I'm working on a project that powers 20 LEDs with a 9 volt battery. What gauge of wire should I use?
A couple of LEDs are in series with a 180 ohm resistor. Then each pair are in parallel.
Wire for project with 9 volt battery
batteriesled
Related Solutions
Here is how you can wire your LEDs. The resistors used are 150 ohms and 1/4 watt. This is assuming that you have 20 ma flowing through each LED.
Wiring Diagram:
LED Polarity:
It's good to hear about family projects :)
I'm not sure I understand your description of the circuit topology. I'm assuming that for each 9V battery, he will have four strings of LEDs in parallel to each other, and that each string consists of three LEDs wired in series. Is this correct?
First, you have to add up the Forward Voltages of each string, and make sure the total is lower than your power source (9V). If there are any string that total more than 8.5V (or so), you'll need to arrange them in a different way.
Then, you need to figure out your desired current for each string of three LEDs. The datasheets will show what the acceptable Forward Current levels are. Since all three LEDs are in series, they each flow the same current. So you want to limit this current to lowest-current LED. Since each LED in a string is carrying the same current, it won't matter which order you put them in.
Now, for each string, add up the forward voltages, then divide that sum by your desired current. This will give you an initial resistance value. It's wise to use a larger resistor that you calculated, and then decide if you want to lower it later by measuring the actual current with a multimeter.
You should use one resistor per string of LEDs. Their forward voltages aren't going to match exactly. If you use only one resistor, and you get a large enough mismatch between strings, then you could burn one of them up.
Regarding the switch, it won't effect the performance of the LEDs. It will cause the battery to drain a bit faster. Basically, the switch is adding one more LED and a resistor in parallel to your circuit.
And finally, regarding battery life, that really depends on your LEDs. Lets assume you drive them at 20mA. If you have four strings in parallel, this will take 80mA all together. A typical 9V battery has around 500mA-hours of capacity. Divide 500mA-h by 80mA, and you get over six hours :)
I hope this helps!
Best Answer
Most of the top results of a search for "AWG wire current" reference the Handbook of Electronic Tables and Formulas, each giving the same numbers, presumably copied from the print edition. If you use a different piece of wire from the battery to each R-LED-LED string, and if R=180 ohms and LED drops 3V each, that leaves resistor current I = (9-3-3V)/180ohm = 33.3mA per string. Ten of these strings in parallel (for 20 LEDs total) gives 333mA total from the battery.
The table offers a spec for 30 AWG of 142mA "Maximum amps for power transmission" which "uses the 700 circular mils per amp rule, which is very very conservative." Meanwhile Wikipedia gives a fusing current for 30 AWG copper wire as 10A for 30 seconds. A 9V battery will not be able to source anything remotely like 10A, so melting the wire is a non-issue. You could probably get away with 30AWG if it's all you have, or want a thin wire bundle for some reason. Anything thicker would remove doubt about current carrying capacity and 26 AWG with table spec of 361mA max would already be above your total expected current.
Whether a 9V battery could actually deliver 330mA for a reasonable length of time is another matter. There is wide variation in chemistry, construction, and thus capacity available. Wikipedia says a lithium model has typical capacity of 1200mAh, giving you perhaps 3 hours runtime. Lithium 9V will run $5-10 each at retail, which may be more expensive than you had in mind. Alkaline will cost less, $3 each at retail, but also have less than half the capacity and also less current capability. An Energizer or Duracell alkaline might only give 1 hour runtime, and a cheapo model with low current capability might be lucky to light it up at all. If you want longer runtime, you'll need a physically larger battery which can store more energy.