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- Опубліковано 5 сер 2024
- A relay comparison - latching, SSR and mechanical. Which is best?
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All details of this video, including links, are on my GitHub:
github.com/RalphBacon/Relay-H...
All relays provide some form of switch. Relays come in various shapes, sizes and purposes. They are operated electrically, electronically or even manually. In our Arduinite world, they are used to enable higher voltages and/or currents to be switched by something that could not handle that requirement. So your Arduino, PIC or Raspberry Pi can now switch high current household voltages without a problem.
So which one to choose? And why choose one type over another?
In this video, we look first at the traditional, electromechanical relay. It's a switch that is operated by an electromagnetic coil. I've already done a complete video on the ins and outs of such a video but we summarise it here.
If you want the full details watch this other video #18 Opto-isolated Relay:
• #18 Add a Relay Module...
We next look at a Solid State Relay (SSR). This is not a mechanical switch at all, but an electronic one. As such there are some disadvantages to using it but also some advantages too. For example, SSRs take up little room and are optoisolated by default. No moving parts, either. But they are connected to the switching voltage at all times, even when off.
There are some precautions to be taken when using Solid State Relays so I've included a PDF document for some bedtime reading:
omronfs.omron.com/en_US/ecb/p...
Finally, we take a look at a mechanical latching relay. It's a bit like the first one, but the switching process, from one contact to another, is a latching process. Once switched, using one coil, you need to un-switch it using another coil. This could be very useful in low power circuits, as an alternative to using MOSFETs, perhaps.
Now be aware that some Far Eastern manufacturers offer "latching" relays that are not the same as the one used here. Their "latching" mechanism still requires power to be applied at all times, and the flip-flop between contacts is controlled by a further on-board component. You just supply a high or low to a single input and the latching process happens - but it's not permanent (across power breaks) and it's not a true latching process at all. Caveat emptor!
Here's an example of a hardware-controlled flip-flop "latching" relay - NOT what we mean in this video at all!
www.aliexpress.com/item/OOTDT...
Do not buy this unless you understand what you are buying!
LINKS LINKS LINKS LINKS LINKS LINKS LINKS
(Some links may be affiliate links which pay me a commission - doesn't affect my editorial content either way)
Opto-isolated electromechanical (traditional) relay double pack (ensure you get OPTOCOUPLED or OPTOISOLATED):
www.banggood.com/2Pcs-5V-1-Ch...
Solid State Relay (SSR)
www.banggood.com/One-way-Soli...
www.aliexpress.com/item/5V-1-...
SSR Spec Sheet as used in the video:
www.openhacks.com/uploadsprod...
Latching (bistable) relay (also other multi-packs available, cheaper)
www.aliexpress.com/item/12V-C...
Also in packs of two (and more, check the website):
www.aliexpress.com/item/2PCS-...
Useful background reading on relays on Wikipedia:
en.wikipedia.org/wiki/Relay
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Nice informative, with a little back to basics.
Glad to have you back!.
Thanks for your post, Bosted Tap, good to hear from you.
Thank you for your explanation, up until now it wasn't sinking in. Now I finally get it!
Thanks for your post, Greg Smith, good to hear from you.
Thanks for another interesting video Ralph. I too have learnt about a latching relay today.
I guess it proves that we're never too old to learn something new. Certainly applies to me! Albert Einstein said, "When you stop learning, you start dying." And he knew a thing or two. OK, a bit deep for a Saturday afternoon but what the heck!
Informative video Ralph. Thanks.
Thanks for that, Phil, glad you liked it. Thanks for posting.
and welcome back.
Thanks for that, Petey Wheatstraw, nice to hear from you.
Thanks for explaining the SSR.
I'm working on a project to control numerous 110V AC lights with SSRs. I wanted to make a mock-up design of them, but using LEDs powered off 5V DC. Your video answered my question of why the DC powered LEDs never shut off on a SSR.
Indeed, that's the reason, Shawn but you could use 5v AC just for the LED supply and the mock up would work.
Very interesting video and good to see you you've been able to shed your piratical alter ego. :)
Yes, I was getting too sea-sick, and the parrot mess down my back was unbelievable. Now I'm back to Terra Firma and what I understand best!
