Better Understanding A Battery Amp Hour
All car batteries have what’s known as an “Amp hour.” This is a rating used to tell drivers how much amperage the battery can offer for precisely one hour. This rating influences the battery’s voltage delivery, potential power, and runtime.
Therefore, a battery with 1 Ah can continuously provide a current of 1 amp for exactly 1 hour. It could also provide a current of 2 amps for 30 minutes.
How Long Should I Idle My Car To Charge The Battery
So this is an interesting question, that came up during my research. During these times of the Coronavirus many of us have our vehicles sitting much longer than they ever had. Even if your area is opening up you are likely not driving as much as you once did. So is it a good idea or even worth the energy spent to let your engine idle to recharge your battery.
In this article from Jalopnik, they interview an electrical engineer who tested a 2019 Toyota Tacoma. If you want a lot of technical jargon the article is worth a read. But the summary is this.
You would have to allow your car to idle for possibly several hours to completely charge your battery. There are many electrical systems in your car all vying for a little bit of power from the alternator. What energy is left over to recharge the battery is very small.
There are a number of variables to this. The amount of computer and electrical systems in your car, the health of your battery, and how much voltage your alternator is producing.
So allowing your engine to idle may put a small amount of charge on your battery, but that may not be the most efficient way to charge your battery. The conclusion of his study estimated that allowing your car to run for only fifteen minutes or so would actually cost you more energy than you would gain.
So, is it a good idea to allow your engine to charge your battery, it would not seem so. Go for a drive instead, you need to get out of the house anyway, right?
Types Of Car Battery Charger
A basic home battery charger incorporates a transformer and rectifier, to change the mains 110/220 voltalternating current to 12 volt direct current, and allows the mains supply to provide a charging current at a rate determined by the state of the battery.
In the case of a battery in good condition, the rate of charge may be around 3 to 6 amps with a normal home charger.
A battery at the end of its useful life may not accept any recharging, and will not, in any case, hold a charge.
Some chargers are fitted with a high and low switch to give a choice of two charging rates – typically 3 or 6 amps – in case you want to give the battery a short overnight boost at 6 amps rather than a longer charge at 3 amps.
Many have a charge indicator which may be a warning light, or a gauge showing the charge rate in amps.
Note that the mains lead on all chargers should be fused. If it is not, use a three-pin fused plug. As an extra precaution, fit a line fuse cable lead to the battery.
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Does A Car Battery Charge Faster When Driving
How long is a piece of string? How quickly a battery charges depends mainly on a few factors:
- Battery charge when the engines turned on
- Electrical load
- Alternator, battery, and electrical circuitry conditions
In general, yes a cars alternator will charge a battery faster than a mains electrical charger.
This is because most car batteries have an average charge storage capacity of 48 Ah . A car puts out much more current than most mains chargers.
Itll take a car less than an hour to fully restore the batterys charge. In comparison, you should expect a basic charger to take at least 4 to 6 hours to resupply the same battery
A trickle charge will, of course, take longer perhaps up to two or three days.
Note: It isnt always safe to use mains battery chargers! You should always check the instructions on the battery to ensure its safe!
How Long To Charge A Car Battery At 15 Amps
A 15 amp charger can charge a 50% discharged small car battery in about 2 hours, a mid-sized battery in 2.25 hours, or a large car battery in 2.5 hours. Double the times if 100% discharged. 15 amp chargers should be used with caution.
15 amp chargers are starting to push the car battery past its ability to absorb all of the current from the charging process. This leads to overheating, the boiling-off of the electrolyte or worse.
It is recommended to use a 3-stage smart charger with a max output of 15 amps if you are going to go this route so that the charger will detect when it needs to scale down the amperage.
15 amp hour chargers would be acceptable for larger deep-cycle batteries, but are a little strong for starting batteries like those in your vehicle.
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Can A Car Alternator Charge A Deep Cycle Battery
A lot of people who own cars with alternators also own boats or RVs that use deep-cycle batteries. People often wonder if they can use the alternator on their car to charge their boat or RV battery. In this blog post, we will answer that question and provide some tips on how to properly charge a deep-cycle battery using an alternator.
