Sa contacts lang ang diskarte nyan. hehe

Contacts

Well, there are terms that may be confusing for young electrical students at para na din sa ibang tao. I mean, like in switches, my mga terms na technical na pag narinig pa lang ay ganito kaagad ang masasabi: "?gh?anfls?".

Isa na rito ang switch configuration. Ano ba ang single-pole single throw, double pole double throw, four pole double throw, at paano mo masasabi kung ang isang switch ay ganyan o ganito?

The definition lies on the two important KEY WORDS. POLE and THROW.

Ang dalawang salita na yan ay tungkol sa switch contact variations.

A "pole" is a set of contacts and terminal para sa ISANG CIRCUIT.

Ang salitang "throw" naman ay para sa iba't ibang posibleng posisyon na pwede sa switch.

For example, a single throw switch has one position that closes a contact, at ang double -throw has two positions, kagaya ng "make-before-break" mechanism ng relay, and so on. ;)

1) SINGLE POLE-SINGLE THROW:

Ang pinakasimpleng on-off switch: The two terminals are either connected together or not connected to anything. An example is a light switch.

American wiring name: two-way switch

2) SINGLE POLE DOUBLE THROW

A simple changeover switch: C (COM, Common) terminal na pwede maconnect sa L1 o sa L2. Pag nakadeenergize ang switch ay magkadikit ang common at L1 pero pag naenergize ito ay lilipat ang common at didikit sa L2.

Double throw kasi DALAWA ang pwedeng posisyon ng switch. Magpapalipat lipat lang ang common sa line 1 at sa line 2.

American wiring name: three way switch

3) DOUBLE POLE SINGLE THROW
Take note na dalawang single pole single throw lang sya na kinokontrol ng isang mechanism. Pag nakaopen yung isa, ganun din sa pangalawa.
At pag nakaclose contact ang isa, ganun din ang isa.


American wiring name: double pole switch

4) DOUBLE POLE DOUBLE THROW

Ito'y dalawang SPDT switches controlled by a single mechanism.
A is connected to B and D to E, or A is connected to C and D to F. ;)




Conclusion:
Switches with larger numbers of poles or throws can be described by replacing the "S" or "D" with a number or in some cases the letter "T" (for "triple"). In the rest of this article the terms SPST, SPDT ;)

Related link:
www.tpub.com/.../neets/14175/css/14175_209.html

Malay sa relay na yan. =( A BIG NO NO. (part 3)

Anong mangyayari pag naconnect ang isang AC relay sa DC?

Ang isang AC relay coil has both inductance and resistance limiting the current.
Generally, ang AC relay ay nakadesign nang may mas mataas ng current kesa sa DC
(kasi mas less efficient ang AC). Pag naikabit ito sa DC at hindi sa AC, magkakaroon ng mas
mataas na current pa rin. The relay would operate properly (for a while) but would eventually
fail due to the coil overheating. Depending on ambient temperature and the specific relay,
failure could occur in minutes, or might take years.

Malay sa relay na yan. =( A BIG NO NO. (part 2)

We can say that a relay is A SPECIAL KIND of switch.

Here are two examples kung bakit kailangan natin ng relay.


On the upper part is a diagram for automobile circuit.

Pag naka-on ang ignition key ng sasakyan, it allows electricity to flow to the starter solenoid ( yun ang relay) which then connects the battery to the starter motor.

So why do we need the "middle man" relay? Pwede ba nating e-eliminate na lang ito at iconnect ang ignition wires sa +battery terminal at yung isang wire sa motor starter naman?

The important point here is that the electromagmet is using a small amount of current to control a large amount of current to the starter motor. (Remember that the electromagnet and the switch are NOT connected electrically).

Have you noticed that all of the wires (except the ignition wires) are purposely drawn with thick lines? That's because some circuits (like the starter) require tremendous amount of current. (kaya kailangan din ng mas malaking kable).

(If you look at an automobile's battery cables, you will notice they are quite thick.)

Pag maliliit na wire ang ginamit natin, di nito kakayanin ng insulation nya ang mataas na current, kaya masusunog ito, at uusok.

We do have a second choice. Pwede tayong gumamit ng malalaking kable mula sa battery gamit
ang heavy duty ignition switch. However, do you think it would be easy to squeeze cables into the steering column and squeeze in a heavy duty switch too?

BURGLAR ALARM SYSTEM

Referring to the diagram, let's trace the electrical flow.

Kung makikita nyo, mula pt. V2, pupunta sa "C". Mula sa negative battery terminal, pupunta sa V1, tapos sa V2, at dahil tuloy tuloy ang alarm loop, pupunta sa "C" at pagkatapos ay sa positive battery terminal na. Sa circuit loop na 'to, dadaloy ang current sa electromagnet causing the common terminal to switch contact mula "C" patungo sa "B" At dahil walang contact sa A, the siren will not make any SOUND.

