Alternator or Voltage Regulator

[radicalfil]

Bought a new Optima battery because the old ones were dead.
I have been having a devil of a time keeping it charged. Sitting over night and the damned thing is not dead, but not enough juice to fire the motor. I then go to the trusty BBS and read multiple post about batteries, alternator and voltage regulator.
I make the measurements at the battery before and after starting. I find that the charging system is running at 14.8-15.0 volts at about 2500 rpm. Ah ha! voltage regulator no good. Get a used replacement voltage regulator and oh no! System says it is only charging at 11.8-12.1 volts. Is it the alternator or regulator?

As a side note the car starts okay once I charge the battery overnight on the charger. However, after initial start and trying to restart it is almost as if the ignition system in not getting any juice.

Phil
1972 911T w/ MFI and Motorola Alternator

[Early_S_Man]

Phil,

A couple of questions ...

1. Did you give the Optima battery an initial charge overnight or for 12- 14 hours at an initial charge rate of 10-12 Amps, tapering off to 2-3 Amps? Batteries you get at a store have alrerady been charged initially, but that is NOT true of mail-order batteries! And, all lead-acid batteries need an initial charge before use!

2. Does your digital multimeter use a 9-Volt battery, and is it fresh? Low battery will cause most DMM's to give a high reading that is not accurate, even if the low-battery annunciator is not on, yet! Unles you can compare your system Voltage with another working car, and get a reading of 1 Volt lower using the same DMM ... I suspect your original Marchal/Motorola Voltage regulator was OK!

[radicalfil]

Originally I did not fully charge the battery overnight. I charged it just enough to start the car. However, since then I've put it on my Die-hard automatic charger and charge it overnight a couple of times, automatic 10 amp and deep-cell 2 amp. I am hoping that I haven't ruined the battery. Prior to changing the VR I took the car on a drive down the coast to Santa Cruz on one Saturday. Everything seemed okay. The symptoms are very similar to another post where the headlamps glow brighter when engine is revved up. The difference in the intensity of the light is noticeable but not like my 6 volt car.

I have used 3 separate volt meters from cheap to expensive and they all seem to be reading in a relatively narrow range.

I am stumped! I am going to try another alternator and see if that works with the newer VR. The old VR was definitely reading that the system was overcharging.

I thought there might be an open circuit draining the battery during the night, i.e circuit no. 1. Pulled the fuse and tested the voltage across the prongs of the fuse block and got a reading of +/- 12 volts with the clock and trunk lamp unplugged, ignition off and interior lamps switched off.

Any suggestions?

Phil

[RoninLB]

Red Top Optima needs 13.8 - 15 v. at alternator. To measure drain from elect.system you have to measure amp. drain with amp setting on VOM. If it has one. Optima is considered 100% discharged at 10.5 v. From this totally discharged state the Red Top needs 6hrs at 10 amps to become 90% charged. I usually wait till charger reads less than 2 amps then give it another 2hrs at this 2 amps or less current.

[radicalfil]

I guess I'll put it on the charger now so when I install the rebuilt alternator it will be ready and won't fry the alternator.

BTW, can you keep it attached to the charger to keep it charged for a couple of days. My charger has an automatic setting which I assume to be for this purpose. (Lost the Instructions).

[RoninLB]

Rad..what you are talking about is a "float charger". The Red Top can be on a float charger of 1 amp or less that is between 13.2v - 13.8v. Pelican has quality goods, float chargers are inexpensive.