5 Volts vs. 12 Volts and Power Injection

Who really cares? The LEDs and your pocketbook.

When our esteemed publisher (Chuck Smith) gave us the task of building a pixel tree, I thought it would be easy because I could build a megatree in no time at all. Get 16 sets of 100 bulb mini-light strings, hang them from a pole, plug them in and you’re done. If I wanted that megatree to dance to the music, I’d plug each string into a channel of a light controller and the WOW would happen.

Mr. Smith hinted a pixel tree might be a bit more complicated. Every light had to be controllable (I got to hear the any light, any color, any time speech.) I soon figured out 16 sets of 100 bulbs meant 1600 individual lights or pixels to control. In this world, since each pixel required three control channels, that’s 4800 channels. All I could think of was a truckload of wire to build a pixel tree.

Just for the record: the image above gives all of us a headache.

We started our ‘pixel’ research and discovered we needed to enter the world of low voltage. I figured this was a good thing since you never hear of anyone dying from touching the electrical connectors of their car battery.
Then the confusion began to set in. A lot of pixel stuff works on 12 volts DC (Direct Current.) The newer stuff works on 5 volts DC. Now we need power supplies to convert normal wall voltage (120-240VAC) down to this low voltage stuff. Then someone said we needed to make sure the power supplies could handle the current load. As if my head wasn’t hurting enough already, Chuck said we should learn about power injection so the pixels could get enough current to work like they were supposed to. Voltage, current, power supplies: this is all new stuff to learn about.

I reached out to an electrical engineer that happened to be an over-the-top decorator. He started talking about wire gauge, current ratings and system loads. In other words, a foreign language. Why does this need to be so complicated?

After some digging, I found an engineer that knew how to speak normal English. She said to think about electricity the same as the plumbing in my house. Since I can see water and understand how my bathroom sink works, I could instantly relate.

Water comes in the house and is distributed through pipes. The bigger the pipe, the more water it can deliver at a given time. The water enters the house under pressure. How fast my sink fills up is based on the water pressure and the size of the pipe.

Skinny wires coming into the transformer and fat ones going out.
Skinny wires coming into the transformer and fat ones going out.

Electricity is like the water in your pipes. It enters as voltage (instead of water pressure) and is distributed through wire (think pipes) to all the different plugs in the house. The amount of electricity you get out of the plug is based on the voltage and wire size. Increase the voltage and/or wire size and you get more electricity meaning more power.

The amount of electricity used is called current. I’m oversimplifying but here’s the key: the current available to an electrical device is based on the voltage level and the size of the wire.

Ever noticed the electrical wires way up on the utility poles going down the street? Those wires provide the power to hundreds or thousands of homes and businesses so that means a whole lot of electricity or power. Those wires look pretty skinny to me knowing how many computers, ovens and washing machines they have to power. If you could get close to those wires, you would see they’re about as big around as your thumb. Put an electrical meter on them and you’d see thousands of volts instead of the 120-240 volts we use at home.

Remember the water analogy about filling up the sink? If water is under a lot of pressure, it can fill up a sink fast even with a small pipe. With electricity, increasing the voltage means you can provide more over a smaller wire. That’s why high voltage wires can be small compared to low voltage wires. The current available to an electrical device is based on the voltage level and the size of the wire.

Close to your house you’ll see an electrical transformer. This reduces the high voltage to what’s provided to your house. Look carefully and you’ll notice some skinny wires going into the transformer and fat wires coming out. Higher voltage in, lower voltage out so you need bigger wire. The current available to an electrical device is based on the voltage level and the size of the wire.

Now think about the battery on your car. Ever notice the really fat wires coming off of it? There are components of your car that need a lot of electricity to function correctly. Since the battery is only 12 volts, you need some pretty big wire to provide enough power. We’re going to say it one last time: the current available to an electrical device is based on the voltage level and the size of the wire.

Now you should understand a little better why low voltage components make using electricity a bit more complicated.

The Pixel Voltage Challenge

Finding the components for our pixel tree became challenging almost immediately. Until last year, most pixel based lights needed 12 volts to work. Now we’re seeing pixels that only need 5 volts. I’m thinking lower voltage means fatter wires. What’s going on?

The pixel manufacturers have apparently figured out that 5 volt pixels can be more efficient and thus a little brighter than 12 volt pixels. Want to know why? Trust me, you don’t. Ask an electrical engineer and take a dictionary with you. The cynic in me is thinking 5 volt pixels must be a little cheaper to manufacture.
Are 12 volt pixels brighter than 5 volt pixels? We really couldn’t tell.

To further challenge us, we learned low voltage power supplies are rated in watts or amps and physical power supplies look the same even with different voltage outputs. A 12 volt 20 amp power supply looks the same as a 5 volt 48 amp supply. The engineer told us they both put out the same amount of power. Did I mention this was really unnecessarily complicated???

Power Injection in Real Life

We built several pixel trees. Some used 12 volt pixels, others used 5 volt pixels. Voltage is fed into one end of a pixel string. Depending on the wire size of the pixel string and how long the string was we would sometimes notice the pixels at the end weren’t as bright as the ones at the beginning.

We figured out there wasn’t enough electrical current at the end of these pixel strings to power the pixels like they wanted. Someone suggested power injection might be the answer. Sure enough, we provided low voltage at both ends of the string and all the lights were bright.

I thought of my “Slip ‘N Slide” when I was a kid. Connect a water hose at one end of this long piece of plastic, let it get wet, run, jump and slip/slide all the way to the end. One day I got burned because the end of that plastic sheet wasn’t wet enough. I ran a water hose from the back of the house, connected it to the not-so-wet end of the “Slip ‘N Slide” and both ends got plenty of water. I had figured out the electrical equivalent of power injection.

Through trial and error (lots of errors) we found out not to power 5 volt pixels with 12 volts or you end up with dead pixels forever. Use 5 volts to power 12 volt pixels and not much happens. Put too many pixels on a power supply and you get an overheated supply that shuts down at inopportune times. Reverse the positive and negative wires and well… don’t do that.

Bottom line: low voltage is more cumbersome to deal with but it’s much safer for humans. Is it worth the hassle? Yep.

This article was included in the April 2014 issue of PlanetChristmas Magazine.

By Sara Casey

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