How long will a 9volt battery last...

[JoeFahey]

For a math project we had to use about 25 equations to make a picture. I chose Mickey Mouse, and for the visual aid I made a big picture of him on some cardboard and made it look nice. i also stuck two lights from a Christmas light set into his eyes, so his eyes turn on and blink when you flip the switch I made.

It has a 9 volt battery attached to them.
1.) How long will the battery last (Its new)
2.) Will just simply having the battery attached to them make it drain? And if so, how long will it last?

I hand it in tomorrow in the morning, so Im hoping it will last.

 

[Ika]

Depends. Do you have resistors attached to the LEDs? As I recall, if you supply LEDs with full current from a 9V battery, they will die. Quickly. Meaning, about 10 seconds or so without resistance.

 

[Heisenberg]

A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

 

[mugs]

You could get one of those big-ass 6V lantern batteries. They probably have a lot of juice in them.

Originally posted by: Heisenberg
A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

Yeah that makes sense... I guess a normal LED uses a lot less energy than one of the bright ones they use in flashlights

 

[91TTZ]

Originally posted by: Heisenberg
A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

But the 9V's voltage is much higher, so it'll bleed off much more wattage.

 

[JoeFahey]

Originally posted by: Aflac
Depends. Do you have resistors attached to the LEDs? As I recall, if you supply LEDs with full current from a 9V battery, they will die. Quickly. Meaning, about 10 seconds or so without resistance.

I have no Idea what resistors are. But I let it run for like a minute and it ran very brightly until I turned it off. So I guess the way I arranged it worked to the same effect.

 

[JoeFahey]

Originally posted by: 91TTZ

Originally posted by: Heisenberg
A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

But the 9V's voltage is much higher, so it'll bleed off much more wattage.

I put a switch on it. When the switch is turned off, does it completely disconnect it? Meaning, will it prevent it from bleeding?

 

[91TTZ]

Originally posted by: JoeFahey

Originally posted by: 91TTZ

Originally posted by: Heisenberg
A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

But the 9V's voltage is much higher, so it'll bleed off much more wattage.

I put a switch on it. When the switch is turned off, does it completely disconnect it? Meaning, will it prevent it from bleeding?

Yeah, if it's off, it's off.

But while it's running, it'll be using a lot more electricity than it really needs to be using.

 

[JoeFahey]

Originally posted by: 91TTZ

Originally posted by: JoeFahey

Originally posted by: 91TTZ

Originally posted by: Heisenberg
A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

But the 9V's voltage is much higher, so it'll bleed off much more wattage.

I put a switch on it. When the switch is turned off, does it completely disconnect it? Meaning, will it prevent it from bleeding?

Yeah, if it's off, it's off.

But while it's running, it'll be using a lot more electricity than it really needs to be using.

So no bleeding?
I won't turn it on again until I have to present it.

 

[Ika]

Originally posted by: JoeFahey

Originally posted by: Aflac
Depends. Do you have resistors attached to the LEDs? As I recall, if you supply LEDs with full current from a 9V battery, they will die. Quickly. Meaning, about 10 seconds or so without resistance.

I have no Idea what resistors are. But I let it run for like a minute and it ran very brightly until I turned it off. So I guess the way I arranged it worked to the same effect.

Oh I see. You took christmas lights and used those. That makes more sense.

If you happen to have a multimeter, you could measure the resistance between one lead of the light and the other lead. Otherwise, without knowing some detailed information about your lights, I don't think there's a way to find out the lifetime of the battery.

However, it SHOULD be quite a long time. On average, 9V batteries have about 450mAh, meaning if something were draining the battery at a rate of 1 mA (milli-ampere), it would take around 450 hours to drain the battery.

In general, LEDs can drain anywhere from 1-10 mAs, so as a rough guesstimate, I'd say your system will run for about 100 hours or so, considering you have two lights in the circuit.

 

[91TTZ]

The current limiting resistors will be using more energy than the LEDs will.

 

[JoeFahey]

Originally posted by: Aflac

Originally posted by: JoeFahey

Originally posted by: Aflac
Depends. Do you have resistors attached to the LEDs? As I recall, if you supply LEDs with full current from a 9V battery, they will die. Quickly. Meaning, about 10 seconds or so without resistance.

