Understanding the limitations and requirements of electrical units is crucial. In the article, we provide some background and an answer to, “how to choose the right transformer?” At MOD, many of our power and lighting solutions are designed to be plug-and-play, but understanding how to pair them when setting up a custom power or lighting project is vital.
Click here to get more.
Let’s start with some key definitions:
The equation can be rearranged as A = W/V and V = W/A.
A useful analogy for Volts, Amps, and Watts is water flowing through a pipe. Volts represent the water pressure entering the system (by, for instance, a valve), Amps describe the flow rate through the system of pipes, and Watts measure the volume of water that flows out of the pipe into a bucket.
In the U.S., voltage for electrical appliances ranges from 110–120V at 60 Hz. If your appliances come from a country with different voltage, you’ll need a power converter. An adapter alone may not be enough. For example, a 220V appliance won’t work properly when plugged into a 120V outlet due to insufficient voltage. Conversely, plugging a 110 or 120V appliance into a 220V outlet could fry the components, cause overheating, or even start a fire. Products that come standard in 220V are often used outside the U.S., Canada, and Mexico. When buying in the U.S. ensure it carries a UL certification and a cUL certification if you are living in Canada, indicating they are rated and approved for safety. All of the products you buy through MOD carry UL and cUL certifications as our guarantee to our customers.
Watts provide a standard way to express a product’s power requirements, which is why we list wattage on our power receptacles. Often when shopping for non-custom options you will see Watts listed on lightbulbs indicating their overall power consumption. However, Watts are used to describe power in many applications, not just lighting. For instance, Apple hasn’t shared exact numbers, online tests indicate the newest iPhone can charge at up to 20 Watts. In comparison, their original charger cubes delivered only 5 Watts.
Our Aficionado charges up to 18 Watts via USB-A and 45 Watts via USB-C, offering an option close to most phones’ maximum charge rate with USB-A, and one that ensures maximum charging speed with USB-C (or even powers a laptop). Charging between 20–30 Watts makes only a small difference, usually just slightly faster from 0–80% charge capacity. Unlike custom lighting, there’s no need to worry about overheating—your will manage its power intake. However, this is just one example of how power outputs translate in the real world, now it’s time we answer that burning question “How To Choose The Right Transformer”?
For almost any power setup, it’s wise to leave a 20% buffer, meaning you should only use 80% of a transformer’s maximum capacity. To select the right transformer, multiply the total wattage of your lights by 1.2. For instance, if you have 10 LED strips rated at 10 Watts each, you’ll need 100 Watts of power. To maintain the 20% buffer, choose a transformer that can handle 120 Watts.
A transformer will list its power outputs on the label on the unit itself. If you cannot locate the Watts you can always do a calculation. For example, with one of MOD’s 5 Amp transformers at 12 Volts, the equation would look like this:
12V x 5A = 60 Watts
As mentioned earlier, it’s best to allow a buffer to keep power outputs manageable. For this transformer, we recommend limiting the power draw to 48 Watts.
Figure 1: Transformer
A transformer is a passive electrical device that uses electromagnetic induction to transfer electrical energy from one circuit to another. Selecting the proper transformer for an application requires careful consideration of several factors, such as voltage, current, type of load, efficiency, environment, and cost. This article gives a step-by-step guide on choosing a transformer and analyzing various powers in a transformer.
Read our overview article on transformers for more information on how they work, their construction, and their types. Transformers are available in multiple designs, specifications, and sizes. It is important to consider the following:
Note: The voltage and frequency of the main power supply vary from one country to the other. Countries like the USA use the main power supply of 120 volts operating at 60 Hz, whereas those in Europe like the UK, Netherlands, and Germany operate at 230 volts and 50 Hz. Choose the transformer accordingly. See the complete list of countries with their corresponding mains power supply voltage and operating frequencies for more details.
Figure 2: Step-down (left) and step-up (right)
Note: Generally, the primary and secondary voltages are listed in the transformer specifications. But in exceptional cases like a current transformer, the primary and secondary currents are listed instead.
The rated load (apparent power) of a transformer is measured by VA (Volt-Ampere). The rated power represents the total amount of power the transformer can deliver to the load. To calculate the rated load needed:
Note: Small transformers rate their deliverable power in volt-amperes, but much larger power transformers are rated in units of Kilo volt-amperes (kVA), and Mega volt-amperes (MVA). Therefore, VA, kVA, and MVA are similar units. For example, 6 VA is equal to 0.006 kVA.
Read our articles on single-phase and three-phase transformers for more information on their working and design.
Transformer load capacity is the maximum amount of electrical power that a transformer can safely and efficiently handle without overheating or causing damage. For example, a transformer with a 200 VA rating can handle 200 volts at one ampere of current or 100 volts at two amperes of current.
Tianya supply professional and honest service.
Knowing the VA value of the transformer, it is possible to determine the current across the load by rearranging the equation for VA.
Note: Loading a transformer above 80% of its VA rating is not recommended. After calculating the VA, divide the value by 0.8 to get the minimum VA rating needed. An electrician or electrical engineer should review and confirm all values for safety reasons.
Calculate the rated power of a single-phase transformer with a load voltage of 24 volts and a maximum load phase current of 5 amperes.
The VA rating of the transformer = (V × I)= (24 × 5) = 120 VA
Dividing the VA by 0.8, the revised VA = 150
Choose a transformer with a VA rating of approximately 150 for the load.
The efficiency of a transformer is given by:
When dealing with transformers, the primary power is generally referred to as volt-amps (VA) to distinguish it from the secondary power. Therefore, the efficiency is given by:
Transformers have high efficiencies due to the absence of moving parts. Transformers are also called static AC machines. The efficiency of a well-designed power transformer is very high, averaging over 98 percent. The only losses are due to core losses, maintaining the alternating magnetic field, resistance losses in the coils, and power used for cooling.
In an AC circuit, the power factor is the cosine of the phase difference between voltage and current. The power factor represents the fraction of the rated power (apparent power) that is consumed (true power) by a circuit.
A low power factor means that a higher current is required to deliver a given amount of real power to the load, which results in higher energy losses and reduced efficiency. The power factor can also help calculate the total power that the transformer can handle without overloading.
The apparent power, real power, and active power can be represented in a right-angle triangle known as the power triangle (Figure 3).
Figure 3: Power triangle showing active power (P), apparent power(S), and reactive power (Q) in a magnetic circuit.
Use Figure 3 to derive the relation between various types of power in a transformer.
There are multiple sources of power losses in a transformer.
The various losses in a transformer can cause the device to overheat, leading to damage and a shorter transformer lifespan. It is necessary to reduce these losses to improve transformer efficiency and ensure the optimal performance of the electrical system. Common measures are:
To size a transformer, determine the load requirements of the electrical system in terms of voltage and current, and then select a transformer with a suitable kVA rating based on the load requirements.
To calculate the VA (Volt-Ampere) rating of a transformer, you need to calculate the product of the voltage and current ratings of the transformer.
The standard kVA sizes for single-phase transformers are: 1, 1.5, 2, 3, 5, 7.5, 10, 15, 25, 37.5, 50, 75, 100, 167, 200, 250, and 333 (KVA)
The efficiency of a transformer is less than 100% due to the various types of losses within the device, like core loss, copper loss, and dielectric loss.
For more Power Transformerinformation, please contact us. We will provide professional answers.