I must say that sharing your knowledge and experience is a very generous thing to do and to do it with added entertainment value is magic. Thanks Clive.
Whilst I'm not an engineer who needs to use these on a day-to-day basis, this was very interesting. And handy tips to designers and manufacturers based on your experiences. Good stuff.
I'm going to use one to detect when my oil boiler is actually fired up by connecting it to the oik switch solenoid. This will then send the data to Home Assistant which will log the hours burnt and tell me when to refill my oil.
@@WINGNUT307 Good to hear of a link to monitoring your oil boiler with a Big Clive practical application. He must have been a very accomplished lift engineer with his approach to repair. Servicing in any trade needs more Clive's, my opinion for fifty years and travelling half the country working for national companies. As an industrial electrician from the sixties I did a crossover to work as an R&D engineer on oil combustion, including boiler design and then gas combustion after the oil crisis. My electrcal knowledge gave me fifty years of advantage to help many good mechanical engineers to improve their electrical thought processes. I made alarm circuits to notify customers when the oil tank was getting low, float switches with mercury switches to prevent any fire risk with arcs and oil vapour venting to atmosphere. All before Watchman or similar systems when I became a heating service engineer in Dorset and Hampshire. Oil servicing had few respectable craftsman so getting paid to drive around the New Forest was a gift.
Did not expect the discussion to cover elevator control circuit boards. As a journeyman elevator tech in Canada I'm impressed by the depth of your knowledge on our trade. Bang on, and much appreciated.
@@user-gx6jb6wc5g we want to see what happens if you disconnect zener and the LED. Boom or fzzz. Whatever, if a cheap zener can prevent just a little goo in your box, fine.
@@colejohnson66 welcome to our age. Sorry. I mean, they literally are, I'm not the only one who thought about them instantly when Clive mentioned that you can easily short the resistor's contact with a metal screw.
Thank you Clive! Another great video as always. This is exactly what I needed for my project. I “reverse engineered” my own circuit, but I found that my Esp8266 was occasionally picking up the ripple from the mains. I ended up putting another small electrolytic cap on the logic side of the optocoupler. Works perfectly!
"It's never gonna spark again, 'till you go reset that breaker, all the black soot settled down, I'm sure that something blew" Yes, Clive, I know that song!
Nice video! 👍 Thank you in all you do!! For myself a retired Electronics Engineer in the past 8 years now and in the "past working in Electronics" from 1972 untill 2013....Iam getting back into Electronics again. It's in the blood!! Thanks for the refreshing videos.
I know the fan timer pcb you mentioned, it's the same size as the one featured here but a bit longer. I think JW made a video about them a while ago. I've had several fail due to the resistor going thermonuclear so I converted them to half wave capacitive dropper using a 0.22uF X2 capacitor. No more heat and they're all still working.
Spot on Clive as usual,! (Lift engineer here) Even back in the day when I was working on the tool- 1970’s, board repair was discounted, even though a few of us could. Niwdays, it unheard of. Otis CMOS control and OI4 boards were just as this control and shorted regularly, cause all sorts of other unpleasantries.
A very similar tech is used in some 3D printers for the power loss resume function. A 3D printer has about 150-300W worth of heaters and 40W worth of motors, and the PSU is guaranteed to hold over at least 25ms dropout from its stored energy. So when the expected mains pulse is not detected, they can quickly turn off all heaters - and they still have about half the capacitor energy in the PSU left, which is enough to run the relatively frugal motors to move the toolhead a little bit up and prevent damage to the print, and then write a cookie to the internal nonvolatile memory, saying which file was being printed, which line was last finished, and where the toolhead is at at this moment, and then just wait until the power drains from the power supply. When the power resumes, they can just continue printing. The voltage sensing needs to be mains side, because when you see the voltage dropping on the output of the PSU, it's already too late, it has basically no residual energy left. Also they insert it before the manual power switch, so when you power it off by hand, obviously you wanted it that way, while if the cord is pulled or the mains just collapses, then the power loss resume is activated. Eventually other ways to implement resume were implemented by just always writing a cookie every layer with no mains side sensing, but it's not nearly as clean.