Excellent video! I watched it completely to see the last relay so I think I also owe Bob a thanks! I want to make a audio switch with relays that would no be powered after the switch is done. Thanks a lot!
Cool, glad you liked it, Max!
Never rely on a relay :D Keep the vids coming, Ralph.
That could almost be a new English (electronics) proverb, Pekka. I wonder if they will add it to the English Oxford Dictionary? Thanks for the quip, made me smile!
Many railway signalling systems currently in use rely on relays in safety critical roles. Mind you; they're not the type of relay you'd buy from Bang-good or Ali-Express.
Good to have you back. On the relay, optocoupler circuit. Make sure you use an isolated voltage for the relay. If you don't it is just a voltage translator. Good video as usual.
Good point you make there, James (and which I also go on about, at length, in video #18). Nice to hear from you.
You too may friend love your videos.
I really liked the SSR explanation. It was very informative. I am interested in the subject of relays and SSRs as I have two projects in mind that would use these. Thanks
Glad it got you thinking, Bruce, I'd call that a win-win! Thanks for posting, good to hear from you.
Keeping it simple. Others go deep into complex math etc and that will only drive one crazy. Nothing is perfect so why try.
Great videos
Well said!
This is a cool video - interesting stuff - thank you!
A slight clarification on the Triac. The zero volt detection will not be necessary to switch the Triac off, since a Triac is naturally self-sustaining once it's in its on state and it will itself switch off as zero is crossed. This is how a Triac is different from a transistor (transistor isn't self sustaining) and also the reason you don't commonly see DC SSRs. Under DC, there's no zero crossing event to reset the Triac out of its self-sustaining state, so it wouldn't turn off.
I thought for a minute we had our wires crossed but yes, that's very true: as soon as you remove the trigger voltage it will switch off at the (next) zero voltage point - so it's the switch on that is important. I knew this, so I've no idea why I indicated otherwise, thanks for the clarification.
@@RalphBacon Thanks for the video, I was having trouble finding information on latching relays. That's an SCR, the double-diode triac thing on the right side of the Solid State Relay, I think. But they do turn them on part way through a cycle, in order to dim lights and slow universal or DC motors. But, as albedo0point39 said, they just stay on until it gets to zero voltage. I suppose the SSR is generally defined as an SCR with a ZVD and an optocoupler. As we seem to have figured out, though, only the latching relay is capable of wasting no power in the on or off state.
Before I was able to buy latching relays, I thought of using an automotive power door lock actuator to flip a household light-switch to cut out the lithium battery in a boombox when it got too low. I had trouble figuring out the latching relays I bought though, so far. I guess I broke the first one, there is really no example circuit in the rather cryptic datasheet I had. Now I think I know where to start on the second attempt with a second relay. Thanks!
Hi Ralph! Hope the eye is much better. You don't look quite the Cyclops you appeared when it first occurred.
Blimey, you didn't waste much time getting to grips with that concept I mentioned. Once again great video.
I was going to add the caveat about some of the Chinese "latching" or "bistable" relays which are nice but as you rightly point out, and I discovered for myself in the meantime, they are NOT "power less" bistable units! They still consume power to maintain a closed connection on the Normally Open contacts. I'm still hoping to find one such proper zero power latch type from China but so far to no avail sadly.
With regard to your other question about whether higher volts, amps and power can be switched - YES! There are relays from other companies available to do that. I've just repaired an underfloor heating timer/thermostat which had a faulty such relay. It was a standard unit from an Austrian company called Schrack (No, not Shrek! 😁) - WELL known in the industrial automation space.
Sadly these I could not find online from eBay in the 3v version I required, at a sensible price for the 2x AA battery operated unit I have. And, although RS (rswww.com) - Radiospares of yesteryear - have 5v versions as well as 12 and 24v ones they had NO 3v ones.. Farnell however (Element14 for US and elsewhere) DID have the exact one. Obtained - next day delivery - fitted and thermostat switch now operating again properly!
The 3v version is manufacturer part number is RT314F03. BUT, a search on the Farnell's website for bistable latching relay should provide plenty of options. The one I procured has 16A switching capability (although the Farnell's short description says 20A which does not agree with the spec printed on the relay itself!).
