Tuesday, November 2, 2010

WOW-- How to control a high-current AC loads by DC circuit

There are a lot of hobbyists who encountered  problems on how to control a high-current AC loads. Building a circuit to control AC loads is easy. Isolating AC load side from the controlling DC circuit, coil relay is used. But when the AC loads require more current such as Air-conditioning unit (ACU), the simple circuit is no longer suitable. The following circuit below is an improved version from the original basic circuit as shown in the illustration. Magnetic contactor is added to act as making or breaking the contacts (Normally-opened, N.O. at K1) where the AC load is connected. The coil side of the magnetic contactor is energized via the N.O. contacts of magnetic relay (K). When the transistor circuits is triggered ON, magnetic relay (K) is energized. In this case, contacts at K are closed and turned ON the AC load side. There are no worries in this design between DC and AC circuitry because they are electrically isolated.

There is another design which is similar to this idea using OPTO-TRIAC. It is an inexpensive design compared to the magnetic contactor counterpart.

An ECE student from a forum or group I participated, send me a private message and ask for a design help about their thesis. Part of their design is how to control a high-current AC load. I quickly grab a paper and pen to sketch the circuit solution of his problem. His problem solved but the cost is not suited to his pocket. He asked if I can give him another design using the cheaper components such as the OPTI-TRIAC.

Another illustration or sketch shown below is the overall block diagram I suggested to them when they want to use SMS to send message in controlling appliances at home while away. Their thesis is to develop a project Sending SMS to control home appliances.


AC load controller, Electrical circuits, Electronics circuits, High-current AC load driver

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