I remember getting a belt off a lift door open detector switch many years ago. The switch was two exposed contacts on the edge of the door at mains voltage, the circuit being closed by the steel of the other door. Being an inquisitive teen-ager I poked them with my finger! They weren't shrouded or anything!
In Ireland, we call stray strands "hairy mollys"! Most common in lift controllers on mains 3ph terminals where 10 sq tails have been stuffed in without ferrules. Always a nice surprise in a dimly lit plant room 😝
During my Electrical and Electronic Engineering degree it was suggested that we rate resistors at twice the power if we want a long lasting stable circuit. However, if you are building in obsolescence use the only slightly higher, this ensures a short but acceptable life and more sales! On the political side, I have a feeling that we are going to be paying a lot more for circuits like this. At least short to medium term.
It's quite common for ceramic resistors to have very high temperature ratings, a couple of hundred degrees C or more, so the board burns and resistor unsolders, completely unharmed.
Unless I'm working with vacuum tubes, I'm not a fan of simply letting things run hot/warm like that constantly, especially for something as simple as voltage detection. Yes, "it works," but needless thermal stress is something to be avoided.
An alternative, and about the same price, is to use an old (functionsl) 5v USB phone charger to your detector pin on your equipment, optionally through an opto-isolator. We use (or have used) this as a solution on ham radio repeaters to detect when we're actually running on battery power rather than commercial power to operate the transmitter at a lower power mode to extend the availability time of the repeater. (Use a resistor, or a voltage divider and resister if needed for 3.3v to limit current going to your micro-controller if you're not running it through an opto-isolator. I'd also recommend validating that the '5v' is correct compared to the ground of what you're sensing with, and isn't incidentally floating at high voltage because someone put in a transformer that's been wound too tight.
Yet another great exploration and explanation! Wee see our share of optos that have been damaged for one reason another. Along electrolytics and comms ICs optos are regularly replaced in industrial stuff under repair.
I'm just one of those Arduino hobbyists who lives up to the cliché of not knowing WTF I'm doing half the time when it comes to electronics. But I understood this circuit and I see the possibilities. I might even integrate this into a little board that I'm trying to design. Thanks again Big Clive.
How does Clive *always* know when I'm laying in bed watching at 3am!?!? Thank you for the 'always' brightness warning!
3 года назад
I wonder why they use resistors instead of capacitors, wouldn't be better to power the the opto isolator using a capacitive power supply? I can only think of cost, a resistor been cheaper that a properly rated capacitor.
These days I prefer to use the AC-input optos, the type with two parallel LEDs that works on either polarity of input. The circuit then reduces to simply the opto and the resistor. OK, the output is then a series of low-going pulses at 100 Hz rather than a solid low, but its easy to either filter that with a capacitor on the output, or do that in code when driving an Arduino
The Zener diode is in there in case the infrared LED inside the optoisolator goes bad and becomes an open circuit. In that case, the full RMS voltage (220 x √2 Volt) would build up across the electrolytic capacitor, causing its explosion. With respect to the canonical design, there is a missing resistor, between the positive of the capacitor and the LED, calculated to limit the current flowing thru the LEDs at 15 mA. In the case of your board is R = 5.1 - ( 1.7 + 1.4) / 0.015 = 120 Ohm. 1.7 V is the Vf of the red LED, and 1.4 V is the Vf of the infrared LED inside the optoisolator. Thank you for the nice video...
Otherwise where is the voltage difference going? Are the leds working on a higher foward voltage on their curve? or is the zener turned off completely? who wins?
@@robegatt The power would be otherwise dissipated in the 1 Watt resistor. If you draw the V/I diagram of the Zener diode, for all operating conditions, it become self-explanatory.
Thing is, BC only raises the prices on *good* stuff. Unless you think that many people bought that high-voltage gay Dalek, as a result of BC's non-recommendation? :-)
I think this video contains some really good advice for circuit engineers... (especially the part regarding using no more than half the resistor wattage)
Been designing and testing quite large industrial systems. Apart from insulating high and low voltage, optoisolators are used for eliminating ground loops. They are often filtered to to suppress voltage spikes and other EMI. Commercially available optoinsulators can have a time constant of 20 ms. Had a problem in Finland where 3 optocouplers was fitted in series. As the machines speed increased, a pulse train fed into one computer disappeared. Every optocoupler shortened pulse length.