I have no Idea what resistors are. But I let it run for like a minute and it ran very brightly until I turned it off. So I guess the way I arranged it worked to the same effect.

Oh I see. You took christmas lights and used those. That makes more sense.

If you happen to have a multimeter, you could measure the resistance between one lead of the light and the other lead. Otherwise, without knowing some detailed information about your lights, I don't think there's a way to find out the lifetime of the battery.

However, it SHOULD be quite a long time. On average, 9V batteries have about 450mAh, meaning if something were draining the battery at a rate of 1 mA (milli-ampere), it would take around 450 hours to drain the battery.

In general, LEDs can drain anywhere from 1-10 mAs, so as a rough guesstimate, I'd say your system will run for about 100 hours or so, considering you have two lights in the circuit.

I have a multimeter, but I'll just assume that it will last for tomorrow. The thing is nothing but trash to me after I get a grade for it tomorrow.

Thanks everyone!

 

[bobsmith1492]

Originally posted by: Aflac

Originally posted by: JoeFahey

Originally posted by: Aflac
Depends. Do you have resistors attached to the LEDs? As I recall, if you supply LEDs with full current from a 9V battery, they will die. Quickly. Meaning, about 10 seconds or so without resistance.

I have no Idea what resistors are. But I let it run for like a minute and it ran very brightly until I turned it off. So I guess the way I arranged it worked to the same effect.

Oh I see. You took christmas lights and used those. That makes more sense.

If you happen to have a multimeter, you could measure the resistance between one lead of the light and the other lead. Otherwise, without knowing some detailed information about your lights, I don't think there's a way to find out the lifetime of the battery.

However, it SHOULD be quite a long time. On average, 9V batteries have about 450mAh, meaning if something were draining the battery at a rate of 1 mA (milli-ampere), it would take around 450 hours to drain the battery.

In general, LEDs can drain anywhere from 1-10 mAs, so as a rough guesstimate, I'd say your system will run for about 100 hours or so, considering you have two lights in the circuit.

You cannot measure the resistance across an LED using a standard voltmeter - they are not ohmic devices. You could measure the forward drop with a diode tester, though.

Also, he said there were two in series - and two super bright ones. LEDs can draw up to 30 mA easily, and more if you don't limit them as he says he is not doing... (hint - you might burn them up quickly without a limiting resistor).

At any rate, if you turn the switch off, your battery won't drain, so you'll be fine.

 

[Ika]

Originally posted by: 91TTZ
The current limiting resistors will be using more energy than the LEDs will.

That doesn't really make much sense. Resistors don't use energy...?


Joe: how long do you plan on having it on? A couple hours will almost undoubtedly do no harm, but if you have some free time, see if you can get the resistance numbers

EDIT: I guess that last part isn't possible. Curse you, delayed electronics chapter in physics!

EDIT 2: bobsmith1492 - actually, I figured that since he was using Christmas lights, there might've been resistors built in. Otherwise, an unlimited LED would probably burn up in a few seconds. At least, this is how it was on the LEDs that I tested for fun...

 

[91TTZ]

Originally posted by: Aflac

Originally posted by: 91TTZ
The current limiting resistors will be using more energy than the LEDs will.

That doesn't really make much sense. Resistors don't use energy...?


Joe: how long do you plan on having it on? A couple hours will almost undoubtedly do no harm, but if you have some free time, see if you can get the resistance numbers

It does make sense, and they do use energy.

If you have a electric heater, does it use any energy? It'll use more than a thousand watts. But it's just a resistor.

 

[91TTZ]

Originally posted by: Aflac

Joe: how long do you plan on having it on? A couple hours will almost undoubtedly do no harm, but if you have some free time, see if you can get the resistance numbers

Undoubtedly do no harm? Have you every seen the current draw curve of an LED? It doesn't work like a light bulb.

 

[mercanucaribe]

You had to make a picture using equations?

 

[JoeFahey]

Originally posted by: mercanucaribe
You had to make a picture using equations?

Yes. So for the 3 circles I wrote up the 3 equations for them. And for something like the eyes, I used 2 sleeping parabolas. Then we restricted the domains and ranges so it look how I want it to. Part of the job was that we had to get it on our graphing calculators with the restricted domains and such, so that was pretty cool. It's only an Algebra II class, so its pretty basic, but it was still fun.

