Alternator Measurements

Because of electrical problems on my spider, shortly after obtaining it 5 years ago, I installed both an ammeter and voltmeter. With an original/replacement alternator from IAP, so no fit problems, I've measured a consistent charging max of just over 30 amps above 2 grand, which gives 13.7 volts with not much load. The problem comes when the Hella lights, electric aftermarket radiator fan, and brake lights are all on at idle, when the charging rate falls to 15 amps, and the juice to 12 volts. But with a good solid battery, as long as idling isn't for a serious period -- which is not pleasant or good for humans or Alfas anyway -- that temporary drop is part of what a battery is for. So far it's carried me where I need to, with my high draw combination still carrying 13 volts at driving speed, as good as the RX7 does. I might think differently where there's a lot of rain, or other add ons, though, so appreciate hearing the alternative approaches.

lightweight said:

Because of electrical problems on my spider, shortly after obtaining it 5 years ago, I installed both an ammeter and voltmeter. With an original/replacement alternator from IAP, so no fit problems, I've measured a consistent charging max of just over 30 amps above 2 grand, which gives 13.7 volts with not much load. The problem comes when the Hella lights, electric aftermarket radiator fan, and brake lights are all on at idle, when the charging rate falls to 15 amps, and the juice to 12 volts. But with a good solid battery, as long as idling isn't for a serious period -- which is not pleasant or good for humans or Alfas anyway -- that temporary drop is part of what a battery is for. So far it's carried me where I need to, with my high draw combination still carrying 13 volts at driving speed, as good as the RX7 does. I might think differently where there's a lot of rain, or other add ons, though, so appreciate hearing the alternative approaches.

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Hi Terence:

As I mentioned, one option (the best, I think) is to simply buy a rebuilt alternator for a 3L Milano, and trade in your old 35 amp original (bring that core in a few days later). The larger capacity alternator bolts right on, and even looks original. The only differences will be the 75-amp output, and you can toss the original external voltage regulator and short harness that connected it to the alternator. You might also consider buying yourself a nice length (3-4 feet) of red #8 stranded copper wire, and a few ring terminals, to replace the original B+ wire from the alternator to the starter.

Your wipers will now work at full speed in the rain, you'll have a better defroster fan, brighter headlights, etc. Also, remember Ohm's law. If your accessories, such as fuel pump, wiper motor, etc. are running on 14 volts (as opposed to 12) they're drawing less current, and will operate at a lower temp and live longer. Not to mention, you'll always have a nice, fully-charged battery, which will also start the car faster, preserving the starter solenoid and motor, Spica cold-start solenoid, and perhaps the bearings in your engine. Better ignition, too. To the point, more volts are good.

Here's an appropriate alternator, just FYI:

http://www.partsamerica.com/ProductDetail.aspx?MfrCode=BAR&MfrPartNumber=1860435&PartType=11&PTSet=A