Should The Alternator Spin Freely?

Disclosure: This page contains affiliate links, As an Amazon Associate, I earn from qualifying purchases (at no extra cost to you). Learn More

What does it mean to have an alternator which has no problem spinning and another which shows some resistance? How should an alternator spin? Freely? Or with resistance? And how does this affect the function of the alternator? The answers to these questions are crucial as they help you decide which alternator is good and which is not.

So, should the alternator spin freely? Yes, an alternator ideally should spin freely. Aside from spinning freely, what is most important is that an alternator should be able to spin smoothly without noise and any form of resistance.

Between two alternators, an alternator that spins freely immediately it is spun and that which does not even when great strength is applied, one of these alternators should be put out of use as it no longer functions properly.

That which is hard to spin is the defective one and should be replaced.

In many of the cases involving an alternator that is difficult to spin, the likely cause of such a problem is with the bearing.

Most times, the bearing of the alternator has been shot in too deep that it makes it very hard for the alternator to whirl around when spun.

Table Of Contents

How should an alternator spin?

When an alternator is on the car, we do not expect the alternator to be able to spin freely as it does when off the car because, in that situation, the alternator is saddled with lots of loads as the electrical outputs are fully connected to the car.

However, when unplugged, that is, out of the car, in this state, a normal and functional alternator is expected to be able to spin freely without any form of hindrance.

The alternator is free and is not hooked to a belt that couples it with the other parts of the car engine, it should therefore not show any form of resistance in spinning.

Trending Searches

What does it mean when an alternator spin with resistance?

So, now that we have established free spinning as the ideal way an unplugged alternator that is out of the car is expected to behave when turned with the hand, what could be the possible reason or explanation behind alternators that resist, and do not spin freely?

It is okay for an alternator not to spin freely when it is connected to the car engine. Its slow movement in this state is a result of the load saddled on it, however, if the same slow movement is experienced while the alternator is out of the car, it could be a result of certain factors impeding its movement.

The alternator bearing plays a crucial role in the smooth and free movement of the alternator. Whenever the bearing becomes bad, the movement of the alternator is greatly affected.

An example of such an instance is when the bearing is shot inside, when this happens, the alternator will prove hard to spin even with a considerable force.

Secondly, when a foreign object gets lodged in the alternator, this creates a considerable impediment to the movement of the alternator.

Once such an object is cleaned out, the alternator can spin freely once more when out of the car. An interest short is also one of the common reasons why an alternator despite being out of the car spin with resistance.

Even with a new bearing, an alternator is not expected to show any form of resistance and a little amount of effort applied to it should get the alternator spinning freely.

As mentioned earlier, what is most important in how the alternator spins is not how free, rather, it is how smoothly it does it. 

When an alternator spins in a manner that it grabs or grinds through this movement, creating some form of noise during this time, this may be an indication that the alternator is bad, requiring repair or replacement. 

Aside from bearing, the alternator’s electrical components such as the voltage regulator or the rectifier are also possible culprits in causing the alternator not to spin freely.

So, why does an alternator that does not spin freely become something of great concern? An alternator that cannot spin cannot generate electricity.

Alternators subserve the function of generating the electricity that recharges the battery and gets to other electronic accessories in the car. It does this by converting the magnetic field into electrical energy.

The magnetic field is generated by the mechanical energy created by the running engine. So, if an alternator cannot spin, it won’t be able to generate the mechanical energy which is crucial to the generation of electricity- the primary function of the alternator. What then is the use of such an alternator?

An alternator that does not spin freely or spins only on maximum exertion when off the car is therefore not a good one and should not be installed in the car.

Depending on how it spins when off the car, the speed is sure to be decreased once the belt is installed, connecting the alternator to the “engine crankshaft”.

Should a new alternator spin freely?

It is not uncommon to find new bearings proving slightly difficult to spin freely or spinning with some form of resistance.

There is a simple explanation for that and it is not because the alternator is bad. New bearings spin a bit more slowly than the old ones or bearings that have been in use for some time because of the seals and new grease in the new bearing.

This however changes immediately after the bearings have been put to use. the movement of the used bearing is freer because the edges of the seals begin to wear out as a result of friction.

The resistance shown by an alternator with new bearings is not something of great concern. However, if the new bearings are not spinning smoothly, this should raise some eyebrows.

You may experience variation in the speed of the alternator when the alternator pulley is bad. This is because, whenever the alternator pulley becomes bad, it squeaks a noticeable sound or slips off, which explains the speed variation.

Whenever you experience a problem of this nature, do not ignore the warning signs, rather, ensure to take your vehicle to your car mechanic for evaluation and diagnosis.

Certain car problems if left unattended could lead to further damage or put the life of the driver and other passengers at risk.

A bad alternator pulley should not be taken for granted; you never know what it could lead to. Changing the alternator belt and checking the condition of the alternator pulley is quite easy and non-time consuming for the mechanic. Do not hesitate therefore to do the right thing.

Why does an alternator with the belt install not spin freely?

So, I use to wonder why an alternator pulley that spins freely when turned by hand outside the car does not do the same when the belt is installed.

Some belief this to be a result of a defect with the bearing, that is, a failing bearing being unable to support the rotor is why this is happening.

While this explanation may sound logical as a failing bearing can create a considerable amount of friction or tension on the belt and thereby prevent the alternator’s rotor from spinning.

However, a second look at this will reveal a simpler explanation as to why this was happening and that there is no need to point accusing fingers at the bearing or infer an underlying problem.

Rather, the simple reason why an alternator that is free without the belt being installed can spin freely has to do with the lack of restriction on such an alternator.

Without installing the belt, the alternator has no frictional force to hold it back from spinning freely, however, once the belt is installed, the belt becomes the link connecting the alternator to the” engine crankshaft”. 

In this state, to turn the alternator, the remaining part of the engine as well as other car accessories that are somehow connected to the belt must be turned too to get the alternator moving freely.

It is either this way or finds a way to make the alternator pulley overcome the frictional force created by the installed belt on the pulley.

Application of a significant force on the alternator may be able to overcome such friction/ tension and get it to slip and turn freely irrespective of tensional force from the belt.

The alternator rotor is the part designed to rotate as the name implies. So, when the alternator spins, it does so via its part known as the rotor.

The stator is stationary, again, the name implies so. As long as the alternator is out of the car, there is no reason it should not spin freely except if there is an underlying problem such as a problem with the bearing, foreign object lodged in it, or internal short.

Should The Alternator Spin Freely  – Conclusion

a good alternator should spin freely, particularly when off the car. When spun with the hand, it should be able to turn without showing any form of resistance or hindrance on its part.

Any contrary finding may mean the alternator is bad and should not be installed in the car.

Leave a Reply