Help understanding power requirements and building a parts l

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upintheco
 
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Help understanding power requirements and building a parts l

Post by upintheco »

Hi!

I need help understanding the power requirements of a particular product, and building a parts list so that I can realize a project idea.

What I want to do is power 5 meters of these Digital RGB LED Strips for up to 8 hours a day. The lights will come on and remain on at full brightness for the first 7 hours, and then, over the course of the last hour, the LEDs would be slowly dimmed until they were completely off. Or, rather than dimming them all at once, I could simply unlight one-at-a-time slowly for a similar effect. So, in addition to a parts list, I would greatly appreciate advice as to which method would be more energy efficient to achieve the fade-out effect.

I have a basic 3 panel, 45w solar setup, which has been expanded to 10 solar panels (totaling 150 watts in all). The setup came with a charge-controller unit, so I have this 80 watt inverter plugged into the DC (cig lighter) inverter port. This gives me an AC outlet. The inverter works good, but has a "low battery shutoff" feature at around 10 volts, so I'm unable to fully utilize the power. I have access to (up to) four of these 12 volt, 35 Amp Hour batteries and would be wiring them in parallel to keep the system at 12 volts. The batteries' sticker information states that they can be repeatedly deep-cycle discharged, so I think the inverter's low battery feature might actually be getting in the way in this particular design. I would like to avoid using the inverter, if possible, not only for that reason, but also because it uses power to light its own display. And of course, I would certainly prefer to not use all 4 batteries, if not entirely necessary. Finally, I have an extra Arduino on hand already and it's clear that I need to order the 5m of RGB strip, but it is unclear what I need beyond that, particularly since I want to nix the inverter altogether if possible. At this point, I'm not even sure all 4 batteries could run the 5 meters of lights for the 8 hours, so any comments on that would be great as well.

I read the page on powering the strip and both the very first and the very last bulleted points at the bottom of the page seem extra applicable to what I'm trying to achieve. For example:

The first bulleted point states that "When creating longer runs, power should be split and applied every meter." I understand this, but do not understand how to "break up" the power and apply it every meter. Would I simply be cutting the strip and splicing it back together but with a new power lead going back to, say, a breadboard with a powered rail? I'm unsure of exactly how to apply the power every meter.

The last bulleted point states that "For a standalone application (not USB connected to a computer), you can power the Arduino from the same regulated 5V supply as the LEDs — connect to the 5V pin on the Arduino, not Vin, and don’t use the DC jack on the Arduino." While I understand the words, I do not understand the actual procedure, or what parts I might need to achieve this. Surely, my non-understanding is making it seem more complicated than it actually is.

So, that's about all I can think of that would be relevant. If you need any additional information to help me get started, I'll get on it right away! Any advice is greatly appreciated!!

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adafruit_support_bill
 
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Re: Help understanding power requirements and building a par

Post by adafruit_support_bill »

The lights will come on and remain on at full brightness for the first 7 hours, and then, over the course of the last hour, the LEDs would be slowly dimmed until they were completely off.
If your main supply is 12v and you are only using these to generate white light, for maximum efficiency I would suggest going with these strips instead. https://www.adafruit.com/products/887
One power mosfet will handle the full 5 meters easily: https://www.adafruit.com/product/355
And you can control it with a single Arduino PWM pin. This tutorial is for the RGB version. For the white strips, just connect all 3 channels to the one MOSFET output.
https://learn.adafruit.com/rgb-led-strips/usage

5 meters will take about 6 amps. If you are fading from 100% to 0% over the 8 hours, your average draw would be 3A and your total power requirement would be 24Ah. That seems well within the capability of your batteries.

Also, 3A at 12v is 36 watts. So this is well within the capability of your solar array.
The first bulleted point states that "When creating longer runs, power should be split and applied every meter." I understand this, but do not understand how to "break up" the power and apply it every meter. Would I simply be cutting the strip and splicing it back together but with a new power lead going back to, say, a breadboard with a powered rail? I'm unsure of exactly how to apply the power every meter.
With a single supply as you have here, there is no need to break up the strip. Just run wires from the power supply and the MOSFET to several points along the strip.
The last bulleted point states that "For a standalone application (not USB connected to a computer), you can power the Arduino from the same regulated 5V supply as the LEDs — connect to the 5V pin on the Arduino, not Vin, and don’t use the DC jack on the Arduino."
This would not apply in your case, since your main supply is 12v. You can power the strips directly with 12v as shown in the tutorial link above and feed the Arduino 12v via the DC barrel jack. You can use one of these to do that: https://www.adafruit.com/product/369

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adafruit_support_rick
 
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Re: Help understanding power requirements and building a par

Post by adafruit_support_rick »

This picture nicely illustrates distributing power along the strip:
Image

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upintheco
 
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Re: Help understanding power requirements and building a par

Post by upintheco »

Bill, thanks for your assistance! I have a couple of follow-up questions regarding your suggestions and then I can start filling my cart.

