Alternator Not Charging Until Revved: 7 Reasons and Solutions

Is your alternator not charging until revved? You need to check out the resistor to see if it has worn out. Here are more possible reasons.

All cars are equipped with an alternator, which provides power to the battery. The battery further supplies current to all the electronic car components. Sometimes, the alternator may not be charging until you rev your car to a high RPM. Until it charges, the battery will also not charge.

This happens because the excitation current provided to the alternator can become weak because of wiring issues or a faulty resistor. Hence the alternator will operate only at higher engine RPM.


Alternator Not Charging Until Revved


What Is Alternator?

Every modern car needs electricity to operate all the electrical components like headlights, taillights, air conditioners, and mos other things. The engine is capable only of producing mechanical energy and not electrical energy. So, we need a device that will produce an electrical current and power all the car’s vital components.

This is where an alternator comes in. The alternator is a device that converts mechanical energy into electrical energy. It has two components, i.e., s tator and rotor. The rotor is the rotating part inside the alternator, and it rotates with the help of a belt and pulley arrangement. It acts as a rotating electromagnet in the alternator.

The second important part is the stator. It is present outside the rotor and comprises several coils wounded on an iron ring. An electromotive force is generated when a conductor is placed between two varying magnetic fields. The same principle is applicable to alternators.

The rotor produces rotating magnetic flux and produces electricity in stator coils. The electricity produced by the alternator is alternating current which is converted into direct current by a rectifier. This direct current is provided to the battery, which feeds all the electrical car components.

Why Sometimes Alternator Does Not Charge Until Revved

As discussed above, the alternator converts the rotational energy into electrical energy by rotating the magnetic flux around the stator windings. The magnetic field is responsible for producing power in the alternator. The field is first created by the excitation current, which is supplied by the parallel resistor on the back of the voltage gauge and the charging warning light.

Excitation current can become weak because of various reasons. For instance, if the resistor goes bad with time, the alternator will require time to charge the battery. Similarly, if the bulb malfunctions or there is an issue in the exciter wire (usually the blue wire) connection, the excitation current becomes weak.

If either of these happens, the alternator will only work at higher engine RPM. Remember, the alternator will never charge the car battery if there is no excitation current.


Alternator Not Charging Until Revved


Other Reasons Why Your Alternator Is Not Charging

Car owners often get confused when there is an electrical car component issue. They think the battery is the main culprit behind the problem. But no, the alternator can also be the primary reason behind it.

Whenever the alternator fails to work, it cannot charge the battery, and hence you find issues in the vehicle’s electrical components. There are various possible reasons why the alternator stops charging the battery. We are listing them below.

#1. Issue In ECU

Almost all modern cars are equipped with an electronic control unit. The ECU is responsible for managing most of the components in a vehicle. It even manages the alternator of your car. So, if there is a problem, it affects the alternator and stops charging the battery.

Well, it will be pretty challenging for you to inspect an ECU. You can take your vehicle to the nearest qualified technician. They will investigate the ECU and correct it accordingly.

#2. Broken Belt

The alternator’s rotor is connected to the engine crankshaft using a belt. The belt has to undergo stress during every operation of the vehicle. Continuous stress can result in wear and tear of the belt, and hence the alternator fails to charge the car battery.

Inspect the belt from time to time. If you find it damaged, replace the belt with a new one.



Alternator Not Charging Until Revved


#3. Blown Fuse

In some vehicles, the alternator relies on a particular fuse for operation. The fuse can blow because of excess current. It can even blow over time due to wear and tear. Whenever the fuse blows, the alternator stops working and hence cannot supply power to the battery.

It doesn’t happen in all vehicles. So, check the car manual to know whether the alternator has a fuse. If the fuse has blown in your car, you must replace it with a new one to fix the problem.

#4. Bad Wire

There are numerous wires which connect to the alternator. The wires can get damaged with time. Sometimes mouse can cut the wires and hence get disconnected from the alternator. Wires issues can be a reason the alternator is not charging the battery.

Check the wires, and if you find them damaged, replace them with new ones.


Alternator Not Charging Until Revved


#5. Bad Alternator

The alternator itself can get damaged with time. The alternator has several parts like a stator, rotor, slip rings, rectifier, and many more. Damage in any of these parts can affect the working of an alternator, and hence it stops charging the battery.

#6. Corrosion In Battery Terminals

The battery terminals can cause corrosion with time. That may be the reason why the alternator cannot charge the battery. This mainly happens in old batteries.

Check the battery terminal occasionally, and if you find it dirty, clean it with a good battery cleaner. If it is too damaged or rusted, replace it with a new one.

#7. Issue In Voltage Regulator

The voltage regulator is responsible for proper power flow from the alternator to the battery. If the voltage regulator malfunctions, the alternator output cannot charge the battery. You will observe other symptoms like your light bulbs will be too bright or too low.


Alternator Not Charging Until Revved


Frequently Asked Questions

#1. Do you have to rev the engine to get an alternator to charge?

Yes, the revolution of the engine faster can charge the battery at a fast rate. When the engine runs at high rpm, it will rotate the belt. The belt connects the engine crankshaft and alternator. So, if the belt rotates faster, the alternator will work fast and provide power to the battery. So, in short, increasing the engine revolution will charge the battery faster.

#2. At what RPM does an alternator start charging

The battery charging occurs when the alternator voltage becomes more than the battery voltage. The alternator does not provide sufficient voltage until its speed exceeds 2000 rpm.

#3. How long does it take an alternator to charge a battery while idling?

The alternator can charge the battery in the idling stage but at a lower rate. It is because the battery has to supply power to so many electrical components. It will take almost 30 minutes for the alternator the charge the battery completely.


Alternator Not Charging Until Revved


Wrap Up

The alternator is a significant component of the car. It helps convert mechanical energy into electrical energy that helps power various parts. But alternators can have various issues with time.

For instance, if the excitation current weakens, it will start working only at high engine rpm. Similarly, blown fuse, damaged belts, and corroded battery terminals are reasons the alternator fails to supply power to the battery.

You need to find out the reason for the alternator failure and correct it accordingly. If you don’t know much about the car’s mechanical components, it’s best to take it to a professional auto technician.

Thank you for reading!

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Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

1 thought on “Alternator Not Charging Until Revved: 7 Reasons and Solutions”

  1. Hi I have w140 300sel 1991
    I parking car around one month when I want run battery less power I jumping power car start but the worning lights in cluster flashing one time only and hide. I mean in postion 2
    Can help


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