One OTHER point worthy of note is that there are BOTH twin coil (as you described) AND single coil versions of latching relays. The latter typically work by providing a reverse voltage to the single coil which then drives the contacts in the opposite direction. Once again caveat emptor! If possible obtain the datasheet FIRST and confirm the relay will do what you want!
Hope that helps. Glad I helped you learn a bit more about these useful relays and once again a VERY well produced and concise video. 👏🙌👍👍
You inspired me Bob! I can't believe I never came across these in my electronics work before, but there we are. Others have mentioned a single coil, latching relay - I wonder how they are supposed to work without the ability to both source and sink the current (ie in different directions). Easy to do on an Arduino, but otherwise?
Thanks for the references I shall check them out, hopefully the information will remain lodged in my grey matter.
@@RalphBacon The single coil relays need an H-brigde to reverse the current for set and reset. Have a look at the Panasonic DE2A-L2-3V capable of 250V ac @ 8A
If switching part way through a cycle is bad, should we be using ZVD for mechanical relays? (And is that even possible?)
A very good point there BaselBantam. After all, if RFI can be generated by a TRIAC then it can be anything that switches mains electricity on and off. What about household light switches?
What I seem to remember (but will research further) is that a single on/off switch (like your household switches) cause no more than a "pop" in terms of RFI, and can often be heard on analog radio sets quite clearly. The more current being switched the louder the pop or click.
It seems we generally suffer (as in, put up with) these, although manufacturers have to take steps to mitigate RFI (from washing machines, for example, that switch large loads). However, if we were to switch the device on and off many times a second (light dimmers, for example) then much more notice must be taken of RFI, hence the zero voltage switch.
It's an interesting, not to mention tricky area, and I shall research further. Thanks for your interesting point, BaselBantam.
Welcome back . . . . .
Thanks for that, Brian, good to hear from you.
Nice video. Almost forgot those bi stable Relais. But I have some in my lab and maybe they might come in handy some day.
One day, someday - probably means "never", Michael. However, I will keep them in mind for my future projects. The best use is when you want to save power and don't want to supply current to the coil to keep it energised.
Ralph S Bacon you are probably right. They are lying around here since 10 years or so. Got them cheap long time before al those Chinese sellers turned up from the German electronic discounter Pollin Electronic. If I think about it I could have used one of those in a project I did a year ago (battery powered bath tube thermometer for my little daughter using an oled, an DS18B20 a nano clone and a 9 Volt battery). But I ended up using a mosfet and an optocoupler besides some resistors and a cap.
And in the Real World, given a free choice, what would I use? A mechanical relay or a MOSFET? I'll leave you to come up with the answer but I can give you a hint. Ich wuerde fast nie ein Relais benutzen! But I do like the "click" they make. Almost like audible feedback that it's working as expected!
Ralph S Bacon eben. And if you really need isolation (maybe because of different ground potentials) you can always isolate your mosfet with an optocoupler. But mostly not needed. Fine for all low voltage applications.
@@RalphBacon mein Gott! Du spricht Deutsch auch!? Ausgezeichnet! Ich muß viel mehr Deutsch zu lernen! 👌
I have a microcontroller function that works with a momentary switch connecting a pin to ground, I want the output from another microcontroller pin to act like the momentary switch, can this be done with just a transistor?
You'll have to explain a bit more what you want to achieve, otherwise I can see me suggesting you do something silly like shorting out a GPIO pin. 😮 From what I can see from your question, any GPIO pin can act like a switch, with or without a transistor - but I need more details.
@@RalphBacon it's just a button connects a pin to ground to make something happen in the code on an esp32, this is not the issue. The question is how to replace that button with the output of a voice recog module (3.3V) I could trigger a relay and close the contact but there must be a way to do it with a transistor.
@@RalphBacon I tried a 2N3904 transistor, connecting the 3.3v output of the voice recog module to the base but it didn't seem to work.
Your driving device (voice recog module, for example) must bring its output either high or low. This can then be used directly (or via a transistor, ideally a MOSFET) with a microcontroller. So the driving module is the one to get working first.
I have worked with many other types of relays from m/a to hundreds of amps. 1.5volt to Kilovolts. But most of them have been replaced with solid state electronics. These Three are about the only ones readily available now.
