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Topic: DC to DC converter for LED Strip (Read 252 times) previous topic - next topic

crazeuk

Hi Guys.

I have a project i am working on and using a RGB WS2812B LED strip.
Here are the specs of the LED's

LED's /M:    144 (288 total)
LED Type:    WS28132B
Voltage:    DC 5v
Power Watt:    43.2W  (86.4W Total)

I want this to be a portable device and ideally run of off rechargeable Lithium 18650 batteries.

So my questions:
1. I presume I would need an 86.4W driver if they where all continuously on on full power.  How can i reduce this for a smaller driver package - Maybe have them flashing at high speeds? (They need to be filmed / photo'd).

2. I was thinking of a driver like ebay 5v/8A/40W or ebay 5v / 3A / 15W will this be sufficient. 

3. My Plan is to drive them via an Uno, can i run them on something smaller like a Nano?

4. Is it possible to run on 18650 Rechargeables? How many would i need and how would i work out how long they will last.

Thanks in advance

Paul__B

#1
Aug 07, 2018, 02:41 pm Last Edit: Aug 07, 2018, 02:41 pm by Paul__B
My Plan is to drive them via an UNO, can I run them on something smaller like a Nano?
You have use the word "drive" for different purposes here.

You cited power converters to supply regulated 5 V power to the WS2812B strips.  That sounds reasonable if you use a multi-cell lithium battery pack - which will require a corresponding purpose-built charger.  There is no necessary connection between the power supply used to supply the LED strips, and the Arduino, the Arduino is in no way whatsoever serving to "power" the LEDs.

It may however be that you use your well-regulated 5 V power supply to power the Arduino via a separate connection of the paired 5 V and ground wires directly from the power supply to the Arduino 5 V input terminals.

Then you use the term "drive" to generate the instruction waveform.  This requires very little power and only connects to the first WS2812B in the strip.  There should be a series resistor - about 470 Ohms - in series with the data pin of that first LED.

A UNO and a Nano are electrically virtually identical.  Actually, a real UNO has a second processor chip - a 16U2 - as the USB interface while many or most fakes branded and sold as UNOs are not UNOs at all but a mutant of the earlier Duemilanove which used a deprecated USB interface chip and was electrically identical to the Nano apart from a couple of connections.

So the "clones" now fraudulently sold as "UNOs"  and those sold - in this case not unreasonably - as Nanos now both use the more readily available and much cheaper (Chinese designed) CH340 USB interface chip and these versions are again, electrically the same apart from a couple of details in the power supply and pin 13 indicator circuits.

So board size is in this regard, completely irrelevant to their identical functionality - there is absolutely no difference whatsoever in "computing power" or electrical power usage.  And for any serious project, the Nano is the preferred module.

crazeuk

Hey Paul__B.
Thanks for the prompt response.

Apologies i was being a little simple when i was writing it.

So the plan:
1. Use a regulated power supply from a pack of 18650 Batteries (probably 2, maybe 4) to power both the LEDs and the arduino.

2. Use the Arduino as the processor. - Thanks for the advice on resistor to 1st pin and the use of the Nano.

I guess the main question is the step down regulated supply.  Which device should i get? Someone mentioned a 3A one would do too.


Paul__B

You cited a strip of 288 LEDs, which would draw up to 17 Amps at 5 V.  About 85 Watts as you say.

You need one of these:

... and a long power cord. :smiley-lol:

You could perhaps use the battery pack from a large laptop rated at 100 W and a heavy duty power converter, but you would need to find a charger for it.

Grumpy_Mike

Quote
Maybe have them flashing at high speeds?
You can't affect the flashing speed of the LED's PWM, it is at a fixed rate and quite slow. If you want faster PWM to film then you need these:-
Dot Star LEDs

crazeuk

Hi Guys
Thanks for the responses so far.

Feeling a bit confused.

I am trying to make a version of: NeoPixel Painter

It uses: UBEC DC/DC Step-Down (Buck) Converter - 5V @ 3A output

They are using the same LED's.

It needs to be a very portable device so the big transformer won't work.

Any ideas?

Paul__B

OK then.  Well, you will note in the Adafruit article quite a number of warnings.  You originally mentioned 288 LEDs, apparently two metres of strip.  The Adafruit article warns not to use more than a 144 LED strip.

It also warns not to use other than the code they give you which is particularly cautious not to activate the LEDs over a certain limit in order not to draw more than the 2 Amps

And it has other advice as well - test one small part at a time, before presuming to put it all together.

As I have pointed out before, if you wish to use multiple rechargeable lithium cells, you will need the charger designed for the job.  A single cell would require a different - step-up - converter and you would be draining it heavily, 3 Amps at least just to provide 2 A at 5 V.

crazeuk

#7
Aug 10, 2018, 06:55 pm Last Edit: Aug 10, 2018, 07:19 pm by crazeuk
OK then.  Well, you will note in the Adafruit article quite a number of warnings.  You originally mentioned 288 LEDs, apparently two metres of strip.  The Adafruit article warns not to use more than a 144 LED strip.

It also warns not to use other than the code they give you which is particularly cautious not to activate the LEDs over a certain limit in order not to draw more than the 2 Amps

And it has other advice as well - test one small part at a time, before presuming to put it all together.

As I have pointed out before, if you wish to use multiple rechargeable lithium cells, you will need the charger designed for the job.  A single cell would require a different - step-up - converter and you would be draining it heavily, 3 Amps at least just to provide 2 A at 5 V.
Hey Thanks for that.

Yeah i see now.
What would happen if i drew 85watt out of a 50watt driver?


I don't intend to use a single Lithium Battery.  My plan was to use 4 x 18650 and use a Dc to DC converter to step it down to 5v that i need to power both.  I have a NiteCore Charger that will charge these outside of the finished device.

Alternatively i can look at using a Lipo power pack like that from a quad copter or RC car Like this

Also the lighting would never be continuously on.  It will just flash patterns over a number of seconds.

Grumpy_Mike

#8
Aug 10, 2018, 08:45 pm Last Edit: Aug 10, 2018, 08:46 pm by Grumpy_Mike
Quote
What would happen if i drew 85watt out of a 50watt driver
Either the power supply would shut down, if you are lucky, otherwise

Bang

Quote
use a Dc to DC converter to step it down to 5v
Have you seen what an 85W D.C. to D.C. converter costs?

Paul__B

I don't intend to use a single Lithium Battery.  My plan was to use 4 x 18650 and use a Dc to DC converter to step it down to 5v that i need to power both.  I have a NiteCore Charger that will charge these outside of the finished device.
So, you have taken the battery situation into account.  Good.

Alternatively i can look at using a Lipo power pack like that from a quad copter or RC car Like this
Ok.  I have repaired your link.  :smiley-lol:

Also the lighting would never be continuously on.  It will just flash patterns over a number of seconds.
Nevertheless, the DC-DC converter originally cited has virtually no reservoir capacity, so you cannot overload it even briefly.

crazeuk

#10
Aug 16, 2018, 02:17 am Last Edit: Aug 16, 2018, 02:18 am by crazeuk
Thanks Paul_B for fixing the link.

And thanks to all the advice

Its a steep learning curve.

Okay so we are slowly getting there.
The small bits are arriving.  Idid order the 50watt driver earlier mentioned, but i can use that for another project.

I just came across this DC-DC-Converter-150W Step-down.

Would this be sufficient?

Grumpy_Mike

Quote
Would this be sufficient?
No.

That converter has a constant current output.

You need a 5V constant voltage output. Concentrate on the voltage and current output and forget the wattage rating.

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