Powering LED's from powerbank

Thread Starter

Semsvh

Joined Dec 20, 2023
7
Hi,
I let a fiverr freelancer design the following pcb to power some LED's from a 5V 3A powerbank. Will this work? Any tips? Thanks in advance!IMG_20231220_083744.jpgIMG_20231220_083802.jpgIMG_20231220_083724.jpg
 

jiggermole

Joined Jul 29, 2016
161
it will kind of work. Your specification on the job isn't the greatest. You specified a power bank that can supply 3A but your list of leds and their operating current adds up to 7A so your specification is failed from the start.
and unless they specified it, those are rendered as 1/4 watt resistors and they are going to be dropping way more than that. The uv ones will be dropping 0.7 watts each.
 

Thread Starter

Semsvh

Joined Dec 20, 2023
7
it will kind of work. Your specification on the job isn't the greatest. You specified a power bank that can supply 3A but your list of leds and their operating current adds up to 7A so your specification is failed from the start.
and unless they specified it, those are rendered as 1/4 watt resistors and they are going to be dropping way more than that. The uv ones will be dropping 0.7 watts each.
Thanks for your response!
The initial order was more detailed but please keep in mind im very very new to electronics . I was thinking of using the LED's in series with an voltage multiplier but hired the freelancers to help me with the design because my knowledge is not sufficient enough in electronics to design it myself. Do you have any tips to make it work that i can ask the freelancers to revise?
 

Thread Starter

Semsvh

Joined Dec 20, 2023
7
it will kind of work. Your specification on the job isn't the greatest. You specified a power bank that can supply 3A but your list of leds and their operating current adds up to 7A so your specification is failed from the start.
and unless they specified it, those are rendered as 1/4 watt resistors and they are going to be dropping way more than that. The uv ones will be dropping 0.7 watts each.
The powerbank has 2 outputs, both 5V 3A max. Will it work better if i power the pcb with the 2 ports parralel to stack the current to 6A?
 

Jerry-Hat-Trick

Joined Aug 31, 2022
552
From the selected resistor values it looks like the target current through each LED is around 500mA so you are maybe looking at a total current through eight LEDs in parallel of around 4A. Can you use two USB outputs from the powerbank, splitting the LEDs between them?

You could get back to 3.5A by putting the two blue LED's in series, maybe with a small value resistor in series but not strictly necessary. The added advantage is that you avoid dropping 2.5V across a resistor which would dissipate 1.25 Watt.

How sure are you that 500mA through each LED is the current you want? If you can live with maybe 400mA you can increase resistor values to reduce the overall current to 3.5 x 400/500 = 2.8A. With your existing design the UV resistors dissipate around 0.7 watt and the green and white resistors around 0.85 watt so even 1 watt resistors are marginal. Again, dropping to 400 mA reduces the power but 1 W resistors are still necessary. I've used four 1/4 resistors instead - two in series in parallel with another two in series, so the overall resistance is the same as the four individual resistors.

You could try a boost converter to boost the voltage. Presumably you intend this with your "voltage multiplier"? You will lose some power in the conversion, but it is possible and you'd probably win more power saving than you lose. But it adds complexity and probably cost, so if splitting between two power bank outputs or reducing overall current is acceptable I'd try that first.

EDIT: Oops, just read your last post. Personally, I wouldn't parallel up the outputs, just split the circuit into 2 x 4 LEDs. The rest of my post is still relevant I think
 

Thread Starter

Semsvh

Joined Dec 20, 2023
7
From the selected resistor values it looks like the target current through each LED is around 500mA so you are maybe looking at a total current through eight LEDs in parallel of around 4A. Can you use two USB outputs from the powerbank, splitting the LEDs between them?

You could get back to 3.5A by putting the two blue LED's in series, maybe with a small value resistor in series but not strictly necessary. The added advantage is that you avoid dropping 2.5V across a resistor which would dissipate 1.25 Watt.

How sure are you that 500mA through each LED is the current you want? If you can live with maybe 400mA you can increase resistor values to reduce the overall current to 3.5 x 400/500 = 2.8A. With your existing design the UV resistors dissipate around 0.7 watt and the green and white resistors around 0.85 watt so even 1 watt resistors are marginal. Again, dropping to 400 mA reduces the power but 1 W resistors are still necessary. I've used four 1/4 resistors instead - two in series in parallel with another two in series, so the overall resistance is the same as the four individual resistors.

You could try a boost converter to boost the voltage. Presumably you intend this with your "voltage multiplier"? You will lose some power in the conversion, but it is possible and you'd probably win more power saving than you lose. But it adds complexity and probably cost, so if splitting between two power bank outputs or reducing overall current is acceptable I'd try that first.

EDIT: Oops, just read your last post. Personally, I wouldn't parallel up the outputs, just split the circuit into 2 x 4 LEDs. The rest of my post is still relevant I think
Thanks Jerry for your excellent feedback. I will split the circuit into 2 x 4 LED's with 2 powerbank outputs .
 

Audioguru again

Joined Oct 21, 2019
6,695
Please check the datasheet for the blue LEDs. A modern blue LED has a forward voltage of 2.85V or more.
Each UV LED has three chips in series which is why the forward voltage is 3 times higher than a single UV LED.
I agree that your tiny resistors will quickly fry and maybe also your eyes.
How will you cool the LEDs?
 

Thread Starter

Semsvh

Joined Dec 20, 2023
7
Please check the datasheet for the blue LEDs. A modern blue LED has a forward voltage of 2.85V or more.
Each UV LED has three chips in series which is why the forward voltage is 3 times higher than a single UV LED.
I agree that your tiny resistors will quickly fry and maybe also your eyes.
How will you cool the LEDs?
Hi Audioguru,
I will cool the LED's with a square tube heatsink (40*40 mm), with an 40 mm electric fan.
I know the uv output will fry my eyes. I have protective gear and need the uv light for the project.
On the frying of the resistors, if i split the pcb as Jerry recommended will that work. Or are the resistors still not suitable? I added the datasheet for the blue LED's.

Please advise some fixes or ideas so ik can revise the project with the fiverr freelancers. Thanks in advance!
 

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