How To Test Alternator By Disconnecting Battery: Detailed Guide

Don’t know how to test alternator by disconnecting battery? We’re here to help!

By turning mechanical energy into electrical energy, an alternator maintains the battery’s charge. It also assists in powering the vehicle’s different electrical systems.

That’s why you need to check it regularly and avoid the vehicle stalling and getting stuck in the middle of the road. Don’t worry, even if you don’t know how.

Step-by-step guidelines will be provided in this article!

Signs Of Bad Alternators

Indication Of Bad Alternators

Before learning how to test a car alternator disconnect the battery, you should note the signs of bad alternators.

Dim Lights

An alternator supplies all of your car’s electrical requirements; when it starts to degrade, so do the accessories that depend on it.

Your automobile may begin to display unpredictable symptoms. It can be fading or bright headlights and dashboard lights, as well as tachometers and speedometers that cease operating.

When you see dim lights, this is probably because your alternator has run out of power and needs to be recharged.

Warning Lights

When this light appears on the dashboard, it’s frequently believed to indicate a problem with the battery.

The battery warning light, however, suggests that there might be an issue with your car’s alternator.

The normal operating voltage for alternators is between 13 and 14.5 volts. The battery warning light on your dash may come on if your alternator malfunctions since its voltage may fall below its maximum level.

Dead Battery

After a few years of use, a battery may be dead or have reached the end of its useful life. Alternatively, you may have inadvertently kept the headlights.

A dead battery may occasionally indicate a problem with your alternator, though.

When the engine is operating, a defective alternator won’t charge the battery. This results in a quicker-than-usual discharge of the charge.

Jumpstarting the vehicle is one approach to determine if the problem is with the battery or alternator.

Loose Connection

In this instance, the alternator in your automobile appears to be functioning well, but the battery and most of the electrical components are dead.

This could hint that the alternator is generating power, but it’s either not moving or the wrong kind.

Smaller and larger cables are used to transport the electricity from the alternator. Any issues with the wires, cables, or connectors at either end can limit or prevent energy flow.

Brighter lights may occasionally signal this problem, as the alternator needs to create more energy to get through the resistance in a defective wire or a damaged or loose connection.

Strange Sounds

Poor alternators frequently make loud or peculiar noises. A belt is used to transfer mechanical energy to the alternator.

You can hear strange squeaking noises from under your hood if this belt has become out of alignment or worn down severely.

The internal stator of the alternator can spin alongside the belt thanks to the bearings inside.

These bearings start to hum as they corrode and wear over time. As the bearings deteriorate further, this humming noise gets louder.

Bad Smell

An overworked alternator can smell something like an electrical fire. Putting too much power into the rotor and stator can be the source of the hot wire smell.

Not all unpleasant odors point to possible alternator issues, though.

The smell is distinctive from other attention-grabbing automotive odors like the overfilled coolant’s sweet smell through vents, the signs of overheating brakes, or the smokey note of burning oil.

Naturally, none of these stenches are good, so if you notice any of them, have them examined.

Difficulty In Accelerating Or Starting

As every automobile is unique, one of the initial signs of alternator problems is likely to be difficulties in starting or maintaining your vehicle.

To find the issue, it’s crucial to consider everything else that is occurring with your car.

If the problem with your alternator is what’s causing your hard starts, they can’t empower the car.

How do you check alternator by disconnecting battery? It’s time to learn now!

How To Test Alternator By Disconnecting Battery? 

Test Alternator By Disconnecting Battery

How to test alternator by disconnecting battery, positive or negative

Start Your Car And Let It Idle

The first step of learning how to check alternator by disconnecting battery is starting your vehicle. Ignite the engine of your car to start the alternator test procedure.

You might choose to keep driving if the vehicle is already running.

Before beginning, be sure that you are conducting this test in a secure location, especially when you cannot access your garage at home.

If you have a pair of rubber hand gloves, use them for extra safety. Otherwise, no problem!

Open The Hood And Locate The Terminals

The next step in checking alternator by disconnecting battery is pulling the hood lever on the driver’s side, which is located beneath the dashboard, to raise the hood.

Depending on your vehicle type, get out of the vehicle to correctly open and hook the hood.

While some auto hoods can remain in place without assistance, others might need a little metal hood-lift support to keep the part in place when it is raised.

Identify And Disconnect The Negative Terminal

How to test alternator by disconnecting battery positive? There is no answer to this!

Since you want to test alternator remove battery cable, it must be negative. On the battery, this terminal is designated with a minus symbol (-). 

