How long does it take an alternator to charge a battery while driving

All cars featuring an internal combustion engine have a charging system consisting of the alternator, regulator, and interconnecting wiring. The charging system is the main source of electrical energy, providing power to electrical components while the engine runs and, most importantly, charges the battery. Without the battery or functioning charging system, your car won’t operate as it should.

Generally speaking, an alternator can charge a car battery sufficiently with a 30-minute drive at highway speeds (55 mph+) or an hour when driving in the city. The time it takes an alternator to charge a car battery usually depends on how much charge the battery has left before you start driving and at what speed you drive.

When you turn the key to engage the ignition or push the on button, a signal is sent to the battery that the starter needs electrical power to crank the engine. It’s then the alternator’s job to recharge the battery when the engine is in motion. How long does it take an alternator to charge a battery?

The length of time it takes an alternator to charge a car battery will depend on how much charge the battery has left before you start driving and at what speed you drive:

• Maintaining a speed of 55 mph or more on the highway can result in your battery being charged in 30 minutes and a little longer if the battery is severely discharged. 
  
• It can take up to an hour for your car battery to charge when driving around in the city (various speeds and RPM fluctuations play a role).
  
• When idling, the battery can take multiple hours before it is fully recharged; on average, it takes about 2 hours to charge it to 80% (depending on electrical demand from other electrical systems and appliances) when the alternator’s output is between 13 to 15 volts.
  
• If your battery is fully charged when starting the engine, the cranking amps needed to turn the engine (provided by the battery) will be replaced by the alternator in a matter of minutes.

At What RPMs Does The Alternator Begin To Charge The Battery?

Studies have shown that the greater the engine speed, the quicker the alternator charges the battery. Generally, an alternator speed of 2000 RPM is enough to generate a sufficient charging voltage. The full output of an alternator is rated at 6000 RPM.

The amount of current output of any alternator is speed-dependent. The lower the engine RPM, the lower the alternator’s current output. If your car idles at 1000 RPM, technically, the alternator will run at almost 2000 RPM, seeing that most alternators are set up to be at least twice as fast as the engine, depending on the vehicle’s power requirement.

Does An Alternator Charge A Battery When The Car Is Idling?

If the engine is spinning, the alternator will turn any mechanical energy into electricity, and the battery will receive a charge from the alternator. The only problem with charging your battery with an idling engine is that it doesn’t charge your battery fast, as the engine doesn’t have a load when idling.

When an engine idles, the RPMs are much less than when the car is driving, and as a result, the belt rotating the shaft will spin slower, directly resulting in less electricity to recharge your car’s battery. While your car is idling, some additional electronics and systems require electricity from the alternator’s generated current.

An alternator that produces around 80 amps when the engine is idling can charge a low battery to 80% full in approximately 2 hours, as long as the alternator can consistently produce plus minus 14 volts at the battery terminals for the duration.

Even though your battery is technically charging when your car engine is idling, it may take several hours before the battery is charged due to the reduced electricity generated by the alternator. The best advice; take your car for a half-an-hour spin on the highway at 55 mph or more.

Some folks swear that starting their car and letting it idle for a couple of minutes helps to maintain the car’s battery. The problem with this thinking is that the energy required to start the car is often not replaced by the alternator over a few minutes. Following this method can aid in discharging your car’s battery instead of charging it.

Can An Alternator Charge A Discharged Or Dead Battery?

An alternator is designed to do many things; charging a dead battery is not what it’s designed for. Alternator manufacturers specifically state that the alternator is not to be used for charging deeply-discharged batteries. If a newly purchased alternator gets burned out, it’s typically due to them having to recharge these deeply-discharged batteries.

While an alternator can charge a battery with a low charge, it won’t be able to charge a dead battery. Most 12-volt batteries are considered full at 12.6 volts or more when resting (no charge). A reading of 12 volts indicates a battery that’s been seriously discharged. The battery is considered fully discharged when the voltage drops to 10.5 volts.

Alternators are designed to keep a battery topped up, not to recharge deeply discharged or dead batteries. Most alternator manufacturers indicate that they can charge the battery when it is measuring 12.6 volts minimum (which indicates that an alternator should only be used to top up the battery level, not charge it back into health when depleted.)

Alternators can charge a low-charge battery, but charging batteries with less than 20% charge left is not a good idea and should be done by an external battery charger. It’s

How Long Will A Battery Last When A Car Is Not Driven?

A battery sitting in a car that’s not used can go from fully charged to completely depleted in less than 60 days. Older batteries (3-5 years) die even faster, especially if it wasn’t fully charged to begin with. A battery maintainer will be your best bet when you know you’re not going to drive your car daily.

A battery maintainer (also known as a trickle charger) can act as a float charger to bring back optimal voltage levels should they drop and maintain a good battery’s charge. It can’t recharge a dead battery, so you must be proactive and connect it to the stationary vehicle as soon as possible.

What Is The Most Effective Way To Charge A Battery?

Many car owners believe they can recharge a heavily depleted or dead battery by driving around for a bit. Most of the time, it will only provide a surface charge to the battery, which is worthless in the greater scheme of things. On the flip side, your alternator can be seriously damaged or destroyed. The best advice is to use a battery charger to charge your car battery.

An alternator does a great job at topping up the energy used by the battery to start the engine. Still, it would be best to use a battery charger to charge the battery as it’s the most effective and safest way. A battery charger that monitors the battery through a 4 to 8-step charging process is advised.

Ensure to get a battery charger compatible with the type of battery under the hood of your car. If you have a lead-acid battery, buy a lead-acid battery charger. Should you have an AGM battery, you will need an AGM-compatible battery charger. Look for a dual charging battery that can charge batteries with different chemistries and at different voltages.