Pixel power requirements

[jrk1963]

Hi

I am planning to build window frames with 2811 5v pixel nodes. I have figured out the spacing to get everything to come out the way that I want. I have three window frames that will need a total of 348 nodes and a fourth that will use 300 nodes.

I was just looking at the power reference by Fast Eddy. According to my calculations using this reference, the large window frames will need 104.4 watts and 20.88 amps and the smaller one will need 100 watts and 18 amps. The total would be 413.2 watts and 82.64 amps at 5vdc.

I am in the US and we use 120v AC power here. I also have two 5vdc power supplies. These should handle the load.

I am wondering about the wire needed to supply power to the pixels. My initial plan was to use a four conductor waterproof cable and tie two together for the positive and the other two for the negative. I'm not sure, but I think these are 18 gauge stranded wire. In the US it is recommended to use a minimum of 12 gauge solid wire for a 20 amp AC circuit. Will two 18 gauge stranded wires tied together in this manner be enough to handle the load to one window frame?

Also I'm concerned about the AC side of the power supplies. I am familiar with ohms law, but, I am confused regarding 120vac versus 5vdc. If I am pulling 82.64 amps at 5vdc, what would the power draw be on the AC side? Would it still be 82.64 amps, or would it be 3.4 amps?

Thanks.

Jerry

 

[scamper]

Doubling the 18 gauge wire will still only give you 14a. So a little shy.
But, if you power inject, and I assume you will need to, to counteract the voltage drop, then the load will be shared.
The 4amps on 120vac is closer, but there are a few things that you need to take into account when converting dc current to ac current. But close enough for your piece of mind I would think.

 

[i13]

The spacing you receive is not very precise. It is usually a little bit shorter than what you ask for.

 

[jrk1963]

Thanks all.

Scamper. The AC current is well within my circuit limit. My Christmas stuff all run on 20a dedicated circuits. One breaker - one run of wire to one plug. I could plug both power supplies into one circuit and still be within tolerance. That puts my mind at ease.

You are correct that I plan to do power injection. My plan is to use the four conductor cables for the power injection and three conductor cables to connect the pixels to the controller. No way to get confused and plug the pixels directly into the power supplies that way.

As far as the wiring from the power supply to the pixels. I guess I will have to add more conductors or switch to 12v pixels. There is a 5amp limit on the pixel controller per output and I need to find over 6 amps. Not good to push things that close to the limit either.

Good point i13. I will check my pixels to be sure that the wire is long enough for the spacing I need. I think it is, but it is better to be sure before I start building things. There is an old carpenters saying - Measure twice, and cut once. lol

Jerry

 

[i13]

Try powering the pixels and checking their current draw. It might be lower than the calculations predict.

 

[scamper]

Also, you don't need to run the power through the controllers, you can just run a common earth and the data line and run power straight from a supply to the pixels, that way it doesn't matter the current draw through the controller.

 

[jrk1963]

Also, you don't need to run the power through the controllers, you can just run a common earth and the data line and run power straight from a supply to the pixels, that way it doesn't matter the current draw through the controller.

Yes, that is my plan. I am told I need to connect the grounds of all the power supplies together, but not the positive.

Thanks

Jerry

 

[i13]

That is correct although it can be done through the light sets. You'll need to have the positive line cut half way between each power supply.