Regarding speed, I took the liberty of downloading the video and loading it into kdenlive: the cycle from the moment the plunger moves to when it's all the way into the solenoid is faster than the frame rate of the video, so on the order of 1/60th of a second.
Ya know, at least in a web browser, you can just run the youtube player frame-by-frame forward or backward, using the less-than and greater-than keys. Using that method you can see that the pull or release motions of the solenoid take between one and two frames. Then right-click on the video to look at "Stats for nerds" to see that this is 60 frames per sec video. So my conclusion is slightly longer than 1/60th sec.
I make sure to watch the adds. I'm retired and only get about $800/Month from my residuals as a side man, no SS or insurance at all. I still want Fran to make as much as she can because it is a good show. It keeps me inspired to still pick up my guitar every day and do a bit of soldering on my old, old & older amps. Thanx Fran! You Rock
Here in France we use 230v coil latching relays in domestic lighting situations where 3 or more push button switches are required to operate a single light, such as in a large room, hall or corridor. The relay is located in the 'fuse box' or more local junction box.
It still can be done without the relay, 2 standart and an infinite number of crossover switches, but the latter ones are more expensive and much more wiring is needed. One relay and momentary switches is the cheaper solution.
Neat device! And not to forget, the latching relays even went to the Moon! A great many of them were used in the Apollo guidance computer DSKY to switch (and latch) the high voltage segments in the DSKY digits. It all goes clickety-clickety when the displayed numbers change.
When I worked in industrial automation, doing PLC programming, I worked with electricians who had been around long enough that they'd worked on the relay logic that the ladder logic I worked with was based on. "Latch" was one of the standard rung outputs (which could either be a physical output or a logical one).
First Mechanically Latching Relays I found was in the '70's, Volkswagen Headlight Relay. Pulling Signal Lever back momentarily put wire to ground, which would Switch SPDT Contacts. These were in ~2" metal cans. They have changed to the Cube design. Smaller, more compact. Great for Alarms Systems as it only draws power when switching. And if used on an Open loop Circuit. Battery would draw no Power til tripped. Only good if wires were not accessible and could notbe cut. Otherwise, close Circuit is Best, Supervised with a resistor is even Better. I used one on a Catamaran for lighting. Just a simple pair of 2 Conductor wires to a Momentary pushbutton. Could switch lights from multiple Locations. That 24 Volt unit you show may work at 12 Volts. Good thing about the VW Cube type is at 12 Volts, they can be used on Cars, Boats, anything. Using 12. I know other Car Manufacturers use them. First I saw was '70's VWs. With a metal chassis(Car), you can get away with running only 1 wire, other wire to chassis. Good job showing operation. Stratmando
Was also used in AC (3 rails / with middle rail) model railroad engines for reversing direction on over voltage. TL;DR: The latching relay switches the feed of the current from one side to the other of the center-tapped stator coil and that changes the direction of the magnetic field in the stator relative to the magnetic fields in the rotor. In order that the over voltage pulse does not make the engine jump, the relay has either an additional contact or mechanical arrangement of the normal-open/close contacts that breaks the circuit as soon as the plunger / lever moves. Voltage for running the AC motor is 6..17V AC, the over voltage pulse is about 20V. The tension of the spring holding the plunger or lever of the relay is tuned to be overcome only by the over voltage impulse (Lionel, Märklin, etc.)
Just like a clicky (retractable) pen! When you showed us the latching relay & started to described it's operation as pulses of power to engage/disengage, it was immediately obvious how that functionality worked. I saw that it uses the exact same principles as a clicky pen, or push to turn on/off buttons, etc. I've long been mesmerized by that type of brilliantly designed technology. Such a simple design, yet quite elegant in functionality.
A timely video Fran. We just had an situation at work where my hardware colleague needed to book time from our software engineer to write code for his design. The MD/CEO said NO so he had to go back and redesign with hard logic and latching relays. Time is money, so a hardware rethink was needed, back to an old school solution.
Within the first ten projects in the manual of my "Radio Shack 120-in-1 (edit: 150-in-1) Experimenters Kit" Circa 1980 - titled something like "A Latching Relay Circuit". I finally decided to READ the header paragraph and description all the way through, instead of simply hooking up the point-to-point wiring. Good lesson. :)
The modern ones are either reversing 2 wire or a 3 wire design with a permanent magnet. I have some 200 amp relays that latch on or off based on which way the H bridge pulses them. They work by sliding one magnet from one side to the other side.
