Instructables

Step 8: Wiring up multiple LEDs in parallel

Unlike LEDs that are wired in series, LEDs wired in parallel use one wire to connect all the positive electrodes of the LEDs your using to the positive wire of the power supply and use another wire to connect all the negative electrodes of the LEDs your using to the negative wire of the power supply. Wiring things in parallel has some distinct advantages over wiring things in series.

If you wire a whole bunch of LEDs in parallel rather than dividing the power supplied to them between them, they all share it. So, a 12V battery wired to four 3V LEDs in series would distribute 3V to each of the LEDs. But that same 12V battery wired to four 3V LEDs in parallel would deliver the full 12V to each LED - enough to burn out the LEDs for sure!

Wiring LEDs in parallel allows many LEDs to share just one low voltage power supply. We could take those same four 3V LEDs and wire them in parallel to a smaller power supply, say two AA batteries putting out a total of 3V and each of the LEDs would get the 3V they need.

In short, wiring in series divides the total power supply between the LEDs. Wiring them in parallel means that each LED will receive the total voltage that the power supply is outputting.

And finally, just some warnings...wiring in parallel drains your power supply faster than wiring things in series because they end up drawing more current from the power supply. It also only works if all the LEDs you are using have exactly the same power specifications. Do NOT mix and match different types/colors of LEDs when wiring in parallel.

OK, now onto to actually doing the thing.

I decided to do two different parallel setups.

The first one I tried was as simple as it could be - just two 1.7V LEDs wired in parallel to a single 1.5V AA battery. I connected the two positive electrodes on the LEDs to the positive wire coming from the battery and connected the two negative electrodes on the LEDs to the negative wire coming from the battery. The 1.7V LEDs didn't require a resistor because the 1.5V coming from the battery was enough to light the LED, but not more than the LEDs voltage - so there was no risk of burning it out. (This set up is not pictured)

Both of the 1.7V LEDs were lit by the 1.5V power supply, but remember, the were drawing more current from the battery and would thus make the battery drain faster. If there were more LEDs connected to the battery, they would draw even more current from the battery and drain it even faster.

For the second setup, I decided to put everything I had learned together and wire the two LEDs in parallel to my 9V power supply - certainly too much juice for the LEDs alone so I would have to use a resistor for sure.

To figure out what value I should use I went back to the trusty formula - but since they were wired in parallel there is a slight change to the formula when it comes to the current - I.

R = (V1 - V2) / I

where:
V1 = supply voltage
V2 = LED voltage
I = LED current (we had been using 20 mA in our other calculations but since wiring LEDs in parallel draws more current I had to multiply the current that one LED draws by the total number of LEDs I was using. 20 mA x 2 = 40 mA, or .04A.

And my values for the formula this time were:

R = (9V - 1.7V) / .04A
R = 182.5 Ohms

Again, since the variety pack didn't come with that exact value resistor I attempted to use the two 100 Ohm resistors bundled together in series to make 200 Ohms of resistance. I ended up just repeating the mistake that I made in the last step again though, and wired them together in parallel by mistake and so the two 100 Ohm resistors only ended up providing 50 Ohms of resistance. Again, these LEDs were particularly forgiving of my mistake - and now I have learned a valuable lesson about wiring resistors in series and in parallel.

One last note about wiring LEDs in parallel - while I put my resistor in front of both LEDs it is recommended that you put a resistor in front of each LED. This is the safer better way to wire LEDs in parallel with resistors - and also ensures that you don't make the mistake that I did accidentally.

The 1.7V LEDs connected to the 9V battery lit up - and my small adventure into LED land was completed.
 
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AliS21 month ago

Thanks for this guide, very useful. I'm having an issue in following something, though - ended up burning out a couple of LEDs presumably due to a mistake I'm making.

