New Vending Machine Power Supply Design
External type power supply
Input – 110VAC – 240 VAC.
Output – 24 VAC @ 3A – 4A (72W-96W).
Input Connection – IEC C13 Male.
Output Connection – Wire (Not terminated) (Optional)
Notes: The power supply must have an A/C input line filter and voltage output regulation.
Customer requested a power supply for a line of vending machines that incorporate computerized vending of tickets, credit cards, postage stamps, etc. The machines require a filtered 24 VAC supply to operate the sophisticated onboard computer efficiently. Their design engineer asked for a supply that would essentially act as a “plug and Play” solution for the vending machine regardless of the input voltage. These machines are sold and installed in various countries where the mains voltage supply is not always predictable.
As a result, they had to use multiple components to achieve the desired voltage for their computer. In order to eliminate the need to stock multiple components and design a custom power source for each installation, they asked for a single unit that could meet all or most of their installations. Their typical approach was to use one of two linear transformers to step down the voltage to 24 VAC. Since the exact input line voltage was unknown, the two transformers only met some of their requirements. In addition, they had to filter the input voltages against common mode noise and regulate the output so as not to damage the onboard computer; the components used were different from installation to installation
CET Technology proposed a solution that incorporates a transformer with five taps that matches most of the standard input voltages found in the countries they sell to. The input is filtered with a common mode choke. The 24 VAC regulation is designed and implemented by the customer. The entire assembly is designed to fit on a mounting plate that is affixed to the vending machines; it is wired for input as determined by the country in which it’s installed. There are two versions; an internal power supply for those machines that are sold and installed in North America, and an external power supply, in a NEMA enclosure, for those units sold and installed in Europe and other countries throughout the world.