In an average car, how long can you leave your headlights on before it drains your battery?

[Syringer]

?

 

[jlee]

My uncles says ~40min. Depends on the quality of the battery, I would imagine.

 

[mwmorph]

lets see, normal headlights are rated at 55-65watts.(5-6A per hour at 12v)
Batteries come in 500-650 CCA usually.

I'm sure someone with the requisite skills can do the math. I'd say a few hours at least.

 

[Heisenberg]

An hour or two usually.

 

[Sukhoi]

Originally posted by: mwmorph
lets see, normal headlights are rated at 55-65watts.(5-6A per hour at 12v)
Batteries come in 500-650 CCA usually.

I'm sure someone with the requisite skills can do the math. I'd say a few hours at least.

You need to consider that the battery is effectively drained when it cannot start the car, not when it has no energy left stored inside.

 

[Syringer]

Good point, how much energy is requird to start a car?

 

[Heisenberg]

Originally posted by: Syringer
Good point, how much energy is requird to start a car?

Depending on the car, the battery needs to provide around a hundred amps to start the motor.

 

[Zenmervolt]

Assuming that the other lights are on with the headlights, you're probably drawing around 150 watts (55 watts per headlight, plus all the ancillary and interior bulbs). That's about 12.5 amps. Your average car battery has between 60 and 100 amp-hours of capacity. So, the time until the battery is completely drained is theoretically between 4.8 and 8 hours. Now a battery's amp-hour capacity diminishes as the amperage draw increases, so you're looking at more realistically between 4 and 7 hours.

In terms of how long until you can't start the car, assuming the car battery is fully charged probably 45 to 90 minutes.

ZV

 

[Zenmervolt]

Originally posted by: Heisenberg

Originally posted by: Syringer
Good point, how much energy is requird to start a car?

Depending on the car, the battery needs to provide around a hundred amps to start the motor.

A loaded starter can draw in excess of 300 amps. You probably need around 400 amps available to start a modern engine.

ZV

 

[Heisenberg]

Originally posted by: Zenmervolt

Originally posted by: Heisenberg

Originally posted by: Syringer
Good point, how much energy is requird to start a car?

Depending on the car, the battery needs to provide around a hundred amps to start the motor.

A loaded starter can draw in excess of 300 amps. You probably need around 400 amps available to start a modern engine.

ZV

Hmm...is that the peak draw or continuous over the few seconds the starter turns?

 

[bwatson283]

each car is differnent. My exploder can last like 1 hour, my mustang like 30minutes

 

[flyboy84]

42 minutes

 

[Zenmervolt]

Originally posted by: Heisenberg

Originally posted by: Zenmervolt

Originally posted by: Heisenberg

Originally posted by: Syringer
Good point, how much energy is requird to start a car?

Depending on the car, the battery needs to provide around a hundred amps to start the motor.

A loaded starter can draw in excess of 300 amps. You probably need around 400 amps available to start a modern engine.

ZV

Hmm...is that the peak draw or continuous over the few seconds the starter turns?

I'm not sure, I can easily imagine it being continuous though since the starter has to be able to spin the engine up to a few hundred RPM (and given the gearing, the starter probably spins close to 1,000 RPM). I'm just making an educated guess here though.

ZV

 

[Heisenberg]

Originally posted by: Zenmervolt

Originally posted by: Heisenberg

Originally posted by: Zenmervolt

Originally posted by: Heisenberg

Originally posted by: Syringer
Good point, how much energy is requird to start a car?

Depending on the car, the battery needs to provide around a hundred amps to start the motor.

A loaded starter can draw in excess of 300 amps. You probably need around 400 amps available to start a modern engine.

ZV

Hmm...is that the peak draw or continuous over the few seconds the starter turns?

I'm not sure, I can easily imagine it being continuous though since the starter has to be able to spin the engine up to a few hundred RPM (and given the gearing, the starter probably spins close to 1,000 RPM). I'm just making an educated guess here though.

ZV

I could see the peak being in the 300-400 amp range, but I thought it dropped down to ~100 amps after the initial surge since you wouldn't have a big inductive load anymore. Maybe I'm wrong however.

 

[blustori]

I think for new cars, the light automatically turns off after a while.

 

[0]

This depends on the following factors:

1. Age of battery. Older batteries have less capacity than on the nameplate.

2. Capacity of battery - based on nameplate.

3. Wattage of load. No explanation necessary.

4. Temperature. Low temps decrease battery capacity dramatically.

 

[Sentinel]

I drained the battery in my mom's car in about 28 min. Sh!t!

 

[funboy6942]

If it is a new car and depending on the battery only to the point the battery volts get to a certin point and the computer shuts off all electricals. In a older car with out the computer feature and the battery is in peek performance a hour or so but at that point dont expect the car to crank over very long so pray it will start right away.

 

[Pepsi90919]

my average GM car has battery rundown protection so it's a moot point.

 

[Eli]

Originally posted by: Heisenberg

Originally posted by: Zenmervolt

Originally posted by: Heisenberg

Originally posted by: Zenmervolt

Originally posted by: Heisenberg

Originally posted by: Syringer
Good point, how much energy is requird to start a car?

Depending on the car, the battery needs to provide around a hundred amps to start the motor.

