Mains converter to 110V outputs 220V at neutral-earth? - Page 1
Forum section: electronics / projects

author: lpc32
author_rank: Frequent Contributor
timestamp: September 14, 2014, 08:14:00 pm
content: I have a voltage converter from 220V to 110V. The line-neutral output voltage is as expected, but neutral-earth is 220V.Would this be considered "valid" in any context? What are the implications for grounded devices?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 14, 2014, 08:29:39 pm
content: You have neutral and hot reversed at the input.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 14, 2014, 08:34:20 pm
content: What are the implications to devices?And BTW, can this happen with isolated transformers?

author: tom66
author_rank: Super Contributor
timestamp: September 14, 2014, 10:15:25 pm
content: It can present a risk as some switches only isolate live side. For example many light switches.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 15, 2014, 02:36:54 am
content: Quote from: lpc32 on September 14, 2014, 08:34:20 pmTo hell with devices------it can zapyou!It looks like what you have is an auto-transformer.If you swap Neutral & Active on them,you will get just the situation you report.An isolated transformer,or more correctly "isolating transformer" has a secondary winding which is electrically isolated from the primary,so thatneitherside of the secondary winding is connected to Active,Neutral,or Earth.An auto-transformer,on the other hand,is just one winding ,connected between Active & Neutral of the higher voltage (in your case,220v) source.To get 110v ,the winding is tapped (in this case,a centre tap),& the 110v device being powered is meant to be connected between the Neutral end of the winding & the tap.If your Neutral & Active are inverted at the transformer input,they stay inverted at the output.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 15, 2014, 03:38:12 am
content: Please define precisely what you mean by "voltage converter"?There are several very different things that could bear that label (assuming it is even correct)."neutral-earth is 220V" is aDISASTER OF THE HIGHEST MAGNITUDE!Forget about connecting ANYTHING to this abortion until it is fixed!It is impossible to overstate how terrible this is!It is NOT VALID in ANY context!

author: lpc32
author_rank: Frequent Contributor
timestamp: September 15, 2014, 10:23:22 am
content: vk6zgo: Never mind me, I can take it.I just wonder what are some possible side effects to grounded devices that are connected, during normal and fault conditions.I mistakenly assumed this was an isolation transformer because it's a laminated core type, but it does indeed seem to be an autotransformer. But can't you get similar results from an isolation transformer, line/neutral at 110V/220V above earth, depending on what output taps you use?Richard: It's just a laminated transformer in a box, with a switch and a fuse. It was a bit surprising to see non-0V there because it's constructed cleanly enough.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 15, 2014, 10:48:01 am
content: I agree with vk6zgo that it sounds like you have an autotransformer and not a proper isolated full transformer.You guys in 220V-land apparently have the notion that both sides are "hot" so you have no idea which side is 0V.Which is fine as long as you are using equipment designed to handle that safely. Including a proper isolated transformer.But when you try to use 110V equipment with proper 3-pin mains plugs, neutral is expected to be essentially zero.Using a conversion solution that delivers "neutral" at 220V is quite possibly LETHAL. I would either fix it or toss it.Your very life is at risk here, IMHO. This is not something to be trifled with.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 15, 2014, 11:02:29 am
content: Neutral is supposed to be at 0V here as well. Or what do you mean by both sides hot?

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 15, 2014, 11:14:36 am
content: There was a previous discussion here where it was revealed that in Nordic countries (at least, if not elsewhere), they treat BOTH sides as "hot", and only the green-wire safety ground can be relied on to be zero volts. If you have only good, modern, double-insulated appliances then it is probably safe. But when you start fooling around converting to 110V and using legacy 110V loads, you can easily have a deadly combination.Since you have not revealed WHERE you are on the planet, we have no clue what "here" means.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 15, 2014, 11:30:21 am
content: That's odd, assuming by default non-0V at both sides. Do you remember what thread it was?What do you mean by legacy loads?Well, here in the general sense of non-110V. Or so I thought.

author: Kjelt
author_rank: Super Contributor
timestamp: September 15, 2014, 12:11:04 pm
content: A lot of countries in the EU have mainsplugs that are symmetrical. Meaning that you can plug them in a socket both ways, result is that both leads can be phase or hot (220V) or neutral (0V) relative to ground earth.So if you use an autotransformer you have to be aware of this.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 15, 2014, 12:13:43 pm
content: Quote from: lpc32 on September 15, 2014, 10:23:22 am110V devices usually treat both sides of the Mains as if they were 110V w.r.t Earth,just in case the wall socket is incorrectly wired with Live (hot) & Neutral transposed.If the "Neutral" connection is 220V w.r.t Earth,the insulation between it & Earth may be insufficient.In countries where there is no convention as to which pin on the Mains socket is the Neutral one,this is always a possibility with an auto-transformer.With an isolation ( two winding) transformer,the only connection between the primary & secondary is the varying magnetic field.The only voltage available on the secondary of a 220V to 110V isolation transformer is 110V between the two ends of the secondary winding.

