Thanks for coming to my site. In case we haven’t met yet, I’m Kevin and I just love passing on my 30 + years of experience repairing and maintaining cars.
I’ve made this site for non-technical drivers who are experiencing problems with their cars.
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Published date: December 5, 2021
Updated date: February 27, 2024
Reading time: 12 min
This article was fact checked
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How long you can drive with a bad alternator depends on whether your alternator is going bad or has completely stopped working.
An alternator that has gone bad and stopped producing power will mean the car battery is now producing all the power your car’s electrical systems need. This is not good.
So, although you can drive with a bad alternator for as long as the battery still has electricity, this only equates to no more than 25 minutes or 30 miles, even if the battery is fully charged.
To prolong the distance, you can drive:
Turn off all electrical systems.
Don’t use air-con
Don’t use power windows,
Turn off electric seats,
Don’t turn on heated screens
Leave the car sound system off.
or the car will stop a lot sooner.
An alternator failing but not completely broken will normally show itself by not charging the battery enough to start the car. If the car starts, the battery will be required to provide the power that the alternator cannot.
How much depends on the alternator and how much charge the battery had at the start of the journey.
This is totally against what the battery is designed to do. The battery should provide power to start the car, that’s all. The alternator then adds charge to the battery as you’re driving.
This is supposed to ensure the battery isIt’sly charged the next time you turn the key to start your car.
It’s difficult to estimate the number of miles you can drive on a bad alternator. It depends on the traffic conditions. For instance, if you get stuck in a queue of traffic or are on an empty freeway and the condition of the battery too.
How Long Can You Drive A Car With A Bad Alternator Bearing?
It depends on how bad the bearings are. Have you just noticed the tell-tale moaning sounds, or is it making a full-blown howl?
Alternator bearings in the early stages of failing can give you a few thousand miles before the alternator stops working completely.
The best way to check how bad they are is to see what charge it produces and if it is fluctuating.
If you’ve been aware that the bearings have been failing for some time, it makes sense to get them replaced.
How Long Can You Drive A Car With A Bad Alternator Voltage Regulator?
Not long at all. When these fail, you risk frying your electrical circuits and cooking your car battery.
In many ways, a bad voltage regulator is worse than having a different bad alternator part. Driving for any time with a bad voltage regulator could result in large bills from a specialist auto electrician and days without your car.
Without a voltage regulator, your alternator would be able to produce 240v. This is double what your house needs to run, so you can imagine what damage it causes to your more delicate electrical systems. A bad voltage regulator can cause thousands of dollars worth of damage.
Is It Safe To Drive With A Bad Alternator?
A bad alternator isn’t dangerous. There are a couple of points to consider, though.
You could be left stranded when the battery runs out of charge. It may be in a queue of traffic or on a highway, depending on where the car stops will dictate how dangerous the situation is.
Alternators can get very hot when they go bad. Sometimes the diode fails in an open position which can cause a build-up of heat and lead to a fire. More likely is that the extreme heat generated will burn wiring, smoke, and, worst case, a fire.
How Long Does A Battery Last With A Bad Alternator?
If we assume that the alternator has stopped producing power completely and isn’t running the car’s electrics or charging the battery, it won’t last very long.
How Long Can You Drive With A New Battery and Bad Alternator?
A brand-new battery should be fully charged when it leaves the factory. Unfortunately, although it’s in prime condition to accept a charge, it will not receive any with a bad alternator.
How long your car will run is determined by how much effort the battery exerts to get the car started.
If your car turns within a second great, but if it takes more than a few tries to fire into life, a lot of juice has been used turning the starter motor.
How Long Can You Drive with A Fully Charged Battery and Bad Alternator?
This depends on how much charge the battery is holding. An older battery will not be able to hold as much charge as a new one. How old is your battery?
A battery in excess of 4 years old and has been used an average amount of miles per year (13,500 miles) will retain much less charge than a brand-new battery.
If you’ve had to crank your engine many times to get it to fire up and the battery is old – even if it is fully charged – you won’t be driving anywhere for more than 5 minutes before the battery is fully drained.
Before the car stops, it may overheat as the cooling system shuts down
Power steering becomes erratic and steering harder
What Causes An Alternator To Fail?
An alternator isn’t a part that needs replacing on a maintenance schedule. It’s a fail and then replace part. Alternators don’t last the lifetime of a car, though, and usually need replacing after 5 – 8 years.
So what parts actually fail inside an alternator?
Bearings
Bearings allow the smooth turning of the rotor. They will turn millions of times over their lifetime. Most alternators are rated to spin over 6000 rpm. The more any mechanical part is used, the more likely it is to fail. The bearings are encased in grease, which will dry out. When this happens, friction between the bearings and the case causes heat and grinding noise.
Diodes
Most modern car alternators have six diodes within them. A diode’s job is to allow current to run one way – away from the alternator and to the battery and car’s electrical systems. They’ll seize in an open or closed position when they do go bad.
Although designed to fail in the open position to allow the charge to escape to the battery, a bad diode seized in the closed position will generate excess heat.
Voltage Regulator
In some cars, these parts are found just outside the alternator, but for most cars, they are an integral part.
Its job is to stop excess voltage from leaving the alternator, which would overload the car’s electrical circuits.
Can I Jump Start My Car If It Had A Bad Alternator?
The alternator plays no part in starting the car. It is fine to jump-start the car by connecting leads to the battery terminal.
This won’t allow you to travel further with a bad alternator. It will simpYou’revide enough power to get your battery to allow the starter motor to turn to get the car started.
If the alternator is completely faulty, the car will start draining the battery once you remove the leads.
If possible, leave the leads attached and get some extra charge into the battery before driving. It’ll help you keep moving for longer.
If you must drive without an alternator, turn off all electrical systems possible to eke out the last bit of battery power.
You’re likely to drive further without an alternator in the summer than in the winter. In the winter you may have no choice but to use your wipers more and also have to use the car demister.
Is There Any Routine Maintenance I Can Do On An Alternator?
Routinely check and clear away any dirt from the air vents on the outer casing.
Ensure the grounding strap is securely connected between the alternator and the engine frame or chassis.
Ensure the serpentine belt is tight and uninterrupted to the alternator.
Check that the connections to the battery are secure and that the cables aren’t split or frayed.
In Conclusion
If your alternator goes bad and as long as the battery is well-charged, you can drive your car for around 25 miles or 30 minutes If your battery is weak, it won’t last this long. You can increase the time you can drive with a bad alternator by turning off systems like air-con and heated seats and sound system.
Thanks for coming to my site. In case we haven’t met yet, I’m Kevin and I just love passing on my 30 + years of experience repairing and maintaining cars.
I’ve made this site for non-technical drivers who are experiencing problems with their cars.