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How Long Does It Take To Charge A Car Battery With A Trickle Charger
A trickle charger usually operates at around 2 amps and it is going to take a long time to charge up your 12-volt car battery . It can take as long as 24 hours to get the battery up to an acceptable charge, depending on how depleted your battery is when you start charging.
Trickle chargers are mainly used to maintain your charge on your battery over a period of time so that it never runs out of charge and you are never left stranded with a flat battery. It takes a long time to charge and will switch off automatically in some chargers once your battery is fully charged.
Often trickle chargers are used in workshops to maintain batteries while the mechanic works on the car, especially if the battery is going to stand disconnected for a period of time, this is so that the battery keeps enough charge to be functional when put back into the car for use.
The length of time it takes to charge your car battery is completely dependent on the size or amp of your battery and the amp of the car charger you are using. If using a low amp charger it can take up to 24 hours to charge your battery properly but a high amperage charger such as a 40 amp charger will get the job done adequately in an hour or less and will get you on the road again in only a few minutes.
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Condition Of The Alternator
Running the car to charge your battery only works if your alternator is in optimal condition. If you have a bad alternator, the engine might be running without charging the battery. At this point, a low battery charge combined with a poor alternator might make it impossible to even start your car.
Also, you might notice a battery warning on the dashboard, and see your headlights dim. However, its possible to jumpstart a car with a bad alternator, although its just a temporary solution. If your alternator is bad, youll have to replace it and check your batterys charge afterward, since it could all just be a consequence of the alternator.
Checking Your Battery Health
If your battery or alternator is causing the flat battery, then jump-starting and driving your car wont charge it. The jump-starting procedure might put enough power into the battery to get the show on the road, but the engine will shut down after a few miles when the battery is empty to truck time.
Batteries typically last about three to four years, or maybe Im just unlucky because some people can get five to six years from theirs. How cold your climate is will affect how long your battery lasts. Batteries hate the cold.
Even a healthy, fully charged battery only supplies about 65% of its power at 0 degrees F. Combine that with the fact the engine oil is thicker in colder temps. Its no surprise most batteries fail in freezing winter conditions.
Anyway, a bad battery can cause other more expensive alternator problems, so it is best to check it. A faulty battery wont build resistance to charge, and that causes the alternator to work at full capacity for longer.
Check Ground Straps
Its worth checking for loose or dirty battery connections, especially in older cars. Bad battery terminals will cause you to believe you have a flat battery, so always check them first. Check battery cables are tight but also check the battery ground straps.
Youll have at least two straps, a strap from the battery to the chassis and another from the chassis to the engine. All must be clean, tight, and in good order.
Check Ground Straps
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Why Does The Car Battery Lose Its Charge
To understand how you can fill up the charge of your battery by simply running the engine, you first need to understand why it loses charge in the first place. There are various reasons behind a draining battery, and if the charge gets too low, you might receive a battery discharge warning on the dashboard.
Car battery cells degrade over time, so thats why you have to completely replace the battery if it dies. However, there are plenty of reasons why your battery might lose its charge without getting completely flat. If you use your cars electronic features without running the engine, your batterys charge only gets lower.
You might use the interior lights or the radio both significantly affect the battery charge if the engine isnt running. Also, keeping your headlights on even for 10 minutes without starting the engine wastes a lot of charges.
Over time, battery connections and terminals also get corroded, and even extremely cold or hot weather affects the batterys charge. Ultimately, your battery loses its charge if you only take short drives for a while. Since you can charge the battery by letting your engine run for 20 to 30 minutes, taking frequent short rides will deplete the battery.
Deep Sleep Mode And The 12v Battery
Depending on how long you plan on leaving an electric car parked and not in use will determine the battery-draining situation. However, the bigger concern is actually the regular 12V battery in every car, not the massive battery packs that propel your EV down the road.
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When you drive a regular vehicle, the alternator recharges the 12V battery that handles all the lights, accessories, and the starter. If you leave any car sitting long enough, the 12V battery will die and need a jump-start.
The massive battery cells under an electric car arent a concern when you leave the vehicle parked or unused for an extended time. For example, Nissan says to leave a Leaf EV at around 50% charge, and itll automatically go into a deep sleep state to preserve everything. But, if youre not paying attention, the 12V will be dead depending on the model of the car you own.