author: German_EE
author_rank: Super Contributor
timestamp: September 15, 2014, 12:20:05 pm
content: I would be tempted to open the case then cut any wires joining primary to secondary. If this is impossible (everything wound in one go) then the common connection between input and output MUST be connected to neutral.I wonder why plugging this in did not trip your circuit breaker?

author: German_EE
author_rank: Super Contributor
timestamp: September 15, 2014, 12:55:54 pm
content: Postscript:This is something that the French and British have done correctly, their plugs can only be inserted into the socket one way.C'est la vie

author: lpc32
author_rank: Frequent Contributor
timestamp: September 15, 2014, 01:09:03 pm
content: The 2 prong Europlug can be plugged in both ways, but the outlet itself still has an official line/neutral sidedness.

author: Monkeh
author_rank: Super Contributor
timestamp: September 15, 2014, 01:28:46 pm
content: Quote from: Richard Crowley on September 15, 2014, 11:14:36 amAll sane standards operate this way. The difference is that certain countries have centre-tapped earth, not a neutral conductor.Green, FYI, is no longer the colour of ground in the majority of countries.Quote from: German_EE on September 15, 2014, 12:20:05 pmI'm not entirely sure you understand how a circuit breaker operates.

author: Kevman
author_rank: Regular Contributor
timestamp: September 15, 2014, 02:41:38 pm
content: Quote from: Monkeh on September 15, 2014, 01:28:46 pmIt should trip if its a GFCI, should it not?

author: Monkeh
author_rank: Super Contributor
timestamp: September 15, 2014, 02:45:17 pm
content: Quote from: Kevman on September 15, 2014, 02:41:38 pmWhy would it?

author: Kjelt
author_rank: Super Contributor
timestamp: September 15, 2014, 02:57:02 pm
content: Quote from: lpc32 on September 15, 2014, 01:09:03 pmAFAIK this is NOT defined in my country. The rule of thumb is to use the left connector (looking from the outside) as hot since most people are right handed they would choose to insert a nail for instance in the right hole (children) but this is nowhere defined AFAIK.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 16, 2014, 12:15:02 pm
content: Interesting. What do you see in practice in the outlets in your house?

author: Kjelt
author_rank: Super Contributor
timestamp: September 16, 2014, 02:14:10 pm
content: In practice you see who connected the outlet

author: ejeffrey
author_rank: Super Contributor
timestamp: September 16, 2014, 04:02:47 pm
content: Quote from: lpc32 on September 15, 2014, 01:09:03 pmI haven't heard of that, but even if true the plugs are symmetric so it wouldn't matter for device you plug in. I think this would only be relevant in a country like France where the outlet accepts both europlug and a polarized grounded outlet. I am pretty sure that in at least the Netherlands, whatever convention may exist is not followed reliably.These days the only thing polarization really matters for is Edison light sockets where the neutral conductor is exposed. Most other devices are required to be isolated and/or grounded, so there should be no more danger of coming into contact with neutral than hot. They do at least keep live and neutral identified for fixed wiring, so at least permanently wired lighting fixtures should be connected with the correct polarity.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 16, 2014, 05:11:57 pm
content: Quote from: ejeffrey on September 16, 2014, 04:02:47 pmYes, exactly so. But if you are in 230-volt land and messing around with 110V auto-transformers and undisclosed loads of indeterminate safety, this could be a lethal problem.

author: Kevman
author_rank: Regular Contributor
timestamp: September 17, 2014, 11:43:54 am
content: Quote from: Monkeh on September 15, 2014, 02:45:17 pmWhoops, I thought the ground and neutral were reversed, not the hot and neutral.

author: German_EE
author_rank: Super Contributor
timestamp: September 17, 2014, 08:50:28 pm
content: Out of curiosity I have been doing some investigating and found the following in our apartment electrical system:1) Apart from the cooker (three phase) every wall socket is a standard CEE 7/4 device with the live connection on the right. I believe this to be intentional.2) If a right angled CEE 7/4 plug is inserted with the lead going downwards then the brown lead is connected to live and the blue lead is connected to neutral. The only exception to this was a Chinese made toaster where plugging in with the lead downwards made blue 'live' and I have replaced the power lead. Straight CEE 7/4 plugs have been marked so that the live connection goes to the brown wire.3) Double insulated appliances can be connected either way and they all have a two pin power plug. Some also have a reversible plug at the other end of the cable but where the power lead is hard-wired I have marked the plug so that the brown and blue wires are correctly energized.The lesson learned is that most European EEVBlog readers need to be careful when connecting mains powered devices to their supply.

