Few questions about relay...?

Question

1) Why D.C. relays are more popular than A.C. relays?
2) What modification is employed to operated D.C. relay on A.C. voltage?
3) What is meant by chattering of relay?
4) What are the causes of chattering of relay?

Till now you must have known that these are my assignment questions... but as my teacher instructed, I searched the answers in books, then google but I couldn't get the answers.

I have to submit this assignment tomorrow itself. I will be very grateful to you if you can help me...

Thanks in advance.

Answer 1

1 A designer is more likely to find a convenient source of DC in a piece of equipment than the right voltage of AC.
2 There is a copper loop added as a short circuiting turn to keep the magnetic field steady. You also typically use a laminated core rather than a solid iron one.
3 It is the periodic rising and falling of the moving part of the relay caused by problems with its electro-magnetic field.
4 When a relay is held closed by a marginally-low voltage there may not be enough magnetic field to hold it firmly closed. Also if it is DC relay and there is any AC not filtered from that DC the weakening of the DC magnetic filed may occur periodically when the AC direction is fighting the DC causing a momentarily weaker field.

Answer 2

In an electronic circuit, DC is a lot easier to provide than AC is. To use a DC type relay with AC, you would need to rectify the AC voltage into DC. It wouldn't hurt to put a smoothing capacitor across the diode and common (or ground) points for the relay power source.
Relay chattering is a rapid open-close sequence as described elsewhere. Relay chatter can be caused by power source fluctuations, excessive force of contact closure, or it can be caused (most of the time) by the removal of it's energizing voltage. This is because as the coil voltage collapses, it generates a new voltage, causing the contacts to re-close, and then to open again. The cure for this is a diode that is connected in reverse to the polarity of the voltage that energizes the relay. For a DC circuit that uses negative potential as ground, the diode would be connected so that the anode of the diode connects to the side of the coil that goes to ground. This way, the diode will not conduct until there is a voltage reversal as seen at the relay being turned off, and the coil voltage collapses but creates a new reverse voltage that would re-energize the coil, but is shorted to ground by the diode conduction.

Answer 3

2) i think the circuit is called a voltage regulator or rectifier it basically converts a.c. to d.c. you basically tweak the circuit and try to eliminate as much of the ripple voltage as you can to try to end up with a d.c. signal

as you know ac is a sinusoid and you want to end up with a flat line for d.c. so thats why you try to get rid of the ripple

3) when a relay is operated (meaning power is sent to the relay coil) the contacts on the relay will chatter meaning close, open, close, open, close, open really quick this is whats meant by chatter. look up a debounce circuit if you have an E.E. circuits book or try online.

Answer 4

Dear Friend

The answers to u r questions are one liners, here they go

1. DC relays work without the interference of harmonics, thats why they are preffered

2. Offline oscillators are nowadays used to operate them on AC

3. The switching surges happening under operation induces a noise signal in the relay this is known as chattering

4. The reason i have already given in the above point.

Answer 5

(1) DC is more reliable, you can use battery as back up for power supply, the current requirement in DC is less than that required in AC,

(2)You have to use rectifier to convert ac supply to DC for using DC relay in AC circuit

(3) Relay get energised and de-energised continuously. the moment it get energised, the relay coil supply got disconnected and the moment it got disconnected it again get the circuit completed. It is called chattering of relay

There are lot of reasons for relay get chattering like wrong circuit wiring, defective NO/NC contact of other relay connected to same circuit, Wrong operation of timer connected to relay circuit.