WS2812b power supply - 10 smaller step-downs vs one bigger?

Using Arduino LEDs and Multiplexing
#1

Hi
I'm making a project for custom underglow for my car. I'm using 10m of ws2812b, 60LED/m. From my calculations for a full brightness I need about 36A with 5V. My car battery is 12V so a DC-DC step-down is needed. I've found one with output of 5V 30A (I think this should be enough, because I probably won't use them as full power), and this one costs about 20$. But I was wondering if I could use eg. 10 of smaller DC-DC step-downs with output of 5V 3A, connected parallel. Those costs 0,5$ each so 5$ instead of 20$.

I want to do it as cheap as possible.
Thanks in advance.

#2

But I was wondering if I could use eg. 10 of smaller DC-DC step-downs with output of 5V 3A,

Yes

connected parallel

No.

You can't connect them in parallel, but what you can do is to break the 5V line on the strips and feed each one with a separate step down converter. Keep all the grounds common.

#3
  1. Why not just use 12V strips?
  2. How do you plan to mount them. The undercarriage takes a lot of physical abuse. Curious minds want to know because I am planning a Christmas display and am looking for mounting ideas.

From FindLaw:
"As a general principle, underglow lights are legal so long as they remain covered and unlit on public roads and do not flash or include the colors red or blue.

Because the laws on underglow lights vary greatly by state, drivers looking to add underglow lights should first check under the unlawful vehicle modification laws of their particular state to avoid potential warnings and penalties."

#4

SteveMann:
Why not just use 12V strips?

Perhaps because they are not rated for the range of voltages, including surges, that might be present on the car's "12 V" supply. Presumably the 5 V regulators in question are rated to at least 25 or 30 V, giving a safety margin.

Grumpy_Mike:
You can't connect them in parallel, but what you can do is to break the 5V line on the strips and feed each one with a separate step down converter. Keep all the grounds common.

And - it's a bit more complex that that! :astonished:

Remember the requirement for a 330 Ohm resistor in series at the data input of the strip and a 470 µF capacitor across the 5 V and ground at this point?

Well, it's not a great problem, but you will require both of those at each point where the 5 V line is broken. And remember that the 5 V and ground must be wired as a pair from the output of each regulator to the point where the power is inserted and the ground must also not be broken where the data line passes from one section to the next.

Not such a great problem because you already had the requirement that 5 V power (with ground of course!) must be fed in to the strip each meter as the foils on the strip cannot carry the full current.

#5

but you will require both of those at each point where the 5 V line is broken.

No, there is no need to add a resistor to the data when you break the 5V line. But yes you need a capacitor at each break point. In fact a capacitor in the middle or end of a strip is desirable whether you break the 5V line or you just have one power supply.

#6

Thanks for all your responses.

SteveMann:

  1. Why not just use 12V strips?

I've done some research and that is a brilliant idea. At first I was thinking that ws2812b are 12V, but never found such thing. So, after your response, I've looked around and found ws2811 which are 12V (money saved on step-downs) and also cheaper than 12b version. Yes, I know that they are controlled as 3 LEDs instead of individually, but with 60LEDs/m it's 5cm per color segment. Good enough for me.

SteveMann:
2) How do you plan to mount them. The undercarriage takes a lot of physical abuse. Curious minds want to know because I am planning a Christmas display and am looking for mounting ideas.

From FindLaw:
"As a general principle, underglow lights are legal so long as they remain covered and unlit on public roads and do not flash or include the colors red or blue.

Because the laws on underglow lights vary greatly by state, drivers looking to add underglow lights should first check under the unlawful vehicle modification laws of their particular state to avoid potential warnings and penalties."

That topic I'm still researching. Probably still some holes in a few places which are not so important, glue it with 3M tape for outside use, of course my strips are IP67, and secure it with zip ties through the drilled holes. About law, I already know about all of it. In my country it's exactly as you have written. Legal, but not when using it on public roads.

Also I'm doing this project more like to learn something than to actually a real thing. I'll be happy when it will work, but not really upset when it comes down to "nothing works, I give up"

Paul__B:
Perhaps because they are not rated for the range of voltages, including surges, that might be present on the car's "12 V" supply. Presumably the 5 V regulators in question are rated to at least 25 or 30 V, giving a safety margin.

Is there a good way (and maybe cheaper than 5V strips with 5V regulator) to keep 12V from ranging? I think I will use ws2811 12V instead.

#7

Grumpy_Mike:
No, there is no need to add a resistor to the data when you break the 5V line.

