LukeScotty

Let me rattle your brains and if you can you give us a brief desciption on how they actually work with the windings n that? why we use them? drawing would be nice

If You Build It, They Will Come n If it aint broken don't fix it!

rumrunner

Hi Luke,
the only winding a contactor has is the coil ,this is fed with a set voltage via the control circuit,most coils are marked with the opperating voltage and can be ac or dc,24volt ,110 volt ,240 volt ,or 415 volt, upon completion of the control circuit the coil is energised and operates as a solinoid and attracts an armature which makes the conection between the contacts, most contactors have three main contacts for the phases and various auxillary contacts for the control circuit ,these can be normally open or normally closed ,for motor control the contactor is often "held in"by taking the coil feed via a n/o contact, hope this helps a bit ,its difficult to explain in words and i cant upload a picture at present
atvbitwww

wayne

i tried to figure out the difference between contactors and relays the only real answer i came up with is size and purpose, nothing definitive
both are used so a smaller circuit can energise a larger circuit

rumrunner

Thats correct wayne ,a contactor is a relay.

LukeScotty

whats the main reason for using a contactor, rather than connecting direct to the board? large currents?

when I helped wire one up, the contactor were feeding outside lights, and had 2 cables coming into the contactor from the board, one to close (i'd say trigger) the contactor, and one fed the lights. would it have been possible to just have one cable incoming from the board to the contactor, and using that to close the contactor and feed to the lights, rather than having 2 cables, get me??? :S cheers

If You Build It, They Will Come n If it aint broken don't fix it!

rumrunner

i presume the cable to "trigger", as you say ,i would say" bring in" ,the contactor went to the coil and was switched in some way

Lofty

Hi,
We've fitted one at a hotel to monitor freezers that are in an remote building.
If the supply to the freezers failed then an external light would come on to alert the staff.

Best regards,
Lofty

Keep your fins wet and your air dry.

LukeScotty

is there some sort of light on the contactor? or are there external lights wired to the contactor, which become lit when power to the freezers is lost?

If You Build It, They Will Come n If it aint broken don't fix it!

Shakey

luke, contactors are absolutely vital for industrial circuits.

lets say you have a circuit carrying, say, 1000A at 1000V, by using a contactor you could control that circuit using 12V dc at 100mA. From miles away if you wish.

imagine a 3 phase motor. If you strapped it accross the supply, it would just run continously. By using a contactor (or a configuration of them) you can start it and stop it at will, and again, remotely.

Regarding the light, a contactor will frequently have 'normally open' (N/O) contacts and 'normally closed' (N/C) contacts. 'Normally' relates to its de-energised state.

So take the circuit mentioned above, by using a set of N/C contacts, when the contactor de-energises (loss of power to the freezer) the N/C contacts will close and complete a circuit to the warning light. The N/C contacts could even be in the 'pull in' circuit for a seperate contactor which will feed the lights.

and so on, and so on

You can use the same principle to bring in a stand-by generator, for, say, a hospital, when the mains fails.

And imagine connecting a circuit to a generator that was off. the genny would be at zero hertz and volts. By the time it got to 50Hz and 230/400V the circuits connected to it would be fried. So we put in a contactor which wont connect the output until its at correct V and Hz. And the same contactor will 'drop out' if it drops to say, 45Hz (when the diesel runs out and its stopping), for example

PLC's are just banks of 'electronic contactors', and without them, most industrial machinery would be buggered.

Many many uses.

hope this helps

wayne

lscotty did you mean how do contractors work because thats a mystery to everyone