Biba, Your alternator should have a rating plate or tag on it. On that tag should be the design volts and amps. In good working order that alternator will deliver that voltage up to the rated amps. So if it says 14.2 volts and 45 amps and you test it at the local big box autoparts store or your favorite local starter/alternator shop they can hook it up and spin it. Monitoring the voltage output while increasing the load up to the name plate rating. Now that is at the alternator output bolt. not the battery.
So putting it back in your car and getting less than the rated output means something is wrong with the car. Things to check: Battery voltage, you've checked it at the battery terminals but what is it at the b+ (d+ ?, I always get them confused), the small wire on the back of the Alt. Anyway you must supply sufficient excitation voltage/current to the small connection of the alternator. If this is not correct the alternator will not "make volts" and you will read battery voltage at the alt. output terminal. Or perhaps you will make just a little more than battery voltage and a few amps. Enough to slowly charge the battery but not enough for long term optimum charge and certainly not enough to run lights, fan, AC, the engine, for long periods of time. If this is the case the battery can slowly discharge after one long night trip, the alt. light may dimly glow. If it starts the next morning you will generally put a few more amps into the battery than you took out and the problem will be slightly masked until it doesn't have enough power to start one day. Ground, got to have the other half of the circuit all the way back to the neg. of the battery. Engine ground strap, battery ground strap and their connections. Got some long jumper cables? Clamp from the engine to the neg post of the battery. Any change? Alt light. the lamp is part of the circuit. It lights when the battery voltage is greater than the alternator output, completing its electrical path through the winding of the alt. to ground. There is a small range of proper lamps for here. Too big or too small, electrically, and things just won't work right. I think there is a fuse in the circuit here someplace as my alt. light used to glow but after regular maintenance one day of cleaning the contacts and fuses coincidentally the alt. light stopped glowing. It is unlikely that it has been changed but these cars are old and have usually passed through several owners. All the connections getting to and from that bulb are part of the circuit which turns on the alternator. In the old days you could full field the alternator to see if it had the capacity to make volts. This involved turning off all lights, the radio, everything and then removing the regulator and "shorting" the field coils ?? (easy with external regulator) so the alt. output went to max, typically around 20 volts. I would not do this to a car with any electronic anything as I don't know if they are all built to take that much voltage without damage. So if you get 14.2 at the back of the alternator and not at the battery, you have voltage drop. That means that someplace in the wiring between the alternator and the battery you have a high resistance connection. High resistance being relative. A single ohm of resistance in the starter circuit for instance can cause huge voltage drops. Ohms law, volts = current x resistance. Get a volt/ohm meter and some long leads, zero the meter with the long leads and see what you measure (battery disconnected) from neg bat. terminal to engine, positive bat. terminal to the alt. output post. Zero? Right? Nope? Should be close to zero, real close to zero. Positive battery terminal usually goes to the starter and a smaller wire to the alternator. Another location for bad connections. My spider had a terrible connection at the terminal block on the fender and the wire from the alternator to that block was absolutely terrrible. I measured 1 ohm resistance in 15-18 inches of wire. So the more amps of power I needed the more volts I dropped across that wire. I replaced that one piece of wire and most of my electrical problems went away. Adjustable regulator: I have one in my spider from IAP. Easiest way to fix, I mean cover-up, the problem. Oh, I also have one from Fred DiMatteo when he was still in Maine in my 76 Alfetta with the external regulator. Adjusted to give me 14v at the battery to keep it happily charged. A lot to go wrong for such a simple system. Good Luck, Wayne -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected]
