - still well into the 14V range, but lower than when I first checked.

So, (I'm impressed you've read this far) is this a sign of the alternator going bad? I didn't give any of the story to the auto store guy, but I do wonder if he was trying to sell me a new alternator ($120 or $135 depending on which I needed).

 

[mikeinri]

Before I even got 1/4 of the way through your post, my brain was screaming CABLES!!!

Replace both battery cables. At a minimum, replace the negative one. Replacing just the terminals is a band-aid. The cables corrode from within, under the insulation. Do a search here if you don't believe me, it's extremely common.

BTW, your alternator sounds just fine. And, welcome to the forum!

Mike

 

[mrphiltx]

Thanks Mike... I was suspicious as well about the cables. When you close the door and the power blips, that's a good sign of a loose connection.

Actually, if I were going to replace cables, I'd replace the positive one - its the one that looks nasty (and I left out the story of how it corroded and quit working on me already) even tho I replace the terminal clamp once already. It looks bad already and has been less than a year.

Time to search and see how bad changing those cables is...