Power Electronics

Auto-Transformers Allow North American Appliances to be used Worldwide

Foster Transformer introduces a new line of Auto-Transformers or autoformers that use a single non-isolated winding to step up or step down the available line voltage to match the requirements of the load. With an integral enclosure to facilitate easy hook-up, they are used to adapt equipment manufactured in one country to operate in another with different line voltage. The new line of Foster 1500VA autoformers is specifically designed to allow North American appliances configured to operate from a 120V source to be operated virtually anywhere in the world. Foster autoformers are ideal for virtually all types of equipment including office automation, medical and dental, commercial appliances, vending and other OEM equipment.

Foster Autoformers are UL/C-UL recognized (file E19598), and TUV certified to EN60950-1 (Certificate R72050845). They have output rated at 115V at 1500 VA. Input voltage taps of 100V, 115V, 127V, 200V, 220V, 230V, and 240V at 50/60 Hz are standard. They can be wired in parallel for increased capacity. UL recognized Class 180 (H) insulation is used - optional resettable thermal overload protection is also available to protect against overheating.

Autoformers forego the electrical isolation provided by a multi-winding transformer in exchange for smaller size, lower cost, improved efficiency and tighter voltage regulation. This is accomplished because only a portion of the power is being "transformed." The use of non-isolated transformers is acceptable in equipment which is being adapted to differing line voltages because the output is supplying equipment that would otherwise be connected directly to the line.

The difference between the incoming and outgoing voltages determines the size reduction available as well as potential cost savings from the use of autoformers. The ratio can be calculated by dividing the difference between the input and output voltage by the higher of the two voltages.

For example, a piece of equipment designed to operate at 120V and draw 10 amps would need a transformer capable of supplying 1200 VA (output voltage times output current). If this equipment is installed in a facility with 240V line voltage, and an autoformer is used in place of an isolation transformer, then the physical size of the transformer is reduced by ½ (240V line voltage minus 120V supplied)/divided by (240V line voltage). If this same equipment is shipped to Japan where line voltage is 100V, then the autoformer becomes even smaller (120V - minus 100V)/divided by 120V equals 1/6.

Foster Transformer
Part Number: Auto-Transformers

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