mains inline powertap with no neutral. - Page 1
Forum section: electronics / projects

author: johnnyfp
author_rank: Frequent Contributor
timestamp: December 10, 2012, 08:20:43 pm
content: Hi,Any one got a schematic or advise on how I can put together a switch that can control a load line, either transformer or candesant light bulb without a neutral line?I basically want to replace a wall light switch with a cpu controlled circuit., which tend to only have live going to the switch where neutral is at the light fitting.I've seen some touch sensitive switches capable of doing this,CheersJfp

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 10, 2012, 08:29:08 pm
content: I looked into this some time ago. One way is to basically very lightly 'dim' the load and use the resultant voltage over your widget during the interruption as supply for your own local supply. You could devise some regulation circuit that only turns off the load when the mains voltage is quite close to the required voltage.

author: c4757p
author_rank: Super Contributor
timestamp: December 10, 2012, 08:39:13 pm
content: I was just going to suggest that. When the load is off, you can get power just by being in series with the load. In fact, if your circuit's power consumption is small, you may be able to get some power while it isonas well by inserting a small step-up transformer in series with it, and running off the stepped-up voltage drop of the transformer. Obviously you need some good protection for that, because if your load suddenly takes a large current it will induce a similarly large voltage in your circuit.

author: IanB
author_rank: Super Contributor
timestamp: December 10, 2012, 09:07:31 pm
content: You could also have a charging circuit and a small backup battery. The circuit charges the battery through the load when the switch is off and runs off battery power when the switch is on. Of course this would only be effective if the switch is off for a decent amount of time every day.

author: ptricks
author_rank: Frequent Contributor
timestamp: December 10, 2012, 09:17:24 pm
content: Safest way is with a battery powered control. Anything else you use to try to take power from the switched device is going to be overly complicated. Whatever you use you will still need battery power during the off stage so why not just make it battery powered from the start.

author: c4757p
author_rank: Super Contributor
timestamp: December 10, 2012, 09:24:23 pm
content: I am in agreement with ptricks. It's fun to think of ways to pull power from the load line, but safety is important with something like this, and this sounds like a good way to go.If you wanted, you could then add aseparatebattery charging circuit that just sits in parallel with the load switch, which should be much easier (I'm sure there lots of reference designs for mains-powered battery chargers out there). It may be prohibitively big, though, in which case I'd just recommend traditional batteries.

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 10, 2012, 09:33:26 pm
content: Unless you are going to mass-market your widget, I'd say go for battery power too. It will save you a lot of hassleI've witnessed a project basically end up in a (sales) disaster because marketing thought that customers wouldn't mind adding a neutral wire. Well, it turned out they *do* mind, even in new constructionsSo they had to design a new version that required no neutral wire in a widget without any significant space left for even more components.

author: c4757p
author_rank: Super Contributor
timestamp: December 10, 2012, 09:35:58 pm
content: QuoteI don't understand why marketing people are permitted to be so clueless about the field they work in. Anyone would decent electrical knowledge would immediately recognize "no neutral wire" as an unusual enough request that there's probably a good reason for it.

author: DarkPrince
author_rank: Regular Contributor
timestamp: December 10, 2012, 10:12:31 pm
content: A generic off-the-wall light dimmer (cheap ones) uses the potential between the switch to determine firing angle. So they use the same concept, except only charging a 100nF cap so a very light load. Nothing crazy about it.

author: G7PSK
author_rank: Super Contributor
timestamp: December 10, 2012, 10:23:57 pm
content: Most lighting switches here in the UK will have 3 wire + earth going to them even if unused as it may be required later if multiway switching is required also unless the fitting is metal the earth wire is blind so you could be naughty and use that at a pinch.

author: Monkeh
author_rank: Super Contributor
timestamp: December 10, 2012, 10:31:16 pm
content: Quote from: c4757p on December 10, 2012, 09:35:58 pmLaziness and tradition is the reason.Quote from: G7PSK on December 10, 2012, 10:23:57 pm*snort*Most light switches in the UK have just two conductors. You're lucky to get a CPC in any house older than about 1975, let alone having three cores just provided in case!And if you use a CPC as a live conductor.. I have no words.

