Contactor and relay's........

Hi all,

Just a quick question in my arduous build,

Whats the difference between a contactor and a relay?

Thanks much very............

Kinda tricky to explain but ill do my best.

A contactor is normally just a off/on switch normally switched on by a magnegtic coil that's pulled into contacts by an induced voltage.

A relay acts like this. Say you have incoming power going to two relays, relay A is normally open and relay B is normally closed. When relay A is closed relay B will open. Relays are normally used in motor controls and they get very complicated.

Hope I helped.

Thanks for the reply Truu,

So I am at present building my 600 watt MH/HPS grow room, but im going to upgrade to a 1000 watts when flowering, what would I need, a contactor or a relay or both?

Thanks again mate.

A contactor is a simple relay. for your needs, either will do.

a contactor i guess is kind of a electro mechanical device, as it has larger moving parts, contactors can deal with high currents without so much fuss,

relays do not have the same moving parts, the high power relays needed to switch off many lights are more costly than a contactor,

using contactors to switch lights is pretty standard, relays can be used, but i think a contactor is better suited to handle the large currents and inductive loads you get from these lights

relays can suffer from the back EMF that is produced when the lights turn off
that causes the contacts of the relay prongs to melt shut,

this can happen to regular house hold timer switches when they are used to switch lights, as they do not have the relays needed to handle high inductive loads inside them .. they are designed for resitive loads

with a contactor when the time switch is set to on, a small current will pass to a coil that is located around the contactor rod this causes physical movement in the contactor rod due to induction

you can hear this movement easy.. its a latching sound the contactor rod inside the device moves foward into the correct position to "fill in the gap" of one of the nodes .. that breaks the circuit inside the device ..

contactors remind me of those buzzer locks some places have to let you in,
you ring the bell and they buzz the door open these electronic latching locks are very similar to the principle of a contactor

a relay is more simple it is just 2 conductor prongs in a glass envelope when a magnetic field is brought close enough, or is strong enough, it will cause the prongs to slam shut this creates a path for the current to flow , take the magnetic field away the prongs open .. rap a coil around the glass relay case, you have made a reed relay switch

sorry for this long winded answer folks but i knew something about electronics once, but its ok i think i forgot most of it now .. long live the weed

What reason do you want to use a contactor? You could still use a switch with 1000w. The light itself would only be pulling 8.8 amps.

Thanks all for the science, +1 to all!!

Truu, I just keep on reading that a normal household timer will need something to take the load of the huge current otherwise the timer will burn out.

Thank you.

Truu said:

What reason do you want to use a contactor? You could still use a switch with 1000w. The light itself would only be pulling 8.8 amps.

Click to expand...

it is not only about the power rating when switching inductive loads

a regular domestic time switch in the uk is rated at 3kw, this is a resistive load rating .. HID ballasts are considered an inductive/capacitive load, therefore they require a suitable switch

a 3k domestic time switch can be used with 400w lights, its even possible to get away with using a 1000w light, but do not be surprised if pretty soon the switch fails/ gets stuck on

I use tyco oz-sh-105lm1 relays with my arduino projects, they are a good general purpose 5v-coil relays and have had no problems running 1000watt lights off them. I currently have one running 1600watts then another running a 1000w and the exhaust fans. These relays do need some extra componeants to keep them safe(a diode, transistor and resistor takes care of a lot of issues) so I put togther a little pcb that can be put in a outlet box, under the outlet. They're really quite handy and have them wired in all sorts of places now, from my garage doors to solenoids for HPA.

You guys are funny and shouldnt be messing with electricity when you dont know what you are doing. Here it is point blank : a relay is a contactor and a contractor is a relay. They are same f'in thing. IN GENERAL a relay is a small current item and a contactor is a large current item. Both terms can be interchanged pretty much. And kdn, the oz-sh-105lm1 is barely big enough for lighting loads it is down right border line dangerous. This is a inductive load NOT a resistive load.

Edit : please listen to skunkd0c he speaks the truth.

You are correct about the loads and the 105lm1 is quite small for what I am putting it through, wont argue with you there. I tried it on recommendation and am very pleased with it and a couple omrons especially for the price. The problem will come with the decreased number of cycles available from the get go as pointed by skunkd0c and shown in the datasheets. It WILL fail (ON) at some point in the future and am counting till it does so I have a good working example for this relay as I have for few others.

I retract my previous statement kdn But I will still question why take the chance on something like that when there are wonderful devices such as this one http://www.newark.com/stancor/120-901/contactor-spst-no-12vdc-100a-bracket/dp/50F3662?in_merch=Popular%20Products&MER=PPSO_N_P_EverywhereElse_None

and something slightly cheaper. These are the kind that I have used for years, slightly smaller but same designs. http://www.newark.com/te-connectivity-products-unlimited/3100-15t1999/contactor-spst-no-dm-120vac-25a/dp/29M9096

Thanks for all the input Guys. Im in the UK, so dont have the selection you do, check this page and pick one for me please, if you could. http://www.hydroponics.co.uk/Lighting-Systems/Timer---Lighting-Accessories . Thank you......

P.S, I will be running a single 600 HPS, then upgrading to a 1000 HPS when blooming.

And PPS, would a small self ballasting 200 watt CFL clones/propagation need to be connected to the contactor too?

Thanks again.