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What color LEDs? If you're talking about three white LEDs, you're right, it won't work. Three of any other color would work with the appropriate current limiting resistor. You ARE using a resistor, right? But if you want to power ten LEDs, with a 9V, white or otherwise, you're going to need a series-parallel combination. Five branches of two LEDs each would probably be best. EACH BRANCH WILL NEED ITS OWN current limiting resistor because LEDs in parallel without a resistor will not share current properly.
Of course, the whole topic is really moot, because when you figure out how fast 10 leds kill a 9V battery, you won't want to do it.
it's actually not enough current to support all the white leds. why? cause white leds now are ultra bright and that takes a lot of current. try to design a circuit that can provide more current or use other alternatives other than battery. hope that helps.
u can't possible use 2 battery in series in that particular circuit or maybe u need to hook it up in parallel? so that the load can be parallel. so it would equally share the load of the leds. not necessery that you have red leds that u have low current consumption. maybe the led is a ultra bright version. ok? i don't know the full spec of your led. try battery in parallel or try those dc adapter where you have a battery outlet. maybe it should work with the dc adapter cause it can supply up to 500mA or 1A. depend on what you bought.
Batteries in parallel gives more current capacity. Batteries in series gives more voltage.
I don't know what you're trying to do with 10 red leds, sort of a weird flashlight, but the path you're on may be good for learning, but not much else. As battery voltage decreases, the LED brightness will too. What you really need is a current source. And a single 9V battery will not last long.
High efficiency/brightness doesn't necessarily mean it needs more current, just that it will give more illumination for a given current.
I put HE LEDs in low power designs, if I have to, drawing only microamps. It won't light up the room, but you'll know it's on.
So this is sounding like a bad idea. I guess my only two option are either adding a second 9v battery, or going with 4 AA batteries. Will I have to wire them in a series-parallel combination even with the extra battery/AA batteries, or would the LEDs in series be good then?
To make 10 LEDs blink based on a 555 timer and a push/pull pot. You can adjust how fast they blink, or if they just stay on. The whole point of doing this is just for show.
hmm.... but i saw the datasheets for some of the high efficiency led. they do consume a bit more current than the normal led. i don't know technologies in other countries cause malaysia is kinda slow in adapting electronics. maybe the led that i bought is already kinda backward thing? maybe manufacturers came up with lower current consumption led? i really don't know.
u can't possible use 2 battery in series in that particular circuit or maybe u need to hook it up in parallel? so that the load can be parallel. so it would equally share the load of the leds. not necessery that you have red leds that u have low current consumption. maybe the led is a ultra bright version. ok? i don't know the full spec of your led. try battery in parallel or try those dc adapter where you have a battery outlet. maybe it should work with the dc adapter cause it can supply up to 500mA or 1A. depend on what you bought.
It is not good practice to connect batteries in parallel since you cannot ensure that they will share the load equally. One may be contributing say 50 mA and the other 68 mA.
Similarily, it is not wise to connect diodes in parallel since they may not share the current equally, eg. two one amp diodes in parallel do not make a 2 amp diode.
I may have misled you. LEDs in parallel are acceptable if there is a resistor in series, see the diagram posted by John Sorensen on Mar 19.
Others have commented on the battery configuration. Two 9 V in series would be workable as you could connect 5 LEDs in series (and a series resistor) in parallel with a similar combination. 4 AA would also be better since there would be less energy wasted in the resistors. But it would be more suspectable to battery voltage, ie. as the battery ages, the LEDs will start going dim sooner than with 2 X 9 V.
Others have commented on 2 9v batteries, but no one ever said if 4 AAs would be better. If it doesn't matter since they both have downsides, I will go with 2 9v because it's easy to get the battery box for them, and I already have the one.
For the LEDs, should I wire them like John's design, but with 2 rows of 5 instead of 3 rows of 3? Would I still use 220 resisters?
I was thinking, and I may be wrong, but with 2 rows of 5 and 2 batteries, isn't this essentially 1 battery with 5 LEDs in series? The on battery had a hard time powering 3 LEDs before.
My earlier response re 4 AA was wrong, I was thinking it would be 12 Volt, but is is only 6 Volt.
sjaguar13 said:
I was thinking, and I may be wrong, but with 2 rows of 5 and 2 batteries, isn't this essentially 1 battery with 5 LEDs in series? The on battery had a hard time powering 3 LEDs before.
No, two 9 Volt batteries in series gives you 18 Volt. 5 LEDs is series will require about 9 Volt assuming they are red, so 9 Volt is dropped across the resistor. So a resistor of 680 Ohm would givve a LED current of about 13 mA or 26 mA for two LED strings.
I don't know why a 9 Volt battery could not power 3 LEDs in series. What series resistor did you use?
There's no reason to use two 9V. In series there would be more power wasted and you'd be right at the absolute maximum voltage for the 555 (above it with fresh batteries). In parallel, well, what's the point?
As for the 555, that should be good to go. It can "sink" puh-lenty (plenty) of current. I would use 5 parallel branches of two LEDs and a 330 ohm resistor in each branch. Tie all the branches together at the top and bottom. The top (the anode side) goes to Vcc (+V) and the bottom goes to the output of the 555 (pin 3). The total current sunk will be about 45mA and the whole circuit will draw between about 55 and 60mA while the LEDs are on (pin 3 low). Depending on the duty cycle, a 9V battery should last in this circuit for about 1 to 4 hours. If this is a full time show, consider a wall-wart or you'll go bankrupt keeping it in cells.
Now I'm getting more confused. I was using a 330 resistor to power the LEDs and it stopped after 2. 1 was fine, 2 was really dim, and 3 was nothing.
I heard 4 AA batteries how more milliamps, so they would be better to power LEDs. Using some equation thing I found, I would need 20 volts for my LEDs. That's where I came up with the 2 9v batteries (I'm still 2 volts low, though).
I was talking to some other people who really don't know, either, but they said that LEDs require very low power and it shouldn't be hard to get them to at least be able to stay on for 24 hours, if not a week. Is this completely not ture? I would like to get 4 hours out of them.
So I should just stick to the 9v I got, but wire the LEDs in 5 pairs instead of all in series?
Now I'm getting more confused. I was using a 330 resistor to power the LEDs and it stopped after 2. 1 was fine, 2 was really dim, and 3 was nothing.
I heard 4 AA batteries how more milliamps, so they would be better to power LEDs. Using some equation thing I found, I would need 20 volts for my LEDs. That's where I came up with the 2 9v batteries (I'm still 2 volts low, though).
I was talking to some other people who really don't know, either, but they said that LEDs require very low power and it shouldn't be hard to get them to at least be able to stay on for 24 hours, if not a week. Is this completely not ture? I would like to get 4 hours out of them.
So I should just stick to the 9v I got, but wire the LEDs in 5 pairs instead of all in series?
I don't know why 3 red LEDs in series with a 330 Ohm resistor would not work on 9 Volt. The current should have been about 10 mA which is more than adequate. Was the battery fresh?
For 9 Volt, you would need 6 AA batteries.
For 10 LEDs you could connect them in 2 pairs of 3 and 2 pairs of 2.
The resistor for the 2 LEDs would need to be 560 Ohm to give 10 mA and use a 330 Ohm for the 3 LED strings.
This will require about 40 mA, so for a 24 Hour operation you would need a battery with at least 1000 mAH capacity. The 9 Volt batteries only have about 110 mAH capacity.
6 AA batteries with 1200 mAH capacity would be a solution.
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