I've been meaning to watch this for days and just got around to it. Interesting little board. Seems like it would be easy to make too. I have all the parts it has. Thanks for the info on changing the resistor for 120 volts.
Interesting module. When I need to detect mains voltage I use a DIY isolator, a neon pilot light assembly shining on an LDR, and heat shrink over both. This kludge provides plenty of isolation and draws hardly any power.
You can also make one from a mains neon and an LDR or other photo sensor. The LDR is a less decisive switch than the opto but the mains neon is much easier to make safe if you need to build it without a PCB.
@@user-gx6jb6wc5g Hussman, Airdale, Denco, Wright Air Con Birmingham. A lot of time on main frame computer rooms, great for biood pressure with financial services leaving London. Plus the MoD Dockyards, heating for Concorde's and the Red Arrows etc. All in my past with a bad experience with a lift during my first week as an apprentice industrial electrician working on the companys lift. 1963, lift room, power off but the brake was jammed off with a wooden wedge as instructed. ?¿? Meanwhile the burly van driver forced a fourth floor lift open to load with 2/3 hundredweight of leather + driver. Fortunately I heard the lift motor spinning. 'Presence of mind by me to grab the wedge and the speeding car gently touched the springs. With a ranting van driver complaining he was a foot below the ground floor and he had never had such a quick trip before, I never explained. 1963, October continued Neon control for industrial timers made by Brook Motors (the only source in the country, allegedly) Huddersfield. Only available on three months delivery and with no other source and 200+ Brook timers in control systems built by the company. Very costly timers and all eggs in one basket. There was zero stocking from any supplier, wholesaler home or abroad. Memory prompt, the neon was 50mm long, the board was 90mm, with very few components. PS the Radiospares catalogue was 20 pages of electronic components. Catalogue page size the Imperial size of A5. Potentiomers, carbon track, for Pittards Leather they were used remote mounted to control the Brooks timers. Prone to arcing or sparking you choose. Point of History. From 1914 in the carTanning machinery, British, Turners ltd, ' had to be Yorkshire based, 1914 designed and all clunky, ' withstood lethal quantities of deadly alkalines, skin layers removed in 20 seconds, deadly for live maintenance to flick moving parts. Massive numbers of scarred employee's at the tanning end. Mercier Frere, a French manufacture of tanning machinery using hydraulics and so quiet. Delivered with control systems, panels included. The original block contactors with a life of weeks, all immediately rebuilt with Brook Motor face plate switch gear for reliability. Everything Brook was on a three months lead time. The face plate was 200mm high, 250mn wide. Large exposed solenoid, Copper contacts with 8mm silver contacts, every copper part was exposed, sou in extremely dangerous. No door isolators that required to be defeated to work live for fault detection. A Brook starter could be rebuilt in minutes with everything exposed for access. Great training. By 1966 my C&G Technicians course stalled at the intermediate level in Somerset. A two year C&G final Technicians course, Industrial Electronics sounded great, all based on 1930's valve theory, forget triacs, quadracs. Our course was the same theory as our lecturers had been taught. Not great for a student who was working in industrial electrics for maintenance and very little contact with electronics other than changing circuit boards and no teaching except the library and a 55-60 hour working week. Keep educating the world Clive.
I live in an apartment building where I've taken a number of fan run on timers out with carbonised resistors and PCBs. Got some still operational examples if you wanted to see them. Grossly under power rated resistor in a capacitive dropper, TRIAC you get the idea. Designed to fit in an Australian mains socket. So quite neat. Low production run too. .
Capacitive droppers are much better at conducting interference spikes generated by high power switching circuits. A spike could trigger the optoisolator, giving a faulty indication. Remember that he said the input may run through switches on all floors of the lift / elevator.
@@acmefixer1 I'm pretty certain cost is an issue too. You need two diodes for a cap dropper. The diodes dont cost much but the caps are about 11p compared to 5p for the resistor. The most expensive component is the opto. However the saving on component cost going from cap to resistor is likely to be 10% of the BOM cost.