I've got a 9v battery power source, trying to drive two blue LEDs (3.4-3.8v rated, 20mA) in parallel. I calculated necessary resistor as R = (9 - 3.4) / 0.04 = 140 ohms; to be on the safe side, I used a 180 ohm resistor (brown/gray/brown/gold) in series (battery + to resistor; resistor - to + pole/anode of both LEDs; - pold/cathode of both LEDs back to battery) on a breadboard. Upon connecting the 9V battery the first time, circuit lit; on 2nd time, it then stopped and I smelled distinct LED burnout - after which both LEDs would no longer light, even when connected individually to a 3v (2x AA) source.

Would appreciate any advise re: what I'm doing wrong. Thank you!

BobyF3 months ago

I have one of those a newer one with a led display, I have been powering a 50w smd bead with nothing but a 24v in and a 32v out. Just make sure your input amp. is rated for the beads. Now since you are wiring it in a series be very careful with your v and amp. make sure it`s outputing a constant 3v and slowly bring it up to 3.3v the chinese buck converters will drop in voltage if the supplied amps are not enough. Also when led`s do that it means either too many volts or amps. check your resistors and see if they are smelly, kind of like a burnt carbon smell. Try adding a

DenisĐ3 months ago

HI!

I see that this topic is little bit old

But knowledge cant get old :)

my question is: what do i need for connecting few leds in parallel, on my "old" USB lamp(i want to use only housing of this lamp).

Becouase on USB power limit, parallel connection is logical way, or?

I think some kind of step down module is needed that drops 5v to desired 3-3.3v that is needed for led's, for ex.

http://www.ebay.com/itm/1PCS-Output-1-25V-35V-DC-D..

Power souce is wall socket->USB 5v 1A,

led's are 5730 3-3.3v 150mA,

or 1W beads 3-3.6v 300-350mA.

Is it ok to connect 6 of 5730 led's, and/or 3 of 1W led's in parallel?

Is there something else needed for make this working?

P.S. this "old" usb lamp has 13 led's(those small ones) and each has resistor in front, but after short time they start to rapidly blinking and at the end stop working. What that mean, led's are dead, or resistors are not ok, or what?

tnx, and sorry for a little long post :)

Denis

i have a big problem i think ull solve it perfect.
i had connected 50 leds parallel to 6 volt battery its working without any problem for 5 hours, i didnt use resisters is there any problems
this has been discussed all over the web. The more leds you use in parallel the less resistance (resistor) is needed before the voltage source. if you used one led and a voltage source of 6volts it will get hot and eventually pop. you can acutally buy led holiday lights from stores that will have hundreds in series or parallel. If you plug it into the wall it will work just fine but if you take one of the leds out of the circuit and plug it into the wall it will pop in no time. I am not onehundred percent sure if what I am saying is correct but I have read it on multiple threads, i have never tested it out.
You should put a resistor in series with each LED as any vdrop differences will result in uneven sharing of the current. (especially as the LEDs age).

techguy561 year ago
In seeing this "article" on wiring multiple led-s, I am seeing 2 resistors in series and 2 led's in parallel. Is that Really the way you wire multiple led's? I was under the impression that while wiring led's together.. in parallel, you have one resistor on each led to keep the led safe.
Hi B5,

I attempted to light up two High power LEDs which connected in series. here are the specs:
. each LED: 2.2 volt 350mA
. power supply: 4.2 volt 500mA

when connected, I see an extreme current drop from 350mA to 60mA!!

COULD YOU PLEASE HELP ME TO IDENTIFY THE CAUSE?
Much regards,
babylonfive7 years ago
The two big reasons why you place a resistor in series with each LED are: - safety - so that if one LED burns out (becomes an open) the remaining LED would use twice the current (overcurrent) and then fail as well - so that the current and brightness will be somewhat equalized Imagine a situation with two LEDs of the same type but a sightly different forward voltage at the specific current - or think of it really as a curve of current over forward voltage. Then, because one LED uses more current for the same forward voltage, it's brighter... sometimes by a lot. Finally, when the battery voltage falls, the higher forward voltage LED winks out. David
LEDcurve.jpg
Hi B5,

Just thinking of improvising, using an existing setup, bicycle leds, already in groups of 5, to string a few together, (typically power is via 4 1.2 - 1.5 v batteries) and the chip connection would be cut (no need for flashing function) not sure if smt resistor/s exist in the globule. LEDs look like superbrights possibly 3.2-3.4V at 20 mA. Using 6v source. Would one use one resistor per set or unsolder and include one per led.?

