# Figuring 300 Watt Power supply

Discussion in 'Power Supplies' started by Rufio, Feb 3, 2014.

1. ### RufioNew Elf

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I need a little help figuring how many lights I can run on this power supply. I did this for the first time last year, and now one year later I can't remember how I did it so this time I will have it in writing. For the lights I have 5vdc (in USA so it 120AC) WS2811 RGB strips I will have sixteen strips 50 pixels long each. On the manufacturers page it states the following; 5V 4.Current: 3.2A and Power(W/M):8 W/M If I'm correct that means that the whole roll of 5 meters or (150 pixels) draws 3.4 amps correct?

The power supply is a 300 watt 5v 60amp. If I remember I should figure at 85% of load. So how do I figure what each of the strips above will require in the form of watts?

Thanks for the help!!
Here is the link for the lights if needed http://www.diyledexpress.com/index.php?main_page=product_info&cPath=42_44&products_id=176

For the Power Supply http://www.diyledexpress.com/index.php?main_page=product_info&cPath=20&products_id=162

2. ### ԆцряєсϮSenior Elf

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Watts = Volts x Current
If each strip is 3.2 A and your power supply can do 60A then 85% of your power supply will give you how many strips you can run
Watts (300) = Volts (5) x Current (60)

3. ### fasteddyI have C.L.A.PGlobal Moderator

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Im a bit suspect about those specified rating if the 2811 chip is running at the designed 18.5mA per colour as i calculate 1.665 amps per metre which should be approx 0.3 watts per LED

I may be missing something here.

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### RufioNew Elf

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Thank you for the post. I think I'm missing something here. Please have patience with me as I'm learning this and not yet confident in my math.

So the information is correct that the roll of RGB strips consumes 3.2 amps? If so that one PS will run 15.6 full rolls of WS2811 at 5m per roll figured at 85%? Seems high to me. Please feel free to correct me if I'm wrong here. Just seeking the truth!!

Thank you!

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### RufioNew Elf

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Thanks Eddy. By the way it was nice to meet you at the 2013 Academy. Did you get a Laptop yet? The computer there was really giving you fits! Anyway, at .3 watts per LED one roll at 5m or 150 LED's consumes 45 watts. Resulting on that PS running 5.66 rolls of LEDs correct? Did you see the link I posted on the products? Does that information look incorrect to you?

6. ### fasteddyI have C.L.A.PGlobal Moderator

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It was a pleasure to also meet you over there and it was a great time. You guys really know how to put on a show. As the saying goes everything is bigger in Texas

I'm basing my information on specifications of the 5050 LED which is normally designed to run around 20mA per colour and the specs on the 2811 which is designed to output at 18.5mA per colour. If this is a 5vdc strip and we work on these known specs then the calculated load is as below

18.5mA per colour x 3 = 55.5mA per LED

5v DC x 0.0555Amps = 0.2775 watts per LED

0.2775 watts x 30 LEDs/Metre = 8.325 watts per metre

so 8.325 watts per metre / 5VDC = 1.665 amps per metre

So the specifications on the web site say 5v, 3.2amps and with 8 watts per metre but mathematically that doesn't work out, the 8 watts per metre seems to be the correct rating but the current seems to be on the low side as I put the current at:

1.665 amps per metre x 5 metres = 8.325amps.

Also from testing that Shell did today with the same type of strip had confirmed these calculations even though Shells results were slightly lower but that's to be expected as in most situations there are variances and they are more times than not you will find that the real load is slightly lower than the calculated load which is a good buffer to have and why I just use calculated loads.

and yes I did buy myself my own laptop which has been a pleasure to use

hope that helps

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### RufioNew Elf

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Thanks for looking at this for me Eddy!! I trust your math and experience completely!! Now i can figure my PS correctly. Great news on your Laptop. Look forward to seeing you again this year if they fly you out. Take care.

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