Power supply and wiring guidance needed to wire an array of 100 LEDs

Hi, I'm in the process of making an LED light ring for my milling machine. I have 100 (3.2v) LEDs and need to know the best way to wire them and what size power supply would be best. Thank you in advance, Nik

by niklnikl
February 27, 2021

You probably don't need to light on all the 100 LED at the same time if you use a frequency of 1kHz, the human eye won't see the flicker. As for the duty cycle, one at 50% is probably even too much, you may be able to go down to 25%, so only 25 LED are on at the same time, in turn (with a multiplexer selecting which sub-circuit receive, momentary, the energy, as example). Anyhow, assuming a duty cycle of 50% (half the LED on, half off at any given moment), all the LED in parallel, each with a resistor, you could target 3.3 volt and 20 mA, 50times, so a power of 3.3 Watt. The resistor in series of each LED will see 0.1 volt, times 20 mA, that makes 2mW resistor 5.6 Ohm ( 5 ohm = 0.1 volt / 0.020 amp; and 2 mW = 0.1 volt * 20mA ). Note that the power supply of 3.3 volt, 3.3 Watt have to be able to sypply 1 Amp. With a multiplexer and 50% duty cycle so only 50 LED are on at a given time. If a LED at 10mA is enough, you can divide by two the power required, but increase the resistor to 10 Ohm. Sure, if the LED is not a 3.2 volt LED, you would have to make the appropriate numerical corrections.Same if the power supply delivers more than 3.3 volt.

by vanderghast
February 28, 2021

Thank you Vanderghast. How would one design a multiplexer?

by niklnikl
February 28, 2021

You could buy one, such as the MC14058, around 1$ + shipping on eBay (check the shipping cost, it may exceed many times the price of the IC), but since you need 1 Amp through it, and most multiplexers are limited to less than 100 mA, you may find easier to use two mosfets that you will open/close in alternance with the help of two GPIO pins of an MCU (Arduino or otherwise), or with an oscillator. The mosfet should be able to handle the one amp through its Draint-Source canal and have a Vgs(th) low enough to be easily below what the MCU can deliver (generally from 3.3 to 5 volt, that depends on the exact micro controller, MCU, that you plan to use) to the gate pin of the mosfet.

I assume that you already know how to use a mosfet as a switch, if not, and if you don't find the missing info, don't hezitate to ask for more details.

by vanderghast
February 28, 2021

You can also use a single relay SPDT (single pole, dual terminal) so that 50% of the time, the terminal 1 is closed and light on half the LED, and 50% of the time, it is terminal 2 which is the closed one, which turns on the other half of the LED. You still need something to alternate which terminal is on though, and at which speed it does it (higher than 1 kHz, preferably, which is slow for a mosfet, but can be limit for a relay).

by vanderghast
February 28, 2021

nikiniki: I also do a bit of home machining and I'm curious about what you are doing. I would appreciate it if you could give a bit of explanation about how you are using the 100 LED's

by Foxx
March 07, 2021

2 Answers

Answer by Foxx

Thanks for the reply. I've been doing some work using Adafruit Neopixels https://www.adafruit.com/product/1586 rings and flexible strips for microscope dark field illumination. The two applications are somewhat similar although I doubt that you need controllable colour. This feature has some attractions for gemmology and mineralogy which we are exploring.

+2 votes
by Foxx
March 09, 2021

Answer by niklnikl

Hi Foxx, I was going to build one myself: https://www.thingiverse.com/thing:732859 But I decided to just purchase this one on eBay as I don't have the time to mess with it. At that price, you can't beat it. https://www.ebay.com/itm/Milling-Machine-Spindle-Light-for-X2-Mini-Mills-Hi-Torque-Bridgeport-HF-IP68/302310170145

I just discovered that you can buy the light ring and make your own enclosure if you want to go that way: https://www.ebay.com/itm/Spindle-Router-LED-Light-Ring/263747602478

+1 vote
by niklnikl
March 08, 2021

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