5V 1amp powerbank driving a 1AMP led

Thread Starter

hroldan

Joined Oct 12, 2016
13
Hi, I have created multiple and different circuits for laser diodes using the LM317 current limit setup, also worked with some leds using resistors instead for low voltage apps using AA batteries. I'm now building a project with LEDS and the desired current goes around 1amp.

I honestly never considered the powerbanks providing 5V - 1AMP so this is my question, is it safe to assume... that a simple powerbank suits the use of a 1AMP led application? after all it's 5V and 1 amp = 5Watts, right? I mean the powerbanks that provide 1amp are designed to provide that as a maximum current, it's already a constant voltage and constant current power source?

I'm interested on testing this but I don't have spares to burn, that will take time but besides testing I also consider a good thing to ask and read to understand. Any info will be appreciated.
 

Externet

Joined Nov 29, 2005
1,706
It may be a constant voltage up to a point of discharge, but not a constant current to drive a LED. 1 Ampere is the capability of that source.
Find the data sheet of the LED.
 

Tonyr1084

Joined Sep 24, 2015
6,465
If you're considering powering multiple LED's from a 1A source you probably want to factor in some resistance. Even if it's to run at 900mA (0.9A). Can you provide a schematic of what you are proposing to do?

I have a 12V 5A power brick that if it's a really good day it can push 3A @ 12V. It's from China. Not that Chinese stuff is bad, it's just that a lot of counterfeit stuff comes from there.

Assuming your 5V supply CAN push 1A then if you figure your LED's for that current then it should work. But just because it's 1A doesn't mean it's current regulated. Some manufacturers will under-rate their equipment for a safety margin. It's possible your 1A supply can push 1.2A (1200mA) at 5V. So to really answer your question intelligently we'd probably need to see your schematic proposal.
 

dl324

Joined Mar 30, 2015
13,573
I honestly never considered the powerbanks providing 5V - 1AMP so this is my question, is it safe to assume... that a simple powerbank suits the use of a 1AMP led application? after all it's 5V and 1 amp = 5Watts, right? I mean the powerbanks that provide 1amp are designed to provide that as a maximum current, it's already a constant voltage and constant current power source?
You can't have constant voltage and current at the same time. It's one or the other.
 

Thread Starter

hroldan

Joined Oct 12, 2016
13
@Externet, true, thanks.

@Tonyr1084, you are right. My little project is quite simple, it's a photography lightbox, already built some but this one is different as I don't want to use any wall power source, instead I want to use high capacity powerbanks to provide freedom of movement and work anywhere.

I have no specs for the leds, these come from some interesting COB remote control lamps that I got from places, pretty decent light but I will combine them all on a proper heatsink, so I have no specs or datasheet, no model # on the leds. I could set the leds in such array to consume 1AMP or 2 AMP, there is always the chance of using some in series and some in parallel, I know each led should ideally have it's own controller but I want to keep things simple and functional, not 101% perfect. My current best is an Anker powerbank capable of 2.1 AMP, pretty steady, I also have plenty of 18650 and modules to build separate powerbanks.

So the schematics would be as simple as power source + driver + led. I'm thinking about the classic LM317 for current limits, or perhaps a resistor, not sure, will do some tests.

@dl324 thanks for the reminder, it's absolutely relevent but I forgot somehow.

- - - - - -

Thanks everyone for solving the powerbank question, so it's a power source but not to fully trust it as a regulated and limited current to drive leds, needs proper driver then.
 

dl324

Joined Mar 30, 2015
13,573
I'm thinking about the classic LM317 for current limits, or perhaps a resistor, not sure, will do some tests.
You won't be able to use LM317 as a current source with a 5V supply. It's dropout voltage at 1A will be 2-3V. That won't leave enough voltage for an LED.

Some power bricks might not provide 1A to USB decorations (dumb devices).
 

Thread Starter

hroldan

Joined Oct 12, 2016
13
You won't be able to use LM317 as a current source with a 5V supply. It's dropout voltage at 1A will be 2-3V. That won't leave enough voltage for an LED.

Some power bricks might not provide 1A to USB decorations (dumb devices).
You are right, thank you; can't believe I'm messing this up, I need to go to the basics and refresh some data/info.
 

Thread Starter

hroldan

Joined Oct 12, 2016
13
Here is my update in case someone feels like commenting on it, or perhaps finds this useful. I'm using 5 donut shape cob leds from some cheap 3AAA battery lamps.

  • 3 of them are about 4cm in diameter (pretty powerful at 5v).
  • 2 are from a separate set about 6cm in diameter, less powerful at 5v.

Both sets of lamps used 3 x 1.5v batteries and I don't have any specs as I couldn't find any model, brand, serial number, etc. I didn't measure at the time the original amps coming from the battery driver, and had these stored already as spare parts, so, original amps = mystery. My setup is quite simple, I tried using diff powerbanks (5v x 1amps/ 5v x 2amps). To cool the leds I attached them to a magnesium heat sink about 22cm x 10cm from a broken Surface RT tablet, in parallel.

  • The power consumption with the supposedly 1amp powerbank goes around 1.45amps, steady, yes you can never trust the powerbanks, specially the cheap ones. And things work pretty well as the leds don't show any heating.
  • Tried with a wall brick rated 1.2 amps and 2.1 amps, and the leds work pretty well, no heating and consumption goes around 1.35amps steady, no ups and downs.

I'm not using any resistor or current driver for the above. I guess the whole thing needs more power than provided, meaning the setup is under powered, and thus no heating? because there is no heating after 15-20minutes on the leds, but the powerbank module does gets warm.

  • :rolleyes: Now, trying a 2.1amps rated powerbank this thing shines amazingly well, a lot brighter, power consumption goes up to 2.2amps, leds get a bit warm after 10 minutes (not warm, but the whole thing doesn't feel cold anymore), and only then power consumption changes (not steady, it goes up). Again no resistors or drivers.

Tried the same setup with one 1ohm 7w resistor and the brightness is the same regardless of the power input (brick, 1amp, 2amps, etc) and shines less than the setups described above. IT SEEMS I can get away with this using no resistor and the 1amp powerbank. I often like not only to ask questions but also to share whatever worked for my project in case someone else finds it useful, I know it's not an ideal setup but this simplicity suits my needs right now.
 
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