I’m starting a project that will need power for 20 meters of LED’s and I would like to bounce may math off the group to make sure I’m correct. I slept through electrical engineering. The 120 Watt requirement I’m coming up with of seems too low to me.
Will use SMD5050 LED’s with 66 LED’s per meter. Could end up to be the older WS2812B or newer APA102 powered. Data Spec’s for the 5050 say 20 Miliamps max draw per chip on full power at 5 VDC.
20 meters X 66 LED’s = 1,200 LED’s
1,200 LED’s X 20 milliamps each = 24,000 milliamps
I have not got my hands on the APA102 but I am fairly sure it has the same power requirements as the WS2812.
My experience with the WS2812 shows that with full brightness white I actually measured closer to 45 ma (that is approx. 15 ma per color on each LED)
So your maths is definitely off. It is more like…
20 meters X 66 LEDs X 3 colors per LED X 15ma -> 59,4 Amps.
But even that is misleading !
On most display, we rarely if ever turn all LEDs on full brightness. You should attempt to figure out what would be a more realistic max current draw by figuring out the most (current wise) demanding animation that you will be requiring from your setup !
Just went through the Adafruit recommendations and I would also agree with their suggestions of using 20 ma MAX per LED as a very valid guideline for most applications !
When doing any design, a safety factor is usually used. Basically, I would design for 125% SF.
Other things to consider (?) ohm resistance for wire length…wanting to add a few more LEDs or LEDs specs out of range.
The NEC has guidelines for electrical design…it gets complicated and you are only dealing with LEDs.
So, why not do it like a fuse design? And it basically uses a 125% safety design factor for the continuos loads and 100% for non-continuos loads.
Personally I agree with the 125% of max method. Obviously if you know for a fact you’ll never run white at full brightness, then fine but the other option is you burn out a power supply, wires from it or just see havoc from starving the devices.
One thing is for sure, you cannot string two sets together and expect that the traces on the ribon will handle that much current. You’ll need to run a pair of supply leads every 5 to 10 meters. Remember voltage drop occurs on both sides ofvthe supply. 24 awg wire will see as much as a volt of drop at 5 amps. This means two volts total. And now you’re only supplying 3 volts.
“Obviously if you know for a fact you’ll never run white at full brightness” Theoretically this is right and practically it means you have to be very sure you know exactly what you are doing while coding. Limiting the master brightness while coding new stuff helps to prevent accidents.
The “rarely turn on all leds full brigjtbess” is often true of you wont use a lot of light, however when you start playing with desaturated colors, guess what, you are going to be using much more than 1/3 the max power draw of the leds.
These days I almost always allocate power and size wires assuming full white everywhere. Saves me a lot of headaches later on.
Thanks all. Not knowing what kind of FastLED program I may be running a year from now; I will over-engineer this and provide power to the strips about every meter and size it at 125% of max which would be:
20 meters X 66 LEDs X 3 colors per LED X 20ma each LED -> 79.2 Amps.
Plus a 25% buffer of 19.8 Amps = 99 Amps.
A whopping 495 watts of power! A 4.1 Amp draw from a 120 Volt source to the power supply.
Now, on to order some 5V regulated power supplies!
@Bernhard_Walter
Nope, your math is off, even using your numbers…the previous breakdown included the 3leds per LED. So your, 20x66x60/1000= 79.2 = 20x66x(3x20)/1000
@Giligain_I Whats wrong? Bob calculated with 20 mA - 24 A total and I said its 3 times - 72A in total
I think this is because ther are no strips with 66 per meter - I saw and bought them with 30, 60 and 144 per meter
@Bernhard_Walter
I don’t know? I didn’t research the product just working with the input data only…but I took a look at this site and it has a lot of good info about the subject.
[edit, forgot link] http://www.ledlightsworld.com/page.html?id=38
However, if in fact 60 is the actual number of LEDs used versus having designed for 66 LEDs, this would only introduce yet another accidental 10% safety factor into the design.
Think of it this way. The next time you are standing in an elevator and the MAX weight limit posted is 2000 lbs. I can guarantee the design weight limit is much higher than that number posted, more like 2.5 times higher.
I’ve been surprised working on an existing building for remodel, that the columns were designed to carry an additional 2 extra floors. The hospital got its rooftop heliport landing pad because of this extra design into the columns.
