Mitchell Electronics Transformer
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Transformer Capacity
Transformer capacity is rated in Volt-Amps (VA). In most cases, the terms “Volt-Amps” and “Watts” are generally interchangeable. An appliance is generally labeled with its proper operational voltage (Volts), current (Amps), frequency (Hz), and wattage (Watts or VA). This information is typically found on the nameplate on the back of the appliance.
How do you know what an appliance’s required VA is? A simple formula provides the answer. Simply multiply the machine’s rated voltage (Volts) by its rated current (Amps). In other words:
Transformer – Volts X Amps
If the voltage is not provided on the appliance, in most cases you may use the wattage. Exceptions are items such as fluorescent lights, neon signs, and specialized electronic controls that require transformers whose VA capacity is 1.5 times the wattage rating.
Some large appliances have nametags showing both running amps and starting amps. In this case, use the running amps to calculate the VA.
Once you have your number, select a transformer with a VA rating equal to or greater than what you have calculated. Keep in mind that if you choose a transformer with smaller VA capacity that what you have calculated to be required by the load, the transformer will overheat and burn out over time.
Example 1:
You wish to run your 120V 60Hz stereo on 230V 50Hz
Step One: Look at the nameplate on the back of the stereo. There, you’ll find the proper operational volts (V), the frequency (Hz), and current (Amps). In this case, you find:
120V – 50/60Hz – 2A
Step Two: Plug the numbers into the formula Volts X Amps:
120V X 2Amps = 240 VA
The VA value tells you what sized transformer you need to operate your stereo.
Example 2:
You wish to purchase one transformer that you can use in different appliances (one at a time).
Repeat Step One Above: to locate the volts and current of each appliance you wish to use with this transformer.
Step Two: Plug the numbers into the formula Volts X Amps:
Fax Machine: 120V X 1A = 120 VA
Television Set: 120V X 3A = 360 VA
Washing Machine: 120V X 7A = 840 VA
Based on the VA values you calculate, choose the transformer with the capacity to handle the largest item – in this case the washing machine 840 Va. It will easily handle the other two items, because remember: you can use a transformer that’s larger than what you actually need, but you CANNOT use a transformer that’s smaller than what you need.
Example 3:
You wish to purchase one transformer that will allow you to run several appliances at the same time.
Repeat Step One Above: to locate the volts and current of each appliance you wish to use with this transformer.
Step Two: Plug the numbers into the formula Volts X Amps:
Computer CPU: 120V X .5A = 60 VA
Computer Monitor: 120V X 2A = 240 VA
Computer Printer: 120V X 4A = 480 VA
Step Three: Add the VA values to determine the total required capacity:
Computer CPU: 60 VA
PLUS Computer Monitor: 240 VA
PLUS Computer Printer: 480 VA
Equals Total required capacity: 780 VA
Choose your transformer based on the total required capacity you have calculated. This way, you can run all three pieces of equipment at once, or one at a time.
