Thread: How many amps for the alternator?

Tweet

I am looking to get a CS 130 probably Powermaster in either 105 amp or 140 amp. The engine is a '97 LT1 and I believe stock was 124. The stock alternator will not work with the low passenger side mount I got. It will have a mild stereo eventually. What other information is needed? I think I convinced myself of a 140 amp through typing this, but reassure me. thanks

I think either would work but if you are going to run a big thumping stereo, I would opt for the 140 unit. Just make sure you do not switch over to a one-wire set up because you will encounter problems with charging. I know that from personal experience.

This really comes down to a math problem. A “standard” alternator is typically 80 amps. There is a "Factory"140 Amp. Delco-Remy 10-SI type with an internal regulator available, but not too widely used. The stock stereo system is typically 100 watts and it operates at about 62 percent efficiency. Operating at full output, the input power required to drive 100 watts becomes 100/0.62 or 161 watts. Now when you put in the 1,000-watt system the input power to the amplifiers is 1,000 / 0.62 or 1,612 watts.

The formula for power is P=V x I, where P is the power (in watts), V is the voltage and I is the current, measured in amps. A typical car battery is 13 volts. Go back to high school math and convert the formula to I = P/V and plug your numbers. I = 1,612/13, or 124 amps.

Remember that about half of your stock alternator is used to run the car, i.e., ignition, lights, heater, etc. If you draw more than the alternator produces, the battery will attempt to supply it, but that will only work for short periods before the energy drains from the battery and the voltage drops which will compound the problem. Then you get to choose – stereo at full blast or lights on?

If it were me, I’d look at the 180 amp from Powermaster and know that you’re covered..

Regards,
Glenn

Nicely done Glenn....

Thanks for the responses guys. Glenn - you're taking me back to high school math . I am finding a lot more sources for 140 amp alternators, but I'll look around some more and price the 180 amp as well. Thanks