Alternator Overcharging

[MrStabby]

After trawling teh interwebz, it appears that overcharging can occur if;

1. The regulator is stuffed (duh)

2. The battery is stuffed, eg its dropped a cell

3. There's a bad engine to body earth

Since my alternator was fully rebuilt less than a year ago and its a pain to pull out, i want to have some confidence its the regulator before i head down that path.

So - to check the battery I will disconnect and check the voltage with a multimeter. Each cell is 2.1 volts, and the battery should be 11.8 (uncharged) to 12.6 (fully charged) so if its 10.5 or less i know its the battery. Of course since it starts well so I know the battery is fine from that....and its newish too.....

How do i check the earth? Is it as simple as checking the resistance between body and engine with a multimeter?

[mad082]

what reading is the alternator putting out when the car is running? 14v is fine, anything much higher isn't. that's generally how you test the voltage regulator as far as i know.

[blind_elk]

If the regulator is stuffed, it will generally put out more voltage as the revs increase. So, with the engine running, measure volts across the battery terminals at idle, then bump the revs up to around 2k and measure again. If the voltage increases, then the reg is stuffed, and it will eventually kill the battery (battery will not be able to hold the charge supplied by the alternator).

[t_revz]

what is the charge rate? 14.7ish should be the upper limit.to testing batt cables for overcharging is easy. if the voltage at alternator is more than say half a volt higher than battery then you have a cable fault. ie 16 at alt and 15.5 at battery wont be cables. if its cables you will see 16 at alternator and 12 or less at batt. dropped cell doesnt necessarily mean it will overcharge. the regulator might be able to be pulled out without removing alternator if its such a big deal. its the black rectangular box on the back of the alternator. just undo the 2 screws and gently pull it out.if the wires to the brushes which are part of the regulator are rubbing on the housing then it can overcharge but it should have a piece of mica in a slot to prevent that.

Edited October 8, 2010 by t_revz

[Duncan]

interesting question....my stagea is currently charging at 15.5v, no change after replacing the alternator.

there is a recent thread elsewhere here where 2 different people have overcharging issues, resolved by adding a missing fuse (or replacing a blown one). I don't understand but it was the same symptom and same fix for both

[t_revz]

yeah duncan both those guys recently have had stageas too!! and they both had a missing fuse not a blown one. i really need to pull a couple alternators down and see how they work to be more specific for testing. i guess from the sounds of it both wires in plug prob will be ignition. the larger white wire are meant to be ignition to excite it and other wire is to do with the regulation side of things i think. i guess check fuses and see if both have power and let me know

[Duncan]

btw mechanic checked all my fuses (specifically told them about missing fuse theory), and did not solve my problem. got a specialist auto sparky looking at it

[MrStabby]

what reading is the alternator putting out when the car is running? 14v is fine, anything much higher isn't. that's generally how you test the voltage regulator as far as i know.

Ive only used the dash gauge so far - 18 volts at any rpm much above idle. I will check at the battery with a multimeter for confirmation. I thought i was going crazy (well, crazier) after checking two times that i didnt have the wipers on the fast setting.....

[Duncan]

jeebus don't run it like that! I fried by boost controller, ecu injector drivers and stereo at only 15-16v in the course of 2 weeks

[mad082]

my grandparents camry had the voltage regulator let go. was charging at 18v. blew a lot of the lights in the car, and they were driving along and all of a sudden the wipers started and wouldn't stop. the voltage had fried the wiper motor too

[Duncan]

mine turned out to be a short in the abs of all things. sorted apparently

[MrStabby]

jeebus don't run it like that! I fried by boost controller, ecu injector drivers and stereo at only 15-16v in the course of 2 weeks

Im not except to get it home. Had the headlights on and I clutched in as much as I could to get the engine back to idle...

Interesting about the ABS - cant understand how that could cause overcharge but i'm not good with electrics. Also reminds me that I also a headlight appeared dead then came one so i guess i'll just check what i can with it in case its related somehow.

[fib]

Mine overcharges also, at 15V and after 15 min of driving it drops down to 14.5 and the battery light goes off. I hate that battery light.

I've checked with the multimeter and it's definitely the alternator pumping out the 15V.

I'm afraid that even if I change the alternator knowing my luck this would not solve the problem :\