3w COB USB breakout newbie help

Thread Starter


Joined Aug 8, 2020
Hi folks. Sorry for butting in like this. I’m trying to build a small mason jar aquarium and looking to house a 3w cob led like this: https://www.ebay.co.uk/itm/113886781401

in the lid of a jar and have it powered via micro USB using a breakout board like this: https://www.ebay.co.uk/itm/123257921572

I’m really struggling to find out how to set up a resistor etc on this breadboard prototype. I am not good at this. Can anyone give me a steer? I feel like this is very basic but perhaps I’m missing something.

everything I try (220?) my Mac tells me to unplug whatever I just tried because it’s using too much power.

I am so over my head and appreciate any guidance. I have a decent selection of various resistors and am completely colourblind. Theyre labelled up which helps but yeah. I’m defeated.


Joined Jan 29, 2010
hi Battt,
Welcome to AAC.

3Watts/3.2V = ~0.9Amps.

5Vusb-3.2Vled = 1.8V..... 1.8V/0.9A = 2 Ohms .. 1.6Watt resistor, say 3Watts.

Audioguru again

Joined Oct 21, 2019
The LED will fail in probably less than 1 minute unless you cool it properly with a heatsink that is designed for it.
But old USB will not provide enough current for the LED to operate anywhere near its max current.

Thread Starter


Joined Aug 8, 2020
Thank you both - so in terms of the original idea, a 2ohm resistor is preferable.
Taking into consideration the advice above around the current etc - I am not set on the design - what would be optimal? My only real requirement is that it’s fairly discreet as I want to mount it on top of a jar. Appreciate your time - thank you.