Switching a 4.4KW circuit remotely - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: March 13, 2017, 10:54:33 am
content: UPDATE: I got a photo of the light switch, they just use the switch on the 20A circuit breaker, how to automate this???Hi Everyone,Thanks for all your help in the past.A friend of mine has some very powerful LED flood lights that he would like to switch on/off remotely, think of a small field, he thinks 220v AC / 20A, he's thinking RPi and cheap relays, I'm thinking mosfets, small relays driving bigger relays or even linear actuators pressing the current switch...I would love and appreciate receiving some of the tremendous insight that the group has.Thanks for looking.CheersRichard

author: tecman
author_rank: Frequent Contributor
timestamp: March 13, 2017, 02:30:58 pm
content: Relay should do the trick. Cheap, reliable and readily available.paul

author: Vtile
author_rank: Super Contributor
timestamp: March 13, 2017, 03:25:00 pm
content: Depend what local regulations have to say, 6kW whispers to me a contactor over relay. The control circuitry can then be anything robust enough that meets the regulations and norms.

author: SeanB
author_rank: Super Contributor
timestamp: March 13, 2017, 05:29:34 pm
content: 6kW means almost invariably a 3 phase supply, so best is a 10kW motor contactor, with a 24VAC operating coil. Add a small industrial control transformer, so you can have a 24VAC rail to do the switching, along with powering the controller using some small 24VAC input power supply, either linear or switching, and use a relay to drive the contactor coil. 20A 3 phase breaker to do wiring protection for the lights, or 3 separate 20A breakers for fail safe operation ( only lose a phase on a fault), and you could add in a motor overload to detect loss of phase or short to cut the contactor coil in case of fault.Reason for 3 phase ( 4 wire plus earth) is you can use regular 2.5mm house wiring for the cabling to the individual light standards, instead of having to use a much more expensive 6mm cable to provide the power. Lower cost ( as you will likely be using 300m of cable at least for the lights) and well worth the extra cost of the supply cable, which have 4 cores instead of 2, but the overall cost of the cable is reduced.

author: james_s
author_rank: Super Contributor
timestamp: March 13, 2017, 05:52:23 pm
content: I would also suggest using a proper contactor, they are made specifically for industrial control applications like this. They're just a really big relay. It's a lot better than trying to use cheap relays to control such a large load.

author: rthorntn
author_rank: Frequent Contributor
timestamp: March 16, 2017, 01:26:36 am
content: A big thank you to everybody that replied.I updated the topic, it's a circuit breaker that these guys want to operate remotely, so i'm looking for the best way to do that.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 03:14:17 am
content: Quote from: rthorntn on March 16, 2017, 01:26:36 amMost circuit breakers are not made for load switching. The circuit breaker will stop working at some point from switching it on and off many times. Sometimes they break down inside and explode this way (I have seen this happen).Again, back to the high current relay. These are normally for switching motors with high inrush current and are sometimes called motor starters. You could put the motor starter relay inline with your outgoing power from the breaker switch.

author: rthorntn
author_rank: Frequent Contributor
timestamp: March 16, 2017, 03:42:16 am
content: Thanks, do we know of a quality motor starter relay that will integrate with an Arduino, has anyone done something similar?

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 04:28:34 am
content: Quote from: rthorntn on March 16, 2017, 03:42:16 amI have not done anything with an arduino, but if you have an output that can drive a small DC coil relay with contacts rated for your voltage of your load that has 3-5 amps capable, that will work. The coil of the starter is probably an amp or 2 at AC 120 or less at 240 AC, so the driving DC relay will need contacts rated for this.I don't know what you have available in Australia, but Allen Bradley, Square D or Siemens may have what you need.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 04:43:25 am
content: You can interface anything you want with an Arduino. To control a large contactor I would probably use a small solid state relay connected to the arduino with that controlling power to the coil in the contactor. Don't take this the wrong way, but if you don't know how to do this, I would recommend consulting locally with someone who knows what they're doing before messing with multi-kilowatt mains voltage loads.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 05:26:53 am
content: Quote from: james_s on March 16, 2017, 04:43:25 amIt's been a long time since I purchased this type of equipment, but the reason that I called out a small coil relay is that they used to be much less expensive than an SSR. The contactor, unless you find someone to donate a used one, will be expensive.

