Can you Jump Start a Car with a Bad Alternator? What you Need to Know

Perhaps it is the car battery voltage is low or the car headlights occasionally dim because the alternator is faulty yet you still need to use the car.

Should you attempt to jumpstart it? Is it worthwhile? What should you be aware of?

If this is your situation and you’re wondering whether or not to o jumpstart the car, then read on.

This post explains whether you can still jumpstart a car with a faulty alternator, what happens if you do and if it is worth it.

Note: This information is only intended as a guide. Your experience jumpstarting the car may be different.

It depends on the nature of the fault with the alternator as the alternator may be charging intermittently, undercharging, or not charging at all.

Can you Jump Start Car with a Bad Alternator?

It is possible to successfully jumpstart a car even if the alternator is faulty. The alternator is not required when starting.

It starts its job of powering the car’s electrical system and charging the battery when the car engine is running.

Considering that the battery is drained (the reason the car is being jump stated) and the alternator is faulty then the car engine will run for a short time before stalling.

This is because not only is the battery low on charge and therefore unable to power the car’s electrical system, the alternator (the primary power source is faulty) is unable to reliably power the car’s electrical system too.

You may also be interested in this post: Brand new alternator failing? Find out why

Should you Jump Start Car with a Bad Alternator? Is it Worthwhile?

In my opinion, it is probably not worthwhile because of the limited power available to keep the car running, the car will not cover any meaningful distance.

There is a high risk of getting stuck on the road when the car engine stalls.

Replace the alternator as soon as possible.

How Long Will a Car Engine Run?

This depends on how much energy is available in the battery, what accessories are switched on, and drawing power from the battery.

You could extend to an extent how much runtime you get from the battery by switching off unnecessary accessories – radio/ amp, and seat warmers that contribute to the draw of power from the battery.

This is still a temporary measure and you should replace the alternator as soon as possible.

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Why Does Car Start after Jumpstarting but Suddenly Die?

There are several possible reasons why this can happen. This could be an issue with the alternator, battery, or wiring.

They are listed in order of least effort/ investment on your part.

1. Loose or corroded battery or alternator cables. Check that the battery and alternator cables (positive, negative, ground) are securely fastened and make clean contact with their corresponding terminals.

2. Loose or damaged alternator cables or a faulty alternator. Use a digital multimeter set to read voltage to measure the car battery voltage (across the battery terminals when the car engine is running).

If the alternator is working well, the voltage should be in the 13.5 – 14.5V range.

A voltage out of this range could point to weak, loose, or damaged alternator wire connections or a faulty alternator.

3. A severely drained or damaged battery may also cause the car to suddenly die down. Have the car alternator and battery tested at a reputable auto parts store.

Do not hesitate to contact a qualified auto technician.

You may also be interested in this post: Bad alternator vs. Bad battery – what you need to know

What Happens if you Drive a Car with a Bad Alternator?

Red Battery Light Lights up

You’ll observe the red warning light on the dashboard indicating that there is a fault with the car charging system.

The car engine may stall

This largely depends on the nature of the fault with the alternator. The alternator may not charge at all or could be undercharging.

Regardless, when the car alternator fails to supply the required power for the car’s electrical system, the required power will then be drawn from the battery for as long as there’s enough power in the battery after which the car engine stalls.

You can extend how long the car battery can keep the engine running by switching off non-essential car accessories like the car audio/amplifier.

Closing Thoughts

It is possible to jumpstart a car even though the alternator is faulty.

How long the car engine runs though largely depends on the nature of the fault of the alternator – is it under charging, not charging at all, and available energy in the battery?

If unsure, always contact the services of a qualified auto technician.

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