Wire length

Other Hardware LEDs and Multiplexing
1

Hello,

Im going to be putting WS2812B (5v) led strips all over a large stage set and possibly other places as well. Im not sure how close ill always be able to get the controller to the led strips, also as much as possible id like to wire them all to a central control box so I was wondering if there were any limits to wire length between

a: the power and the leds
b: the leds and the controller
c: the controller and any switches I want to wire into the circuit (assuming the ctrlr and power are both near the leds)

also, if anyone has any tips about making long and robust lengths of wire that would be cool. I havent looked at sleeving yet but I assume you can get something easily enough?

Thanks,

2

After a bit of Goggling you will find that each pixel needs 60mA maximum.

Long strips will experience voltage drop on the supply buses.

To offset voltage drop you can power strips from both ends or even in the middle.

Don’t forget about the voltage drop on the supply cabling too.

Invest in a DVM to troubleshoot voltage problems.

3

larryd:
To offset voltage drop you can power strips from both ends or even in the middle.

Invest in a DVM to troubleshoot voltage problems.

ooo I didnt know you could do that! :smiley:

I have no idea what a DVM is

I just found this Voltage Drop Calculator

I'm using 10m as a theoretical maximum - cant imagine it will be anywhere near that length but just in case.

I found this cable - does it seem reasonable?

Since most 5v battery packs I can find are 2.4 amp its a max of 40 leds (I'll search for some decent batteries later).

At 10 meters the voltage drop is 50% which is obviously terrible - presumably this just means the leds at the end would only be able to pull 30ma and there fore be dimmer? Or would they not light at all?

4

think I was using that voltage drop calculator wrong?

for the amps, am I supposed to put in the pull of each led or the max that can be supplied?

the calc says 22awg wire cant carry 12 amps much past a few meters but at 60ma the drop over 10 meters is only 13% - 4.36volts at the end

5

but at 60ma the drop over 10 meters is onyl 13% - 4.36volts at the end

It is 60mA per LED, so multiply that by the number of LEDs you have in the strip.

There is another big problem and that is the signal used to tell the strip what LEDs to light up. That will not go those sorts of distance so you will have to use a differential driver and receiver at each end of the cable run to the strips.
see OSH Park ~ Shared Projects by PaulStoffregen

6

cheers for the heads up on the signal. Ill look at getting some for testing.

Going back to the power question then.

Say were using 200 leds and 22 awg wire;

That's a 12 amp draw which means after 1 meter the voltage is 3.73 :frowning:

So If I want even a 5 meter extension to the led strip, Id need 12 awg wire (giving 4.37v at the end) which I assume will be too thick to solder to the led contacts.

I guess the only answer is to significantly reduce the number of leds or add a power source at the other end of the led strip?

If I cut down to 100 leds id need 19 awg to get 3.41 volts at the end of 5 meters which I think is just enough to run an led?

Of course none of this is taking into account the length of the led strip :frowning: is there anyway to know what kind of wire it uses? thin I'm guessing.

Might be simpler to just do loads of practical tests :confused:

7

You are quite correct in that you need to provide power to each end of the LED strip and also at least each 100 LEDs (6 Amps) along the strip as the foil on the strip is indeed, quite thin. Of course, this presumes you will need to illuminate all LEDs at some point and I suspect that you indeed will.

Using batteries will be a problem as the required voltage is 5 V which does not directly match any particular battery and of course you would only be considering rechargeables. For 12 Amps, you will really want to use a mains power supply directly at the strip. Mains extension cables are readily available, so this is probably the most practical approach when all is said and done.

With 10 metre cabling distances (or even a third of that!), you will really want to have a controller at each LED strip. This could be a Pro Mini with the cabling carrying basic 5 V serial data at a modest baudrate (say, up to 9600) or it may be necessary to resort to RS-232 using MAX232-type interfaces. An alternate consideration would be to use ESP8266s and WiFi instead of cables. You need a 74HCT14 level converter to connect these to the LED strip. So everything - power, data - would be bundled to each LED strip, fully flexible arrangement.

8

cheers for the reply.

Power sockets are often at a premium and I think using 2 or 3 for a single led strip will be hard to justify unless that strip is a very prominent part of the display.

is 3.4v enough for a WS2812B led? I read they can run at a lower 3v but I wasn't sure if that meant a dimmer output? If its ok then I think Ill just tell the art director there's a 5 meter, 50 led limit per strip (or less if 3.4v isnt enough).

That way a single strip should be able to run off a mobile phone battery pack (5v, 3a) -

Also - If I used a single 5v, 12amp mains power adapter - would I be able to run 4 led strips off of it ok if each strip would only pull a max of 3a ? Or does it not work like that?