A loaded starter can draw in excess of 300 amps. You probably need around 400 amps available to start a modern engine.

ZV

Hmm...is that the peak draw or continuous over the few seconds the starter turns?

I'm not sure, I can easily imagine it being continuous though since the starter has to be able to spin the engine up to a few hundred RPM (and given the gearing, the starter probably spins close to 1,000 RPM). I'm just making an educated guess here though.

ZV

I could see the peak being in the 300-400 amp range, but I thought it dropped down to ~100 amps after the initial surge since you wouldn't have a big inductive load anymore. Maybe I'm wrong however.

This is correct. It would only draw that peak amperage, whatever it is, for the split second that the starter isn't turning..

But it would vary as the starter is turning the engine over. Each compression stroke would present resistance and increase amperage draw.

A 4 cylinder engine takes a lot less juice to start than an 8cyl, also.

Most car batteries are only ~50Ah. I've never seen a 100Ah car battery... the deep cycle marine battery I have is 115Ah, and it's significantly larger than the average car battery.

I'm sure there are truck batteries that are close though.

I'm going to agree and say about an hour.

I know I've drained my car battery down to 11V on accident, running a peltier-powered cooler.. and I was surprised when it started my car right up, could barely even tell a difference in the starter pitch. I don't think it takes much juice to start my little Tercel.

 

[DaTT]

Newer generally won't allow it. They automatically shut off after 10 minutes.

 

[Zenmervolt]

Originally posted by: Eli
This is correct. It would only draw that peak amperage, whatever it is, for the split second that the starter isn't turning..

But it would vary as the starter is turning the engine over. Each compression stroke would present resistance and increase amperage draw.

A 4 cylinder engine takes a lot less juice to start than an 8cyl, also.

Most car batteries are only ~50Ah. I've never seen a 100Ah car battery... the deep cycle marine battery I have is 115Ah, and it's significantly larger than the average car battery.

I'm sure there are truck batteries that are close though.

I'm going to agree and say about an hour.

I know I've drained my car battery down to 11V on accident, running a peltier-powered cooler.. and I was surprised when it started my car right up, could barely even tell a difference in the starter pitch. I don't think it takes much juice to start my little Tercel.

You make a good point, my amp draw figures were for a V8.

Last battery I bought for a car was a monster too, 875 CCA, 1,000 CA. Guess I'm just used to cars that pull more power than most.

ZV

 

[j00fek]

depends n the battery, iv left my lights on all day at work and drove home, nothing happened and im still on the same battery

 

[Eli]

Originally posted by: Zenmervolt

Originally posted by: Eli
This is correct. It would only draw that peak amperage, whatever it is, for the split second that the starter isn't turning..

But it would vary as the starter is turning the engine over. Each compression stroke would present resistance and increase amperage draw.

A 4 cylinder engine takes a lot less juice to start than an 8cyl, also.

Most car batteries are only ~50Ah. I've never seen a 100Ah car battery... the deep cycle marine battery I have is 115Ah, and it's significantly larger than the average car battery.

I'm sure there are truck batteries that are close though.

I'm going to agree and say about an hour.

I know I've drained my car battery down to 11V on accident, running a peltier-powered cooler.. and I was surprised when it started my car right up, could barely even tell a difference in the starter pitch. I don't think it takes much juice to start my little Tercel.

You make a good point, my amp draw figures were for a V8.

Last battery I bought for a car was a monster too, 875 CCA, 1,000 CA. Guess I'm just used to cars that pull more power than most.

ZV

Wow, no sh!t!? Yeah, that's a big battery.

My 115Ah deep cycle is only 600CCA. 😕

CA/CCA isn't really the best way to tell the Ah capacity of the battery, though it gives you an idea I guess.

My truck pulls the battery down to ~9V while cranking with the engine cold. That's some serious pull.

 

[OrganizedChaos]

Originally posted by: Eli

Originally posted by: Zenmervolt

Originally posted by: Eli
This is correct. It would only draw that peak amperage, whatever it is, for the split second that the starter isn't turning..

But it would vary as the starter is turning the engine over. Each compression stroke would present resistance and increase amperage draw.

A 4 cylinder engine takes a lot less juice to start than an 8cyl, also.

Most car batteries are only ~50Ah. I've never seen a 100Ah car battery... the deep cycle marine battery I have is 115Ah, and it's significantly larger than the average car battery.

I'm sure there are truck batteries that are close though.

I'm going to agree and say about an hour.

I know I've drained my car battery down to 11V on accident, running a peltier-powered cooler.. and I was surprised when it started my car right up, could barely even tell a difference in the starter pitch. I don't think it takes much juice to start my little Tercel.

You make a good point, my amp draw figures were for a V8.

Last battery I bought for a car was a monster too, 875 CCA, 1,000 CA. Guess I'm just used to cars that pull more power than most.

ZV

Wow, no sh!t!? Yeah, that's a big battery.

My 115Ah deep cycle is only 600CCA. 😕

CA/CCA isn't really the best way to tell the Ah capacity of the battery, though it gives you an idea I guess.

My truck pulls the battery down to ~9V while cranking with the engine cold. That's some serious pull.

voltage drop in the cables.