Car battery -- charging questions

Hello,

I am a Telecommunications student who does not have a lot clue about cars.Does a car charges up its battery when it moves? What power supply is used for lighting in car, the battery? So if car charges the battery when it moves, why sometimes external/additional charging of battery is vital ?

johnnyrev

anorlunda
Staff Emeritus
The engine in the car spins the alternator. The alternator produces DC energy to charge the battery, and to power lights, radios and so on.

If for some reason the battery can't start the engine, then external energy must be supplied.

johnnyrev and berkeman
I appreciate your answer. How many alternators are in the car? 4? or 2?

johnnyrev
anorlunda
Staff Emeritus
I appreciate your answer. How many alternators are in the car? 4? or 2?

Usually one. Do you have a car nearby? You can open the hood, see the engine and the alternator.

johnnyrev
Unfortunately, I don't have a car nearby.But how much power does it output so a battery charges?What about its speed ?

anorlunda
Staff Emeritus
A typical alternator can make 50 amps at 14 volts. That's a lot.

A voltage regulator controls the alternator so the speed doesn't matter much.

Here is a picture of a car engine. The alternator is the part spun by the rubber belt.

johnnyrev
davenn
Gold Member
2021 Award
So if car charges the battery when it moves, why sometimes external/additional charging of battery is vital ?

the car doesn't need to be moving ... the engine only has to be running

I don't have a car nearby. But how much power does it output so a battery charges? What about its speed ?

around 14V at a few amps. The alternator rotor spinning speed is around that of the engine revs so as the engine revs faster so does the alternator

have a look at this pic that I put some text on ......

the V-belt connects the alternator to the engine crankshaft, so that when the crankshaft turns, it then turns the rotor of the alternator

Dave

johnnyrev
Thank you so much guys !

johnnyrev
jack action
Gold Member
The battery has only one purpose: Powering the engine starter.

Once the engine is running by itself, the alternator will power the entire electrical system of the car. In addition, it will recharge the battery for the next engine start.

The size of the alternator depends on the electrical system. If the electrical system is only the ignition system, the alternator will be quite small. If you also have a lighting system, a sound system, power windows, etc., then you need a proportionally more powerful alternator.

johnnyrev
davenn
Gold Member
2021 Award
The battery has only one purpose: Powering the engine starter.

Once the engine is running by itself, the alternator will power the entire electrical system of the car. In addition, it will recharge the battery for the next engine start.

I would have to disagree with that

I find my car starts to fail quite rapidly if the battery fails during operation ..... the battery has the current capabilities that the alternator/generator doesn't have

Dave

johnnyrev
davenn
Gold Member
2021 Award
A typical alternator can make 50 amps at 14 volts. That's a lot.

didn't realise it was capable of 50A, can that be sustained or only in bursts ?

anorlunda
Staff Emeritus
didn't realise it was capable of 50A, can that be sustained or only in bursts ?

50 is sustainable, but it is not often needed in a car.

RVs and boats often install 100 amp alternators because they have big battery banks to charge.

cnh1995 and davenn
wirenut
Gold Member
I believe Ford has a 130 amp alternator in some of their vehicles.

johnnyrev
jack action
Gold Member
didn't realise it was capable of 50A, can that be sustained or only in bursts ?
50 is sustainable, but it is not often needed in a car.

RVs and boats often install 100 amp alternators because they have big battery banks to charge.
50 A was the standard 30-40 years ago. Today, a small car like a Toyota Yaris have an 80 A alternator. A typical car will have one producing 100-130 A. A fully loaded luxury car/SUV can have a 150-180 A alternator.

Again, it's not as much of a question about the battery size, but the demand of the electrical system.
I find my car starts to fail quite rapidly if the battery fails during operation ..... the battery has the current capabilities that the alternator/generator doesn't have
The battery may be needed if the engine is idling and you flip on every switch on your dash, but that is certainly not a normal situation. I'm not even sure it is still a problem in today's car.

The largest (battery) wire in a typical car is a 2-gauge which can withstand a current of 130 A. So the battery will not be able to give more current than the alternator can provide without destroying the wires. You need a https://www.amazon.com/dp/B000CQ23MK/?tag=pfamazon01-20 for a 170 A current, which is the largest I found in a quick search.

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johnnyrev
rbelli1
Gold Member
The battery has only one purpose: Powering the engine starter.

