How many volts should an alternator put out at idle?

Asked By: Tasawar Laphurdi | Last Updated: 22nd March, 2020
Category: automotive auto parts
4.4/5 (9,971 Views . 10 Votes)
A car alternator needs to be putting out at least 13-14 volts (ideally between 13.8 and 14.2 volts) to effectively charge a 12 volt car battery. If the alternator is putting out too much voltage (15+ volts), it is likely your battery acid will boil over out of the battery.

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Herein, what should voltage be at idle?

14.3 volts

One may also ask, what causes an alternator to put out low voltage? Poor ground connections are an often-overlooked cause of low charging output and alternator failure. Voltage drops on the positive side of the charging circuit can cause undercharging. Voltage drops on the negative side can cause overcharging.

Considering this, what should an alternator charge at idle?

At idle, most charging systems will produce 13.8 to 14.3 volts with no lights or accessories on (although some may charge at a slightly higher voltage depending on temperature, engine RPM, type of battery, and the battery's state of charge).

Do alternators charge at idle?

Yes, the alternator does charge the battery while the car is idling - regardless of the load on the battery. However, if your electrical use load (radio, lights, fan, etc) exceeds the amount of charge the battery is receiving from the alternator, you will end up with a discharged battery at some point.

35 Related Question Answers Found

Is 14.8 volts too high?

14.8V is considered overcharging. A bad regulator over charging would most like shoot upwards of 16.0V. State of charge, temperature, age of batteries all have an effect on the charging rate. If it's cold out and you ran the batteries down some then it will be higher than normal.

Where is the voltage regulator?

The voltage regulator can be mounted inside or outside of the alternator housing. If the regulator is mounted outside (common on some Ford products) there will be a wiring harness connecting it to the alternator. The voltage regulator controls the field current applied to the spinning rotor inside the alternator.

Is 14.5 volts too high?

If the alternator is working well, your multi-meter should read somewhere in the vicinity of 14 volts (typically 13.8-14.2). If it is reading excessively higher than 14 volts (greater than 15 volts) it is possible that the voltage regulator on your alternator is faulty or going bad.

Is 14.9 volts too high?

If it's old school, this is pretty normal, and it's time to stop charging. So, to answer your question, Yes, 15 volts is too high. Most car alternators, that normally recharge your battery after every start, and provide power while the engine is running, are normally voltage regulated to about 13.8 to 14.0 volts.

Where should the battery gauge be?


How to Read a Car Battery Gauge
  1. Look at the voltmeter on the dashboard of your vehicle. Cars operate on a 12-volt electrical system.
  2. Look at the voltmeter while the engine is running. Readings of 14 to 14.5 volts on the gauge when as a good sign.

How do you check an alternator with a screwdriver?

Test the alternator for magnetism. Use a metal screwdriver and place the metal end very near the bolt on the alternator pulley. It's on the front of the alternator and the alternator belt goes round the pulley. The end of the screwdriver is not drawn towards the bolt as there isn't any electrical magnetism.

Does idling a car drain the battery?

Idling a car won't kill or drain your battery, unless your battery has a problem holding a charge or your car is heavily laden with high-energy consuming electrical accessories.

Does revving the engine charge the battery?

But when your engine turns faster, the engine's alternator also turns faster. That way, all of the alternator's power can be directed to recharging the battery. Once the car starts, you CAN rev it up to charge the battery faster, but the best way to do that is to just drive it.

At what RPM does an alternator charge?

The minimum RPM is highly dependent on the specification of alternator. But a basic alternator will produce charging current anything above 2000 rpm. We can safely say, an economy car will idle around 750 rpm, a sports car around 1250 rpm and a race car around 2000 rpm.

What are the signs that your alternator is going out?


Six Alternator Warning Signs:
  • Dim lights. The alternator is part of the electrical system of your vehicle.
  • Warning light. Most modern cars have a dashboard warning light that alerts you when the alternator is on the fritz.
  • Weak or dead battery.
  • Weird smells.
  • Odd sounds.
  • Visual cues.

What is a good alternator reading?

The voltage should read a minimum of 13 volts. A good alternator should put out between **13.5-14.5 volts. Stress test the alternator - Place a load on the alternator by turning on the headlights, the radio and the air conditioning. The voltage should remain high with these circuits on.

Is 12.2 volts a good battery?

Car battery voltage. 12 volts is the standard automotive battery in today's vehicle and each of the battery has 6 cells with a voltage of 2.1. At 12.4 volts, a car battery is 75% charged while at 12.2 volts its 50% charged. Consider your car battery charged at 12.4 volts or higher and discharged at 12.39 volts or less.

How do you check alternator amps?

Turn on all the electrical equipment in the car: lights, stereo, wipers and everything else you can. Let the engine idle at around 1200 rpm. Check your car's manual or parts manual to see what your alternator's maximum amperage should be. The amp reading on your meter should be near the maximum output.

What is a normal alternator voltage?

Normal Output
An alternator should put out between 13.5 and 15 volts of power. The alternator should be tested with the engine idling and electrical accessories, such as the radio and headlights, turned off.

How do you know voltage regulator is bad?


Signs of a bad voltage regulator in a vehicle include dimming or pulsing lights or a dead battery. If you have electrical equipment that won't turn on, that could also indicate a bad voltage regulator—the regulator could either be letting no power through or letting through too much and damaging the other components.

How do I increase the voltage of my alternator?

In the case of an alternator charging at 13.8 volts, this will increase the output voltage to 14.4 volts. A diode drops a voltage of around 0.6 volts at low currents, increasing up to around 1.2 volts at high currents. So if we use a diode at low current, it will drop just about the right voltage.

Can you check an alternator by disconnecting the battery?

If you're tempted to test an alternator by disconnecting the negative battery cable, don't do it. A good alternator may indeed keep the engine running, but it was never a good test. The second you disconnect the battery, the voltage regulator pegs the alternator to put out maximum power.