Third alternator and still overcharging...

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   Hi, I’m new to this forum, hopefully you’ll be able to help me. My car: 1996 Almera 1.4 SI 16v
A few weeks ago, my battery light came on and I went to the scrapyard and got a new alternator. I put this is and the battery light stayed on.
I then changed the battery with a known good one and checked again, first with the scrapyard alternator, then with my original alternator. The battery light stayed on both times. 
I then checked with two multimeters, and both batteries were overcharging, putting 15v or more into the battery.
I took the alternator I got from the scrapyard back and got another one. Put this one in and the battery light goes out.
Foolishly, I then decided to check the voltage to find that this one is putting in nearly 15.5v! But the battery light is not out. 
This voltage is much steadier than with the other to alternators, however, it is obviously still overcharging. 
What could be causing this? As I can’t believe both ‘new’ alternators I have got have faulty regulators?
The battery is at 12.6v when the engine is off, and the 15.5v is constant regardless of just idling or idling with heaters, hi-beam, radio etc.
I’ve seen the odd account of random shorts at the starter motor etc. causing this problem on other cars, but it’s going to take quite a lot of stabbing in the dark to find a fault like that! 
Thanks in advance, Doug!

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doug Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 05 July 2012 Location: York Status: Offline Points: 3	Post Options Post Reply Quote doug Report Post Thanks(0) Quote Reply Topic: Third alternator and still overcharging... Posted: 05 July 2012 at 18:42
	Hi, I’m new to this forum, hopefully you’ll be able to help me. My car: 1996 Almera 1.4 SI 16v A few weeks ago, my battery light came on and I went to the scrapyard and got a new alternator. I put this is and the battery light stayed on. I then changed the battery with a known good one and checked again, first with the scrapyard alternator, then with my original alternator. The battery light stayed on both times. I then checked with two multimeters, and both batteries were overcharging, putting 15v or more into the battery. I took the alternator I got from the scrapyard back and got another one. Put this one in and the battery light goes out. Foolishly, I then decided to check the voltage to find that this one is putting in nearly 15.5v! But the battery light is not out. This voltage is much steadier than with the other to alternators, however, it is obviously still overcharging. What could be causing this? As I can’t believe both ‘new’ alternators I have got have faulty regulators? The battery is at 12.6v when the engine is off, and the 15.5v is constant regardless of just idling or idling with heaters, hi-beam, radio etc. I’ve seen the odd account of random shorts at the starter motor etc. causing this problem on other cars, but it’s going to take quite a lot of stabbing in the dark to find a fault like that! Thanks in advance, Doug!

crazytaxi Members Profile Send Private Message Find Members Posts Add to Buddy List Management Board Cleaning God Joined: 26 August 2006 Location: Salford Status: Offline Points: 489	Post Options Post Reply Quote crazytaxi Report Post Thanks(0) Quote Reply Posted: 06 July 2012 at 23:09
	Hi Doug and welcome to CN Sorry i can't offer anything on this, i thought all alty;s are supposed to throw out around 15v anyway. The only time i've come across anything like this way on my Bluebirds, there is a diode in them that used to burn out eventually and that let more voltage through, when it did the battery light and all other electrical items would shine brighter than normal. The only suggestion i have is that there may be something similar in the charging circuit somewhere.
	Don't ask me, i just work here!

Mick Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Management General Dogs Body Joined: 08 October 2005 Location: Cheshire Status: Offline Points: 2113	Post Options Post Reply Quote Mick Report Post Thanks(0) Quote Reply Posted: 08 July 2012 at 02:13
	Hi Doug. The only reason a battery would over charge is the alternator on an Almera. Have you tried a different multi meter to check in case yours has a fault? On idle it should charge somewhere between 14.4 and 14.8 volts. If you leave it idling and put on your rear heated screen, heater blower on full speed and headlights on main or dip beam it just drop just below 14 volts. Does the battery smell as though it is overcharging? I would try a different multi meter before you dig any deaper. Mick

doug Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 05 July 2012 Location: York Status: Offline Points: 3	Post Options Post Reply Quote doug Report Post Thanks(0) Quote Reply Posted: 09 July 2012 at 17:26
	Hi Mick, thanks for your reply. I have tested it with two multimeters and tested both of those on new batteries so I'm pretty sure that they're accurate. With a high load the charge stays the same at 15.5v, it drops when the electrics get put on but then picks right back up. There are no signs of damage to the battery (yet), its not hot/smelly/bulging but I have only used it for a couple of short (2mi) journeys. I wonder why the battery light has gone out with this third alternator even though it is still overcharging. Thanks for your help, Doug.

Mick Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Management General Dogs Body Joined: 08 October 2005 Location: Cheshire Status: Offline Points: 2113	Post Options Post Reply Quote Mick Report Post Thanks(0) Quote Reply Posted: 12 July 2012 at 01:25
	Hi Doug. The battery light is an important part of the exciter circuit. If the bulb doesn't work your alternator won't start to charge. However the system is not clever enough to detect such a small overcharge. As long as your battery doesn't start to smell it will be fine. To be honest it's only when they get up near 18V that they begin to boil and cause damage. If I was you I'd leave it for now and just keep an eye on it ove the next few weeks. Give it a couple of long runs. Mick