Yes, indeed. I nearly used some SSRs in my most recent (Barrel Pond Controller) project but decided I'd use up my relay. But they are still readily available from supplies like Mouser, RS Components, Digikey etc.
Good day sir
is it possible to combine Wemos esp8266 d1 r1 and 5v 1 channel Solid State Relay ?
Possibly, Kol. The relay is triggered via the relay's onboard optocoupler (basically an LED, as far as the ESP8266's GPIO pin is concerned). So, as long as the LED lights up (you won't be able to see it) the optocoupler will energise the relay. You'll have to power the relay (VCC) with the 5v from the ESP8266 but that's easy too. You'll have to try it to make sure!
@@RalphBacon this is too much to ask sir.. but can you help me for the right code that will work for these two cause is it hard to find the right code in the internet and the app that will be use .. so please sir help me for this project of mine, sir.. cause it is my first project and i want to know more about arduino but this gives me a hard time :(
Sorry, Kol, I'm not going to write your code for you. Follow the demo in the video(s) and then see if it works with the ESP8266. There are no shortcuts. That way you will gain the experience you need, too.
@@RalphBacon hahahaha its okay sir
@@RalphBacon sir can i ask the app that used for arduino or compatible for it ??
DC SSRs are quite easy to obtain. They use photo mosfets instead of photo triacs. I use CPC1706Y in my projects. Don't forget to put a current limiting resistor on the driver LED or you'll destroy your SSR.
Ah, indeed, ms3bain, I mentioned in an earlier post that in some ways this is "cheating" inasmuch that the word "relay" is now being used for MOSFETs - just like I used in video #123 albeit the ones I used were not main voltage capable.
Oh well, as long as the item works OK I guess they/we can call it anything we like! And, at least, Arduinites understand what a relay does so whether it's a mechanical switch, a TRIAC (which stands for TRIode for AC, who knew?) or a MOSFET I guess it doesn't matter too much!
Thanks for the heads-up about the SSR limiting resistor; although the one I have has one built in others might not.
Ralph....good video as usual!
However some of the info about the zero voltage detection is not correct. It's not wrong (maybe it's bad) to switch on during the sine wave - this is called phase angle control and it's how dimmers work. There are many product that is this for dimming. And no it will not mess up your WiFi and your neighbor will not be at your door. But you are correct..it is electrically noisy. But to your point, the relay probably does work that way..but it's not wrong to switch during the sine wave.
Expanding upon the foregoing. The idea of ZVD on an SSR is to switch the triac on as close to the zero voltage (hopefully zero current) point thus minimising RFI. It can get its knickers in a twist sometimes if your switching into a reactive circuit.
From experience, James, it can most certainly be bad (and hence wrong?) to just switch the mains when not at zero.
In the 1970s (yes, I'm that old) I made some sound-to-light units for my teenage disco stage. The partly rectified sound signal was fed to a triac which then switched on when the trigger voltage was met. Great! Worked like dream. I was the hero. But the RFI had to be heard to be believed. Probably have more than the neighbours knocking on my door if I did that sort of thing today!
I'll look into phase switching. I know that special precautions have to be taken to prevent that RFI as otherwise, an old-fashioned rotary light dimmer would do what my sound-to-light units did. Just the thought...
Stay tuned and see what I discover! Thanks for posting.
16:45 - I wish my bottom was 3 times smaller...but that's a different story. [that was a spontaneous good one right there..]
the SSR snubber short circuit explanation was in place..(-:
The less said about my Gluteus Maximus the better, quite frankly, Ronen! Thanks for posting.
maybe good for a 3D printer!
the heated bed and extruder
friendly greetings from The Netherlands!
Rob.
Glad to see you're thinking about possible uses, HobbyRob, nice to hear from you. Greetings back from a wet, cold and rainy UK!
@@RalphBacon I have seen videos of flooding!
:-(
I wish these people a lot of strength!
I have a few of these and they all seem to have flimsy terminals, are they safe? I wont get my "knickers in a twist" if not answered. lmao
Which ones do you have, Vic? The traditional relay seems fine, the SSR, at lower currents is good too. The latching relay I would not use on UK mains voltages.
