Programmable timer operating high power loads with Bolt 18F2550 microcontroller.

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FIGURE 1: Connections of devices for testing



Bolt 18F2550 board includes a low power relay for handling loads up to 100 watts, typically to activate lights and  low power consumption appliances. However, when control is required for higher power loads, it is necessary to connect an auxiliary relay.

For this project, a Schrack model MT206127 relay, double pole, double throw, whose photos are shown below, was used. With this relay, loads up to 10 amps at 250 VAC, ie home appliances such as a heater, a coffeemaker, a microwave oven or electric grill can be controlled. In industrial environments, devices like valves, actuators, contactors and medium capacity engines may be controlled.


Schrack MT206127 Relay. Front view.


Schrack MT206127 Relay. Back view.


General description:

Using a programmable timer firmware for Bolt 18F2550 microcontroller, the project No. 6 in this link, configured for switching a coffee maker during a 3 minutes lapse. In the figure below the wiring diagram is shown. Note that for digital operation (ON-OFF) of high power loads from a microcontroller, a chain of several devices is necessary, each of which increases the capacity of load current:

Microcontroller output pin (100 mw) >> transistor BC337 (1 watt) >> relay SONGLE 9 volt (100 watts) >> Relay Schrack (1000 watts)

During testing, the load current of the coffee is obtained, which in this case reaches 6 amperes, that is, a power of about 700 watts.


FIGURE 2: Connection diagram for programmable timer for high power loads project


Relays: what you always wanted to know but were afraid to ask