They call them remnance relays, finder make them in the ice cube style, I use them for reversing conveyors that have a proximity switch at each end so even if you have a power failure the conveyors will always re start the correct direction.
The old 80s 240 Volvo my dad still drives & refuses to get a new car burned out its shift to overdrive relay. A replacement was rare & truly expensive with wreckers offering me stuff that was also not working at big prices. So i used a modern standard relay and tripped it with a smaller mechanical latching relay sold at an electronics hobby place, all for like $10 & now Dad doesn't have to drive around that old car engine screaming the revs to stay with traffic....
The style showing in this video was not used in telecom. It wouldn’t have been reliable enough. There were no self-latching relays used until computerization came in the 60s. All of the latching relays I’m aware of used coils that were constantly powered. The latching relays that were used in the computerized systems were magnetically latched. A brief pulse would magnetize a piece of metal, which would then close a reed relay. A pulse of the opposite polarity would demagnetize it, allowing the relay to open. The Bell System’s Ferreed switches are a good well documented example of this, and they formed the backbone of the 1ESS.
Some volvo high beam relays were mechanically latching. They usually had 2 coils. One was powered any time the ignition was on. This coil would reset the latch to the low beam state when de-enengized. This way of you had your brights on when you parked and then were driving when the automatic headlights turned on, they would not be on high beam. These relays were in metal cans and were about the size of a D cell battery. All the contacts were 1/4" spades. It could handle about 10A on locking contacts. The turnsignal stalk had a momentary switch. When you closed that switch, if the ingition was on but the headlights were off, it would pulse the high beams. If you then turned on the headlights they would come on high beam. So it didn't work perfectly, but it could be an interesting part for some project. The cars that had that relay were late 70's to early 80's. If you find a volvo where the turnsignal switch pulls back but makes no clicks and does not push forward you might find one of these relays. Most were under the hood forward of the shock tower opposite side from the battery. The oldest 240's had this relay. One other quirk. It was possible to get both outputs on by holding the switch on. I can't remember if that happened when going from.low to high or vice versa, but you could overheat the bulbs and on some cars melt the reflectors this way.
Technically this would be called a toggle relay, alternating relay or impulse latching relay. A latching relay would have two coils (one to pull the armature under a catch which will hold it in the on position, and the other to open the catch and allow the armature to return to the off position) or a polarized coil. (as you described, a magnetic latching relay)
My Dad made his own with bits of Masonite and phenolic coil form tubes, copper wire, etc. He could've just bought them, but he wanted to experience the craft and the operation. He even built a pushbutton lighting system for his first house this way, using doorbell buttons to switch lights on and off. This was in the 60s. Unfortunately, he neglected basic failsafe protections and as such, if you pressed one button twice, the fuse would blow. Don't get me started on his Rube Goldberg air compressor unloader...
I have used exactly one of these in a project...building a "game show circuit" for a college quiz show event. It was taken from a mysterious huge case of relays bought as surplus.. At my last job , there was a door sized slab of bakelite with hundreds of relays on it, each with a indicator lamp across the coil ( elevator controls). It was in a dark room, and looked cool.
Yes - they are sometimes referred to as "bi-stable" devices also. But one important diff is that the relay doesn't lose its "memory" if power is removed - "solid state flip-flops" lose their memory if power is removed.
You could get a idea of how fast it switches by putting a wire between coil and both of the switches of the relay then power to one side of the coil and to the switching contact... Then on a smartphone run a tone generator until it's the same sound as the relay is making and boom you have a frequency which could divide into 1 and get the ammount of time it takes to action that relay
When I first saw this title on Patreon, I thought well that's easy.... wait. Then didn't get round to watching it until now. I didn't actually know, now I do, thanks, Fran :-)
Electro-mechanical relays are still used in the power industry. Most relay coils are rated 125 VDC, some rated 120 VAC. Also many large circuit breaker control schemes use "ice cube" style relays. Thanks Fran.
I haven't seen these before... pretty neat toggle action! However, I did used to work with satellite power systems that used magnetic latching relays. Other than not needing continuous power for the coil, they were useful because they stayed in the last state that was commanded. Of course, this was back in the 90's and it was an old design even then. Very little digital circuitry, and not very sophisticated analog stuff even. It was very interesting stuff to work with, though!