author: pachuma
author_rank: Contributor
timestamp: December 10, 2012, 10:42:38 pm
content: I designed about two years ago an interchangeable capacitive glass light switch that retrofitted on a regular wall lightswitch.The switch was powered in series with the load while it was off and while the load was on, I used part of the waveform to power the switch, aka widget, and then the rest to the load (dimming slightly the load).One thing to be aware of is that it only works spotlessly when switching a resistive load. Driving an inductive load this way is not a very good idea. Therefore, CFL are not recommended. Even when the switch is off, some CFLs glow with a few milliamps going through them.The PSU of the widget is capacitive, with a cross by zero detection being done by a micro-controller.I'll try to dig up a picture of the fitted gadget and its little explicative PDF.To be honest the thing I am most proud that gadget is the way you only see a clear sheet of glass on the wall and the fixing mechanism of the glass to the switch/sensor.

author: c4757p
author_rank: Super Contributor
timestamp: December 10, 2012, 10:43:00 pm
content: Quote from: Monkeh on December 10, 2012, 10:31:16 pmI'm sure it runs thoroughly afoul of every electrical code on the planet, but I doubt there is any real technical/safety reason why it couldn't sink a couple mA. Still, don't do it...

author: Monkeh
author_rank: Super Contributor
timestamp: December 10, 2012, 10:49:32 pm
content: Quote from: c4757p on December 10, 2012, 10:43:00 pmSafety reasons like the CPC being present in certain cable types to allow a protective device to operate in the event of cable damage? Can't be anything to do with that.

author: T4P
author_rank: Super Contributor
timestamp: December 11, 2012, 04:30:55 am
content: where i live in the electrical standards are similar to the ones in UK and ... i've got 2 earths going into my lights

author: SeanB
author_rank: Super Contributor
timestamp: December 11, 2012, 05:05:29 am
content: In and out to the light. They just cut the cable to put in the switch, and leave the neutral uncut. The PE would be used to earth the metal parts if a switch surround if needed.

author: Monkeh
author_rank: Super Contributor
timestamp: December 11, 2012, 05:06:52 am
content: Quote from: SeanB on December 11, 2012, 05:05:29 amUh.. Yeah, nobody does it that way.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 11, 2012, 06:17:52 am
content: Maybe use a capacitive power supply with a Y rated cap to ground? And what about the idea of using a current transformer to derive a little more power when on?

author: T4P
author_rank: Super Contributor
timestamp: December 11, 2012, 07:04:12 am
content: Quote from: SeanB on December 11, 2012, 05:05:29 amYeah but nobody does it that way ... no sloppy neutral uncut switch here, mostly 2 poles unless you're talking about the 3 way switches controlling 3 light fixtures which sometimes are very ODDLY wired in the trunking. Like seriously the one's in my parent's room requires jumpers and some puzzle solving

author: johnnyfp
author_rank: Frequent Contributor
timestamp: December 11, 2012, 08:26:48 am
content: This is a retro fit idea, so most places will have a 2 core wire going to the light switch with live and load. Sux because there is no neutral to put a decent psu circuit. Hence the query. I have an X10 light switch which I may tear down to find out how they do it.I like the captive approach suggested and would indeed be interested in the circuit diagram.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: December 11, 2012, 09:57:32 am
content: The earth conductor should never be used as a return path. It's so far outside of the regs for very good reason.

author: somlioy
author_rank: Regular Contributor
timestamp: December 11, 2012, 11:25:25 am
content: I asked about something similar earlier:https://www.eevblog.com/forum/beginners/1-phase-motion-detector-how-does-it-work

author: johnnyfp
author_rank: Frequent Contributor
timestamp: December 11, 2012, 07:26:56 pm
content: What I found weird was in NZ the neutral and earth are tied together in the fuse box.! Is that normal? I''ve seen this in a few houses in NZ so not dodgy wiring in my hours.

