Over Charging!

Pete · Post by **Pete** » Thu Sep 09, 04 7:52 pm

No, not the Banks or Petrol Stations or Parts companies............

I have a problem where the indicated Voltage at Idle across the Battery Terminals is 15.0v with minimal load, and 14.5v with the lights/High Bean on. If you rev the car up the maximum voltage seen is 15.2v under load/no load conditions, so some Voltage regulation appears to be happening.

Now my problem....I think it is cooking the battery (it seems to boil and over-flow fluid)....... but I have changed out the Alternator and the Voltage Regulator and I get the same results regardless which combination I use.

Can anyone confrim the correct charging voltage (I would have guessed about 13.6v); and in addition suggest any avenues to test out what is going on.

The Charging Wiring is not original so limited scope to use the in dash ameter.

Help!! illogical, Captain

Dave-R · Post by **Dave-R** » Thu Sep 09, 04 8:47 pm

Is the regulator earthed correctly? Check the resistance between the body of the regulator and the -ve battery terminal. You want very little resistance at all.

14.4 is the voltage to aim for on a normal lead/acid battery. 15volts and over will boil the acid out as you have found.

Pete · Post by **Pete** » Fri Sep 10, 04 11:24 am

Hi Dave,

In a separate conversation with Alex he too suggested that there may be an earthing problem with the Voltage Regulator.

I have taken this on board and have removed the Regulator, Cleaned all paint off the Bulkhead contact points, drilled a 3rd Location point and re-installed the Regulator.

This has resulted in the idle voltage being about 14.5v with no load and 13.4v with lights & full beam on. This does rise off idle to about 14.8v with or without load.

The resistance between the Battery negative Terminal and the Voltage Regulator case is negligeable.

I guess the only real thing now is a road test (or drive around with the lights on all the time!!)

Still not convinced I have got to the bottom of this.........

Thanks to both Dave and Alex for their advice.

Dave-R · Post by **Dave-R** » Fri Sep 10, 04 12:27 pm

Sounds about right Pete. You've cracked it. As long as it is under 15v you are fine.

This is always a problem with newly restored and well painted cars. There are always electrical problems due to bad earths.
The regulator has to short to earth to kill the voltage going to the field in the alt. If it can't do that then the field does not regulate correctly and the output of the alt goes up.

You should be OK now.