These stepping relays use the same principle that you find in (many) ball point pens. You press the back button once and the ball tip comes out for writing. You push a second time and a spring inside the pen makes the tip retract. A mechanical "Divide By Two" mechanism, also referred to as Flip-Flop in electronic implementations. I was not aware of their use in any computers, but I have for a long time known their use in controlling corridor lights. You probably know the two-switch implementations, where each one can control the same (set of) lights. When the corridor is really long or at several floors, extending the two-switch system is better handled by these relays. Of course, in condominiums and similar, you may prefer a timer version to automatically turn the light off at a certain delay.
just an FYI..Fran's not saying this model was used in a computer or telecom, she's explaining how relays worked in the pre-transistor days of electro-mechanical switching & computers.
I worked in a plant that used a cutler hammer latching relay that had 2 coils one to latch and the other to unlatch. You could unplug it and manually latch or unlatch by hitting it on the side.
I think I have a few of those in my house electrical wiring, I don’t know if the mechanism is still the same. They are used for the stairs lights, all the light switches are temporary switches wired in parallel and connected to a 230V latching relay, so you can push any one of them and the lights toggle, if you are close to the electrical panel you can even hear the relay clicking in and out
It is also good today for micro controller load switching where you want to avoid the ongoing current flow and warming to keep a socket or lamp turned on.
Made use a latching relay 30 years ago to isolate a intermittent problem on a recurring aircraft environmental system fault. The system fault indicator would not differentiate between the two items it monitored. But was, intermittent, unsolvable issue in the maintenance shop We constructed a test circuit, using FAA approved parts to test for the intermittent issue, solved next flight cycle. The relay, while permitting normal operation, latched into the fault side of dual monitored circuit to indicate which side of the system was indicating the discrepancy. A simple temp sensor out of calibration was the end issue ..Replaced, and months of complaints fixed.
In my electrical class i used to make circuits by taking regular relays and running the output through a switch to the input so you pulsed it on and used another seperate input to open it again.
If you have an electronic thermostat for your home heating/air conditioning system, you have at least one latching relay, possibly more. It doesn't work anything like that toggling relay in the video though, as others have already pointed out.
Surely, a serious disadvantage to using this type of relay in many applications would be that it would not be easy at the begining of a process to know the starting positions of all the relays. Perhaps the single on/off contact was used to signal whether a reset pulse was needed?
@Stan - Or, you could use a DAW which can record and display two waveforms. Set it up to record the pulse to the relay on one channel, then record the output of the relay on another channel. The relay would need to have some audio on its output to record on the 2nd channel of the DAW. It would be similar to using a scope but not such a fleeting display. I could explain that better if I was less sober.
If you had enough of them in an electro-mechanical computer, they could be used to store a program, even when the power was off. Also ypu could attach one chan of a digital scope to the coil and the other chan to contacts to measure the switching time.
The other obvious issue is that less heat is generated in operation. Which means you can pack several hundred/thousand devices into a fairly small space with less concern about cooling.
Logic circuitry triggered by which contacts are closed and so on. For instance, these could be hooked up in a series to record binary numbers, participate in addition operations, etc. If you look at an old computer adder design and substitute these things for flip-flops, with a motor providing pulses to substitute for the clock, that's about it.
Years ago, Went to Reair an Old Ademco Alarm System. It used the Ace Keyswitch, key could be removed at the 12 and 3 O'clock position. They way Original Installer Instructed the Customer. He had customer Remove key in wrong position, which the coil was constantly energized, using the key only momentarily removed power to coil. It worked, BUT, It drew Power Continously. Reducing Time when on Battery Back up. I explained to them, they didn't understand. They continued the Idiots way? Stratmando
I remember decades ago wondering how an AC signal would hold a contact/solenoid arm down (excluding the zero-voltage spot where the shading pole helps)..It's 'cause the coil attracts the solenoid metal in one direction regardless of the direction of magnetic field, provided the solenoid metal is magnetically neutral. So, little field, big field, positive, or negative the solenoids will go the same way (of course depending on geometry, springs, etc. )
I've been using some DC latching solenoids on some irrigation control valves. They require very little power to operate and a single nine volt battery can power the timer for an entire season. I've yet to dissect one to study it. Maybe you should do one and make a video. :)
I have Spectroid on my Smartphone so I can see but not measure how long it takes. For that I'd need a time based oscilloscope that can freeze the trace. I noticed some of the audio spikes were shorter than others and wonder how short it could be and still switch.