Cheers
What's a 'bicycle' LED? Are they in series or parallel?
Hey, so I don't know what 'bicycle LEDs' are...

I assume from your knowledge that these are five LEDs in series with each other, providing the same ganged 3.2-3.4V drop but five times the light for five times the current - about 100mA total.

In this case, if there are already five in parallel, then they were carefully chosen to have the same (or very close to the same) forward voltage drop, and thus will distribute the current nearly equally. If you were building your own board, the best would be to give each LED a resistor, but if they are already ganged and the LEDs are matched, just figure the single resistor:

E
R = -------
I

R = 3.4V / .1 A

R = 34 ohms (33 ohms is the 5% value)

If there's some other configuration I didn't "get", please let me know.
Hi, Just surfing looking for some help - not done electronics since school 28 years ago. Looking to link 100 leds in parralel to a 12 volt leaisure battery. this is the spec for the LED's off ebay - with them being 12v does this mean I don't need any resistors in? Also is there much heat generated looking to set them in to an MDF panel.

Thanks in anticipation

Prewired 12V LEDs

High quality LED, soldered to a resistor for 12V (including 12V automotive) use. Strong connections are neatly wrapped with heat shrink and attached to colour coded wire terminating in stripped tinned connections.
Technical Spec

High Power 3mm LEDs - 7000mcd

12V DC
Presoldered Resistor

20 mA
20 cm Wire Length
High Intensity - Low Power 0.36W

Simple to Use
Long Life and Energy Saving


So, if you use these LEDs with built-in resistors, you are golden. All the variation in voltage of the LEDs is equalized by the series resistor selected to properly drive each one. So, even multiple colors on the same bus will work as expected.

You can do it like this:

+12 ------------------------------------------------------------------
| |
R R
| | o o o as many as you like
led led
| |
gnd ------------------------------------------------------------------

Concerns:

- multiply the current per LED (shown on the specs for each LED, above you say it is .020A) times the number you want (100?) = 2A. Therefore get a power supply that can provide 12V for at least 2A (more is ok). Repeat this formula if the current is different to determine the max ps current needed.

- I wouldn't group a big pile of these RIGHT TOGETHER of in a confined space. Each dissipates .36W (almost all in the resistor), so three or four tightly together (or out of air flow) will be a watt of power, and will start getting a little hot. For this issue, a much better solution would be to create your own LED 'cluster' of series LEDs and a single resistor setting the voltage. If you created 33 sets of three LEDs on the same line with a single custom resistor value to limit to 20mA, then your power dissipation would go way down. This is because the power would go toward light instead of being boiled away in the resistor - resistors just waste!

So this:

12V+ ------- led ------- led ------- led ------- resistor ------- gnd

3.2V 3.2V 3.2V 12v-9.6=2.4V
2.4V /.020A = 120ohms
2.4V x .020A = .048W

Note this dissipates lots less in the resistor. and there are only 33 resistors instead of 100. it uses the voltage much better.

But if you can easily get air to these guys, you'll be fine.
Thanks I think I'll look at the 2nd option as these are to be enclosed in a shallow box in the roof of my camper and I don't fancy setting it on fire. Cheers
So if you add a resistor in series with each LED, does the resistor have to be the full value? So for example he used two 100ohm resistors in series above. If he did what you said, would it be a 200ohm resistor for each? My guess would be yes but I am new to this.
resistor question.JPG
No, you would use the same working configuration for a single leg or multiple legs, up to the limit of the power supply.
So: in your example above you have a 5V supply, and an LED that uses 20mA at 3V, then the voltage 'left over' across the resistor on any one leg is 2V. 2V/100ohms = .020A (20mA). Thus each leg would correctly function with a 100ohm resistor.
Each leg draws the 20mA as a separate subsystem, as it's own circuit. You should see it as if the + point in the drawing above were two independent batteries. The only limitation would be the maximum current available at the + point... remember that mA are thousandths of Amps, so a power supply rated 1A @ 5V would provide enough power for 50 LEDs... 50 x .020A (20mA) = 1A... batteries can do much better than 1A without much voltage reduction.