@@RalphBacon The ssr I have does have rugged terminals but the typical blue ones you show remind me of sonoff terms. use em for lamps only.
I do have a latched relay with just one coil. Apply voltage and it switches and latches. It requires to have the voltage reversed to switch the contact back again
Ah, Ed, fashionably late to the party again! Two earlier comments here on single-coil, latched relays both elicited the following comment from me:
I wonder how they are supposed to work without the ability to both source and sink the current (ie in different directions). Easy to do on an Arduino, but otherwise?
Perhaps you can answer?
@@RalphBacon i just like to give other people the opportunity first to make intelligent remarks Ralph :-) Anyway I am a practical man so I am just happy they do, but I presume that there might be a permanent magnet that if under a certain polarity goes one way and under the reverse polarity goes the other way, both directions than push or pull the switch in a position it mechanically holds. www.edn.com/design/analog/4324841/Circuits-drive-single-coil-latching-relays
Uh huh, he said, nodding his head in a knowing fashion.
As I suspected, Ed, it's tricky if you have to change the polarity of both ends of the single relay coil to get it to switch the other way (like a DC motor). Without the simplicity of two output channels which can be configured for current SINK or SOURCE in an Arduino (or similar), I'd use the dual coil version, frankly.
But it's good to know that the single channel versions are available and easy to use on an Arduino.
I don't know if anyone else has responded, I'm working from top to bottom in the comments today!
@@RalphBacon correct, using H bridge for that
That was very interesting...I have 6 military grade latch relays and they are very reliable, but I do not have projects with them for the moment... I would give 2 of them to you if you are interested.
Ooh, can they switch 240v mains electricity, Pierre?
Sorry, they work with 12 volts and are rated for 28 volts at 3 Amp. but If you are still interested, I could send you 2 of them ...@@RalphBacon
That's very kind, Pierre. If you email me at the email address on my main channel page (on the About tab) I'll send you my actual postal address. I daren't be more specific here or the bots will find it and I will be spammed to death!
I totally agree! @@RalphBacon
Re latching relay - not necessary two coils. There can be one coil, and you just put different direction current there. And the contact group is magnetic, so it feels the current or rather magnetic field direction, so it switches off or on depending on the polarity on the coil. I remember in the USSR the name was like polarized relay. They were fun to play with :)
You're referring to what's known in the telecoms world as a Carpenter Relay.
I've just replied to Bob Lewis here, and posed the question:
I wonder how they are supposed to work without the ability to both source and sink the current (ie in different directions). Easy to do on an Arduino, but otherwise?
Any ideas?
@@RalphBacon The ones that I had could stay infinitely in any of the (two) stable states. Like a system of magnets, you know, it can't be in between, but can have a few stable states. And those relays definitely had quite a complex magnet system inside their coil and contacts. Looked really pretty inside, like swiss watch :) Fun to play with. Such a pity I can't take a photo now - they must be have been thrown away, what a shame. They were from either some mainframes of the 70s-80s or from rockets of that era or their supporting equipment. Maybe from telecom, I dunno, had relatives in the first two areas.
From the way you describe it, it sounds almost over-engineered! Especially when two coil relays are easy to implement and work well (and it makes the logic easier too, I feel).
Not to worry, the dual coil versions are cheap and plentiful, but if anyone has a single coil version we can use it easily on an Arduino as we don't need to permanently ground one side of the coil.
@@RalphBacon You have probably figured out already how to drive a single coil latching relay (Carpenter relay electronics.stackexchange.com/questions/76666/understanding-the-polarized-relay-concept) by an Arduino. Subject to current limitations connect it between two outputs. To SET the relay momentarily make one O/P HIGH and t'other LOW. To RESET it rinse and repeat t'other way around. To de-energise the coil make both O/Ps the same.
BT must have scrapped thousands as they were use in many Strowger Telephone Exchanges. One such use was in what was known as a DC2 Relay Set. They we used on lines(trunks) between exchanges.
I use this, maybe nice for a look, input between 3,3 & 30 volt, max 15 amp, 400 watt. High-power MOS buis, trigger schakelaar, drive module, PWM regelgeving, elektronisch gestuurde schakelaar Cost one dollar,....