author: Monkeh
author_rank: Super Contributor
timestamp: December 11, 2012, 07:42:38 pm
content: Quote from: johnnyfp on December 11, 2012, 07:26:56 pmYes, it's called TN-C-S. One combined conductor in the supply, separate earth and neutral in the installation.Although sane countries leave doing this to the supplier.

author: pachuma
author_rank: Contributor
timestamp: December 11, 2012, 09:19:04 pm
content: OK, so here is an image of one of the light switches I've got installed around the house that uses the capacitive PSU and load switching.

author: pachuma
author_rank: Contributor
timestamp: December 11, 2012, 09:34:17 pm
content: And here a few renders of the board: top layer load switching + micro-controller and sensor interface. botton layer - PSU + decoupling + filtering.

author: ptricks
author_rank: Frequent Contributor
timestamp: December 11, 2012, 09:38:29 pm
content: Quote from: johnnyfp on December 11, 2012, 07:26:56 pmIn the past items used the neutral as the chassis ground. In the USA it wasn't until a few years ago that appliances like a clothes dryer used a separate ground.Homes in the USA are connected to a transformer that steps down the 4-8KV from the utility to 240VAC with a center tap that becomes the neutral . Appliances were shipped from the factory wired for Hot-Neutral-Hot wiring, 240VAC between the two hot and 120VAC from either hot to neutral. There was a tab that connected the metal frame to the neutral wire. The idea was that if one of the Hot circuits contacted the metal it would short and trip the breaker. It was done that way for over 75 years before changing to the new system required 4 wires, the same 3 as before plus a dedicated ground .The idea behind having a dedicated ground wire is that nothing on the circuit normally uses that wire for a return path so if a device fails the wire is more than capable of carrying the current back to the panel and also in conditions where the neutral comes loose from the socket you would normally have the Hot now flowing through the chassis. A separate ground fixes those issues.

author: pachuma
author_rank: Contributor
timestamp: December 11, 2012, 09:42:29 pm
content: And to finalize the image, here is the light switch on my daughter's bedroom which I engraved by hand for her.

author: Unknown
author_rank: Unknown
timestamp: December 11, 2012, 10:32:35 pm
content: Quote from: Monkeh on December 11, 2012, 07:42:38 pmIn ANZ it's known as MEN, Earth conductor should never carry anything other than fault current, they are not a handy return path. The regs are quite specific to how and where a neutral link is grounded. Nothing sane about leaving this to the supply authority, the M in MEN stands for multiple, and caters better for service with multiple structures than any supplier based scheme.Still if your populace resides in limpet like council flats, clung together on a cold damp rock in the north sea, you'd likely see less advantages from an MEN scheme.

author: Monkeh
author_rank: Super Contributor
timestamp: December 11, 2012, 10:52:14 pm
content: Quote from: Uncle Vernon on December 11, 2012, 10:32:35 pmNo, the system is quite clearly known as TN-C-S. MEN means Multiple Earthed Neutral. The equivalent term over here is PME: Protective Multiple Earthing. This merely refers to method of connecting the PEN to earth in multiple locations due to the risks of a lost neutral, there are many TN-C-S installations which are not PME/MEN, although you won't find them being freshly installed, not for domestic customers, anyway. The facts are the same: One conductor in the supply cable, separated into neutral and a protective earth within the installation.QuotePlenty sane about it. It's their network, it's their neutral and earth to maintain, how can they reasonably place their trust in homeowners to ensure it's good? You put an earth stake in the trench with every joint on the cable, and hey presto, PME/MEN.Now, there's equipotential bonding, which is another matter, and never to be used as an earth.QuoteThere's no need to be insulting, especially when you're wrong.

