I'm currently troubleshooting my car's ongoing electrical issues and during the troubleshooting process so far I have gone through multiple OEM alternators and multiple OEM & non-OEM batteries. One of my theories is that out of the box these OEM alternators have faulty components or are simply under powered and can't handle the load of powering both the car's electronics and charging/topping off the battery (even when the alternator AND battery are new and installed at the same time). I'm experiencing system voltage sag - anywhere from 0.5 to 2.4 volts below normal at times. The OEM alternators are rated at 155 amps max. If I get a non-OEM direct fit high output alternator, 240 or 320 amps max, will it help prevent voltage sag?

  • \$\begingroup\$ You should get the electrical system tested. There should be no sag at 1000 RPM. 800RPM maybe. What non-stock loads exist? What engine and vehicle? \$\endgroup\$ – Sunnyskyguy EE75 May 14 at 4:14
  • \$\begingroup\$ It will, but only if the source was the origin of the voltage sag to begin with (it will have lower output impedance since it was designed for a higher current), but if something else is causing the sag replacing the source wont' do anything since whatever impedance is causing the sag will still be there. \$\endgroup\$ – DKNguyen May 14 at 4:23
  • \$\begingroup\$ It may well depend on whether your alternator has an internal controller, or external. You don't provide enough information to decide. Your battery should be charging to at least 13.8V with the alternator connected. What are your absolute droop voltages. 0.5 - 2.4V is meaningless without knowing the battery voltage. \$\endgroup\$ – Jack Creasey May 14 at 5:15
  • \$\begingroup\$ The dealership techs essentially had the car for a year, testing and replacing supposedly bad electrical parts and the problems still exist. Electrical system tests keeps passing. They, and most mechanics, have to go by the book, so I have to think outside the box and tackle it myself. \$\endgroup\$ – crashintoty May 14 at 11:06
  • \$\begingroup\$ The battery voltage is not pertinent as it may be affected by a bad alternator. The system voltage however is 14.7 when running properly, but ranges anywhere between 12.3 to 14.2 when error lights are on. I'm hoping this higher output alternator can act as a cover all; handle the possibly higher than spec'd load from the car's electronics and the load for charging a possibly low/damaged battery. I'm okay with the car failing to start, not okay with the alternator giving up and the car shutting down on the highway \$\endgroup\$ – crashintoty May 14 at 11:29

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