Hello!

I came across this old article in need of help which helped me understand somewhat how to solve my problem!

https://forum.allaboutcircuits.com/threads/wiring-multiple-leds-to-one-12v-dc-power-source.52820/

I understand the whole, voltage is consumed, so for a forward voltage of 2.5, with 7.5v running in you can essentially have a max of 3 LED's in a row.

But what if I had 30 LED's in a row? Do I need a 75v+ PSU?? Im a little concerned.

Im trying to make a little project, its very simple, its 3 series in parallel, but each series has a different number of RED LED bulbs.

The red led's have a forward voltage of "DC 1.8V - 2.4V " according to the amazon listing, theres not really much more information than that..

In series 1 I have 39 red LED's in a series,

In series 2 I have 24 red LED's in a series,

in series 3 I have 12 red LED's in a series.

So I need atleast 39x forward voltage of 2.5, plus a little extra so that I can have a resistor, then Ill need 3 different resistors for each series?

I dont really know what criteria im trying to meet for my power supply when it comes to watts, amps and voltage?

Would appreciate any help in this matter x)

 

But what if I had 30 LED's in a row? Do I need a 75v+ PSU?? Im a little concerned.

Yes, your understanding is right.

The voltage required will depend on the number of LED's in series.

 

Sounds like what you are trying to do is impractical.

Voltage isnt consumed either. Resistance causes voltage drops.

Without knowing what you are trying to do, and instead assuming you just want to light some stuff up. Make 3 circuits, and parallel all the LED's, with each LED having its own resistor. LED light strips are done this way I believe.

Why must the LED's be in series?

 

You need to verify the voltage drops. Then you need to determine the amount of current that supplies the brightness needed. Then total power. You have not mentioned the application. If you go the series route.....one defect/open.....will cause that whole branch to go down. The advantage is that the same current can light many LEDs. You could use low voltage supply....parallel route.....if you have enough current.......to supply many separate LED currents.

All depends on what you're doing and what resources you have.

 

Hello!

I came across this old article in need of help which helped me understand somewhat how to solve my problem!

https://forum.allaboutcircuits.com/threads/wiring-multiple-leds-to-one-12v-dc-power-source.52820/

I understand the whole, voltage is consumed, so for a forward voltage of 2.5, with 7.5v running in you can essentially have a max of 3 LED's in a row.

But what if I had 30 LED's in a row? Do I need a 75v+ PSU?? Im a little concerned.

Im trying to make a little project, its very simple, its 3 series in parallel, but each series has a different number of RED LED bulbs.

The red led's have a forward voltage of "DC 1.8V - 2.4V " according to the amazon listing, theres not really much more information than that..

In series 1 I have 39 red LED's in a series,

In series 2 I have 24 red LED's in a series,

in series 3 I have 12 red LED's in a series.

So I need atleast 39x forward voltage of 2.5, plus a little extra so that I can have a resistor, then Ill need 3 different resistors for each series?

I dont really know what criteria im trying to meet for my power supply when it comes to watts, amps and voltage?

Would appreciate any help in this matter x)

What is the basic problem you are trying to solve? Light up a bunch of LEDs? What is the reason, if any, that you have to have 39 LEDs in series? Why can't those LEDs be in, say, 3 parallel strings with each 13 in series? Or 13 strings in parallel each with 3 in series.

What kind of current do you need in each LED? How accurate do you want it to be?

Let's run some numbers with 39 of them in series and see what you are looking at. Let's say that you want 20 mA within 20%, so no less than 16 mA and no more than 24 mA. The forward voltage of each LED is between 1.8 V and 2.4 V. So, assuming a exact resistor value (let's say that 1% is "exact" as far as we're concerned, at least for now) and an exact supply voltage (at least for now), what would both have to be?

If all of the LEDs were 1.8 V, then you'd drop 70.2 V across them. This is the end of the tolerance that would give you the most current and it would be no more than 22 mA.

(Vs - 70.2 V)/R = 24 mA

On the other end, if they were all 2.4 V, then you'd drop 93.6 V. This would give you the lowest current and it would be

(Vs - 93.6 V)/R = 16 mA

Solve this for Vs and you find that the minimum supply voltage in order to get within 20% of your target current is just over 140 V. With three strings each drawing 20 mA from such a source, you will be delivering 8 W. Most of that will be being dumped in the current limiting resistors since your LEDs are only going to be needing about 3 W.

This may well work out just fine for you. Or, depending on what you are trying to actually do, there may be much better ways.

 

Wow thank you for your interest and help! Sorry if I'm slow to reply I've had flu all week and now on Xmas eve joy!

So I'm a beginner with led projects and electronics in general, ive only once built 3 x 8 x 8 red 5mm led matrix and powered them off a pcb that were daisy chained and attached to an arduino nano, this is what confuses me. If the max I can have is 5, then how the hell was I managing to light 3 x 8 x 8 grid of red Leds with an arduino nano plugged into a USB 2.0?? How is this possible?

