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Forum Index : Microcontroller and PC projects : How to switch 1000W 220V with uMite
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MicroBlocks Guru  Joined: 12/05/2012 Location: ThailandPosts: 2209 |
What would be the best way to control a 1000W (220v, so about 5A) heating element. I am going to convert a rice cooker into a sous vide. :) Plan is to use a 28 pin uMite and use that to monitor the temperature and switch on/off the heating element. I would prefer solid state.There is also a small motor to circulate the water but i figure it would be easiest to just have it on as long as the sous vide is on. Microblocks. Build with logic. |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
a mainly resistive load? - a few of these in parallel http://www.mouser.com/ds/2/307/g3mb_0609-298620.pdf or similar. Zero-crossing detect inbuilt. Available on fleabay for around £6 for 10 |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
I just use a decent quality relay, the ALE1PB05 I've had this controlling a 1000W fan heater for 3 years without any issue |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Yes i like the simple relay. It is small, generates no heat and fits on a PCB. I'll need to make sure that it does not switch on/off too fast but that is simple to make sure the on/off times are within reason for a relay. I looked at the heater element and it has two coils. A 'boil' and a 'warm'. So once it is up to temp i might be able to use the 'warm' coil with a very long duty cycle to maintain temperature. Thanks for the suggestions. Microblocks. Build with logic. |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I like to have plenty of separation and use remote controlled switches. Search the forum for "arlec" You can either add a relay or two to the remote control or, with the Arlec, use a simple 433MHz transmitter module. I use both methods and fond them reliable. Jim VK7JH MMedit |
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Quazee137 Guru Joined: 07/08/2016 Location: United StatesPosts: 593 |
I have been using the cheap 4 relay modules for 120VAC at 5amps and at 220VAC at 3.5 amps no problem. They max out at 10 amps so I like to keep things at 8 amps or less. I looked for the ones with the high voltage slot and got them for $1.20 each buying a 100 of them. I have been looking for the 16 versions with the high voltage slot.  I use my mains detector adjusted to give me a zero crossing on a pin that is part of the switching on a relay code. That way suppression circuitry in not needed. Quazee137 These are the type used on the modules I using. ebay relay |
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| Alastair Senior Member  Joined: 03/04/2017 Location: AustraliaPosts: 161 |
I agree with relays. Just make sure you get the "cheap" relays with the opto isolator. Not all have it. Keeps the spikes away from the MM. Cheers, Alastair |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
@Alastair. You mean mechanical relays with integrated opto isolator (Any examples)? Or an opto coupler as a step before the relay? Microblocks. Build with logic. |
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| Alastair Senior Member Joined: 03/04/2017 Location: AustraliaPosts: 161 |
@microblocks Yes there are lots of different ones some with & without opto isolator built in. Some have selectable high or low active. Search ebay but I buy quite a lot from Banggood. Here are some. Cheers, Alastair |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
I pretty much use SSR devices, exclusively. Please see attached. There is quite a range from this manufacturer.2017-11-17_000138_CPC1998.pdf |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2950 |
GDay MicroBlocks, I would be wary of using `standard' Relays for switching a 1000W load.. You could end up burning `pits' into the relay contacts.. which could weld the contacts closed... Not good for your sous vide machine.. I would use a solid state relay of at least 20A capability. I am looking at doing a controller for a toaster oven SMD solder machine and am looking at having a stand alone box that plugs into the mains and has a mains socket on the case that the oven then plugs into ie. it plugs in series with the oven mains. Kind Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
Hate to disagree, but a quality, premium manufacturer, relay with a 15A 275VAC rating is designed to do exactly what is required. SSDs are much more expensive to buy to get the required rating and need significant heatsinks to meet their ratings |
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KeepIS Guru Joined: 13/10/2014 Location: AustraliaPosts: 1882 |
Our 3hp single phase dust extractor (15A socket rated) draws 45A at power on then drops to 9.2A running, it uses a relay. In other workshops these things have been running for over 13 years. I do like SS relays for a lot of power switching applications though, I have one in my 120A, 5 to 30V linear regulated power supply that I designed and built over 20 years ago, never missed a beat. NANO Inverter: Full download - Only Hex Ver 8.1Ks |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2950 |