It will also run all of the electrical equipment when the engine is not running. In many (most? all?) cars you will notice that the lights aren't quite as bright and the motors are a bit slower when the engine is stopped. This is because the alternator runs at the battery charge voltage which is a bit higher than the typical loaded voltage of the battery itself.

Having a good battery is crucial as often the regulator needs the battery as part of its operation. If the battery is not present or severely worn the regulator can operate at a voltage that may damage the electrical system. I would suspect as you look at newer models this failure mode will be less severe or absent due to improved design.

BoB

johnnyrev
russ_watters
Mentor
50 A was the standard 30-40 years ago. Today, a small car like a Toyota Yaris have an 80 A alternator. A typical car will have one producing 100-130 A. A fully loaded luxury car/SUV can have a 150-180 A alternator.
I drive a Kia Optima midsize sedan. It has electric power steering. Googled -- it has a 95A alternator.

I'd be curious to know what it draws in normal operation. At 14V that would be 1.8HP. I calculated once that at 30mpg and 60 mph, the engine generates about 17hp, so the electrical load would be about 10%.

jim hardy
Gold Member
Dearly Missed
They've complicated things immeasurably in new cars
With electrical load getting bigger and engines getting smaller
Mr EngineControlUnit directs Mr Voltage Regulator granting permission for Mr Alternator to produce high current if and only if Mr Engine has reserve torque available .
There are dozens of microcomputers chatting over something called "CANBUS" . That's how hackers take remote control of electronic throttle, steering and brakes through the entertainment system.

I am getting too old to put up with such design shenanigans so bought myself a '68 Ford truck .. It'll outlast me. And appreciate not depreciate.

http://www.forbes.com/sites/andygre...-with-me-behind-the-wheel-video/#564897ac5bf2

johnnyrev, cnh1995 and davenn
256bits
Gold Member
I drive a Kia Optima midsize sedan. It has electric power steering. Googled -- it has a 95A alternator.

I'd be curious to know what it draws in normal operation. At 14V that would be 1.8HP. I calculated once that at 30mpg and 60 mph, the engine generates about 17hp, so the electrical load would be about 10%.
Look at the fuse boxes to see the maximum load for a particular circuit.
That will give some initial idea, but what failsafe they have before a fuse blows would have to be factored in.
Adding up all the fuse rating would ( should ) be more than 95A.

johnnyrev
davenn
Gold Member
2021 Award
I calculated once that at 30mpg and 60 mph, the engine generates about 17hp, so the electrical load would be about 10%.

sounds a bit low ? considering .....

As with most mid-size four-door sedans on the market, the 2014 Kia Optima is offered in several different performance flavors--all including a four-cylinder engine under the hood. A 200-horsepower, 2.4-liter four-cylinder engine with direct injection is standard on all but the SX model.

haven't found a HP rating at a given speed and RPM which would be the quantifying factors

Dave

found a maximum power out
Introduction
The Optima 2.4 is a front wheel drive saloon (sedan) motor car with a front positioned engine, from Kia.
Power is supplied by a double overhead camshaft, 2.4 litre naturally aspirated 4 cylinder motor, with 4 valves per cylinder that produces power and torque figures of 177.5 bhp (180 PS/132 kW) at 6000 rpm and 231 N·m (170 lb·ft/23.6 kgm) at 4000 rpm respectively.

grrrr why quote totally different units for the different RPM ... how confusing !!

this one for the 1.6L

Horsepower: 178 @ 5500 RPM

@russ_watters would be interesting to know what RPM it was doing at your 60mph ?

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johnnyrev
SteamKing
Staff Emeritus
Homework Helper
found a maximum power out

grrrr why quote totally different units for the different RPM ... how confusing !!
Max. HP and max. torque output for a given engine usually occur at two different RPMs, with max.torque occurring at the lower RPM.

All of the power figures are consistent, as are all of the torque figures given for this engine.

