Have been having alternator trouble so I bought a brand new 200 amp one. I put it in and it would drift from a full charge and hover around 9.5 10.5 volts. So I sent it back and they said they "fixed" it. In the course if getting ready to install it I ran across a mechanic that said that the single wire that plugs into the voltage regulator on the back of the alternator should have some level of voltage showing all the time. It should be more when the key is on and less when it is off. On mine, when the key is off I have nothing showing and when the key is in the on positon - not running - I get a reading of 11 volts. Normal or not??? Battery is showing 12.2
Thanks

 

What improvements have you noticed after they said they "fixed" it?

 

None. In fact when I put it in, and tried to start it, the battery was dead so I jumped it from my SUV and it idled briefly putting out about 14 volts. Then it slowly drifted down to between 9.5 and 10.5. So I took it off again and took it to a local guy to have it bench tested and see if it was OK or not. He said some plastic piece was broke inside that held the brushes in place and that two diodes were crapped. He rebuilt it for me and then told me that my wire that plugs into the back should have a voltage reading. I told him it was reading 11 volts with the key on and he said he wasn't entirely sure but thought that was too high and I needed to find out for sure. So I wanted to find out before I put the alternator back in.

 

The small plug-in wire in the rear is tested with it REMOVED from the alternator. When you do so, it should show battery voltage with the key on and 0 when the key is off. If it's lower by more than a volt, then start looking for voltage drops. If it's 0 with the key on, start with the fuse #9 in I/P fuse box. From there through the instrument panel and on to the alternator from connector C220.

As far as output from the alternator. Don't troubleshoot the function of the alternator from the small terminal on the back. Determine it has battery voltage when disconnected and use the output to the battery to determine a good unit. 14 volts across the battery with a GOOD battery while it's running.

Be sure you have ALL the connections clean by removing them and cleaning them. Start with the battery and move to the clusters on the inner fender and last the ground strap from the frame to the engine.

Last, unless you have a VERY reputable name like Powermaster, ditch the aftermarket stuff and stick with OEM. from what I see in your list, you don't need anything greater than 140 AMPs.

 

and charge the battery before you kill the alt.
alternators are not designed to charge a dead battery and can very easily fail when doing so, they are only designed to provide power to run the vehicle, and to maintain the battery, a good battery is absolutely needed to get proper output from the alt

 

I think that's what happened before. Somehow the battery had lost it's charge so I jumped it and . . . . . well you know the rest. So I took the battery out - an optima red top - and took it to Advance to have it checked and they said they couldn't check it properly until it was fully charged. So I picked it up later that afternoon and they said it was fully charged and showed no signs of damage or wear but was in good shape. I now have everything back together but was afraid to start it because I wasn't sure if the 11 volts I was getting on the single wire to the back of the alternator was the right volts. Seems now that the reading is normal so tomorrow I will give it a crank!!

 

Spiral wound glass mat batteries can NOT be charged with conventional chargers. Ask any Snap-On salesman. Sorry but I believe your battery is cooked.
I quote from the December 2005 issue of Super Chevy Magazine.

"However, gel cell batteries introduce silica to the electrolytes, immobilizing the acid and making it less likely to spill. Gel cell batteries typically require a specific charger because the recharging process must be precisely controlled with lower voltages and slower recharge rates, adding to the higher average battery cost of gel cell technology."

It's a shame you didn't give us ALL the information upfront.

So after you test the small plug in wire on the back of the alternator CORRECTLY and eliminate it as the bad guy.

The next thing to do is test the voltage across the battery while the engine is running. Should be about 14 volts. If it's less, swap in a known good battery, (not a spiral wound battery that some numb nuts from Advance or you may have charged on a conventional charger). Then retest it again to see if the voltage across the battery is about 14 volts with the engine running. If it now is about 14 volts, you have definitive proof your spiral wound battery is trashed from charging it with a conventional battery charger.

 

Sorry for the info on the altima - first time I heard of that info. As for CORRECTLY testing the wire, as stated above I have already done that. It is difficult to test it unless it is unhooked. However, unless i am misunderstanding your battery testing method, I may have a problem. If, indeed, the optima is "cooked" then is there not the possibility that I could damage the alternator again if I start the car and then test the battery with the car running as you suggest?? It shows 12 volts just sitting there so will it hurt to start it up long enough to test the voltage as you suggest and then do the swap if it doesn't measure up????

 

12 volts across the battery is not good. Unless you are in a cold environment but Fla hardly qualifies for cold. A standard LA battery should read about 12.6 volts. A spiral battery will read higher. With one of the wires off the battery, measure it again. If it only reads 12 volts, either it is low or the battery is shot or your meter is shot.

If the battery is bad, there is no use in testing the alternator since you won't know if the problem you have is the battery or the alternator. The only way to do so is to have all known good components except the last unknown one you are testing for.

Incidentally, have you checked all the connections by removing and cleaning them and particularly the fender clusters and the engine ground strap?

 

Yea, I have all brand new ground cables and straps. Did them about 3 - four months ago. I will test the battery again. If there is a bad component at this stage I would guess it is the battery because I had the alternator off - even though it is near brand new - and took it to an alternator shop and had them do a complete bench test and he said everything is A OK. So I will test again and if the battery isn't up to the specs you gave me I'll get a new one. This one is only about 3 years old but I know that doesn't necessarily mean anything.

Thanks for your help!!!

 

OK speedy, here is an update. I put in a brand new battery and fired it up. The guages still read about 10 amps. I check across the battery with the engine running and I get about 12.6 at best. I took the ground wire off the alternator and used a Dremel and ground down the area around the ground bolt to make sure it was getting a good ground. No difference. Pulled the plug from back of alternator and checked it with the key on and i get 11.8. Where do I go from here??? I should be getting around 14 with the engine running when I check the alternator, right??? The alternator shop swears that this was cranking out 14 consistently yesterday when I picked it up. I'm lost at this point.

 

OK, last night I did a complete check on everything. The single wire coming to the alternator is reading 11.6 with the key on. I put in a brand new optima battery. I took an old OEM alternator I had here in the garage and had it rebuilt today and when I picked it up he showed me it was charging at 14 volts. When I put everything in I still have the same problem. I cannot get a charge reading above 11. Something is preventing it from charging or is draining voltage. Any suggestions as to where to go from here??? Someone had suggested the switch might be bad. I don't know if it is but would that cause this problem?? The cars starts instantly but I just can't get a charge working the way it should.

 

you checking at the battery or the post at the back of the alt?

if at the battery, check at the post, I have seen a few with a bad(high voltage drop) charging lead to the batt from the alt., and it does what you are describing

 

I have been checking at the battery. I was told that was the best place. Let me ask you this, A few months ago I was upgrading and checking all my grounds, etc. So I went to a stereo store and bout about 15 feet of the large red cable and cut it into pieces to use for ground, etc. So I made up a ground wire from this for my alternator and also for the charge wire going to the top post - even though it's a side mount - of the optima. Is this cable OK for this?? I will do a check at the alternator and see it it's OK there. By the way exactly where does the feed for the guage come from?? I have the stock guage but I also installed a set of three custom guages on the console - oil, volts, and water temp. Both guages for the votage read about the same when the car is running but I don't know where they get their info from.

 

I just checked at the alternator and I get the same reading as I do at the battery. Right now it is reading 12.0 which is still low - even though on the inside the guages are reading about 10 so I'm still lost.