MullOverThings

Useful tips for everyday

How do I choose the right relay?

How do I choose the right relay?

An easy way to determine the limit of a relay is to multiply the rated Volts times the rated Amps. This will give you the total watts a relay can switch. Every relay will have two ratings: AC and DC. You should determine the AC watts and the DC watts, and never exceed these ratings.

What are the two important information needed when selecting a relay?

Consider these factors when choosing a relay for use in industrial controls: Voltages driving loads are the first concern. The voltage rating of a relay must be greater than or equal to the voltage driving the load. The frequency of the switched voltage is also critical.

What is NO and NC In contactor?

In every control circuits and automation systems, logic is developed based on the open or closed state of switches, sensors or relays. Normally open(NO) and Normally closed (NC) are terms used to define the states of switches, sensors or relay contacts under when its coil is not excited.

When would you use a contactor instead of a relay?

Contactor: It is a device which is used for repeatedly establishing and interrupting an electric circuit under normal conditions. Control Relay is more commonly used in control circuits which are single phase circuits. Contactors are typically built for switching 3-phase load.

What kind of relay is used for make and break?

There are other contact configurations discussed below but make & break and changeover relays are the most commonly used.

What is the terminal number on a 12 volt relay?

Terminal/Pin number Connection: 85: Coil: 86: Coil: 87: Normally Open (NO) 87a: Normally Closed (NC) – not present on 4 pin relays: 30: Common connection to NO & NC terminals

Which is the terminal on the changeover relay?

Changeover relay. Two circuits (terminals 87 and 87a ) have a common terminal (30). When the relay is at rest 87a is connected to 30, and when the relay is energised 87 becomes connected to 30 (but never both at the same time).

What is the difference between normally open and normally closed relays?

Relay terminology. If the contact is broken with the relay at rest then the relay is referred to as Normally Open (NO) and if the contact is closed with the relay at rest then the relay is referred to as Normally Closed (NC). Normally Open relays are the more common type.

Which function is used to control the relay?

Relays are switches that open and close circuits electromechanically or electronically. Relays control one electrical circuit by opening and closing contacts in another circuit. As relay diagrams show, when a relay contact is normally open (NO), there is an open contact when the relay is not energized.

How to calculate the base current of a BJT amplifier?

This means the base will be at about 1.45V and this allows you to calculate R1 and R2 (but be prepared to revise those values should the base current drawn be a little high). You want 10mA thru the collector and this is virtually the same current through the emitter so now you can decide what Re is – 0.75V/10mA = 75 ohms.

How do you determine the watts of a relay?

An easy way to determine the limit of a relay is to multiply the rated Volts times the rated Amps. This will give you the total watts a relay can switch. Every relay will have two ratings: AC and DC. You should determine the AC watts and the DC watts, and never exceed these ratings.

How to determine the limit of a relay?

Volts x Amps = Watts – Never Exceed Watts! An easy way to determine the limit of a relay is to multiply the rated Volts times the rated Amps. Every relay will have two ratings: AC and DC. You should determine the AC watts and the DC watts, and never exceed these ratings.

How does a transistor turn the relay on and off?

The transistor should turn the relay on and off based on whether D2 is at 5V or GND. The relay is a 5V relay and has a coil resistance of 63 Ohms, so the coil current is 79.4mA. How do I determine what value the base resistor (R7) should have for the circuit to work?