author: Unknown
author_rank: Unknown
timestamp: December 11, 2012, 11:16:21 pm
content: Quote from: Monkeh on December 11, 2012, 10:52:14 pmTheir earth? What frigging earth? Their is no distributed earth to maintain.QuoteWhat the hell has it got to do with home owners? Earth stakes and neutral links are the responsibility of installing contractors.QuoteNo you don't! You can have 50 joints in an earth conductor without any of them requiring a ground stake. You link the neutral at the point of supply (no, not the point of attachment) of each premises. Multiple earth stakes are permissible (desirable) but all need to bond to the main earth link.QuoteI wouldn't know, I am seldom wrong!A note to the UK, having plugs the size of dinner plates does not mandate your system to be better or safer than other countries schemes.

author: Monkeh
author_rank: Super Contributor
timestamp: December 11, 2012, 11:25:44 pm
content: Quote from: Uncle Vernon on December 11, 2012, 11:16:21 pmThe PEN!Or are you suggesting that the nice low earth impedances seen in your MEN systems are nothing to do with that big conductor linking all the earth stakes (wherever they may be fitted) together?QuoteWhich is exactly the same as putting an earth stake in the trench at supply cable joints. You're just moving it out of the supply and into the installation.QuoteAnd neither do your damn-near identical plugs except for the lack of fuses!You want to try having a technical discussion without assuming I know nothing because I'm from the UK, or are you just going to insist your system (which isthe same, you just leave the earthing arrangements to the installation instead of the supply, in which case you may as well use TT) is better because you use different letters?

author: ivan747
author_rank: Super Contributor
timestamp: December 11, 2012, 11:42:52 pm
content: Quote from: pachuma on December 11, 2012, 09:19:04 pmLooks beautiful! Where can I get more info on these? They use a microcontroller, so the OP may want to take a look.

author: johnnyfp
author_rank: Frequent Contributor
timestamp: December 12, 2012, 02:27:49 am
content: I like the glass. Is it normal or toughened? Because I asked around and nowhere would do small light switch sized toughened pieces for reasonable prices.My idea for that project, which wouldn't' use this one live setup was to control two cap sensitive strips with led feedback through the glass.Then it would dim some led lights in the room.But I may actually resort to using a android unit instead as they are as cheap as chips these days. Specially a cap based one with WiFi.

author: pachuma
author_rank: Contributor
timestamp: December 12, 2012, 08:01:33 am
content: The glass is plain glass, you can use any type of glass you want.This is a project I got on commission to do a reference design. I will publish the "micro-catalog" that I delivered to the customer so that you can see they entire idea behind it. The switch also has a see through the glass LED that indicated the switch status and you could change its color depending on the glass too.Thank for the comments, they are very much appreciated.

author: Unknown
author_rank: Unknown
timestamp: December 12, 2012, 11:45:43 am
content: Quote from: Monkeh on December 11, 2012, 11:25:44 pmI'm questioning that definition of all.QuoteBut not the same as at every joint, which is what you had previously suggested.QuoteIdentical? Fitting fuses to AU plugs would be of little use particularly given the difference in the way we reticulate cable to GPOs.QuoteWhile our standards may have distant origins from some British standards, the current ANZ practices are worlds apart from those.

author: Monkeh
author_rank: Super Contributor
timestamp: December 12, 2012, 12:04:04 pm
content: Quote from: Uncle Vernon on December 12, 2012, 11:45:43 amNow you're picking holes because you have nothing else to do.QuoteSee above.QuoteThat doesn't change the fact that the earthing system is the same. In fact, you probablydoearth the neutral on the supply cable directly, rather than at the installation, you just insist on making the connection between PEN and PE in the installation, rather than the supply head.

author: Unknown
author_rank: Unknown
timestamp: December 12, 2012, 12:09:00 pm
content: Quote from: Monkeh on December 12, 2012, 12:04:04 pmI'd consider it more pulling chains!QuoteSo you're saying yours is better but still the same. OK. you run with that.

