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Power Wiring for Large LED Strip
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Please be positive and constructive with your questions and comments.

Power Wiring for Large LED Strip

by cweinhofer on Sun May 02, 2021 11:17 am

I'll start with my questions for TLDR and then give details below:
1) Does adafruit sell a toggle a switch that would handle 5V 20A? If not, where can I find one?
2) Can I power my micro-controller from the same live power source as the LED strip or should I use a separate source?

I'm trying to control a strip of 144 individually addressable LEDs using an ESP8266-based micro-controller. I got it to work at a basic level, but it seems a little flaky, so I've been reviewing the neopixel uberguide which shows the following diagram: https://cdn-learn.adafruit.com/assets/a ... iagram.png

Question 1
The guide says "When connecting NeoPixels to any LIVE power source or microcontroller, ALWAYS CONNECT GROUND (–) BEFORE ANYTHING ELSE. Conversely, disconnect ground last when separating." After looking at the diagram above, it looks like the simplest way to accomplish this would be to have a toggle switch on the 5V line, so I could plug the power supply in first and then send power through the 5V line.

But I've done some searching on adafruit and can't seem to find a switch that's rated for 20A. Can anyone provide a link or otherwise suggest how to handle this?

Question 2
Up to now, I've been powering my micro-controller by running a line from the 5V pad on the LED strip to the Vin on the board. The ground on my board also connects to the ground on the LED strip -- as opposed to directly to the live power supply as shown on the diagram. Is this safe / reasonable? Or should I be providing an independent power source through the USB port as shown on the diagram? (If it matters, I am always careful to disconnect the live power supply before connecting the board to the computer for any uploads.)

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Re: Power Wiring for Large LED Strip

by dastels on Sun May 02, 2021 11:31 am

Why do you need a 20A switch? 144 NeoPixels will take a bit over 8.5A with all 144 at max brightness white. A 10A supply will be plenty, and you could probably get away with less depending on how the strip will be used (i.e. how much light will be generated at any time). Also, even if you have a 20A supply, the strip will only draw at most that 8.5ish amps. (60mA per NeoPixel * 144 NeoPixels). Granted if you have RGBW it could go as high as 11.5A since there are 4 LEDs instead of 3.

1a) Yes, that sounds right.
1b) I would have a look at Digikey for anything you can't find at Adafruit.

2) As long as the wires are short, and the currents are fairly low ... ground is ground. You start running into problems with long wires and high currents: the resistance of the rise becomes a factor as voltage drops are introduced causing the ground at either end to not be the same. Keep your ground wires short and/or thick.

Generally, if you need to power your LEDs from an external supply, I would look to powering the MCU board separately.
- It avoids any switching noise leaking into the MCU's power.
- It avoids having to remember to disconnect the external power when you want to connect to USB.
- It lets you test/debug/update while having the lights working.

Dave

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Re: Power Wiring for Large LED Strip

by adafruit_support_bill on Sun May 02, 2021 11:41 am

The guide says "When connecting NeoPixels to any LIVE power source or microcontroller, ALWAYS CONNECT GROUND (–) BEFORE ANYTHING ELSE. Conversely, disconnect ground last when separating." After looking at the diagram above, it looks like the simplest way to accomplish this would be to have a toggle switch on the 5V line, so I could plug the power supply in first and then send power through the 5V line.

The full text reads:
Avoid connecting NeoPixels to a live circuit. If you simply must, always connect ground first, then +5V, then data. Disconnect in the reverse order.

Note that data is the last to be connected and the first to be disconnected. The chip does not like the voltage on any pin to exceed the supply voltage. So disconnecting 5v and leaving a live signal wire connected can damage the first pixel in the strand. The simplest way to deal with this is to power the Arduino from the same supply, so the signal stops at the same time as the power.

ut I've done some searching on adafruit and can't seem to find a switch that's rated for 20A. Can anyone provide a link or otherwise suggest how to handle this?

We do not have a switch rated for 20A @ 5vDC. You can check with DigiKey or Mouser.

Up to now, I've been powering my micro-controller by running a line from the 5V pad on the LED strip to the Vin on the board. The ground on my board also connects to the ground on the LED strip -- as opposed to directly to the live power supply as shown on the diagram. Is this safe / reasonable? Or should I be providing an independent power source through the USB port as shown on the diagram? (If it matters, I am always careful to disconnect the live power supply before connecting the board to the computer for any uploads.)

You should connect ground and power directly to the strip - because that is by far the biggest load. Then you can run 5v and GND from the strip back to the Arduino. That avoids issues with 'ground bounce'. Since the ground is also your signal reference, fluctuations in the ground can interfere with your signal.

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Re: Power Wiring for Large LED Strip

by cweinhofer on Sun May 02, 2021 9:09 pm

Thanks, appreciate the responses.

Why do you need a 20A switch?

I was only thinking a 20A switch because that's the size of my power supply. I went that big because they are RGBW and I was afraid 10A wouldn't be enough. But I checked DigiKey as you suggested and they have lots of switches with a 20A rating.

You should connect ground and power directly to the strip - because that is by far the biggest load. Then you can run 5v and GND from the strip back to the Arduino.

That's exactly how I have mine wired as the LED strip already had two wires running to the pad.

Keep your ground wires short and/or thick.

The wires from LED strip to power supply and LED strip to micro-controller are both around 70 cm. Is that in the acceptably short range?

The simplest way to deal with this is to power the Arduino from the same supply, so the signal stops at the same time as the power.

Is it sufficient for the LED strip and micro-controller to all receive power at the same time? Or should I place a second switch on the 5V line from LED strip to micro-controller so I can get power to the LED strip before/after the micro-controller?

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Re: Power Wiring for Large LED Strip

by cweinhofer on Sun May 02, 2021 9:18 pm

I should also mention that, while they would be a big deal for some people, "having to remember to disconnect the external power when you want to connect to USB" and being able to "test/debug/update while having the lights working" are not big deals for me as I plan to rely mainly on OTA updates. The LED strip sits behind a false window (functioning as a sunrise alarm), so I pretty much have to disconnect the micro-controller if I want to connect it to my desktop for USB updates.

I'm not familiar with the "switching noise leaking into the MCU's power". How big of a problem is it compared with some of the other issues we're talking about?

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Re: Power Wiring for Large LED Strip

by adafruit_support_bill on Mon May 03, 2021 5:34 am

The wires from LED strip to power supply and LED strip to micro-controller are both around 70 cm. Is that in the acceptably short range?

The power requirements of the microcontroller alone are pretty small, so if you are running power to the strip first, there is not much danger of a voltage drop on power and ground. But 70cm is long enough that you could encounter problems with the Neopixel signal. Be sure to add the termination resistor at the end of the signal wire nearest the first pixel.

I'm not familiar with the "switching noise leaking into the MCU's power". How big of a problem is it compared with some of the other issues we're talking about?

We do see to from time to time. Some supplies are noisier than others. Ground bounce is a more common issue. We see that a lot when people run power to the microcontroller first.

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Please be positive and constructive with your questions and comments.