AFLAC: You saying it will be fine if its only on for a couple hours comforts me. The total time it will be on will probably not amount to be over 30 minutes.

Again, thanks everyone.

 

[91TTZ]

Originally posted by: JoeFahey

Originally posted by: mercanucaribe
You had to make a picture using equations?

Yes. So for the 3 circles I wrote up the 3 equations for them. And for something like the eyes, I used 2 sleeping parabolas. Then we restricted the domains and ranges so it look how I want it to. Part of the job was that we had to get it on our graphing calculators with the restricted domains and such, so that was pretty cool. It's only an Algebra II class, so its pretty basic, but it was still fun.

AFLAC: You saying it will be fine if its only on for a couple hours comforts me. The total time it will be on will probably not amount to be over 30 minutes.

Again, thanks everyone.

LEDs don't work like light bulbs. At 1.5 volts a certain LED might be completely off, while at 2 volts the thing is on the verge of burning out.

 

[Ika]

Originally posted by: 91TTZ

Originally posted by: Aflac

Joe: how long do you plan on having it on? A couple hours will almost undoubtedly do no harm, but if you have some free time, see if you can get the resistance numbers

Undoubtedly do no harm? Have you every seen the current draw curve of an LED? It doesn't work like a light bulb.

I'm assuming there's some sort of resistor contraption in the LED of a Christmas light; otherwise, wouldn't it burn up while strung up in the light? Or is there something I'm missing?

And, to get it over with now, I'll say it: I really don't know that much about electronics. What I said is basically what I thought I learned, and assumptions that I'm making. You should probably bring a spare 9V battery or something, just in case

 

[Rubycon]

Originally posted by: mugs
You could get one of those big-ass 6V lantern batteries. They probably have a lot of juice in them.

Originally posted by: Heisenberg
A long time. I made a simple blinking LED circuit when I was a kid and the thing ran for months off a single AA battery.

Yeah that makes sense... I guess a normal LED uses a lot less energy than one of the bright ones they use in flashlights

Sounds like an LM3909. They will flash an LED with a single capacitor, one BRIGHT flash per second for well over 3000 hours on an AA alkaline battery. Good flasher for dummy alarm panels. Remember when optical mice were state of the art? Logitech used them in their retail packaging to get attention.

 

[91TTZ]

Originally posted by: Aflac

Originally posted by: 91TTZ

Originally posted by: Aflac

Joe: how long do you plan on having it on? A couple hours will almost undoubtedly do no harm, but if you have some free time, see if you can get the resistance numbers

Undoubtedly do no harm? Have you every seen the current draw curve of an LED? It doesn't work like a light bulb.

I'm assuming there's some sort of resistor contraption in the LED of a Christmas light; otherwise, wouldn't it burn up while strung up in the light? Or is there something I'm missing?

And, to get it over with now, I'll say it: I really don't know that much about electronics. What I said is basically what I thought I learned, and assumptions that I'm making. You should probably bring a spare 9V battery or something, just in case

LEDs are strange. With a normal light bulb, the current draw increases gradually with voltage. But with an LED, it stays off until a certain voltage is reached, then the current draw increases drastically over the next few tenths of a volt.

Check out this graph that shows the LED's current draw:

graph

 

[Rubycon]

Originally posted by: 91TTZ

LEDs are strange. With a normal light bulb, the current draw increases gradually with voltage. But with an LED, it stays off until a certain voltage is reached, then the current draw increases drastically over the next few tenths of a volt.

Check out this graph that shows the LED's current draw:

graph

That's a forward bias - after all it's a diode.

Laser diodes have a true hockeystick curve when it comes to point of threshold and coherent output increase with increase of forward current.

 

[91TTZ]

Originally posted by: MS Dawn

Originally posted by: 91TTZ

LEDs are strange. With a normal light bulb, the current draw increases gradually with voltage. But with an LED, it stays off until a certain voltage is reached, then the current draw increases drastically over the next few tenths of a volt.

Check out this graph that shows the LED's current draw:

graph

That's a forward bias - after all it's a diode.

Laser diodes have a true hockeystick curve when it comes to point of threshold and coherent output increase with increase of forward current.

But it's magical- it's a diode that *glows*.

 

[Ika]

Originally posted by: 91TTZ
But it's magical- it's a diode that *glows*.

So, what's your verdict on the battery life of OP's contraption?