Author Topic: Calculating power requirements  (Read 2900 times)

Offline sdbgtrman

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Calculating power requirements
« on: April 09, 2016, 09:33:23 AM »
I'm doing my first RGB setup this year. I have my F16v2 on order and just got my pixels from Ray Wu. I have two 350W power supplies (12V) but in reading through all these posts, I don't know if that's going to be enough now.

I see the Blinky Flashy calculator and was going to give that a shot to help figure out how many supplies I needed, but was a little unsure of the specs for my pixels. Ray Wu has the pixels listed as 30mA and 0.3W for what I ordered. Is that for the string of 100, or is that per pixel? Sorry if that's a dumb question, I just want to make sure I understand what's going on so I can plan accordingly.

Thank you,
Steve


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Offline JonB256

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Re: Calculating power requirements
« Reply #1 on: April 09, 2016, 10:53:21 AM »
Ray Wu has the pixels listed as 30mA and 0.3W for what I ordered. Is that for the string of 100, or is that per pixel?

Thank you,
Steve


That would 30mA per pixel or 3 Amps for a string of 100. 

Offline sdbgtrman

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Re: Calculating power requirements
« Reply #2 on: April 09, 2016, 12:19:48 PM »
Ray Wu has the pixels listed as 30mA and 0.3W for what I ordered. Is that for the string of 100, or is that per pixel?

Thank you,
Steve


That would 30mA per pixel or 3 Amps for a string of 100.
Thank you, I appreciate the answer

Offline sdbgtrman

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Re: Calculating power requirements
« Reply #3 on: April 09, 2016, 12:26:45 PM »

That would 30mA per pixel or 3 Amps for a string of 100.

So, I'm going to exceed one household fuse with 1,000 lights running 30Amps? Are you guys running multiple circuits to do large displays? I'm looking at around 1,800 lights this year, so do I need to pull from different circuits in my house?

Offline DSMJuggalo

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Calculating power requirements
« Reply #4 on: April 09, 2016, 01:33:03 PM »
30a 12v is only roughly 2.8 amps when converted to 120v. You can run well more than 1000 pixels on a 20a home breaker, roughly 3600 on full white.


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Offline JonB256

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Re: Calculating power requirements
« Reply #5 on: April 09, 2016, 01:35:48 PM »
No. Amps are not quite that literal.

30 amps at 12vdc only needs 3 amps from 120vac  (30 x 12 = 360watts as does 3 x 120 = 360watts)

Wattage is important.

Wattage equals Amperage times Voltage
Amperage equals Wattage divided by Voltage


Offline sdbgtrman

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Re: Calculating power requirements
« Reply #6 on: April 09, 2016, 01:48:02 PM »
No. Amps are not quite that literal.

30 amps at 12vdc only needs 3 amps from 120vac  (30 x 12 = 360watts as does 3 x 120 = 360watts)

Wattage is important.

Wattage equals Amperage times Voltage
Amperage equals Wattage divided by Voltage
Doh. Ok, I should have seen that. Thank you.

Offline sdbgtrman

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Re: Calculating power requirements
« Reply #7 on: April 09, 2016, 05:57:22 PM »
30a 12v is only roughly 2.8 amps when converted to 120v. You can run well more than 1000 pixels on a 20a home breaker, roughly 3600 on full white.


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Yeah, I missed that conversion from 12V to 120V in my math. Thank you for helping.

Offline tbone321

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Re: Calculating power requirements
« Reply #8 on: April 09, 2016, 06:53:31 PM »
Lets add a gotcha's into this.  While the calculations made are correct, they are making the assumption of 100% efficiency and that is simply not the case.  Many of these low cost power supplies are around 75 to 80 percent so that needs to be taken into account when determining the total load on the circuit.  I would also keep the total load on the circuit to around 85% of the breakers rating or you may wind up with an unexpected surprise during a long all white run in the sequence. 

Offline sdbgtrman

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Re: Calculating power requirements
« Reply #9 on: April 10, 2016, 06:55:38 PM »
Lets add a gotcha's into this.  While the calculations made are correct, they are making the assumption of 100% efficiency and that is simply not the case.  Many of these low cost power supplies are around 75 to 80 percent so that needs to be taken into account when determining the total load on the circuit.  I would also keep the total load on the circuit to around 85% of the breakers rating or you may wind up with an unexpected surprise during a long all white run in the sequence.
Good call. I'm going to start with 80% to be sure. It looks like the calcs I worked up today have good break points with my elements right around 80% anyhow.

Thank you all again. Working through the logistics of all of this is a lot more intense than I anticipated. But it is fun.

Offline AAH

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Re: Calculating power requirements
« Reply #10 on: April 11, 2016, 02:44:26 AM »
  To be sure of a safety factor I always assume that all pixels are 55mA (just over the typical 18.5mA per colour 2811 current) regardless of the specs given. The manufacturer can actually adjust the current down from that but I would personally rather rely on the maximum white light current that a WS2811 pixel can draw rather than generic specs provided by a cut and paste on Aliexpress. You can work out current and wattage for a string on http://www.da-share.com/calculators/led-strip-string-current/ and factor the required current/wattage back to your power supplies. Loading any power supply to 100% isn't ideal but depending on the enclosure and weather conditions you may need to reduce the loading even further. In Aussie where the temp at the start of an Xmas show might be 35C the derating for the power supplies can mean that you need to reduce the load per power supply to well under 80%.
  To work out what power supplies that you need you can either work off the current per string/s and then factor that into the current that a power supply supplies. For example a string of 100 pixels is 5.5A and a 360W 12V supply supplies 30A. Theoretically you could put about 5 strings of 100 off the power supply with a safety factor or 6 if you really wanted to push the friendship.
  As far as power supplies per power circuit a 360W power supply will draw something like 450W at full load. At 110V AC this is just over 4A. For 240V it's a little under 2A.


 

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