author: Monkeh
author_rank: Super Contributor
timestamp: September 17, 2014, 10:05:09 pm
content: Quote from: German_EE on September 17, 2014, 08:50:28 pmIt is.Quote... Why bother?

author: German_EE
author_rank: Super Contributor
timestamp: September 18, 2014, 07:05:51 am
content: In most cases so that switching is on the live lead.

author: Kjelt
author_rank: Super Contributor
timestamp: September 18, 2014, 07:18:10 am
content: Quote from: German_EE on September 17, 2014, 08:50:28 pmAnd how about that second right angled plug in a double socket? That is going to be wrong then

author: Monkeh
author_rank: Super Contributor
timestamp: September 18, 2014, 11:47:14 pm
content: Quote from: German_EE on September 18, 2014, 07:05:51 amIf it's inside equipment, it just doesn't matter. Unless the equipment for some reason cares, in which case it would have been designed to ensure polarity.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 19, 2014, 12:34:15 am
content: Quote from: Monkeh on September 18, 2014, 11:47:14 pmSo how do you "ensure polarity" if your country uses symmetrical plugs and indeterminate wiring standards?

author: Monkeh
author_rank: Super Contributor
timestamp: September 19, 2014, 12:35:26 am
content: Quote from: Richard Crowley on September 19, 2014, 12:34:15 amYou use a polarized plug or hard-wire it.

author: Kjelt
author_rank: Super Contributor
timestamp: September 21, 2014, 12:40:19 pm
content: Quote from: Richard Crowley on September 19, 2014, 12:34:15 amYou do not. You make sure for instance that with a mains switch inside equipment you always switch both connections to the mains.Even in our country (netherlands that is) the utilityboard (entrance of electricity to the house) with it's automatic fuses and GFCI's have to switchbothpoles, so also neutral.Not all countries are so rigid (germany does not have this for instance).Most (80%) equipment is double isolated any way, only the washingmachines, dishwasher, fridge etc are not and those need a ground connection for safety.

author: Monkeh
author_rank: Super Contributor
timestamp: September 21, 2014, 01:30:35 pm
content: Quote from: Kjelt on September 21, 2014, 12:40:19 pmNo, you don't. There's actually no reason to.QuoteThat has no relevance to switching in an appliance.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 21, 2014, 02:24:42 pm
content: BTW, with the input flipped the neutral is as it should be, but curiously it's 0.13V and not ~0V like the wall. Why might that be?

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 21, 2014, 03:13:09 pm
content: Quote from: lpc32 on September 21, 2014, 02:24:42 pmThat's not unusual. There are several factors that could be causing that. But unless it is caused by an open circuit, it is nothing to be concerned about.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 21, 2014, 03:19:01 pm
content: I'm curious what causes it, since it's more or less straight through. Not a concern, just knowledge.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 21, 2014, 03:28:56 pm
content: First of all, the measurement of "0V" at the wall is arbitrary by itself. Relative to WHAT? There are no perfect ground systems. They all have some amount of series resistance and "source-impedance". Even the crust of the earth itself has "series resistance".Furthermore, modern meters have rather high impedances, so they can be measuring induced voltages that are "imaginary" in the sense that they are effectively zero when connected to Real World circuits. And some of the imaginary voltage could be coming from induced signals from adjacent wires (the hot and neutral wires in the power cord), etc. etc.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 21, 2014, 03:41:34 pm
content: Why doesn't it happen (as much) in wall sockets?

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 21, 2014, 04:18:21 pm
content: Quote from: lpc32 on September 21, 2014, 03:41:34 pmSorry, I don't understand the question.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 21, 2014, 06:55:16 pm
content: Why no/less induced voltages when measuring directly at the wall?