My current project is very simple and it's just for a little new year present for someone.. I figured I could make it if I could do my matrix but now im confused.

Basically I have a wooden shape, around the perimeter I have 40 LEDs and then about an inch inward the same shape, contracted down this time 25 LEDs and finally 12 more. Imagine a circle for example with 2 smaller circles inside and you put LEDs around the perimeter of each.

I want simply to be able to just light and control each perimeter separately from my arduino. Literally light them separately. That's why I was saying a string. Because I figured if I wanted to light from the start to the end of the perimeter slowly not instantly light them all they have to ideally be part of the same Line. I'm not amazing with arduino I just followed a guide so I didn't want to get into a complex problem.

Then ideally I want to power them from a simple little adapter that I can plug in a wall. Treat it like a little LED light. But im a) confused about how I should be setting my LEDs up with my arduino in terms of series vs parallel and b) kinda scared of using a small power supply. I dont want to break the light or create an unsafe little lamp thst would potentially go on fire or something.

Thanks so much for any help, I really appreciate it.

And have a great Christmas if I dont hear back from you before then!!

 

if I wanted to light from the start to the end of the perimeter slowly not instantly light them all

For that, each LED (or small group) would need to be individually controlled. That rules out a string of many LEDs in series.

 

Wow thank you for your interest and help! Sorry if I'm slow to reply I've had flu all week and now on Xmas eve joy!

So I'm a beginner with led projects and electronics in general, ive only once built 3 x 8 x 8 red 5mm led matrix and powered them off a pcb that were daisy chained and attached to an arduino nano, this is what confuses me. If the max I can have is 5, then how the hell was I managing to light 3 x 8 x 8 grid of red Leds with an arduino nano plugged into a USB 2.0?? How is this possible?

The LEDs are multiplexed so that each one is controlled by a combination of outputs. There are many ways to do this, so without seeing the schematic it is impossible to tell. If we knew how many pins of the Arduino went to the matrix, we might be able to guess. Also, if there are any other chips between them. Again, seeing the schematic is the best way to tell.

[/QUOTE]
My current project is very simple and it's just for a little new year present for someone.. I figured I could make it if I could do my matrix but now im confused.

Basically I have a wooden shape, around the perimeter I have 40 LEDs and then about an inch inward the same shape, contracted down this time 25 LEDs and finally 12 more. Imagine a circle for example with 2 smaller circles inside and you put LEDs around the perimeter of each.

I want simply to be able to just light and control each perimeter separately from my arduino.
[/QUOTE]

This wouldn't be hard at all, at least conceptually. Figure out how many LEDs you can run from your supply -- probably only one or two. Let's assume two. So you make strings of two LEDs and a resistor. Then you connect all of the ones you want on at the same time to a single transistor that is controlled like a switch from the Arduino.

Literally light them separately. That's why I was saying a string. Because I figured if I wanted to light from the start to the end of the perimeter slowly not instantly light them all they have to ideally be part of the same Line. I'm not amazing with arduino I just followed a guide so I didn't want to get into a complex problem.

Any time you have an LED that behaves differently in any way from another LED, then there has to be a way of controlling it separately. That makes things more complex. Yes, you could treat them like your cube matrix from a schematic standpoint, the problem is the that the cube structure lends itself to the physical wiring associated with the multiplexing and that becomes a lot more difficult when you want to position the LEDs in a different pattern. Not impossible, just a lot more difficult.

 

I understand yeah about doing them individually.

How about just keeping each perimeter seperate and being able to light them instantly but separately then on the arduino being able to code to light each perimeter separately?

This is much more simple?

Merry Christmas all!!! Hope you have a fantastic day!

 

Yes, this is much more simple. You only need to control three pins, with each one turning on the respective perimeter.

 

I understand yeah about doing them individually.

How about just keeping each perimeter seperate and being able to light them instantly but separately then on the arduino being able to code to light each perimeter separately?

This is much more simple?

Merry Christmas all!!! Hope you have a fantastic day!

Yes Yes,
I attached a schematic of how I would do this. This site has some excellent information under the education tab above with respect to using transistors as switches.
Each perimeter consists of an array of LEDs in parallel.
Your concern over power consumption is well founded. Assuming only 10ma per LED and all LED's on at once, you have 780ma, which is far too much for a USB connection.
You can put them in series pairs, assuming the Vfwd of your LED's allows which could almost half the power requirements, but this can bring its own issues. Problems with this are Vfwd isnt a static number, it changes with temperature and current, so your resistor calculations might not be very accurate, and you may end up burning up the LED's or the transistors, or your USB power supply, or all 3. I wouldn't trust it. At 12 volts, maybe, but at the low resistances you would be working with, where a .1v difference in Vfwd would make a huge difference in current, No.
I think you need a secondary power supply. Or use fewer lights.