9

would I be able to run 4 led strips off of it ok if each strip would only pull a max of 3a ? Or does it not work like that?

Correct it doesn’t work like that.
Current is additive so if your power supply has a 3A capacity the total current from all strips when added together must not exceed 3A.

In fact it is a bad idea to draw 3A from a 3A power supply, you should only run power supplies at about 80% full capacity.

but I wasn't sure if that meant a dimmer output?

Yes it means a dimmer output, you don’t get something for nothing.

10

A suggestion, one I've not tried myself but I can't think why it would not work OK. Instead of supplying 5V over long, thick wires supply 12V or even 24V over thinner wires and put a 12V (or whatever) to 5V buck converter right next to the LED strips. You should be OK to use multiple converters along the length of the LEDs.

11

PerryBebbington:
A suggestion... supply 12V or even 24V

That brings up the question as to why the OP wants to use 5V leds at all. They are to cover a large stage and other areas, so is there truly a need for individual control of every led, or would control of groups of 3 or 6 leds be adequate. If so, 12V or 24V supply would preferable.

12

The leds are to be used in all manner of weird and wonderful ways. Some will be just for added flash on some parts of sets (around DJ booths etc), others will be to add effects to stage structures (like if theres a giant fiberglass dragon head, using leds to produce a flame effect from its nose etc etc).

Theres an overall art director but also lots of artists, none of whom know anything about electronics but I want them to be able to come to me with a design and say "id like this kind of light or lighting effect in this part of it" etc

There are multiple set "themes" that will be transported all over the place, some indoors, some out. Stuff will be in storage for a a year or more and then brought back into circulation for a year etc.

I need standardization as much as possible. I want to use the same kind of leds in as much as possible so I can run around and hook/unhook power and controllers quickly and easily without having to worry about different types.

Also - I'm no electrician so Id like to keep away from high voltages as much as possible. Tho - I think the danger threshold is 30v? So 24 should be safe even at 12a ? If there's a chance I could hurt myself or someone else if I screw something up id rather leave it alone.

@paul_b I think you may have misread my post - I mentioned a 12a power supply for 4, 3a strips. Given what you said about overhead, 3 strips (9a total) would be ok?

PerryBebbington:
A suggestion, one I've not tried myself but I can't think why it would not work OK. Instead of supplying 5V over long, thick wires supply 12V or even 24V over thinner wires and put a 12V (or whatever) to 5V buck converter right next to the LED strips. You should be OK to use multiple converters along the length of the LEDs.

this is interesting. I had thought about something like this but didn't know if the voltage converters were a thing - I'll look into buck converters. :smiley:

I have been focusing on 5v because I found WS2812B strips that were perfect for the various projects people wanted to do (size, functionality etc) they are nice and cheap which is very important and I thought 5v was a good area to be learning in since most hobbyist electronics stuff seems to be natively 5v.
Also - those 5v phone batteries are a very handy size for props where a mains connection just isnt viable. 12v batteries are huge and heavy and might be ok for some things but not others.

I may have just been paranoid out of ignorance but I had the impression that converting voltages from one to another was something I could easily get wrong and start frying things left and right :stuck_out_tongue:

13

PerryBebbington:
A suggestion, one I've not tried myself but I can't think why it would not work OK. Instead of supplying 5V over long, thick wires supply 12V or even 24V over thinner wires and put a 12V (or whatever) to 5V buck converter right next to the LED strips. You should be OK to use multiple converters along the length of the LEDs.

That is essentially how power over IP works.

It is what I recommended my friend to do when he had to chain LED clusters attached to buoys in a wet dock for an event. It worked well.

I think the danger threshold is 30v?

No it is 50V according to the EU legislation of the low voltage directive.

Also - those 5v phone batteries are a very handy size for props where a mains connection just isnt viable.

Those actually contain batteries and a buck converter, to take the voltage down to 5V.

14

That is essentially how power over IP works.

Yes, of course. It's also how the electricity distribution system works, although I suggest that the 400kV used in the UK might be a bit excessive in your situation!

15

Also - I'm no electrician so Id like to keep away from high voltages as much as possible. Tho - I think the danger threshold is 30v? So 24 should be safe even at 12a ? If there's a chance I could hurt myself or someone else if I screw something up id rather leave it alone.

I work in telecoms, telecoms kit typically runs on 50VDC. I can't feel 50VDC, let alone get a shock from it. I know some people can feel ~30VDC.

