Driver's Guide

Can You Jumpstart a Car with a Bad Alternator?

Can you jumpstart a car with a bad alternator? Yes, you can jumpstart a car with a bad or failing alternator. However, this is merely a temporary solution to get you to a nearby car service station before the vehicle comes to a standstill once more.

You have just done your grocery shopping on a cold winter day, and you come back to your car only to find it won’t start after you’ve just finished your grocery run. You’ve recently replaced your battery, so it seems inconceivable that you’re dealing with a dead car yet again. You reluctantly request assistance from a fellow customer to jumpstart your car. If your battery isn’t the issue, what is causing your car to constantly die?

More than likely, you have a bad alternator. The alternator helps in powering the electrical components in your vehicle, which includes the task of charging your battery. Therefore, when the alternator goes bad, the only sustainable solution is its replacement.

What is an Alternator in a Car?

Your car’s alternator is a compact generator powered by the belt or chain that directs your engine’s combustion. This belt spins a combination of copper and magnets, effectively turning it into an electromagnetic generator. The alternator fuels all the electrical systems and features within your vehicle and also maintains the battery’s charge.

Can You Jumpstart a Car with a Bad Alternator?

Can You Jumpstart a Car with a Bad Alternator

Fortunately, the answer is yes. If your car won’t start and needs to be taken to a garage, you can jumpstart it. To jumpstart a vehicle with a faulty alternator, the charge must come from a car with a functioning battery.

This might sound obvious, but it’s necessary. The defective alternator leads your vehicle’s battery to draw more power than it typically would, making it necessary for the other car to have a sufficiently healthy battery to manage this extra load.

How Do You Start a Car with an Alternator Problem?

Below are the steps to jumpstart a car with a bad alternator:

  1. Connect your jumper cables.
  2. Fix one red clamp to the positive (+) terminal of the dead battery.
  3. Connect the other red clamp to the positive (+) terminal of the working battery.
  4. Fix one black clamp to the negative (-) terminal of the working battery.
  5. Secure the other black clamp to a bare metal part (nut, stud, bolt head, or bracket) in the engine bay of the car with the dead battery.
  6. Start the donor car and let it run for a few minutes:
  7. Whilst the car with the alternator issue is off, start the car with the healthy battery and let it run for around 3-4 minutes with the cables connected. After this, attempt to start the car with the bad alternator. If it doesn’t respond, wait a few more minutes before trying again.
  8. As soon as your car starts, switch off all power-drawing accessories like the radio, lights, air conditioning, USB ports, and so forth. This is to save battery power while you make your way to the closest mechanic.

You should jumpstart a car with a bad alternator only during the day in clear weather conditions. Since you need to switch off the lights and windshield wipers to save battery power, ensure you won’t require these features while driving your car to the service station.

How Long Does it Take to Jumpstart a Car with a Bad Alternator?

The time it takes to jumpstart a car with a bad alternator depends on the condition of the battery and the vehicle’s overall electrical system. However, typically, once you’ve connected jumper cables correctly, you would need to run the functioning vehicle for about 3 to 5 minutes to transfer enough power to start the car with the bad alternator.

Remember, this jumpstart is not a permanent solution but just enough to get the car running. The battery won’t recharge properly, so drive directly to a mechanic or auto repair shop as soon as possible.

How Do You Tell if it’s the Battery or the Alternator?

If you jumpstart your car, but it stops working right after, the issue probably lies with your alternator. There are several indicators of a bad alternator:

  • Dim or excessively bright lights
  • The smell of burnt rubber or wires
  • Depleted battery
  • Regular stalling
  • Squealing or screeching noise post the vehicle’s ignition
  • Battery dashboard warning light
  • Difficulty starting your car

How Do You Test if Your Alternator is Bad?

How do you start a car with an alternator problem


Visual Inspection

Inspect the alternator visually for wear and tear, including frayed wires, corroded connections, or other visible damage. If any such signs are present, it indicates a potential issue with the alternator.

Check Dashboard Lights

Check the dashboard for warning lights related to the alternator. Many vehicles have an alternator warning light represented by a battery icon or the letters ALT or GEN. If any of these lights are illuminated, it suggests a problem with the alternator.

Use a Voltmeter

Start the car and use a voltmeter to measure the voltage at the battery terminals. A properly functioning alternator should produce a voltage between 13.5 to 14.5 volts. If the reading is lower, it indicates a possible failure of the alternator.

Professional Diagnostic Test

If uncertainty remains, consider consulting a professional mechanic who has specialized equipment for accurately diagnosing alternator problems. They can provide a comprehensive diagnostic test to identify any issues with the alternator.

How Long Can You Drive on Bad Alternator?

The answer to this is “not for long”. The specific distance you can cover with a faulty alternator isn’t easy to pin down without understanding the exact condition of the alternator. The mileage you can achieve with a malfunctioning alternator hinges on several factors:

  • Driving speed
  • Electrical load
  • Condition of the battery
  • Age of the car
  • The current state of the alternator

Under most circumstances, you can expect to run your car for roughly 20 minutes or cover about 15 miles before it powers down. A slower speed and a low RPM might be able to increase this duration marginally.

After you jumpstart a car with a bad alternator, you should have approximately 10 minutes, or about 7 miles, to reach a mechanic.

Frequently Asked Questions

How long does it take for a bad alternator to drain a battery?

A faulty alternator can quickly drain a battery, sometimes within 1-3 hours or overnight.

Will the battery be dead if the alternator is bad?

If the alternator is bad, the battery will cease to recharge while the engine is running and may die.

How much does it cost to replace an alternator?

The cost of replacing an alternator varies depending on the vehicle, typically ranging from $350 to $900.

Does banging on an alternator work?

If your car refuses to start, there’s a belief among some individuals that banging or tapping the alternator with a hammer might help initiate its operation. Unfortunately, this won’t work.

Conclusion – Jumpstart a Car with a Bad Alternator

If you notice any of these warning signs indicating a bad alternator, try to book an appointment with your local vehicle service department for a replacement. You certainly don’t want to be stranded in an unstartable car.


Read also: Easy Steps to Fix Tire Pressure

Latest posts by Bernard Juchli (see all)

Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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