@@acmefixer1 Just out of curiosity (noob here): Would that be fixable with an inductor in series or maybe a common mode choke? I get that there is also beauty in a simple solution. But assuming I actually were competent enough to fiddle with mains voltage stuff (which I'm not) and wanted to get rid of the -heating- -element- resistor, could I do it that way?
@@Foobar_The_Fat_Penguin Inductors are almost always the worst choice; big-ish, heavy-ish, hard to manufacture, difficult to measure, fragile, and hence expensive compared to other components. As Gordon implies, a cap dropper is almost certainly the best route forward if you don't want to burn a Watt in the resistor; but if the load is multi-kilowatt, wasting less than 0.1% in the resistor is a don't-care.
People might laugh at the part about getting legs reversed going to an elevator but I have seen it happen. On our campus we lost a major distribution leg. The electricians spent several days replacing everything without sleep. I was there when everything was kicked on and out of habit from working in a manufacturing plant with dodgy wiring I looked at the nearest motor and it was indeed spinning backwards. It was decided that it would be easier to redo all the motors on campus than to try to undo the transformer.
Where I need to sense AC in my Arduino projects, I use a plastic encapsulated neon indicator (like a panel indicator lamp with an inbuilt resistor) and an LDR stuck on the outside, and wrapped in black tape. LDRs are pretty slow and I've found that typical response times are around 1/4 sec. The advantage is it's cheap, almost no heat dissipation, and I estimate better than 2500V isolation.
I use stuff like this all the time we have crazy machines that have to control 5 12 and 24 DC and 12 and 24 AC from PNP sensors and the switching thresholds and voltages get crazy to manage Gotta love older Italian packaging machines
The input resistor and the capacitor in the schematic actually shift the detection by adding a delay. I wouldn't use this for a safety switch especially on an elevator as even half a second of a delay could matter a lot.
33k says 24VAC control circuits in that lift controller, though often you find them running on anything from 24-48VAC as they are often a retrofit board to replace old relay or switch logic during an upgrade. Yes running resistors at rating is bad, especially when it is inside an enclosure and thus ambient for it is going to be 100C plus. Had that with an industrial timer, replaced the original 1W resistors with 10W ceramic, which barely fitted in the space, though I was able to do so as the original controller was multivoltage, and had 3 resistors to allow 120VAC, 230VAC and 277VAC so there were 3 1W resistors in a string. 10W resistor was just short enough to replace all 3, and with that, and replacing the 3 well cooked electrolytic capacitors in it, it ran cool and long lasting. Did not need the 2 other voltage tappings, so those wires went away, as the original installer left them bare end loose in the enclosure, despite a note saying to insulate the unused connections.
I wonder why they opted to use a resistive dropper, instead of capacitive? Surely the cost of a chunky 1w resistor is greater than the cost of a small 400v polyester film capacitor... Even with the addition of the standard 1/4w 1MR discharge resistor accross the capacitor, I think it would still be cheaper.
Perhaps longevity? As seen in past videos the capacitance slowly drops with time due to self healing when there are spikes in the line, I've seen a lot of capacitive droppers fail after a while.
We used optoisolators in the reverse direction. A logic level low would turn on the optoisolator. The output of the optoisolator connected to the gate of a triac (solid state relay) would turn it on and provide 120vac/240vac power to the load.
Another great video Clive, thanks for keeping us both informed and entertained. The HCPL 3700 opto-isolators which have almost all this circuit built in, see 0033mer’s channel for a video on this chip.
@bigclivedotcom This is way orthogonal from the subject of opto-isolators, but you've reminded me of something I think you'll find interesting anyway: Tektronix used to make a scope called the Power Scout which had channel grounds isolated from each other by over a kilovolt, yet they somehow stayed referenced to each other. So you could plug Ch.1 into the five volt trigger signal coming from a motor control logic circuit and Ch.2 into one phase - even across a delta without any ground connection - of say a motor control's 440V output. Try that with a normal scope, and the leads and scope will literally go up in flames along with the control board. I dunno how they did it, and I don't know what - if anything - they have replaced it with. Maybe a competitor like Fluke has something similar in the scopemeter line. oh, and it had a cute little CRT display about 3" across too. I want one still and I don't even have a use case, they're just sexy.
