February 18, 2019

One of the biggest challenges for people just beginning with smart pixel Christmas lights is power.

Unlike traditional lights, which just plug into the wall and turn on, pixels need both data from the controller, and power via power supplies.

While I’ve covered “the how” to get your pixels plugged into power here, it’s also really important to get the right size power supply.

While you can’t really go too big with your power supply, going too small can cause major issues in your light display.  And as your display grows (as most do!), the need for multiple power supplies will arise.

How do you know what power supplies to buy?  Are more expensive power supplies worth it?

In this article, I am going to share with you how to figure out how many lights you can fit on a power supply, and help you figure out how to best distribute them.

Then, I’ll show you the very best power supplies available, and how you can save money when you buy them.

How Many Pixel Lights Can I Put on a Single Power Supply?

Like most tasks when you’re designing your light show, figuring out your power supply needs starts with the layout of your display.

Before buying power supplies, you want to have a really good idea of how many lights you’ll be using, what lights you’ll use, and where you’ll be putting them.

Then, look at the specifications of your lights.  We’ll be doing a little math here – but don’t worry, it’s not too difficult, and there are calculators we can use that make it really easy.

You need to figure out how much power (Watts @ Volts or Amps) your lights will consume.

The voltage of your pixels (usually 12v or 5v) determine the voltage of your power supply.  Then, we add the watts together:

Take this example from Smart 12v Bullet Nodes on WiredWatts.com:

At full, (1) 50 count string of these lights will draw 3a (amps), or 36w (watts).  Let’s use 10 strings, for a total of 360w, or 30a at 12v.

What size power supply do I need for this?

The quick math tells me that I need 360w of power.  But the truth is, electrical engineers (and the national electric code) tell us to never load up a power supply or breaker past 80% of its capacity.  So, we would need 450w of power supply to power these 360w of lights.


This is at full intensity, and at full white on EVERY light.  Let’s step back a minute and think about your show.

[thrive_text_block color=”red” headline=”How Much Power Do Your Lights *Really* Need?”]

If you’re new to this hobby, you’ll want to know that most people do NOT run their lights at full.  Inside of your controller, you’re usually able to set a maximum intensity for each string of lights you are connecting.

I personally run most of my pixels at 30%.  Pixels that are further away from the viewer will need to be brighter to look “balanced”, and pixels closer can be dimmer.


When a pixel is at 30%, it takes about 30% of the power to drive it.  For conservative, safe numbers, let’s give ourselves an extra 20% and run the numbers based on 50%.

360w @ 50% = 180w, 225w of power supply capacity.

Even this number is a little bit conservative when you think about your show.  While you may occasionally hit everything at full white, it’s not something you’ll do often.  So, size your power supplies for the “highest-case” scenario, and you’ll be fine. 

Most of the time, as your lights are dancing to the music, the overall load on the power supplies will be much less!

Now, that does sound like a lot of math, that I’m sure you’re not eager to do – I’m sure not, either!

Thankfully, Spiker Lights has an excellent calculator that allows you to plug in all of the information you need, including the size of wire that is feeding the lights.

Once you find out how much power you need for each of your props, it’s time to decide on sizing.

Power Supplies – A Few Large Ones, or Many Small Ones?

As we’ve covered above, it’s always most ideal to get your power supplies as close to your lights as possible, for minimal voltage drop.

If you follow this rule, you end up with many small power supplies at the end of each of your strings of lights….which is kind of a pain to set up.  On the other hand, this approach wins when you do have a power supply failure because very few lights are affected.

The opposite approach is to use a few massive power supplies with long cords to many of your strings (but short cords to other strings).  The big disadvantage of this approach is that you really begin to lose voltage over distance, and that can severely limit the number of pixels that you can run in one string.

(The Spiker Lights Power Calculator can really help you discover this!)

My Approach to Power Supplies

I like to keep any 12v power lines in my Christmas Light rig under 25′ on 18 AWG wire. (Thicker wire = less voltage loss).

This means that I can approximately space my power supplies 50′ apart, and still reach all of my strings.

This is kind of a combination of both approaches, and I think it’s a healthy middle ground.

What Brand and Type of Power Supply Should I Buy?

You really don’t want to cheap out on power supplies.  But, the good stuff doesn’t have to be expensive, either.

I’m not an engineer, but when I talk with engineers, they tell me about how superior good power supplies are, especially when they fail.

All power supplies will fail someday.  When the good ones fail, they do so safely and protect the connected equipment.  When the cheap ones fail, they send out high levels of rogue voltage and kill equipment.

What Are The “Good Ones”?

Pre-2017 or 2018, your one and only choice for quality power supplies was Meanwell, particularly the LRS series.

Meanwell’s are still good, particularly if you keep your individual power supply needs under 360w.

If you need more power or don’t mind an extra accessory, using power supplies from servers has become very popular.

These “HP common slot server power supplies” can be found for ridiculously low prices online (used).  Combined with a breakout board, these can carry ratings of 750-1200w at 12v to power your lights!

From what I understand, the reason why these are so cheap is that IT companies run these in their servers, and switch them out regularly so that they are far from a failure.  We get to reap the benefits of this in our hobby!

While I haven’t used any of these yet, I’ve got my breakout board ordered from a presale, and I’ll be sure to update with my experience!

No matter what type of power supply you choose, I truly hope this article has helped you to understand how to size your power supplies so that you don’t get into trouble later!

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