LED Sign Tech & Spec: Providing Correct Power Voltage to LED Signs and Why 120 VAC and 240 VAC are Both Important

- Scott Hofheins

Since we're on the subject of power (see Deacons Post), I thought I would write a little bit about Voltage, Amperage, how they affect LED signs, and why it’s important to supply the correct voltage. I will try not to get too technical, but stay clear and straightforward. 


What is Voltage and Amperage?
To keep it simple, I’ll explain power by using a water system filled with sand particles as an analogy.

• Voltage: How strong the “water pump” is pushing the electricity through the system. The water pump is consistent, and it’s pushing force doesn't change much (+/- 10%). If you capped the end of the “pipe” (flip the switch off) the voltage level would never go above the strength of the “water pump”. Typical outlets here in the U.S. supply 120 Volts and large appliance outlets (clothes dryer) supply 240 Volts.

• Amperage (Electrical Current): How fast the water is being pulled through the system. This “flow rate” is measured in Amps and will vary depending on the devices connected to the system. Signs can pull 20 -100+ Amps, and your smart-phone charger usually pulls only .5 - 2.1 Amps. Most residential outlets are rated for 10-15 Amps.

• Wire Size: How big the water line is. The sand in the water will cause friction, generating heat. The faster the “flow rate” the the larger the wire size needs to be to protect the line from overheating.

• Electrical Breakers: These are like emergency shut off valves. If the line does overheat, these valves immediately break the connection completely. They do this at specific Amperage levels depending on the breaker. The main breaker for your home is typically 100 amps, broken down into smaller breakers like 20, 30 or 40 Amps that connected to specific areas of a house.

How do these items affect LED signs?
LED signs are usually configured for 120 Volts AC (Alternating Current) or 240 Volts AC. These are standard voltages for most commercial and residential systems.The lower the voltage the faster the device has to “pull” the power. A sign configured for 120 Volts will pull about double the amperage when compared to the same sign at 240 Volts.

Smaller LED signs are usually configured for 120 VAC. This is because 120 VAC is more common, and is usually already supplied at an existing sign site. The larger amperage draw isn’t usually enough to justify pulling a new 240 VAC circuit to the site. Most signs in this category will pull 10 - 40 Amps, depending on the size.

As they get bigger, LED signs will start to pull more Amperage becoming less efficient. More amperage means a larger electric bill. So rather than using a 120 VAC sign that pulls 80 Amps per side, you will use a 240 VAC system that only pulls 40 Amps per side.

Why not just connect 240 VAC to a sign configured for 120 VAC to save energy, or 120 VAC to a 240 VAC sign?

• Amperage, Breaker Size, and Wire Size: As we discussed earlier, the amperage draw is directly related to the voltage. If your system was built to support a 240 VAC sign that pulled 30 Amps, and you installed the same sign configured for 120 VAC, the amperage would double to 60 Amps. This will affect both your Wire Size and Breaker Size. If you only account for a larger breaker size, you could start an electrical fire at 40-50 Amps when the wire overheats because the larger breaker will not “trip” until 60 Amps.

• Component Damage or Inefficiency: LED signs have many different electronic components. Some of these like the power supplies and cooling fans take AC (Alternating Current). Other components like the LED modules and video boards use DC (Direct Current). The power supplies are responsible for this AC to DC conversion (again, see Deacons Post). If you supply the wrong AC power, you can affect the other components in the system with mixed results.

• Power Supplies: Quality manufacturers use “Auto Switching” power supplies that will output a solid DC current within a range of AC voltage (120 - 240). This might save your power supplies from damage due to incorrect voltage, but the rest of the system can still suffer. However, the damage is much worse if the manufacturer does not use Auto Switching supplies. As soon as you supply the wrong power, many of them will burn out completely.

• Cooling/Exhaust Fans: Most cooling fans in an LED sign are connected directly to AC power. This means that their rotational speed is directly related to the alternating “cycles” in AC power. A cooling fan designed for 120 VAC that is connected directly to 240 VAC may blow completely. Conversely, if a fan designed for 240 VAC is connected to 120 VAC it may blow, or turn much slower causing the sign to overheat.

• Other Components: If the power supplies blow, they can surge the DC power for other components causing damage. If they don’t blow (if you supplied a lower AC voltage) they will sometimes provide a corresponding lower DC voltage. This will cause long term damage to the components and they will fail in variable degrees over time.

Why can’t I connect Three Phase 208 VAC to my 120 VAC or 240 VAC Sign?

I won’t get into the details, but unless you pay for a very custom build LED signs will only be configured for Single Phase Power. You will have issues if you connect directly to Three Phase power. Don’t Do It.

Can I connect to Single Phase 208 VAC?

I do not recommend this either. LED signs are more sensitive to voltage than a clothes dryer or refrigerator that operate just fine in the 208 range. An LED sign might work initially, but you run the risk of long term component damage due to under-voltage. You would also see poor performance of any AC direct components like cooling fans.

If the LED sign is configured for 120 VAC, the safe operating range is typically  110-120 VAC. If the sign is configured for 240 VAC, the safe range is usually 220 - 240 VAC.

The bottom line is: Voltage Matters.  Now (hopefully) you know why.

-SH




I hope this post has been informative and helpful. As usual, I welcome ALL constructive comments. Please feel free to comment and add anything I’ve missed, or additional tips you may have regarding this topic. Please visit www.vantageled.com for many other resources, white papers, and of course: Great looking LED Signs!

**All posts/thoughts/writings are strictly the viewpoint of me and me alone and do not reflect nor speak for Vantage LED’s beliefs, attitudes, thoughts, etc. unless specifically stated.