author: Gregg
author_rank: Super Contributor
timestamp: March 16, 2017, 06:16:39 am
content: The refrigeration and air conditioning industries use what is called a definite purpose contactor. They are generally 2 or 3 pole relays with various coil voltages in the 20 to 60 amp range although I have seen them with as many as 6 poles. Some are available with low current auxiliary contacts, also. A google search should show up lots of pictures. Ebay may work as a source for you. I would suggest getting one rated for at least 50% over the current you are switching as it will last longer than if it were rated for the actual load. You can activate the coil with an arduino by whatever means you have at hand.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 03:30:12 pm
content: Quote from: tpowell1830 on March 16, 2017, 05:26:53 amContactors are cheap, ebay is full of them. Here's just one of many examples.http://www.ebay.com/itm/MARS-780-Definite-Purpose-Contactor-61445-replaces-42CF35AJ-3-POLE-24VAC-Coil-/361927674051?Small SSRs are cheap toohttp://www.ebay.com/itm/Gordos-Arkansas-INC-Solid-State-Relay-3-32VDC-Ctrl-240VAC-Out-5A-GB13451-30-/222434639062?I only suggested the SSR because it can be driven directly from a microcontroller IO pin in most cases without requiring a drive transistor or snubber. Beware that there are many cheap Chinese SSRs on ebay that are nowhere near the ratings they claim, although in my experience they do work fine for low power stuff.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 04:31:00 pm
content: Wow, things have changed in the last 25 years. That contactor would have been at least $75 back then. The SSR would have been $30 to $50. Wonder if Australia has access to those.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 04:54:01 pm
content: Well if you walked into Grainger, a contactor probably would be (at least) $75, but ebay has given us access to vast supplies of surplus equipment and parts.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 05:00:07 pm
content: Quote from: james_s on March 16, 2017, 04:54:01 pmYes, that is true, the internet is where I buy almost everything. However, I haven't bought contactors for many years, as I explained.Why would you use an arduino to control this circuit when a simple toggle switch would do the job?

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 05:01:43 pm
content: He wants to switch them remotely, I'd imagine the Arduino will be the bridge between another medium such as RF or the internet and the contactor. That part was never explained in detail though.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 05:10:09 pm
content: Quote from: james_s on March 16, 2017, 05:01:43 pmAgain forgive my ignorance of arduinos, but how would you control it from the internet? I have a Raspberry Pi that I connect to via internet/locally via wifi, does the arduino have this capability?

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 05:12:12 pm
content: There are ethernet modules that can interface to an Arduino. Personally I think it's generally more trouble than it's worth these days since ethernet is complex enough that it's rather taxing to implement on an 8 bit micro, but it can and has been done and it works ok if you just want something simple like using UDP packets to control a relay.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 05:26:32 pm
content: Quote from: james_s on March 16, 2017, 05:12:12 pmAgain WOW, I just checked the price of an ARDUINO SHIELD - WIRELESS on Digi-Key and for only $14. I have been playing with the Raspberry Pi a lot, maybe it's time I started looking at Arduino for some projects.A long time ago, the first PIC board that I bought was an OOPic from Savage Innovations. Unfortunately, Savage Innovations went away and so the OOPic. I still have my 2 original OOPic boards and have done a few fun projects with them a long time ago. I was digging around in some old projects and found them again a couple of days ago.

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2017, 05:32:04 pm
content: If you're interested in ethernet, the Pi is a much better solution IMHO. The Arduino is ok for RF wireless stuff though. I've used the RFM12B and similar cheap modules a few times and they work pretty well.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 16, 2017, 05:37:29 pm
content: Quote from: james_s on March 16, 2017, 05:32:04 pmYea, if the wireless works well enough on the arduino, you can't beat the price, for this application.