I need the link, Erik, so I can take a look...
Ralph, It would have been useful to include power transistors in this video for completeness
Building on the comment below, I'm working on leading and trailing edge AC control at the moment. The former is easy and there are standard builds available using zero-cross and interrupts to the Arduino then firing the triac. However, trailing edge phase control is a bit more of a challenge (using back-to-back MOSFETs?)
This leading and trailing edge phase control would be a good subject for one of your future videos. You could then discuss the various merits of switching at various points of the sine wave, although there is scope for you being put on the Naughty Step if you go too far off-piste
My application (and now your homework) is to control a 500W 240V AC motor used in power showers. Why? My daughter comes home at vampire time, takes a shower and wakes the house up. As these pumps are overrated I believe she will never know if its running at a lower power.
I presume we no longer have to keep an eye open for you?
Thank goodness I'm not already on the naughty step after that mains connected relay so close to my hand!
On the power shower front, have you considered a variac? Basically, an infinitely adjustable tapped (non-isolating) transformer. They would be too expensive new, I suspect, but second hand might do the trick rather than phase control of 240v which might make the motor very noisy and possibly stall. Just to rub salt into the wound, my power shower pump has three settings on it - if I set it on level 1 I suspect it would do what you want. I have it on the highest level normally (and don't change it because the pump is in the attic). On the other hand, just leave it another two or three years and she will have flown the nest, problem solved!
I'll look into this subject a bit more but that just struck me as I read your comment.
And yes, my eye is healing nicely, not yet as it was but getting there. Need new specs, I suspect. More cost.
@@RalphBacon I realise I could buy a variac and there are several leading and trailing edge phase angle controllers on the market. But that's not why we do this is it? This phase angle stuff would bring many of your videos together (Arduino interrupts, timer register setting, zero cross, opto coupler triac firing, mains safety, etc etc.) As its then controlling AC mains it will have many applications for the Arduinites. There is a standard leading edge build on the Arduino Forum so start there?
I've got the leading edge version working. The motor is quieter. I am just curious to have a back-to-back comparison of leading and trailing edge control of these general purpose AC motors (same as in AC electric corded drills) .... with you doing all the hard work. I sort of feel that switching the trailing edge OFF is somehow 'kinder' to the load, rather than banging up to half a waveform into the load .... but that may just be me getting all emotional again.
You will need a twin-beam scope though ....
Glad the eye is better.
On the "leading" vs "trailing" edge debate, don't all new dimmers have to be trailing edge dimmer, as otherwise the EU universe will end? Partly because they have a lower minimum load requirement, and are much smoother and don't have that annoying buzz. But they are more complex and hence a bit more expensive.
LED dimmers are a different kettle of fish as the LED has to be compatible with whatever dimming technology you / the universe is using these days (due to the LED being run on DC, not AC). I'll look into that phase control, see what I find without killing myself...
@@RalphBacon I believe the choice of LE vs TE depends on the type of load to be controlled. Resistive loads are pretty straightforward, but inductive and maybe capacitive loads can be troublesome due to power factor and back EMF causing 'ringing'. This is where the snubber circuit comes into play. To simplify things start with a pure resistive load and get your waveforms then stick a transformer in the load circuit and see the effect of inductance. Finally put a fluorescent tube starter in there and try and control that!
Ref LEDs, yes you are right. This is because the retrofit LED lights have a transformer ( = inductor) and smoothing capacitors in the light housing so the dimmer has to accommodate this. Perhaps this is why TE is used, if it is, I'm not sure.
This can all very involved, but that is where you hand it back to us to take it further if we wish. Those that do will need a twin beam oscilloscope though.
I haven't used latching relays for years (40+ of them, probably) - for the simple reason that you can never be sure of the initial state, thus making them potentially dangerous.
They do, I'm sure, have their uses, but I'd struggle to think of one.
The code (on a microprocessor) could sort out the initial state if it was that important, Duncan. After all, if the relay had switched on some mains equipment, it would turn back on for less than 1/2 second as the microprocessor started running the code before the µprocessor switched it off again.
One application I've encountered where latching relays are used is for switching between two pieces of equipment where one is a main and the other is a stand-by that needs to be "exercised", say, week and week about. I have some Spinner Coaxial relays that were removed from VHF base-station equipment. Uber-expensive when brand new.