I hope this helps you think about this in a way that allows you work with LEDs and resistors in the future. Please reply with any questions or comments.
I'm making a color organ and each of the three panels has 100 leds on it. So what is the voltage, current, and resistor value needed to light 100 and 300 leds?
What's your desired power supply value? Do you have a 12v supply? The components wl be different for each color. Also holler back with how you are controlling the leds... Pulse width modulation? Variable voltage output? Let me know.
Thanks for your reply!

Sorry I wasn't clear. I was referring to step 8 where he used the 9V and wired the two LEDs in parallel.

R = (9V - 1.7V) / .04A
R = 182.5 Ohms

So in that case it would be a 200ohm resistor for each correct?
If you mean about 200 ohms (i.e. 180 ohms) on each leg, then yes. In fact, up to the limit the 9V battery will source, you can keep adding legs with an LED and a resistor; it'll keep adding current, and reducing battery life obviously. Two will use 80mA, 3 will use .12A etc.
It seem you know a lot about led i'm looking to go to led on my reef aquarium to save energy and money I have now metal halide total 500 watts. the heat is crazy hot and the light bill is through the roof, what would you recommend for a 60"x10" strip
So how do you wire resistors in series?
You connect the resistors end to end. So one resistor will connect to the wire to the battery, the other end will connect to the lead to another resistor, and so on. Connecting in parallel is when the leads of each resistor are connected to the wire from the battery.
jnajmy2 years ago
Thanks for the instructions, but i do not get some parts.

For my project I am going to us a 9 volt battery and have 20 LEDs and each LED has a voltage of 3.2-3.4V at 20 mA each. I want to run every LED in a parallel circuit.

How would I go about doing this? What size resistors would i need? I bought 1/4 watt resistors could i use those? or would i need to get a 1/2, 1/4, 1/8, ect.?

Also do i need to have 20 different resistors for each LED or could i just use one at the bottom of the parallel circuit?

Do I have to keep in mine about anything else? I would be using a 9 volt 1000+ mAh battery

Thank you in advance!!!
Fireson132 years ago
Can this be modified to flash?
arduinoer4 years ago
If you wired a car battery to any amount to leds, it would burn it out. I car battery has hundreds of amps. Leds take .08 amps
babylonfive5 years ago
One extra correction I just noticed in my original answer: If two LEDs are wired in parallel and use a single resistor, that CAN work if the resistor is sized for the combined LEDs desired current, and if the voltage drop is very close to each other (i.e. they come from the same lot of material)... this is not a horrible thing to do, and could work... it just usually doesn't work terribly well, because LEDs can easily have different drops and the orginal comment still holds... I just realized I sounded like "it won't work"... and really... it will work for a while.
However, strongly not recommended, since, as stated above, if one LED fails the others will be overdriven, so multiple parallel strands without per-strand overcurrent protection will result in a cascading failure.
bananashake4 years ago
I am wiring six 2.1V led's with 25mA each in parallel to a 11.5V power source. I am going to put a resistor on the positive leg of each individual led. What formula should I use to determine how many Ohms of resistance I need to put on each resistor of each led in this situation? Should I use (11.5-2.1) * .150=62.66 Ohms or should I find out how much resistance one 2.1V led with 25mA would use with a 11.5V power source? Ex. (11.5-2.1) * 25 ? I really don't know which formula to use, please someone help me find the answer to this question. I'm only 16 years old and I'm new to this kind of electronic stuff.
Titus_Taber5 years ago
 Just to clarify, your parallel resistance formula is a little off. For n resistors in parallel it should be 1/Req=1/R1+1/R2....+1/Rn
However just for two resistors you can do (R1 x R2)/(R1 + R2) which is why your 100/2 = 50 worked in the previous step.
oil41216 years ago
Thanks, this does help me alot.
Thanks for the explanation with concrete examples. For some reason electronics is the one part of physics I always had problems with.