How much can my car's stock electrical system handle?

I’m trying to figure out what is draining current from my car’s system and battery. I drive my car a lot for work, and it’s been causing problems on very important workdays with clients! I’m not sure if the alternator or something needs to be replaced. How much do you think my car’s stock electrical system can handle? Thoughts?

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Answer provided by
Tara Malenfa
Answered on Apr 28, 2022
Oh no! It’s no fun having an unreliable car that will make you late for your big presentation.
Your car’s alternator is its main power source while the car is running. Generally, you’ll need about 50% on average of the capability of that alternator. Here’s what we know about the capacity of a car’s electrical system:
  • Multimeters can measure the amp load in a circuit. Some come with an inductive amp probe. Most cars should be less than 50 milliamps once the engine has been off for half an hour.
  • To provide enough power to run your car’s accessories while charging the vehicle’s battery, a 250- or 300-ampere alternator from the automotive aftermarket should do the trick.
  • Consult with your new alternator’s installer or vendor to calculate the correct output size of a high-output alternator.
  • If you know the watt rating on your car, calculate the amp load by dividing the wattage by the system voltage.
Working with the electrical system in your car can be dangerous, so make sure you consult a professional to help with new upgrades and installations. It’s also a good idea to talk to experts when it comes to choosing the best car insurance policy.
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