@@RalphBacon And a lot of damage could be done in half a second!!!
Duncan, you are absolutely correct in that unless you use some kind of logic ladder to maintain a non volatile state log, the relay could be in either state on return of power. However, given that in MOST cases it's likely only being used as an electronically controlled mains toggle switch, it has EXACTLY the same issues as a normal mains toggle switch in the same circumstances e.g. a light switch or a panel toggle. It is therefore a relatively easy safety test to simply ask the question "would a normal mechanical toggle switch be safe to have/use in this circuit in the event of a power failure and return?"
If the answer is NO, they each fail and then other design elements would need to be considered and included. Equally however, the electronic toggle relays (pulse triggered normal relay, using an electronic hold mechanism) DON'T work that way and DO change state to Normally Open on power fail. This is the reason why self latching relays are useful in zero to low power switching environments such as many (if not most) underfloor thermostats which are battery powered plus have LCD displays and are expected to last years on one set of alkaline batteries.
These are commercially available units for domestic electrical heating and wouldn't pass the relevant British Standard if they were considered.potentially dangerous or lethal.
Table lamps dont turn their switch off if there is a power cut. Potentially dangerous? Yes. Practically dangerous? Meh. In fact that is exactly the use case, making a lamp that can be switched by a human, or remotely controlled without a lot of complicated feedback mechanisms.
SSR for high current ac loads to prevent contact burnout vs. Mech
I have an SSR, Dehv, plus heatsink and the whole thing is huge. I'm not sure whether I'll use it yet. I have some very good 30A relays now (verified, certified) so that might still be a better solution. Options, options!
i've been tinkering with a latchable dpdt relay to simulate a crossover switch in a lighting circuit to make a 3 way switch. I just wanted it to change each time it was pressed. And stay that way over power cuts. Used with a H bridge as the one i used would need the polarity reversing to make it do it's stuff and gets very hairy with an arduino... Only trouble is, I don't really like messing with 240v, so project never got any further than experimental stage.
You can get DPDT latchable relays, Adam, (my demo relay had two sets of switches) so would do just fine for your project, except you would need an official 240v version (I don't think I'd trust this relay on 240v despite what the datasheet says).
See the post from Bob Lewis here, he mentions higher powered ones.
I sure wish you were working with DC-DC SSRs.
I have bought several of them with, usually pretty poor results. You can get a 60 amp model for as little as about USD$10 or as much as well over USD$100. Lots of fakes out there.
I've got a mains 10A SSR but it is a fake and I would not use it in a real project, just for experiments. And it's quite big, even bigger with the heatsink.
DC SSR's are widely available, uk.rs-online.com/web/p/solid-state-relays/2448993/
edit; They are out of stock because i just ordered a load lol
That's a clear cheat, Spark Doctor! They might be called a relay but they are really super high power MOSFETs. No different, in principle, to what I did in video #123.
And OMG how expensive is that? Nearly 40 quid ($50) EACH?!!? I don't think I will be ordering any (even if they do come back into stock)! Did you really order some? If so, what possible use are they for?
@@RalphBacon Hi Ralf. Sorry for the lateness of the reply. Yes, i ordered 20 of them. We use them in a underwater application where they are in effect potted so it is a complete pain to get to. As to why we spend that much on them, yes we could buy them from Ebay or AliExpress but we would not get the certificate of conformity and for us to comply with ISO2009 and various other certifications, we have to have trace-ability especially when dealing with the military.
Have a look at the data sheet on the RS site again, The circuit diagram is almost the same as what you drew in your video.
👍 & Abo
😎
Typo (ewhen) on the tungsten comment
And that typo will be there for all eternity, Andy, as it is part of the video and cannot be removed. UA-cam don't let me replace a video once it's been released. I can take it down (with all the comments, viewing figures etc) and upload a new one but I'll just have to let this one stand. I guess you win the *EAGLE EYES* award of the video, though.
I see your patch is gone. Good.
Yes, Ed, I was fed up being called a pirate, and being asked where my pieces of eight were stashed. Gone for good, I hope...
@@RalphBacon hope your eye will be ok