16

messy87:
I need standardisation as much as possible. I want to use the same kind of LEDs in as much as possible so I can run around and hook/unhook power and controllers quickly and easily without having to worry about different types.

And on that score, I would reiterate my suggestion of sticking to mains power and using modular 5 V power supplies - 3 Amps is within the ambit of current 5 V "Phone chargers", readily available ready-built and perfectly safe. Using WiFi would mean no interconnects other than the power cable so you could deploy them anywhere needed.

messy87:
I may have just been paranoid out of ignorance but I had the impression that converting voltages from one to another was something I could easily get wrong and start frying things left and right :stuck_out_tongue:

That is to some extent, true. I did consider that suggestion myself in my first posting, but it does massively complicate the wiring and conflicts with the data communications. (POE is based on an isolated data circuit. :astonished: )

messy87:
There are multiple set "themes" that will be transported all over the place, some indoors, some out. Stuff will be in storage for a a year or more and then brought back into circulation for a year etc.

Which means batteries become a major problem.

messy87:
Also - those 5v phone batteries are a very handy size for props where a mains connection just isn't viable. 12v batteries are huge and heavy and might be OK for some things but not others.

I am not sure which of these "Power bank"s will handle 3 A for any substantial period. 12 V 8 Ah SLA batteries are not all that "huge and heavy" - or expensive - and with a switchmode "buck" converter would be quite practical. Relatively easy to charge also.

Grumpy_Mike:
Those actually contain batteries and a buck converter, to take the voltage down to 5V.

Which ones are these? All the basic "Power bank"s contain a single 18650 or similar battery - or sometimes up to three in parallel since putting them in series requires special charging circuits - and a boost converter.

I still have - but sadly never used - some of the batteries from the Sydney 2000 Olympics performances. 12 V sets of six "Gates" premium quality SLA cells. Basically used a couple of times and then disposed of. :astonished:

17

Which ones are these?

Every one that I have ever pulled apart. They have had batteries in series and a buck converter. They are much more efficient than a boost.

18

Paul__B:
I still have - but sadly never used - some of the batteries from the Sydney 2000 Olympics performances. 12 V sets of six "Gates" premium quality SLA cells. Basically used a couple of times and then disposed of. :astonished:

I think 20 year old SLA batteries are going to be scrap....

19

I have been focusing on 5v because I found WS2812B strips that were perfect for the various projects people wanted to do (size, functionality etc) they are nice and cheap

Its true that sticking to the same voltage throughout would make your project simpler in some ways. But it brings disadvantages too. The LEDs need an amount of power, depending on the colours and brightness of the patterns they are showing. To get that power to them with a lower voltage means more current. More voltage means less current. P = V x I

The amount of power lost in the wires, and in the strip itself, depends on the resistance of the wires. The resistance depends on several things, but longer wires have higher resistance and thinner wires have higher resistance. The power lost is calculated with P = R x I^2. So keeping R low is important. But even more important is keeping I low, because the power lost goes up in proportion to the current squared. That's why electrical power is always transmitted over long distances as a high voltage. That keeps the current low when transmitting a given amount of power. Also, there is less voltage drop, which can make your LEDs dimmer and alter their colour

That's why it would be easier for you to power your strips with a higher voltage like 12V or 24V. You can use longer and thinner wires compared to 5V, without loosing a lot of power and voltage. The downside of using 12V and 24V strips is that you don't get individual control over every led like you do with 5V strips. In 12V addressable RGB strips, the LEDs are connected in series as groups of 3, which reduces the current required by a factor of 3. But you only have control over each group, not each led. All 3 LEDs in the same group will always be the same colour/brightness. This may be fine for the effects you want because they are large-scale effects.

With 24V strips, the LEDs are in groups of 6, reducing the current down to one sixth compared to 5V strips, but you can only control the groups of 6, and 6 neighbouring LEDs will always be the same colour/brightness.

With 12V and 24V strips, you can't cut the strip at any place like you can with 5V strips. You have to cut them only at the marked positions, so you don't cut the middle of a group of 3 or 6.

20

PaulRB:
In 12V addressable RGB strips, the LEDs are connected in series as groups of 3, which reduces the current required by a factor of 3.

Apparently not always. You need to be careful. :astonished:

As surprisingly noted in other threads, a proportion of the "12V" strips available control one RGB LED per WS2811 chip, which "wears" the consequent voltage drop. the current draw is the same as corresponding 5 V strips.

Why would you do that? Simply for the convenience of using an available 12 V supply it appears. Mind you, it also means that the strips can tolerate a substantial voltage drop (like 5 V or more!) along the supply foils since the WS2811 is a constant-current driver.