About the cool white strips, I'm wondering if these strips can be mixed-n-matched with the warm white strips. For example, can I connect 3 cool white and 2 warm white strips (5m in all) or are there any special considerations/tweaks required for this to work?

About the power adapter, is it safe to use only this between my Arduino and a 12v battery? My 12v batteries show 13-14v when fully charged and I'd hate to fry the project due to ignorance.

Thanks again for your help -- I'm really looking forward to this project!

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Re: Help understanding power requirements and building a par

Post by upintheco »

Rick, thanks for the great graphic. You confirmed exactly what I needed to understand in terms of splitting and applying power every meter. Much appreciated!

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Re: Help understanding power requirements and building a par

Post by adafruit_support_bill »

You can mix the cool white and the warm white. Other than the color temperature of the output, they are identical.

14v is going to put some stress on the Arduino voltage regulator. Since the Arduino itself runs at 5v, it will need to burn off the excess 9v as heat. One approach is to use a DC/DC converter to drop the voltage down to 5v: https://www.adafruit.com/product/1065

14v will also put some stress on your LED strips if you run them at full throttle. But you can compensate for that in your code - If you run them at maximum 85% PWM duty cycle, that is equivalent to an average of 12v.

A proto-shield would be a good way to mount your MOSFET driver and your DC/DC converter. You can tie the output of the converter directly into the Arduino 5v bus on the proto-shield. https://www.adafruit.com/product/51

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upintheco
 
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Re: Help understanding power requirements and building a par

Post by upintheco »

Bill,

Thanks for confirming the LED strip mix-n-matching, and for the tips on incorporating the protoshield and duty cycle compensation.

I've used MOSFETs on a breadboard before, but haven't used a DC/DC converter. Is there an Adafruit tutorial on using these types of components?
I figure it's pretty much plug-n-go, but it's nice to learn about things instead of just doing them.

Thanks!

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Re: Help understanding power requirements and building a par

Post by adafruit_support_bill »

They are pretty straightforward to use. The data sheet has some examples. For a 12v supply, the capacitor shown is optional. http://www.adafruit.com/datasheets/tsr1.pdf

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upintheco
 
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Re: Help understanding power requirements and building a par

Post by upintheco »

I think I've now got enough information to dive in, thanks!

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upintheco
 
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Re: Help understanding power requirements and building a par

Post by upintheco »

So, I grabbed the parts you recommended and am trying to test a 3' light strip with MOSFET. They light up with a 9v battery directly, but don't light when I wire them up with the MOSFET as shown in the RGB LED strip tutorial. I have:

- LED's positive to Arduino VIN
- LED's negative to MOSFET pin 2
- MOSFET pin 1 to Arduino pin 6
- MOSFET pin 3 to Arduino GND

And there's a 9v power supply plugged into the Arduino. I'm just trying to get them lit at this point...PWM next. The following isn't working...can you see any issues with the code or the wiring?

Code: Select all

#define stripPin 6
 
void setup() {
    pinMode(stripPin, OUTPUT);
}
 
void loop() {
    analogWrite(stripPin, 127);
}

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adafruit_support_bill
 
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Re: Help understanding power requirements and building a par

Post by adafruit_support_bill »

That all sounds right. Maybe if you post a photo we can spot the problem.

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upintheco
 
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Re: Help understanding power requirements and building a par

Post by upintheco »

Thanks for confirming. In the end, this graphic pointed out the problem. There was no ground from the Source Pin back to the power supply's ground. Easily overlooked as my 9v power supply is a simple battery pack with barrel jack with intact wires, so everything only seemed to be hooked up. To fix my setup, I swapped my power supply for a 12v battery (ie, a supply with exposed leads) and swapped out the LED in the graphic for the LED strip and didn't use the resistor. I was then able to easily connect the power supply's negative to the MOSFET's source pin. It worked and the strip was lighted. Another 60 seconds and I had it pulsing on and off. Thanks for following up.

Additional search keyword: rgb, cool white, warm white, MOSFET, PWM, Arduino, fade, analogWrite

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