I really enjoyed your video, but have a question. It seems that when you used the wires to pulse the transformer it did move to one side and then come back, each time, as best I could tell. But if you only pulsed the transformer once, should not the transformer stay latched on the left side and not go back to the right side until you pulse it again? Also, how are you accounting for mechanical bounce, which causes many millisecond pulses (and is there a minimum pulse width to operate)?. Thanks, Shayle
In the mid-60's, we had someone visit our lab to do an interview with the director. The interview took place in our computer room (a PDP-6). The article talked about "the clicking of countless transistors." As I recall, nothing much was clicking at all -- mostly A/C noise.
Nice video. This is technically not a latching relay. This is an alternate action relay or most commonly referred to as an impulse relay. Think of an impulse relay as an electromechanical version of a divide by two counter. A latching relay would have two coils, one latching and one unlatching. Think of a latching relay as an electromechanical version of a JK flip-flop.
The only downside to this wonderful little gadget would be that there is no was to "easily" determine it's state at any given time. In other words, if I just powered a bunch of them up, I don't know which ones are in one state and which are in the other. Still... very cool. Thank you, Fran, for showing us this! I love this older technology.
Well, first, that would hardly be the only downside. They have a very limited update rate, for one, and the operating voltage has to be enough to power the mechanical switch. As far as determining state, in situ the secondary terminals (the contacts being made and broken) are a part of another powered circuit, and those circuits have lots of voltage/current detectors in them. All of those detectors feed back to the input layer of the control scheme, along with various human-controlled switches and various other detectors. As you can imagine, then it was a very common "pattern" to have the "turn on the output" logic "AND"ed (by other relays) with "the output is off" sensor. But, yeah, if someone built a circuit without any feedback, they would quickly have an unstable system. Then they wouldn't build those any more.
Wait! When were these actually used in telecom industry? You only said "back in the day". If I were to hazard a guess I'd say from the 60s to the 80s. I also think I might be a little too naive in my intuition, and wouldn't be surprised if it was something more like 50s to 80s. I think I might have to bludgeon myself into the ER if they were still using these by 1990.
Could one of these used to act as a bypass switch in an effects pedal? Not sure if a smaller verison exists, or if it would be cost effectfive versus a DPDT stomp switch.
@fran Great video. Quick question. You used a similar blue paper on your workbench, when you were repairing an old LO-TONE CLASSIC FUZZ pedal. Can you please tell me: is that a specific kind of material or is it just like a paper towel or something? Just curious. Keep the great videos coming.
They usually are called "shop towels" and are much thicker than a usual paper towel and a bit cushy. I like to use them as a clean and disposable work surface.
. Very well explained. Thank you . I have a linen ironer of WESCO MODEL NO BM 10025. It has Finder SPDT DIN Rail Latching Relay - 16 A, 24V ac.mi would appreciate if you tell me how to check if it is working as required. Pls do reply thank you from Antonio Goa the state of India. Thank you in advance
what specs do you need? There are over 300 in stock of the modern 2 wire or 3 wire type in stock at Digikey. For example G5RL-K1-E-DC5 is a dual coil unit where it's pulse one to turn on and pulse the other coil to turn off.
My programmable thermostat at home contains a small latching relay G6CU2117PUSDC3 from Omron. It probably uses a magnet instead of a mechanical latch as Fran mentions. Saves on battery life as only a small pulse of current is required to turn the furnace/ac on or off.
There are silicon versions of that type of relay. Also, Check out small relays on Amazon. I don't know how prices compare to bigger electronics suppliers. I usually figure an item is available on Amazon, it is somewhat easily available.
Thanks for the suggestions here. A project from my past was a SLA battery supply where I was using a relay to control the output while the battery was in its working range. A latching relay would have worked well here. I ended up using standard relay which used quite a lot of power given that the units ran for 12 hours at a time. The units are not used as much now and battery technology has also changed so I'm not likely to upgrade them. Anyhow, I'd probably use a mosfet now since I've learnt lots since then.
Odd, as soon as I got to your channel I got a pop up window in the lower right asking me about how well notifications are. I have never seen this before. I wonder if this has any thing to do with your past problems, Fran?