Knowing the relationship between torque, RPM, and HP, you should be able to calculate the HP output of the engine when the max. torque reading occurs.

johnnyrev and davenn
What if RMP is low ? Does alternator also produce lower amps? And what happens if we charge a battery higher than 14v? Why charging should be only max 14v?

johnnyrev
davenn
Gold Member
2021 Award
And what happens if we charge a battery higher than 14v? Why charging should be only max 14v?

because the battery will be damaged

johnnyrev
SteamKing
Staff Emeritus
Homework Helper
What if RMP is low? Does alternator also produce lower amps? And what happens if we charge a battery higher than 14V ?
There's a voltage regulator in the charging circuit which prevents the battery from being overcharged by the alternator. When the battery is fully charged, the charging circuit opens, and any current put out by the alternator is kept from charging the battery. When the battery voltage drops below the set point, the regulator closes the charging circuit, and current flows from the alternator to the battery again.

johnnyrev
anorlunda
Staff Emeritus
50 A was the standard 30-40 years ago

Man oh man, I am so dated.

johnnyrev
SteamKing
Staff Emeritus
Homework Helper
Man oh man, I am so dated.
I've owned 2 cars:
1. A 1984 Chevy Camaro Z-28 which had a 94-Amp HD alternator
2. A 1997 Ford T-bird V-8 which had a 130-Amp alternator.

The Chevy still used multiple belts for the engine accessories (4 in this particular model), while the Ford used a single serpentine belt to drive everything.

johnnyrev
jim hardy
Gold Member
Dearly Missed
Man oh man, I am so dated.

A/C clutch maybe six amps
A/C fan ten amps
Fuel pump three
fuel injectors ?? maybe two
luxury stereo six when real loud
alternator field four
solenoid valves for ABS, fuel tank vent, EGR, maybe three amps (seems i learn of another one every time the "Check Engine " light comes on...)
heated O2 sensors maybe three ?

now consider intermittent ones that might stay on for several minutes so i'll count them,
rear window defroster six
seat "butt warmers" ten
auto levelling system air or hydraulic pump fifteen

electric locks, windows and seats are so brief i'll not count them.

i'm up to ninety three amps
i'd want a 150 amp alternator to leave me 57 for charging the battery

johnnyrev
jim hardy
Gold Member
Dearly Missed
1. A 1984 Chevy Camaro Z-28 which had a 94-Amp HD alternator
2. A 1997 Ford T-bird V-8 which had a 130-Amp alternator.

Glad to hear there's somebody else who appreciates that "Detroit Iron" .

"Hot Rod Lincoln " (count the sparkplugs)
that'd be a 30 amp generator (black cylinder just in front of the carburetors )

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jack action
Gold Member
If the battery is not present or severely worn the regulator can operate at a voltage that may damage the electrical system.
The regulator output voltage will not depend on the battery. If the output voltage is too high, it is because the regulator is not working properly.
I am getting too old to put up with such design shenanigans so bought myself a '68 Ford truck
I, myself, drive a '69 El Camino.

For the people interested in that stuff, it is fascinating to study those electrical systems.

Read BRIGHTER HEADLIGHTS to learn why headlights had a big impact on the electrical system back then (HINT: It has nothing to do with the alternator power output or the battery capacity).

Read CHEVY Main Electrical Power System to learn how important the component locations and are they are connected together can be.
sounds a bit low ? considering .....

haven't found a HP rating at a given speed and RPM which would be the quantifying factors

Dave

found a maximum power out

grrrr why quote totally different units for the different RPM ... how confusing !!

this one for the 1.6L

Horsepower: 178 @ 5500 RPM

@russ_watters would be interesting to know what RPM it was doing at your 60mph ?
When you are cruising on the highway at 60 mph, you never used the full power of the engine (You don't have the gas pedal to the floor). The power is mostly needed for aerodynamic drag and rolling resistance. For a typical car: ½ρCdAv³ + Crrmgv = ½(1.225kg/m³)(0.33)(1.7m²)(27m/s)³ + (0.01)(1500kg)(9.81m/s²)(27m/s) = 10 736 W = 14.4 hp. Divide by a 90% efficiency due to internal losses, you are at 16 hp. You now just need to add the power to run the accessories. So 17 hp sounds about right to me.

@jim hardy: In your list of intermittent loads, you forgot the power steering where electrical is becoming the norm rather than the exception.

jim hardy
jim hardy
Gold Member
Dearly Missed
@jim hardy: In your list of intermittent loads, you forgot the power steering where electrical is becoming the norm rather than the exception.
Thanks !
just the concept of electronic brakes, steering and throttle is anathema to me. See my signature.
There's some sort of electric pump on brakes now too ?

donpacino
Gold Member
i'd want a 150 amp alternator to leave me 57 for charg
ing the battery