wiring LEDs to 9v or 6v battery

[glamiskid395]

as the title says, i need to know how to wire 10 LEDs together to be powered by one 9v battery or a 6v rechargeable battery pack.

what would be the best way to go for a battery for 10 LEDs? 9v or 6v?

i would also like to know how to wire 2 LEDs to a 9v battery.

THANKS

if you would like to know what i am trying to do, im making a light setup for my RC truck (team Losi LST)

[glamiskid395]

does anybody know how to do this?
do i need resistors?

BUMp


thanks

[pro-rider46]

i might be able to help ya, well you can check out ebay, they have some really bright leds that are prewired for 6-15v, if you have just leds with no resistors, you will need to soder some in, and along with wires, do you have the leds already?, if you do, find out how many volts they require(normally says on the package) and then somebody can tell ya what kind of resistors you will need, why are you running this on their own circuit? if you putting these on a truck it will be easy to run it off of itself, and you will not notice any power drainage because these things use like a few milli amps i think. but if you want to run these through the truck take a positive wire from the battery teminal through a fuse, the through a switch, and then finally to the led, and then ground it to the frame of the truck, and you will have a complete circuit and will not worry about having to replace or recharge batterys, and you can mount your switch in the dash, and some come with leds and look even more trick. any questions?

[pro-rider46]

also if you want contact wilkin250r on this stuff, he is extremely good with this, he is a electrical engineer i think, but he can tell what kind of resistors you would need for just about anything probably.

[glamiskid395]

ok thanks
this is going on a RC truck not full size truck
im pretty sure on the size of the resistor but would want a for sure from someone who knows.
i'll contact wilkin250r and ask him about this.

[pro-rider46]

oh. sorry, i thought this was a full size, doesnt it allready have a battery? you could just do it throught that

[wilkin250r]

Really, it doesn't matter which you use, 6V or 9V. Use whichever is easiest for you.

One LED is really simple. 10 LEDs is a little more complex, but certainly not "difficult".

LEDs come in several different styles, sizes, and colors. But they ALL will have two very important characteristics. A voltage rating (or voltage drop), and a current rating. Voltage will change based on size and color, but the current rating is almost always right around 20 milliamps (which is 0.020 amps). This current rating is a max, and cannot be exceeded.

They will require a little bit of calculation. It's unavoidable. First, we will go over the calculation for a single LED, and then learn how to chain them together.

[wilkin250r]

Ok, so on to calculations.

It's called a voltage "drop" for a reason. It drops the voltage. So for the calculations, you want to subtract this voltage drop from your supply voltage.

If you are using a 9V battery for supply, and an LED with a 2.1V drop, you get a very simple: 9V - 2.1V = 6.9V

This 6.9V is your leftover voltage.

Now, you need to find a resistor that will limit this leftover voltage to some value UNDER your maximum current rating. Current equals voltage divided by resistance.

A common resistor is 330 ohms. 6.9V divided by 330 ohms is 0.021 amps. Just a little high. So you need a larger resistor. The next size up is 360 ohms.

6.9V/360 = 0.019 amps. Perfect. Maximum brightness, but not over our limit.

[wilkin250r]

So, that was for a single LED. If you connect two of them together, you simply get twice the voltage drop.

9V - 2.1V - 2.1V = 4.8V


Now, limit the current on this leftover 4.8V.


4.8V divided by 270 ohms is 0.017 amps. Close enough. Notice that you use a smaller resistor value. More voltage drop means a smaller leftover voltage. You need a smaller resistor to limit the current.



Now, there is a limit to how far you can take this. Obviously, your voltage drop cannot exceed your supply voltage. You can't connect a 9V supply to 12V worth of LEDs.

In fact, you can't even come close. You couldn't use four 2.1V LEDs (8.4V drop total) on a 9V supply. It's too close, it will be really unstable. You might burn them all out, or it might not light at all. You need at least 1.5V left over.

[pro-rider46]

hey wilkin, can you explain how you calculated the volts divided by the ohms to get the amps.

[wilkin250r]

Now, this is where you are asking "But that limits me to only about two or three LEDs. How do I hook up 10 of them?!?"


The rules above apply for a single string of LEDs. You can connect several strings in parallel to get as many LEDs and your supply voltage can handle.


The key word is PARALLEL.

[wilkin250r]

Originally posted by pro-rider46
hey wilkin, can you explain how you calculated the volts divided by the ohms to get the amps.


I'm sure you know how to use a calculator, and you know what a division symbol looks like, so the MATH part can't possibly be your question.

What part are you confused about? The terminology (volts and ohms?) How I calculated the current rating?

Or are you confused where the equation comes from? (why did I divide volts by ohms, and not the other way around?)

[MOFO]

Originally posted by pro-rider46
hey wilkin, can you explain how you calculated the volts divided by the ohms to get the amps.



Ohms Law.

V=Voltage
I=Current
R=Resistance (Resistor)

V=I*R <----- Ohms Law

You can change the formula around, but make sure you follow basic mathematical rules on how you solve for other variables.

[glamiskid395]

wow, i'm gonna have to check out the LEDs that im planning on buying, then figure everything out.

your explanations help out a lot. everything else i was reading did help much.

heres the spechs on each color:
blue:
Characteristic: 3 mm
- Forward Voltage: 2.8 - 3.3 Volts
- Forward Current (max.): 30 mA
- Lifetime: 100,000 Hours
- Viewing Angle: 25 Degree
- Typical Wave Length: 472 nm
- Luminous Intensity: 2500 mcd


Characteristics 5mm: WHITE GREEN
- Forward Voltage: 3.0 - 3.3 Volts 1.8 - 2.1
- Forward Current (max.): 30 mA 30 mA
- Lifetime: 100,000 Hours 100,000
- Viewing Angle: 20 Degree 20 Degree
- Typical Wave Length: X:0.28 , Y:0.28 522 nm
- Luminous Intensity: 5000 mcd 10000 mcd


Characteristic 5mm: RED yellow
- Forward Voltage: 1.8 - 2.2 Volts
- Forward Current (max.): 30 mA
- Lifetime: 100,000 Hours
- Viewing Angle: 20 Degree
- Typical Wave Length: 660 nm
- Luminous Intensity: 2500 mcd


setup is 4 white, 2 blue, 2 red, 9 volt battery.

for the 2 green i will just be using a AA battery.


the battery in the truck is a 6 volt but that runs the reciever and radios, and i dont need lights draining that, and risk the truck running away at full throttle and blowing up the engine!!