View Full Version : Cooking my Battery?

08-07-2007, 11:58 AM
Gents,I've been having a bit of a problem with my charging system this season and am looking for some help. My battery seems to be getting cooked. I have had acid leaking into the tray and down the firewall. The thing is, sometimes the voltmeter will read 16v and then go back to normal. I thought it could be a wiring issue because I had some exposed wires over on the starter side of the car, but in thinking about it they probably aren't related; I've fixed that anyway. Used a multimeter to verify; 16v at the posts with the car running and 13.75v with the car off. I'm guessing the internal regulator in the alternator; but could it be anything else? Thanks.

08-07-2007, 12:03 PM
You're on the right track. The regulator in the alternator is first component to replace. Then probably the battery will be sulfated.

08-07-2007, 12:11 PM

08-07-2007, 12:19 PM
Can an alternator shop verify the problem with some kind of test?

08-07-2007, 01:18 PM
Yes, an alternator shop can verify the problem you have just verified.

And by the way, over charging a battery does not cause it to sulfate, it is just the opposite. As a battery is cycled through charge and discharge sulfate will build up on the plates thereby reducing the battery's ability to fully charge. many batteries that are deemed not able to hold a charge are in reality heavily sulfated which can be corrected.

A process known as equalization places a higher then normal charge on the battery which over eight hours returns the sulfate to solution. However, 16 volts is way above what an equalization charge should be. What you are doing at that voltage is making a lot of hydrogen and oxygen as well as boiling the fluid.

08-07-2007, 01:43 PM
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gifDoesn't even need to be an alternator shop, almost any place that works on cars will be able to do the test. Sears used to do it for free, but AFAIK they charge for it now.

Some TR6 alternators have a separate 'sense' wire to the battery cable. If that wire is loose or broken, the output voltage may go too high. Otherwise, it pretty much has to be inside the alternator; although it might be a short or bad connection inside rather than the regulator itself. There is no provision for "equalization", the output voltage shouldn't go above 14.4 (@ 70F) even if the battery is badly sulfated (or disconnected).

08-07-2007, 01:46 PM
Sulfated? https://www.flex.com/~kalepa/technotes.htm

08-07-2007, 01:57 PM
... There is no provision for "equalization", the output voltage shouldn't go above 14.4 (@ 70F) even if the battery is badly sulfated (or disconnected).

Sorry, did not mean to imply that automotive alternators had an equalization feature, because as you point out they don't. My intent was to explain sulfate build up and how to correct it. Clearly charging at 16 volts is way outside the norm for an equalization process and is damaging, however it does equalize the battery, but in this case it does it all over the car. /bcforum/images/%%GRAEMLIN_URL%%/crazyeyes.gif

08-07-2007, 08:28 PM
Mea Culpa, sulfated was not the proper terminology. But the results are the same;i.e. when you boil out the water in a lead acid battery the coating of the plates DOES fall to the bottom of the cell,over time it will build up to touch the bottom of the plates, which is the PROPER term of a sulfated battery.

So even if the battery has not been boild out long enough to be suffering sulfation, it will have lost plate covering and charging capacity.

08-07-2007, 09:51 PM
Had the same problem a year ago on my TR6.
It's the alternator internal voltage regulator, $30 repair in Canada at an automotive electrical repair shop, perfect since.
However, it cooked my brand new battery literally and warped the plates giving a short inside; so add another $100.