Pwedeng lagyan ng isa o mas maraming magnetic switch in series sa alarm loop para magkaroon ng warning signal o alarm sound. Kaya lang, ang mangyayari dito, tuloy-tuloy nga ang kuryente mula pt "C" to pt. "A" hanggang sa siren, NGUNIT HINDI sa electromagnet.

Alarm Circuit 1 does suffer from one serious flaw. Can you see what it is? Pag nareconnect ulit ang alarm loop, madidisconnect lang ang siren. This is a VERY IMPRACTICAL WAY AND NOT RECOMMENDED TO ANY ALARM SYSTEM. The siren goes off! Kung nabuksan ng isang magnanakaw ang pintong me magnetic switch nang pwersahan, sasarhan lang nito ulit ang pinto at di na tutunog ang siren.


Para maging efficient sa tao, kinakailangan natin ng isang device na pagproprovide ng additional contacts na mag-aallow ng isang circuit na gumana habang ang isang circuit ay putol. At yun ang nagagawa ng transfer mechanism ng common contact ng isang relay. =)

Malay sa relay na yan. =( A BIG NO NO.

Lam mo ba kung ano ang relay? Bakit ginagamit ito at paano sya nakakatulong sa atin?
Well, it's time for electrical wareness na rin.

Ang relay ay isang simpleng electromechanical switch na binubuo ng electromagnet at mga contacts.

There are three important functions of a relay:
1) A relay provides isolation from one electrical circuit to another.
2) A small coil voltage can control a large load. This is usually how computers control the outside world. (gamit ang relay, hmmn)
3) A high control voltage can control a low load.

Nosebleeding ba? Well, let me explain further. ;)
Ang relay ay pwede nating maconsider as an ELECTRICAL AMPLIFIER. Paano ba? As an amplifier, ang relay ay isang device na gumagamit ng maliit na electrical energy para macontrol ang malaking amount ng energy. Kung paano kailangan lang ng isang relay ng 24 V para makakakontrol ng 220 V ay isa sa mga unique qualities nito.

Or for example, you might want the electromagnet to energize using 5 volts and 50 milliamps (250 milliwatts), while the armature can support 120V AC at 2 amps (240 watts).

Ngunit, datapuwat, at subalit, ang relay ay dependent sa ibang devices like pilot devices o mga sensors. It opens or closes a circuit UNDER THE CONTROL of another electrical circuit. Gumagamit sya ng electromagnetic force to open or close one or many sets of contacts.















Ang tatlong me itim na bilog ay switching contacts ng relay.

When the electromagnet coil is turned off, ang dalawang contacts sa taas ay magkadikit, thus called "normally close" contact.

When power is applied, ang gitnang bar ay bababa at didikit sa isa pang contact. This opens the "normally closed" contact and closes the "normally open" contact.

Ito ang tinatawag na "make before break" contact na may dalawang contact para sa normally open at normally closed, at may common terminal. ;)

A relay actually consists of two separate and completely independent circuits.
The first drives the electromagnet. Pag nagkaroon ng power supply, ang first circuit (internal circuit) ang bubuhay sa electromagnet na nasa relay. Ang electromagnet na to ang magaattract ng armature para maenergize ang second circuit. Yun na ang papunta sa load.


Ang picture sa taas ay nagpapakita ng isang napakasimpleng relay.

The coil is attached to the bottom two lugs. Ang dalawang pinakababa na rin ang ikakabit para sa power supply.

Ang nasa taas naman ay ang normally open at normally close na contact na meron common terminal sa gitna.


Pwede lagyan ng wire directly sa lugs, o ilagay sa isang socket.

Ngayon, what are the important considerations when choosing a relay?
Tatlo lang po.

1) coil voltage - This indicates how much voltage (AC or DC) ang kailangang isupply para maactivate ang relay. Ito yung parang input voltage ng relay. Take note lang po na hindi puwede magsupply ng mas mataas na voltage sa isang low voltage relay kasi masisira ito.

2) contact ratings -This indicates how heavy a load the relay can control. If you can't find exactly what you want, you can use a relay with a higher rating.

3) contact geometry - There are many kinds of switches, kaya marami din ang uri ng relay na babagay sa mga ito. The contact geometry indicates how many poles there are, and how they open and close.

Some examples are: single-pole single-throw; single-pole double-throw; and double-pole double-throw. Kung ala yung hinahanap mo ay pwede gumamit ng may mas maraming poles kasi pwede namang pabayaan ang mga unused contacts.

Ang relays ay karaniwang makikita sa ting mga bahay gaya ng mga appliances na merong eletronic control turning on something like a motor or a light. Pwede din siya sa mga sasakyan na gumagamit ng 12V supply voltage.