OK, but you have stated in the past that the resistor protects the chip from data being driven when the 5 V power has failed, so I will have to amend my advice in future. :astonished:

#8

So are you envisaging one of the many 5V supplies failing?

#9

Is that possible?

Is it possible in any system where you have two parts to the power supply? I thought that was one of the points of using the resistor. :roll_eyes:

#10

I've got some more questions about my project:

-Is there a way to "stabilize" 12V from car battery? I've found a solution with one step-down 12V->5V DC-DC and then step-up 5V->12V DC-DC, but it's more expensive than i would want this project to cost. I was also reading Grumpy_Mike's article about De-coupling, and it might be a solution, but I don't understand it very well. If someone would explain it to me a little more, or propose better solution, that would be much appreciated. Also my friend told me that this jumping voltage shoudn't be a problem becouse max voltage on battery is ~14,3V while charging from alternator and usually LEDs don't have problem with those. It also helps about voltage drop from cables. How much of this is true and what's the range of voltage acceptable by ws2811 12V (3 RGB LEDs controlled by one chip)?

-How should I connect cables together? I mean to not burn everything. Controller (arduino nano) with switches to control it will be soldered on PCB prototyping board, so will the solder bridges be enough for this purpose? From battery I want to use max 1m of 16AWG cable connected to board, from where it will split into 8 2-pin 22AWG cables to power 2x2m+2x3m of LEDs.

-If i connect same data pin to two strips will they both work with same pattern?

#11

Also my friend told me that this jumping voltage shoudn't be a problem becouse max voltage on battery is ~14,3V

Get a more knowledgeable friend.

I was also reading Grumpy_Mike's article about De-coupling, and it might be a solution,

No not rearly, if you want to protect against spikes then look at:-
http://www.thebox.myzen.co.uk/Tutorial/Protection.html

or

These are things that you use in front of a regulator. However the impedance might be too high as these things are designed for protecting inputs.

Maybe you would be better off buying a power converter especially designed for cars.

#12

If you were to cite the Web reference of these "smaller DC-DC step-downs with output of 5V 3A", we might be able to determine how suitable these might be for automotive use. A common suggestion here for lesser 5 V requirements is to use the module from a cigarette-lighter phone charger as it is supposedly "designed" for the application but that is actually dubious.

As I pointed out in #3, it is particularly doubtful that the 12 V LED strips are specified to withstand the potential surges of greater than 14.4 V that might occur in a car, so using 5 V strips with switchmode converter modules of known specification is most likely the safest approach and quite efficient.

Bl4ck_B0y:
If i connect same data pin to two strips will they both work with same pattern?

Of course.

#13

Ugh. Looks like the more I dive into this topic the harder it gets. Guess that's how it is with designing anything.

Paul__B:
If you were to cite the Web reference of these "smaller DC-DC step-downs with output of 5V 3A", we might be able to determine how suitable these might be for automotive use.
[...]

As I pointed out in #3, it is particularly doubtful that the 12 V LED strips are specified to withstand the potential surges of greater than 14.4 V that might occur in a car, so using 5 V strips with switchmode converter modules of known specification is most likely the safest approach and quite efficient.

I'm sorry if I'm getting too ahead if myself trying to be smarter than someone who is knowledgeable enough on this topic.

Wouldn't 12V ws2811 be a better solution? Less power consumption, cheaper and also I think that 11-15V to 12V conversion would be more efficient than 11-15V to 5V. I mean less difference between input and output. I've found voltage regulator which has "car" in title. I know it doesn't mean much on site like AliExpress.com, but when I'm looking at parameters this one looks suitable for my project: DC DC 60V 48V 36V 24V 6.5V to 30V 24V 12V 3V Adjustable 10A Car Charger Regulator Step Down Buck Converter Power Supply Module|supply regulator|supply 5vsupply 12v - AliExpress. But I don't really know how they work. If I regulate them to 12v will they output 12V no matter what voltage is on input (but in allowed input range of course)?

#14

Bl4ck_B0y:
I'm sorry if I'm getting too ahead if myself trying to be smarter than someone who is knowledgeable enough on this topic.

No fear. We are perfectly used to that here. :grinning:

Bl4ck_B0y:
Wouldn't 12V ws2811 be a better solution? Less power consumption,

Well, as you go on to say, you are not aware of just how things work. The switchmode converter (which is what you originally mentioned, but never actually cited) which converts the car 14 V to 5 V draws about 40% of the current at 12 V than is drawn from it at 5 V, so the power consumption will not be much different.

Bl4ck_B0y:
cheaper

I would be a little surprised .