On the flip side, Tesla instructs owners to plug in their EVs if it isnt being used for long periods. That way, the battery management system can again keep the battery packs at safe charge levels, prevent over-charging, and maintain optimal 12V battery levels. This ensures owners return to a car that still has juice in all the batteries and is ready to go.
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Volt Drop Test Alternator
If you suspect an alternator fault, go ahead, volt drop tests the circuitstill with me? Okay, cool, this stuff is really easy, I promise. Youll need a voltmeter and the engine running to perform this test.
A voltage drop test simply measures the difference in voltage between the two test probes. A large difference means theres resistance in the wiring or terminals, i.e., the power cant flow through the circuit with ease.
Its a great test for locating dirty, corroded, or damaged cables/terminals. Anyway, follow the diagram below to nail the volt drop test like a pro.
With A Battery Charger
Dont get stranded. Simply keeping a battery charger unit in your trunk can save you from a dicey situation. With this type of charger, you dont need another car to help you recharge the battery. Simply hook it up and charge up the battery, then get back on the road.
These devices generally cost between $30 and $120. The prices vary with the brand and the number of output and charging settings provided. You can purchase one at any automotive accessory store. Most battery charger devices work with standard 12V car batteries, including deep cycle or gel batteries.
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Check Alternator Voltage Output
An alternator can be checked with a simple voltmeter. Youll need a simple voltmeter for these tests. Ive listed a good meter on the Auto electrical repair tools page.
- Place a probe on the battery terminals in the normal way and note the voltage
- Start the car and let it idle with all consumers off
- A healthy alternator will read about two volts higher approx. then the resting battery voltage
- Readings above 15 volts suggest the alternator is overcharging
- Voltage reading should fall as the car tops off the battery the time it takes depends on the battery state of charge about five to ten minutes is normal
- Turning on lights and other consumers should cause the voltage to rise immediately as the alternator reacts to the extra electrical demands
Maintaining An Electric Car Battery After Not Driving
Electric cars and hybrids have 12V batteries , like standard vehicles, but they charge differently. The most common way to do this is by pressing the start button to turn it on, which will automatically operate a charging system which in turn gives the battery more power.
If youre concerned about how much charge the auxiliary battery in your EV has, you should start the vehicle up at least once a week for 10 minutes each time for a sufficient recharge.
At the same time, you should check the status of the main onboard battery to see whether it needs charging. Even though you may not be driving, lithium-ion batteries in EVs can gradually lose the capacity to hold a charge over time, and you may see the effects of this in the form of loss of range/percentage.
Should your car need charging, make sure this is done through a designated home charge point or public station. While each EV comes with EVSE that includes a Type-2-to-3-pin cable for charging from a mains socket, this can overload the outlet and potentially be dangerous.
Remember: Check your vehicles handbook before choosing to maintain the 12V battery by plugging into your domestic mains socket.
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The Use Of A Solar Panel
Though this is not the best way to charge a car battery, especially if the battery is totally dead. It requires tools like voltage and amps. The are a few different ways to achieve this but for your safety, I would recommend the use of a solar charge controller which will block reverse current and prevent the battery from overcharging. The size of the solar panel needed and how long it will take to charge the battery is dependent on the size of your car battery.
Ways A Battery Can Be Charged:
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What Are The Different Types Of Battery Chargers
So what do you do if you have a car that you dont typically drive all that often? Your best bet is to pick up a battery charger. A battery charger will help keep your battery charged up and healthy so that its ready to go. When shopping for a battery charger, youll want to follow two basic rules. Rule number one: the charger you select must be compatible with your batterys chemistry. So what do we mean by chemistry? For a lead acid battery, youll need to find a lead acid charger. If you have an AGM battery in your vehicle, youll need a charger that is AGM compatible. Many modern battery chargers have different settings that enable them to charge batteries with different chemistries.
Rule number two, the voltage of your charger must match the output voltage of your battery. So, for a 12 volt car battery, you need to get your hands on a 12 volt charger. If you have a truck that uses a 24 volt battery, be sure that you get a 24 volt charger. Its important that you follow both of these rules. Charging a battery with the wrong charger can permanently damage your vehicles battery.
Another thing to keep in mind is that there are three different types of battery chargers: standard chargers, trickle chargers and battery maintainers, each of which works a bit differently. Learn the difference between these three types of chargers in our blog entitled, When Should You Use a Battery Maintainer?