When you’ve located the negative terminal, you may yank the cable attached to it while the engine is still running. If you don’t have a wrench, you can use your hand to pull it straight out.

Test The Alternator

To test alternator by disconnecting battery, pay close attention to the results. If the car’s engine performance decreases, stalls, or completely stops, you have a faulty alternator.

In the meantime, should the engine run continuously, the alternator works properly.

Alternative Methods

Alternative Measures

Disconnecting battery to test alternator isn’t the method you want to process. We’ve other alternatives!

Using A Voltmeter

Except for the alternator test disconnect battery, a voltmeter can be helpful in this case.

  • Prepare your voltmeter. 
  • Between 12.5 and 12.8V is the best range for battery voltage with the engine off. 
  • If it is less than that, you should recharge the battery using a battery charger before doing the test. Start the engine after that, and then look for elevated voltage readings. 
  • Higher numbers suggest that the alternator is likely in good condition.
  • If your alternator is in a good shape, it’s expected that a computer module that isn’t shutting down when you switch off the automobile is to blame for your dead battery. 
  • Get your car into a shop and hire a qualified mechanic to identify and fix the malfunctioning module if it passes the voltmeter test.

Using A Multimeter

  • Rotate the multimeter dial and set the knob to measure DC voltage in the range of 15-20V.
  • Connect the positive (red) and negative (black) leads to the positive and negative terminals of the car battery, respectively.
  • Check the multimeter’s display and note the voltage produced. The value should be approximately 12-13V. 
  • If the value is below 12V, charge the battery with a charger before proceeding to the next step.
  • Ignite the car, and when it’s running, check the battery voltage again with the multimeter. 
  • If the reading falls between 14-15V, the alternator works as it should. 
  • If there is nothing wrong with the alternator, the battery is depleted because a computer module can’t turn off when the engine is off.
  • See the additional methods discussed below when the noted voltage remains constant or drops when the vehicle is running.

Using A Screwdriver

You don’t have to disconnect battery to test alternator but can conduct this task with a screwdriver!

  • Wear insulating gloves and take precautions to keep yourself safe. 
  • Insert your key into the ignition. Avoid starting the car. 
  • Find the latch on the hood’s underside and pull it up to open the car hood. 
  • Locate the alternator, a sizable coil-shaped device with a belt that passes over other engine components. 
  • Test the screwdriver by putting it close to the alternator. 
  • Start the engine before grasping the screwdriver. Make sure to not start the car. 
  • The tip of your screwdriver’s blade should be in contact with the alternator pulley bolt as you hold the tool near the alternator. 
  • Your alternator operates well if you sense a magnetic field drawing the screwdriver to it.


How To Maintain The Alternator Working Smoothly?

To maintain the best condition of it, you can consider some tips below:

  • Perform periodic inspections of vehicle components.
  • Look for abnormalities and diagnose them as soon as possible.
  • Clean it regularly and properly.
  • Repair or replace parts quickly, avoiding further damage to related components.

What Happens If I Disconnect Car Battery Terminals When It’s Running?

The car components can be at risk when disconnecting the battery while your vehicle is running to check an alternator.

For instance, the process may impact cruise control, ECU, car stereo, speed-sensitive steering, etc.

Overall, this method can be applied and gives quick results. However, it still carries potential dangers if you make mistakes in the implementation process.

Can I Test The Alternator Without Tools?

Yes. Some steps you can take without specialized tools:

  • Look for wear and tear or cracks in the drive belt. The alternator won’t run properly once the driving belt is damaged. 
  • Inspect the alternator pulley for any damage. 
  • To check for excessive play, examine the alternator bearings. 
  • Start the engine and unhook the battery terminal to test the alternator. The machine ought to keep running without stalling. The alternator is not working properly if it does stall.

How Much Does It Cost To Fix The Alternator?

Depending on the type, alternators cost you from $100 to $350 on average. If no other parts need to be changed, the replacement will typically require between $350 and $400. 

In the event that the serpentine belt also calls for a new one, your payment will increase by $20 to $50.

Expect the cost to exceed $500 in many circumstances if you want to use dealership components and labor. 

You can anticipate spending anywhere from $350 to $900 for repair because the final price depends on the car.

Bottom Lines 

And it’s all about how to test alternator by disconnecting battery! You can learn and apply it step-by-step to finish this task without obstacles.

It’s essential to ensure your safety first. You should be clear about the process and carry it out properly. If you can’t, driving your vehicle to the repair shop is the best solution.

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