author: Monkeh
author_rank: Super Contributor
timestamp: December 12, 2012, 12:11:57 pm
content: Quote from: Uncle Vernon on December 12, 2012, 12:09:00 pm*yawn*QuoteAnd here I was thinking this forum was for discussion, not pointless trolling.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: December 12, 2012, 12:27:57 pm
content: QuoteIn Tassie, Australia the whole pen of the conductor is within the installations main switchboard. I did one the other day, its about 50mm long. Here supply authority normally does not do it.There might be other allowable way you can do it when attaching to different suppliers.MEN is really just a flavour of TC-N-S, is says as much in AS3000.Now I have said my bit I can safely say:Ok lets not hijack the original posters thread.Ps Nice light switch, can you make them smaller?

author: Unknown
author_rank: Unknown
timestamp: December 12, 2012, 12:50:29 pm
content: Quote from: HackedFridgeMagnet on December 12, 2012, 12:27:57 pmAbout 10 years back the major suppliers released several competing ranges of inline control devices, motion sensors, time-clocks etc They worked effectively with incandescent loads but were next to useless with everything else resulting in most lines being withdrawn from sale. With the humble light bulb now almost a museum piece I cannot see the situation being any better for such devices.Those switches do look good but it appears they suffer the same shortfall with most commonly used loads.

author: pachuma
author_rank: Contributor
timestamp: December 12, 2012, 09:39:36 pm
content: Quote from: HackedFridgeMagnet on December 12, 2012, 12:27:57 pmThe current PCB is about 45mm x 45mm it is perfect to retrofit in the light switch socket. You can integrate a bit more the UC componentes, but the components that are imposing the size is the main X2 capacitor, large'ish bypass caps, filter (the coil has to withstand 3A) and track clearance. I guess you could still shrink the design another 10mm x 10mm.As far as the glass sheet is concerned, you can have it in any size. Perhaps the smalles size is that of the sensor PCB or the size of the wall switch potting box.QuoteThanks for the comment, here is the flyer/catalog I pitched for the customer a while ago to present to him his reference design.QuoteYes, I think that was what I commented in the first post. Driving incandescent loads is great and it works spotlessly. However, inductive loads, switched loads they don't behave as they should nor is it recommended. I tried it out with a good range of CFL bulbs with various degrees of success. For example, those sold by Ikea work well on all their CFL range. Dimmable CFLs work just as good as incandescent bulbs. For fluorescent lights is a big no, no (given how the load is driven).For inductive load configurations you would need a separate phase feeding the switch's electronics which was the other configuration I developed for the customer (didn't say much about it because of the subject of the thread).The last thing was that you can calibrate it to be touch or proximity sensitive (the latter is great fun seeing people do their Jedi swipe to switch on the light)Anyway, here is the "catalog" that went on as part of the final delivery hope you like it.One thing I do love about the switches I have around the house is that I no longer need to clean finger marks around light switches, and they do look very cool.

author: somlioy
author_rank: Regular Contributor
timestamp: December 14, 2012, 05:06:51 pm
content: How do you mount the glass sheet to the wallbox?

author: pachuma
author_rank: Contributor
timestamp: December 14, 2012, 06:21:43 pm
content: Quote from: somlioy on December 14, 2012, 05:06:51 pmThat's a quiz question

author: SeanB
author_rank: Super Contributor
timestamp: December 14, 2012, 06:36:23 pm
content: You take a blank wall plate and use clear epoxy to attach the glass to it?

author: pachuma
author_rank: Contributor
timestamp: December 14, 2012, 07:00:43 pm
content: Quote from: SeanB on December 14, 2012, 06:36:23 pmGood answer but no. If you look at the pictures the glass surface is flat with the wall. The solution doesn't use any epoxy at all. The glass can be removed without effort but it doesn't move once fitted.Also remember that the capacitive sensor probe has to be touching the glass too.

author: SeanB
author_rank: Super Contributor
timestamp: December 14, 2012, 07:10:01 pm
content: You made a recess in the wall to accommodate the plate then simply held it in place with either velcro or a magnetic hold down on a metal plate behind the glass.

author: pachuma
author_rank: Contributor
timestamp: December 14, 2012, 08:04:28 pm
content: Very, Very close. The sensor probe is fitted by screwing it to the wall potting box. The glass is fitted to the sensor PCB with neodymium magnets.

