How many amp alternator to go with? - Impala Tech
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post #1 of 4 (permalink) Old 12-28-2014, 11:52 AM Thread Starter
Join Date: Mar 2013
Location: Roselle ILL
Posts: 37
How many amp alternator to go with?

I have a 64 SS that the alternator is only putting out 12.08 volts. Not sure how many amps the stock alternator came with, but trying to figure out how many amps I want to go with. I want my lights to be brighter and have enough power to run a good size amp to power a sub. Any suggestions?
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post #2 of 4 (permalink) Old 12-28-2014, 01:45 PM
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I would bolt on a one wire Delco-Remy CS122 120 Amp alternator. You can find them on 1986 and up vehicles. You will have to remove the serpentine belt pulley and press on your V-belt pulley, which requires a $35 tool (you can rent one) and an impact to run the V-belt pulley back onto the alternator. The wiring you have now will not bolt up directly, but there are adapters that allow you to wire in your white and blue field wires.

They are called a one wire alternators because once the alternator is spun up to cruising speed (about 2400 RPM), the windings are self actuated (powered) and rare self regulated so you no longer need the external voltage regulator. You should get about 120 Amps (the full rated power) just above idle and it doesn't produce any more amperage than your system calls for (so it doesn't waste any horsepower to spin it with no load on the alternator). Because it is out putting about four times the amperage of your stock alternator (with a lot cleaner power while doing it; holding the output voltage stable for computerized cars and clamping all transient spikes to protect any devices hooked up), you need a heavier wire running to a power distribution buss. From that power distribution buss you can reconnect the original factory wiring and any additional loads you want without over taxing (melting) the factory wiring.

You can read all there is to know at this web site (well maybe not about rewiring the external voltage regulator, but that is a subject that is well covered on line.):

You can read the rated amperage right off the alternator case as they are all stamped. You might have to look with an inspection mirror as the stamped rated power is located near where the field wires come out (either from the top or back). There are alternators in the CS series rated from 87 to 140 Amps: actual cop cars (a C91 RPO vehicle and not a Taxi purchased to save the department money) and medium duty trucks up to semi trucks have them rated up to 230 Amps, but the frames (size of the case ) is larger.

Finally there are companies that will not only rebuild but rewind your existing alternator to out put a lot more power (pushing 90 Amps) that reuses your old case and looks exactly like the factory date correct number matching part if you are worried about that kind of thing. If you want to forgo the hunt you can buy an old SI series alternator (what you have now) from these guys already tricked out and polished up:

And another without the polish:

Only the CS series with the corrugated steel on the out side of the case gives full power at near idle speeds, the SI has to be spun faster to get full power.

Big Dave
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post #3 of 4 (permalink) Old 01-03-2015, 09:49 AM Thread Starter
Join Date: Mar 2013
Location: Roselle ILL
Posts: 37
Thanks once again Big Dave for the advice. I ordered the chrome 100 amp Eastwood for $106 delivered that came in as an 111 amp and I’m back up to around 13.75 volts. I can actually see at night now with the headlights shining.
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post #4 of 4 (permalink) Old 01-03-2015, 03:48 PM
Join Date: Aug 2008
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