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 21, 2014, 07:06:52 pm
content: Without knowing HOW you are measuring this, it is impossible to attempt any explanation.When you say that it is 0 volts "at the wall" what does that mean, exactly? "0 volts" relative to what exactly?When you say "0.13V" what are you measuring it against? Under what conditions?

author: lpc32
author_rank: Frequent Contributor
timestamp: September 21, 2014, 07:18:34 pm
content: Neutral-to-Earth measured with a DMM, nothing else connected, at the wall outlet (0V) and the 110V converter output outlet (0.13V). The path through the converter includes a 2m cord, switch, fuse, transformer, socket.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 21, 2014, 07:54:59 pm
content: "Neutral" could very easily be volts above "ground" because of current being drawn by OTHER loads on the same branch circuit.It gets very tricky when you try to measure these things, there are dozens of factors that must be established in order to understand what you are seeing.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 21, 2014, 09:36:02 pm
content: The 0V "direct from wall" measurement was on the same outlet the converter was connected to when it showed 0.13V (not at the same time). The results were similar on a different wall outlet on another circuit.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 21, 2014, 10:34:24 pm
content: Sorry, apparently I am not communicating clearly here.When you say you are measuring "0 volts" at some particular point (perhaps a ground pin on a wall outlet), you are presumably probing that point with one side of your DMM. OK. That's fine.But where are you placing the OTHER side of your DMM? In other words, when you say that point is "0 volts" what are you measuring it AGAINST? Or to put it another way what is your REFERENCE or DEFINITION for '0 volts" or "ground"?In modern building mains wiring schemes, the only point that you can legitimately call "ground" is the big terminal strip where all the green wires connect inside the circuit breaker box. In most domestic installations in North America (the 115V territories), it is at that ONE point where the green-wire "ground" and the white-wire "neutral" actually connect together. Everything else is a far extention out from that definitive spot. And there are any number of things that can cause the actual voltage out at the far ends of the branch circuits to deviate from "0 volts" or "ground".In the photo below, there is a large silver-color terminal block where the white (neutral) and green (safety ground) wires all terminate....

author: vk6zgo
author_rank: Super Contributor
timestamp: September 22, 2014, 05:09:45 am
content: Quote from: Monkeh on September 21, 2014, 01:30:35 pmSome often used appliances do offer the possibility of contact with exposed Mains .My daughter received a shock from a Toaster,which had three bad design features.(1) The element reached up too close to the top of the bread slot.(2) When it was not in use,but still plugged in,one side of the Mains was still connected to the element.(3)The power lead was wired with the Active & Neutral inverted.(In Australia,you can't reverse the plug in the socket,& pin allocation at the power socket is mandated by law)All would still have been well if the internal switch which opens when the toast pops up had been DPST,instead of SPST,which would have eliminated (2)In this case,the switch only opened the Neutral line,so no matter how the element was wired,the shock hazard remained.By the way,she didn't stick a fork into the Toaster,she just reached over the top off it & obviously part of her arm just touched the element (1).She has a little "El Cheapo" Toaster,but bought this new one because it could toast bigger slices.On testing,I found that the cheap one did have a DPST switch,so it was put back into service.

author: Kjelt
author_rank: Super Contributor
timestamp: September 22, 2014, 07:56:30 am
content: Quote from: Richard Crowley on September 21, 2014, 10:34:24 pmOMG what a mess!

author: miguelvp
author_rank: Super Contributor
timestamp: September 22, 2014, 08:07:56 am
content: Quote from: Kjelt on September 22, 2014, 07:56:30 amYou are more than welcome to show us your non messy fuse box

author: Kjelt
author_rank: Super Contributor
timestamp: September 22, 2014, 09:46:58 am
content: Will do when I have time, here it is normal that the inlets are positioned below and then through mains switch and RCD's to the fuses up to all the seperate groups.Newer systems have bridges where you can bridge the neutral to more fuses so you do not need so many wires, older have more wires but still since it goes from bottom to top it is IMO more clear then the box above.So they look something like this:

author: Monkeh
author_rank: Super Contributor
timestamp: September 22, 2014, 11:32:19 am
content: Quote from: vk6zgo on September 22, 2014, 05:09:45 amThere is no purpose to a double pole switchwhen the conductors are enclosed inside the appliance. Crappy electric toasters need not apply.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 22, 2014, 04:26:06 pm
content: Quote from: Richard Crowley on September 21, 2014, 10:34:24 pmMaybe I am not getting something indeed.The probes are on the same two pins/contacts this whole thread is about, and as mentioned in my previous post: neutral and earth. The two non-hot contacts in an outlet.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 22, 2014, 05:50:23 pm
content: OK, so you are declaring the green-wire safety ground pin on your wall outlet to be "ground"Then you are measuring the voltage on the neutral wire relative to ground.In a Perfect World those two nodes would be equal, zero volt difference.Now, as nice as your country may be, the laws of Ohm and Thévenin, et.al. still apply.So in the Real World one or more of these factors may be causing that non-zero reading...1) You are measuring high-voltage, high-power circuits with a high-impedance meter. There are probably places in that overall circuit where you would see similar readings (fraction of one volt) just by PROXIMITY to the mains wiring without even touching anything. That is because the meter is designed with a high impedance to prevent loading sensitive circuits and rendering false readings. But mains power is at the other end of the spectrum from "sensitive circuits" There are meters have have a built-in (switchable) load resistor like maybe 1K just to avoid this kind of problem.2) The connection all along the line for both ground and neutral are not perfect. They may not have been specified properly, they may not have had the proper materials (wire, connectors, outlets, etc.) used. They may have deteriorated over time. In some cases, some years ago here in North America, aluminum wiring became popular during a time of high copper prices. If the joints (mostly screw terminals) weren't really tight, there was a problem with joints becoming loose over time. The only solution was to go through the whole house, removing outlets, switches and fixtures and re-tightening all the screws. All the way back to the circuit breakers, and the main feed into the panel.3) The ground wire is never supposed to be carrying any current (except briefly in a fault condition). So barring (1) and(2) above, it would seem reasonable to define the ground pin of a particular outlet as "local ground" even if it might be a volt or two above from the crust of the planet.HOWEVER, the neutral line is designed to CARRY ALL THE CURRENT LOAD, closing the circuit from the "hot" wire. If there is a significant load up-stream (or even DOWN-stream) from the point where you are measuring, then the neutral wire is going to reflect the IR drop of that load current. That will be seen as some small voltage out at a particular outlet. I suspect that is what you are seeing.If you really wanted, you could do a detailed analysis of your power distribution system in general and that branch circuit in particular. If you could discover the exact path of that branch circuit, you could measure the neutral-ground voltage offset all the way from the distribution panel (where it should be zero volts with the wires connected together) all the way out to that particular mains power outlet.However, since that is an entirely common and expected, and explainable and safe voltage measurement, most of us would simply ignore a reading like that.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 23, 2014, 05:35:53 am
content: Quote from: Monkeh on September 22, 2014, 11:32:19 amUnfortunately,the use of the word "appliance" brings Toasters & the like squarely into contention.The very popular "cordless" Electric kettles also come into the category of "appliances".These are the sort of things that the general public have a lot more to do with than the stuff we commonly play with.Double pole switches are as cheap as single pole,so it is just as easy to use them in any case.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 23, 2014, 08:52:06 pm
content: Richard, the .13V difference is only due to the converter. Wasn't this what you referred to in your first post about induced voltages? I wasn't comparing neutral-earth voltages between different outlets, and anyway the few I looked at showed 0V when I checked. Though it will be interesting to check a few more, and with different nearby loads.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 24, 2014, 12:16:56 am
content: Quote from: lpc32 on September 23, 2014, 08:52:06 pmWithout knowing exactly how the converter is designed and configured, we would be shooting in the dark trying to explain that.You have one equation and a dozen unknowns. I never could solve those.

author: lpc32
author_rank: Frequent Contributor
timestamp: September 26, 2014, 03:29:33 pm
content: So the mystery remains. Well, thanks.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 26, 2014, 03:35:48 pm
content: It is only a mystery as long as you treat your converter as an unknown black box.

author: Hardcorefs
author_rank: Regular Contributor
timestamp: September 27, 2014, 12:36:19 am
content: Many of these 'mysteries' are down to:Capacitor dropper circuits, you know the ones where they use a capacitor in series with the mains feed to produce a lower voltage 'offset' without using a transformer or switched design.Seen in :Toasters ( for the timer circuit)Touch lamps ( for the touch circuit)Security productsInsect 'zap kits'The problem with this crap is the lower voltage is only an 'offset' with reference to the internal design, when referenced from "ground/Earth" the design is actually at an offset of mains voltage minus the voltage you are looking to generate.so if your internal 'dropper' circuit voltage is 10 volts from a 120vac feed, then with reference to 'ground/Earth' the voltage is actually ~110v.A second cause of 'electric shock' is a faulty Earth connection.Many modern electronics use a Capacitor delta from Live /Neutral to Earth, which is THEN grounded to an internal GND and finally external metal parts of the product.( it's all Ground right ;-))If your external Earth/ground connection fails(or gets a slight resistance…. no Earth connection at the wall is 0R), then you feel the leakage from the delta onto external metal parts, nearly all switched mode power supplies do this.And in many cases ( touch lamps, toasters) they have have a two pin plug, which allows the 'N' to go to the capacitor and the 'L' to act as the internal GND connection!!!!!

author: briselec
author_rank: Regular Contributor
timestamp: September 27, 2014, 09:26:55 pm
content: Quote from: vk6zgo on September 22, 2014, 05:09:45 amYet amazingly there is no law governing which way active and neutral are connected in the plug top( at least this was the case for many years, I haven't kept up with the regulations for the last few years but I wouldn't be surprised if this is still the case).