Designers often don't consider the temperature rise when resistors are run at their full rated power. A normal carbon film or metal film resistor can have a maximum body temperature (hot-spot) of 150C when run at full rated power and high ambient temperatures. A power metal oxide or wire-wound resistor is even worse and can have a hot-spot temperature of 250-300C when run at full power. It is not surprising that the PCB material, which usually has a maximum continuous temperature rating of 125C, gets burnt when the designer plonks the resistor hard down against the PCB and then runs that resistor at full power for an extended period.
Interdasting. The lift safety circuit looks like one my mate used for an "IOT" mains frequency logging application in his old job. He asked for my advice on the circuit and I think I just said it definitely needs to be optoisolated. Pretty sure I also told him I'm not exactly comfortable working with mains, and he should probably ask a real EE.
I have seen quite a lot videos of you now but every time when you say something like "watch your eyes" before turning on the light/changing the exposure I kinda flinch and then be like "wait ... stupid me" XD
Where i used to work i made Scoreboards for football clubs each character was approx 12" X 12" with 8 x 8 lamps fitted these lamps where 240 Vac 5w all switched by Optoisolators but of coarse worked in the opposite direction all controlled by a Amstrad 486. Later on i made my own 8 channel board which i connected to my Sinclair computer to control Christmas lights Which was Fun.
I've been trying to grasp the sensing circuits on my heat pump defrost board that uses a PIC micro-controller. The board sends 24vac out to, say the high pressure switch, then back to the board and to a 1K power power resistor to the AC common traces. A thinner trace runs to a 47k resistor then a zener to the 24 vDC negative, thus then through the discrete diode FB rectifier. A 47k resistor also goes to the pin on the PIC m-controller. This video answered some question for me on the software sensing the fluctuation signal and such. I've been thinking of building circuits to sense when my thermostat energizes a signal to track what is being called for when. Such as when it calls for the back up resistive heat, etc. The opto-iso would ensure I'm not loading the signal wires.
Undersized zener resistors is a very frequent failure on the pre of guitar and bass amps. They reduce the power stage voltage with a resistor plus zener to save a winding, but the reliability goes down a lot
20:06 I personally would design a board with an indicator LED on both sides of the Opto-Isolator so you can see both when the unit sees Mains Power and sends a Low Voltage signal.
Looks more like there was a roof leak, and that was a drip landing on the cabinet, and coming in a gap in a knockout, and falling on the board all full of goodness from the dust and bird poo there. Could also be a bird nesting on the cabinet top, a pigeon can be pretty fast nesting if you only go into the lift room once a month.
12:24 I guess the main problem is wetting current (minimum required current for dry contacts). When the current through a contact is too low it might fail to "break through". We have had this problems on a bunch of relays in our locomotives where contacts started to fail after several years. The current through some of those relay contacts was too low and under the manufacturers specified wetting current. At first we replaced the relays by new ones, but soon found out that we could "electrically clean" the contacts by applying a higher current (about 10% of the max rated current) for several cycles and AC seems to be the best choice for this method.
You need another disclaimer beside 'mind your eyes light is coming back', "Mind your brain, you will learn something interesting!" I always manage to pick something up from these, even the soda stream vids.. :D
You are wrong about the zener. It does come into play. Both the LED and the optocoupler are semi conductors that have a resistive component, the are not pure diodes. It is possible to increase the voltage beyond Vf, shortening their life dramatically.
I was looking for something like this a while ago, but ended up designing my own. I did initially use just a couple of resistors and a diode, but found the combined heat from 14 of these circuits in the same enclosure, was not the way to go. I ended up with a capacity dropper and a full bridge rectifier instead, any thoughts?
I suspect that the reason they're so casual about locating those mounting holes is that rather than using screws as you mention they're probably assuming the use of those plastic thingies that you find all over equipment these days, which would just push in, and not get all that close to the resistor...
The weirdest encounter with lifts for me was Aston Uni main building. It was designed with 9 lifts and had had 2 more added to it externally. Using one of the new lifts, I opened the car doors as it was going up. It stopped, as expected. After closing the doors, it set off again - this time going down BUT the floor counter was still counting upward ! I think it got down to the third floor before correcting the counter.
