How does work a DC relay to use it with 16F84???

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terka

Joined: 15 Dec 2003
Posts: 102
Helped: 1

26 Jan 2005 5:38 16f84 relay

I saw an circuit with a PIC controlling a 12 volt DC relay...a transistor for switching purpose and a protecting diode.....my dude is

. The transistor must be in constant on/off to make a coil of relay generates a electromagnetic field, for relay operate ( switch funtion) ???? something like PWM???, or the relay is ON when transistor is in ON mode?

I dont know how a relay does it work in DC mode as source of power for coil of relay..I know how a relay works in AC mode, with V= L* d(i)/d(t) to generate a electromagentic field and relay is ON ( normal open to close change)

Sorry for my bad english

Help me please

Thank you

nicleo

Joined: 06 Sep 2004
Posts: 717
Helped: 60

26 Jan 2005 6:18 how dc relay works

The output from a PIC is usually not powerful enough to drive a 12V DC relay. That's why a transistor is required to boost the power to drive the relay. When there is a DC supply across primary coil, the relay will be energized and the contact will be closed. There are few types of relay, e.g. normally open or normally close relay.

platonas

Joined: 14 Aug 2004
Posts: 165
Helped: 5
Location: Universal Citizen

26 Jan 2005 7:06 how does a relay work

You need a 12V DC relay first. Then you must drive it via a transistor. You need a series resistor (R1) from PIC output pin to transistor base and another one resistor (R2) from base to emmiter. R1=1-3,3 Kohms depending on transistors gain. 2,2K is almost always OK. Then R2=4,7 to 10 Kohms, prefered is 4,7K.

Now have in mind that, PIC is supplieed by 5V and relay by 12V. So you need two different voltage supplies unless you find a 5V DC relay.

I advice to use good filtering of the relay's supply in order to avoid RESETTING the PIC due to spikes caused by the relay during activation.

terka

Joined: 15 Dec 2003
Posts: 102
Helped: 1

26 Jan 2005 14:34 relay 16f84

Hi

I understand it, but how DC current can produce a electromagnetic field to activate the terminals of relay, if an coil (bobbin) in DC in a short circuit???

I think about V= l*d(i)/d(t), where (i) is changing, then i dont understant that of DC instead AC current

Thats is my problem, that is I dont understand.

Thank you

btbass

Joined: 20 Jul 2001
Posts: 1187
Helped: 113
Location: Oberon

26 Jan 2005 14:55 how relay works

The current through the coil produces the magnetic field. The relay has an electro magnet to switch it.
I think you are getting confused with a transformer, which requires a changing magnetic field to produce current in a wire.
The coils in the relay have many windings. The resistance is quite high. ~1K.

nicleo

Joined: 06 Sep 2004
Posts: 717
Helped: 60

26 Jan 2005 15:24 how does acoil and a relay works

When there is current (dc or ac) flows through a piece of conductor, a magnetic field will be created around the conductor. I think you have confused both Faraday's Law and Ampere's Law.

Faraday's Law
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

Ampere's Law
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/amplaw.html

irfansyah

Joined: 29 Dec 2004
Posts: 105
Helped: 8
Location: New South Wales

26 Jan 2005 18:03 16f84 transistor relay

Shortly speaking, the coils of the DC relay will generate a constant magnetic field. While if you give AC voltage to a coil, the magnetic field generated would then change periodically by time, hence generating an electromagnetic wave. CMIIW

A magnetic field is enough to cause the realy to switch.

Now this makes me wonder, what is actually the difference between AC relays and DC relays, in terms of the internal structure??

IanP

Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast

27 Jan 2005 2:20 use of dc relay

Some interesting explenations you can find here:
http://www.eng-tips.com/viewthread.cfm?qid=59361

terka

Joined: 15 Dec 2003
Posts: 102
Helped: 1

27 Jan 2005 2:33 dc relay and ac relay difference

irfansyah wrote:

Hi, googling I come to following data:

Solid State Realy : its works like opto-couple, a led inside of package activates the relay, It have more life than electromecjanics relay

Electromechanics relay: it works with a magnetic field, the load can be AC or DC, resistive, inductive, capacitive. Magnetic field on coil is the activator of relay.

Other types exists, but the above are the most imporant types.

Thank to all

Bye

Ace-X

Joined: 25 Jan 2002
Posts: 590
Helped: 26

27 Jan 2005 2:54 how does a relay circuit work

terka wrote:

Solid State Realy : its works like opto-couple, a led inside of package activates the relay, It have more life than electromecjanics relay

Reliable. Expensive. Low values of max. currents and voltages. No inductive feedback current.

terka wrote:

Electromechanics relay: it works with a magnetic field, the load can be AC or DC, resistive, inductive, capacitive. Magnetic field on coil is the activator of relay.

Very cheap. Can switch high currents and voltages. Should have protection from inductive feedback current (usually, diode). Recommended to use special drive IC, like ULN2003.

Google
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27 Jan 2005 2:54 Ads

mipedja

Joined: 20 Sep 2004
Posts: 28

27 Jan 2005 14:36 how relay work dc

http://www.mikroelektronika.co.yu/english/product/books/PICbook/7_05chapter.htm

terka

Joined: 15 Dec 2003
Posts: 102
Helped: 1

28 Jan 2005 4:39 how electromagnetic dc relay works

WOW midepja

I understand all, i was confused about transformer and current induction

Thanz to all

Terka

Added after 33 minutes:

Hi again

What types of relay can i use to activation functions??

Thank you