author: ivan747
author_rank: Super Contributor
timestamp: December 14, 2012, 08:26:20 pm
content: And you have a patent on that. It's a great idea, I'm glad you applied for a patent.

author: pachuma
author_rank: Contributor
timestamp: December 14, 2012, 08:30:35 pm
content: Pending.

author: PetrosA
author_rank: Frequent Contributor
timestamp: December 15, 2012, 03:02:44 am
content: A lot of the occupancy sensors sold here in the US explicitly said to use the earth wire if there was no neutral available and with states like California mandating the use of these sensors, some buildings have pretty large loads on their earth wires. The 2011 code addresses this by mandating that all switch boxes must have a neutral run to them. This will also change how we wire three way switches and what kind of cables we need, but it will stop the loading of the earthing system.

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2012, 04:27:52 am
content: It is not a good idea to use a protective conductor as a supply return inside the house. It is not an expectation that disconnecting it at any point will lead to a shock hazard. Outside the supply authority treats all wiring as having a shock hazard unless proven otherwise, so the risk there is mitigated by having trained crews and rigorous use of procedures and test gear for work done.

author: Zero999
author_rank: Super Contributor
timestamp: December 16, 2012, 12:03:55 am
content: Try the attached schematic.The MCU needs to be programmed to switch Tr1 for no longer than the amount of time required to discharge C1 and C2. Tr1 could easily be replaced with an SCR or IBGT.

author: atwoz
author_rank: Regular Contributor
timestamp: December 19, 2012, 04:01:13 pm
content: Quote from: Hero999 on December 16, 2012, 12:03:55 amHero, have you tried this circuit? What happens when you use a CFL? Does it blink? That's what happened to me when I tried a method of suppling power through it.

author: johnnyfp
author_rank: Frequent Contributor
timestamp: December 21, 2012, 02:45:29 am
content: So I put hero's circuit in a spice simulator. And there seems to be a 18v to -240v at the zener diode. Is that normal?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: December 21, 2012, 11:38:39 am
content: There shouldn't be 240v across the diode, if that is what you mean.if the spice ground is at neutral then you will get a large voltage but not exactly 240v. maybe something closer to sqrt2 x 240v.post your sim. (.asc)Personally I think the way to do it is with an extra wire. ( neutral ) Ten years down the track people will see that black wire and know what it is for.

author: Unknown
author_rank: Unknown
timestamp: December 21, 2012, 01:02:07 pm
content: Quote from: HackedFridgeMagnet on December 21, 2012, 11:38:39 amMore like 20 to 30 years. But your point is quite correct. Wiring practice has changed to reflect more complex needs and now it is more common to see Neutral and Earth at switch locations. Older practice was to run a twin of active and switched to switch locations and it was as a work around to this that the neutral less schemes were developed.It's never going to be easy however, systems like C-Bus are becoming more common and these will throw an entirely different curve ball to many control solutions.

author: johnnyfp
author_rank: Frequent Contributor
timestamp: December 21, 2012, 11:12:25 pm
content: I moved the and to the low voltage part of the circuit from the neutral and now am getting sensible readings.So trying to understand the circuit and why a zero threshold detect is needed. I can see that when the fet is on the light bulb lights but the control part of the circuit does not get any charge through it. So does this mean that with this circuit you have to switch of the fet to allow the main cap to charge to allow power to the control circuit?What if the fet was moved to be in series of the bridge rectifier and a resistor put in parallel with the fet for when the fet is of to allow continued power to the control circuit?

author: Zero999
author_rank: Super Contributor
timestamp: December 26, 2012, 02:51:39 pm
content: No I haven't tried the circuit.Yes, the MOSFET needs to be off to allow some of the power to be taken from the lamp to power the control circuit. The zero crossing is required so the MOSFET only turns on/off when the mains voltage is near zero. Obviously, the MOSFET needs to be off for long enough to allow C1 and C2 to charge.There's no way to do this without a neutral, other than to take some power from the load to power the control circuit or use another power source such as solar power or a battery.