Hi Peter, All, No problem in disagreeing, that is what a discussion is all about. All that aside. I have a spa (240V 10A) that I switch using an RF wireless remote. I drive a small 12v relay to switch in a 30A contactor (Relay) to drive the current.. I have had 1 contactor let go but that was a strange failure as the electro magnet wouldnt pull in fully (I could put a bit of pressure on and get it to pull in) so I replaced it and it has been running now for a couple of years.. I made my comment based on experience with incandescent lamp indicator display panels that were 48V relays pulling in 110Vac to drive up to 5 or 6 Lamps (I guess they were 50W each).. Many a time we had these `blow' sometimes in smoke and fire.. but they were in enclosed rooms (read SHEDS) with little ventilation and running continuously for up to 12 hrs on days that could be upto 40 degrees Celsius.. Of course these were subject to condensation and spiderwebs etc.. Was a lot of Fun, Don (Dontronics) would have `fond' memories of those days. Kind Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
well, i did once have some relay contacts fail that were simulating the pressing of the electronic 'on' button on a piece of computer gear. the contacts were passing just a few milliamps when closed, but after a million or so cycles they burnt out! it was supposedly a high-quality relay from farnell. this was an extreme case - we were stress-testing the computer gear's power supply, and the relay used was also switching a counter on a seperate set of contacts (that did not fail) so the number of cycles was known - it was checked daily. more recently, i've had a couple of relays switching a hot water cylinder once a day burning out their contacts in 6 months - so around 180 cycles. the timers that contained the relays were rated fine, but supplied from china. it does all depend upon both the nature of the load and, as peter says, the quality of the relay contacts. in the past i've generally ended up using SSRs from ebay as replacements, similar to these ones: https://www.ebay.com/itm/222649153211 just don't trust the ratings given, the chinese SSRs are ok for 10A/15A domestic stuff, but not anything more! the current rating written on the front is not real. cheers, rob :-) |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
I've used a few, & at the low price it's easy to grab a few spares & rip one open, at the expense of destroying it to ascertain it's true rating. Used some 50A ones here, & the device inside it was from memory 10A max. Many of the ebay ones are not potted & easily opened up. Phil. |
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| Tinine Guru Joined: 30/03/2016 Location: United KingdomPosts: 1646 |
Recently, I was troubleshooting a metal forming machine. The PLC's outputs drove mechanical relays that, in turn, drove the hydraulic-valve-solenoids (24v DC ~1A). Although none of the relays accounted for the malfunction, I cycled the machine, many times with the electrical cabinet's door open and I observed every darned relay contact arcing. Maybe it's just me but in this day and age, it just seemed, well, wrong! OTOH, I assisted with the installation of a new brushless servo drive on a CNC machine. The reported problem was that the drive's Enable would not switch off. This was an opto-coupled input but driven by a SSR. It turned out that; even in the "off" state, the SSR leakage current was enough to drive the opto. THIS is where I prefer to see a dry-contact (relay). They didn't want to replace the SSR so I simply loaded-it-up with a resistor. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
For safety add a temperature fuse of some sort. If the software crashes with the relay on, you could burn your house down. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
@MicroBlocks - With a resistive load this is a little simpler. You don't have to worry about the ridiculous locked rotor current you would get when starting a motor, or about any inductive kickbacks. A relay would probably work just fine. But, you could use a Fairchild MOC3031M 6 pin DIP zero-cross triac driver optocoupler ($1.20 at digikey) driving an NXP BT138 triac (95A surge, 12A rms, 600v, $0.86 at digikey) through a 330 ohm resistor. https://media.digikey.com/pdf/Data%20Sheets/NXP%20PDFs/BT138%20Series.pdf http://www.onsemi.com/pub/Collateral/MOC3043M-D.pdf Paul in NY |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
The intended use is indeed for a purely resistive load. The rice cooker that i want to modify has two heater elements (or one! with 3-wires) to choose between 'boil' and 'warm'. Probably the 'boil' will need to be on for about 5-10 minutes until the required temperature is almost reached. Then i would need to switch it on and off to slowly reach the temperature. I am not sure if the 'warm' option is powerful enough to be useful. The uMite will have some PID software and i am not sure at this moment how many times and for how long it will need to be switched on. If it is hundreds of time per cooking session then probably a mechanical relay is less optimal. If it is on for long times there might be problems with a SSR as it will probably get hot. That is my main concern. Or is that wrong? A 1000W (about 5A on 220v) seems not that much and i could always use a beefier version. Does a triac or SSR rated for 20A get hot at all when used with 5A? Microblocks. Build with logic. |
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