Bl4ck_B0y:
and also I think that 11-15V to 12V conversion would be more efficient than 11-15V to 5V. I mean less difference between input and output.

Actually, generally the reverse. Switchmode "buck" converters tend to work better at wider conversion ratios. Point is, when you say "11-15V to 12V", you are talking about a "buck-boost" converter which is more complex and possibly less efficient.

Bl4ck_B0y:
I've found voltage regulator which has "car" in title. I know it doesn't mean much on site like AliExpress.com,

Perhaps not.

Bl4ck_B0y:
but when I'm looking at parameters this one looks suitable for my project: DC DC 60V 48V 36V 24V 6.5V to 30V 24V 12V 3V Adjustable 10A Car Charger Regulator Step Down Buck Converter Power Supply Module|supply regulator|supply 5vsupply 12v - AliExpress. But I don't really know how they work. If I regulate them to 12v will they output 12V no matter what voltage is on input (but in allowed input range of course)?

You (not surprisingly) misunderstand the description there. This is not a "buck-boost" converter, just a "buck" converter. It can reduce voltage, but not boost it. The numbers given represent corresponding input-output voltage pairs - 60V to 30V, 48V to 24, 36 to 24, 24 to 12 and so on. Actually more versatile than that, generally a 2 to 1 reduction ratio is pretty efficient but always with the input voltage significantly higher than the output.

#15

Paul__B:
I would be a little surprised .

Yeah, I've checked ws2812b and ws2811 with the same parameters (amount of LEDs/m, waterproof certificate) and looks like 11 is cheaper. Not sure, but it may be because of 3 times less LED controllers.

Anyway, if I'm back at 12b, can this step-down be good enough?
DC-DC 5V 3A
I know that those 3 amps are max value and normal operational is 1,5A, but can I just use this max value in my calculations? In my project I will probably use only one color of one led at a time. In this case I would need 12 of those converters, which is still cheaper than this one: DC-DC 5V 40A

Paul__B:
Well, as you go on to say, you are not aware of just how things work. The switchmode converter (which is what you originally mentioned, but never actually cited) which converts the car 14 V to 5 V draws about 40% of the current at 12 V than is drawn from it at 5 V, so the power consumption will not be much different.

By less power consumption i was thinking about how ws2812b 60LEDs/m are ~18W/m and ws2811 are ~14W/m.

But now: what will be the best way to make it as cheap as possible without everything getting burned and to make it actually work?

#16

Bl4ck_B0y:
Yeah, I've checked ws2812b and ws2811 with the same parameters (amount of LEDs/m, waterproof certificate) and looks like 11 is cheaper. Not sure, but it may be because of 3 times less LED controllers.

Yes, it just might be. It's hard to balance up the manufacturing costs of these things but going by eBay, it seems that WS2812s are at least 25 cents each and tricolour LEDs themselves are presumably much cheaper.

Bl4ck_B0y:
Anyway, if I'm back at 12b, can this step-down be good enough?
DC-DC 5V 3A
I know that those 3 amps are max value and normal operational is 1,5A, but can I just use this max value in my calculations?

If as you say, you will probably use only one colour of one led at a time, that will make sense.

Bl4ck_B0y:
In my project I will probably use only one color of one led at a time. In this case I would need 12 of those converters, which is still cheaper than this one: DC-DC 5V 40A

So it seems. And the 40 Amp one specifies 20 V maximum while the 3 A one says 28 V, so there appears to be a better safety margin! :roll_eyes: Also, if one fails, you have limited the replacement cost!

By the way, the 3 A listing has a starting shipping cost, have you noticed how on aliexpress, ordering multiple (small) items switches from free shipping to a significant fee?

And I love this picture:

Magnify!

Bl4ck_B0y:
By less power consumption i was thinking about how ws2812b 60LEDs/m are ~18W/m and ws2811 are ~14W/m.

Not a great deal and that latter power consumption is quoted/ calculated at 12 V, not 14 V, so you can add 2 W!

Bl4ck_B0y:
But now: what will be the best way to make it as cheap as possible without everything getting burned and to make it actually work?

I am still siding with the 5 V strips and multiple converters. Note the need for the capacitors, we have still not quite reconciled with Mike, but it might amuse him to look at this module:

You are certainly having an excellent lesson here in industrial design. :grinning:

#17

Yes I have some of those modules, in fact I made a 180 or so LED racing project recently. I did note that 75R is quite a bit lower than I would normally use, I suspect this is because they are only coping with short distances between the LEDs.

#18

Perhaps because of the existence of 75 Ohm co-ax - though that is of course, quite inappropriate here. :grinning:

#19