# When calculating LED power consumption, how precise must one be for selecting power supply values?

#### Dolmetscher007

Joined Mar 21, 2019
36
Newbie Preface: I have read a lot and have a descent grasp on electronics theory. However, this is my first actual electronics project, and I mean... my very first. First time ever even using a soldering iron.

Project:
I'm building a light panel using three different reels of LED strips. I'd like to include as many LEDs as possible but still be safe with my power supply. Below is a list of links to all the items I'm using. I've also attached a full scale drawing of the panel and how I've wired it all up. I looked up the current draw and power consumption of different 12V LED types, and I found the following... SMD5630 pull 150mA per LED and SMD5050 pull 60mA per LED. My panel will be 27 strips of 30 LEDs, broken down like this...

 270 (9 strips of 30) SMD 5630 - Daylight White - @ 150mA ea. 270 x 150mA 4.05A 270 (9 strips of 30) SMD 5630 - Warm White - @ 150mA ea. 270 x 150mA 4.05A 270 (9 strips of 30) SMD 5050 - Blue - @ 60mA ea. 270 x 60mA 1.62A Total Amperage Draw 9.72A Total Power Consumption: P = 9.72A x 12V 116.64 Watts
Questions:

1. I bought a 12V - 10A Power Supply on Amazon. My current draw is 9.72A for a 10A power supply. Is this perfectly fine, or is there a best practice % over/under for amperage?
2. I only have 22 gauge wire. On this online chart it says the max amps for "chassis wiring" wire is 7 amps, but for "power transmission" it's only 0.92 of an amp. I don't know what either of those things are. Is it absolutely imperative that I order some thicker gauge wire?
3. Since there are three different color temperatures of LEDs, I want to be able to control the amount of each color I can "dial in", so I am planning to wire up each color to it's own individual dimmer knob, using three PWM 12V - 5A - 90W LED Dimmer. My total amps is 9.72A, but each strip is under the 5A max for the PWM dimmer modules. Is that fine?
4. If you look at the wiring diagram I've attached, you can see where I am taking the input from the power supply and splitting it into three +'s and three -'s to go to the + and - terminals of the dimmers. Is that fine, or am I missing something?

I really appreciate you guys' help!

#### SamR

Joined Mar 19, 2019
4,548
The first thing I would do is find the PDF (Product Data File) for the strips. Something that you will not find on Amazon, fleaBay, or AliX. The PDF will give you the needed parameters that otherwise can only be guessed at.

#### Dolmetscher007

Joined Mar 21, 2019
36
The first thing I would do is find the PDF (Product Data File) for the strips. Something that you will not find on Amazon, fleaBay, or AliX. The PDF will give you the needed parameters that otherwise can only be guessed at.
I did try to find some data sheet material for these LEDs, but they arrived in those typical generic sealed silver zip bags with no marketing or even any real branding. The sticker does say, "Model: Marswell-A5630-60-V12" but when I look for data sheets or Product Data File (as you suggested) I see tons of hits taking me back to Amazon, but there does not even seem to be a website for "Marswell LEDs" much less a Product Data File. (I am pretty confident, however, that I have all the information I need about the LEDs. My questions are about best practices regarding power supplies.

#### SamR

Joined Mar 19, 2019
4,548
Sounds like typical chinesium products. We don't know if they are current limited by resistors, they should be. Are they wired serial or parallel? Was there any paperwork other than the package label included? You could guestimate by counting the LEDs, then ~0.3V drop across each LED but it would be a very rough guestimate without a real datasheet. I googled what model info you had and mostly found listings for sale and no data. You could try contacting the seller.

#### ScottWang

Joined Aug 23, 2012
7,327
About the draw current that I will provides it about 80% of rating current, and that is for the LED luminance decrease, you have to do a good choice between brightness and luminance decrease, some of the LED strips can be provides lower voltage of the Vcc to reducing the draw current, some may need to in series with a resistor.

#### BobTPH

Joined Jun 5, 2013
6,310
Your current numbers make no sense, no matter how I compute them.

you say 270 LEDs at 150 mA each. This is 40 A all by itself!

Or, did you mean each of the none strips takes 150mA? That would be only 1.3each for 2 of your sets of white of LEDs, and .5A for the the blue ones, for a total of 3.2A.

The first way of calculating them is way too much, and the strips would melt if it was right. The second is probably correct since there are probably three LEDs in series on the strips, so each LED is seeing 15mA 10 / 150. But then the total current should be 3.2 A.

If you are seeing 9A, something is wrong.

Bob

#### BobTPH

Joined Jun 5, 2013
6,310
Okay, I looked at your table again and I see your mistake. You multiply 150 mA, which is 0.15A x 270 and come up with 4.05A. Try again, it is 40.5A. And it has to be wrong.

Where did you get the 150 mA from? I see no current rating on the listing.
Bob

#### Alec_t

Joined Sep 17, 2013
13,337
We don't know how your strips are wired (series/parallel), nor how the LEDs are wired within a strip.
If your picture is an accurate representation of the actual LED strips then it appears to me that the LEDs are grouped in threes. It's likely (but you'd have to check with a test meter) that 12V supplies a group of 3 LEDs in series with a resistor which limits current to 150mA. So one strip of 30 LEDs comprises 10 such groups, giving a total current of 10 x 150mA = 1.5A per strip if the 10 groups are wired in parallel. An alternative supply arrangement would be a constant current 150mA from a 120V (at least) source if the groups were wired in series.
But however the LEDs are wired, the 12V 10A supply is inadequate . As Bob says, you need a ~40A supply.
(9 x 1.5A daylight-white + 9 x 1.5A warm-white + 9 x 0.6A blue = 32.4A, + allow some margin).
There'll be some serious cooling needed to dissipate hundreds of Watts of heat!
Edit: I've just noticed that the dimmer rating of 5A is also inadequate. Each colour temperature set of LEDs draws more than 5A.

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#### BobTPH

Joined Jun 5, 2013
6,310
There is no way those LEDs can handle 150mA. That is why I ask where he got that number. My guess is that they are 3 in series so 10 in parallel on each 30 LED strip, giving a current of 15mA in each LED, but this might be low. I can see them being as high as 50mA, but no more due to dissipation.

When they talk about a 5A dimmer I think that is for the entire 5m strip, which, would be 5A at 50mA each and 3 in series.

TS needs to measure the current.

Bob

#### Tonyr1084

Joined Sep 24, 2015
7,248
I bought a 12V - 10A Power Supply on Amazon. My current draw is 9.72A for a 10A power supply. Is this perfectly fine, or is there a best practice % over/under for amperage?
My best practice is to have a capacity 1.33 times (133%) of anticipated normal use. For 9.7A, using my rule, I'd go with a power supply capable of at least 12.901A (13 amps). For life critical - or mission critical, 1.5 times is common engineering among medical, aerospace or military equipment. Under that rule, 9.7 x 1.5 = 14.55A. I'd use a 15A supply in that case.

When yo provide "Enough" power you don't have head room for unexpected circumstances and can experience failure. Also, with "Enough" power - you run at near max capacity, which leads to excess heat and fatigue of the components. Life expectancy will be shortened under such conditions. In your case, 9.7A is too close to 10A. And I'm assuming your numbers to be actual requirements.

I only have 22 gauge wire. On this online chart it says the max amps for "chassis wiring" wire is 7 amps, but for "power transmission" it's only 0.92 of an amp. I don't know what either of those things are. Is it absolutely imperative that I order some thicker gauge wire?
22 gauge wire can't handle 10 amps. 18 gauge is pushing it. 16 amps is more than sufficient for 10 amps. Again, I'm using your numbers.

#### Audioguru again

Joined Oct 21, 2019
5,585
The listing says that each strip of 300 LEDs is tested at 40-60W which is a current of 40W/12V=3.33A to 5A.
The image shows 3 LEDs plus a resistor. The LEDs are each around 3V each so they are in series and in series with the resistor to be powered from 12V.

Since 300 LEDs use up to 60W then his strips of 30 LEDs will use up to 6W. There are 27 strips of 30 LEDs so the total power is 27 x 6W= 162W and the total max current is 162W/12V= 13.5A.
With 162W in that small space then something (the LED strips?) will get cooked quickly. People's eyes also might be blinded.

#### Dodgydave

Joined Jun 22, 2012
10,694
PSU wise, use an old ATX gives out 20A easily.

#### Deleted member 115935

Joined Dec 31, 1969
0
Seems that the numbers you have are not of much use ,
at this point, I'd be looking at experimenting,

Don't suppose you have a current limited power supply , a lab type one ?
you could set a voltage and slowly increase the current to see what happens.

If you have not, then you could use a selection of resistors and a variable voltage supply to implement similar,

as for the original question,
voltage accuracy,

if the circuit is using a simple resistor to current limit, then good old V = I R , dictates that as the volts go up, the current goes up linearly. And led brightness is proportional to led current. Luckily, the variation in each leds intensity with current change is none linear, so once light, the brightness varies a lot less than those first few mA before it turns on.

Also the variation in brightness led to led, unless they are matched to some degree, is quiet variable.

#### Alec_t

Joined Sep 17, 2013
13,337
There is no way those LEDs can handle 150mA.
I certainly wouldn't want to pump that much current through them, but did you study the data in the post #8 link?

#### BobTPH

Joined Jun 5, 2013
6,310
Yes. And with sufficient heat sinking they probably can take take 150 mA. But not on these strips, As AG and I both calculated, these seem to be designed for 50mA.

Bob

#### MisterBill2

Joined Jan 23, 2018
14,269
I was just experimenting with LED strips from tube lights with failed power supplies. Of course I have no information on them because there is no label that tells me anything. Each strip has 52 groups of 3 LEDs in parallel, with the groups in series. So I connected them to my adjustable Dc power supply with a milliameter in series and I find that they start to glow around 34 volts and are quite bright at around 35 volts and at that point the current is 100mA. The current rises very rapidly as the voltage increases in very small amounts. So that is one configuration of LEDs .
The TS needs to gat a multimeter and an adjustable power supply and discover what the actual voltage required really is, and then measure the current at that voltage to know what the actual current for a strip will really be.
The rest is all guesses. In my strips the individual LED current is about 32mA. At least that is what my measurements indicate. It might be that there are larger groupings in parallel because it seems strange that it works on 35 volts.

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#### BobTPH

Joined Jun 5, 2013
6,310
The strips he has are designed to be powered by a fixed voltage of 12V. They are arranged in groups of 3 in series with a resistor to limit current. The only question is how much current. The way to determine that is to connect them through an ammeter to a 12V source.

Bob

#### Audioguru again

Joined Oct 21, 2019
5,585
The manufacturer says the LED strips are tested to be 40W to 60W for 300 LEDs. Since there are 100 groups of series LEDs then each LED uses 33.3mA to 50mA.

#### djsfantasi

Joined Apr 11, 2010
8,792
22 gauge wire can't handle 10 amps. 18 gauge is pushing it. 16 gauge is more than sufficient for 10 amps. Again, I'm using your numbers.
Tony,
Did you mean gauge, not amps?