Cheap, electronic US-to-EU mains converters - Page 1
Forum section: electronics / general

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: November 03, 2023, 09:38:40 am
content: I'm possibly moving to the US in the near future for a job opportunity. When I was young (>20 years ago) I also moved there for a few years with my parents. Back then, we only have 1 or 2 US-to-EU mains transformers, capable of like 1 kW output. They were big, bulky and expensive, so we only used them for expensive things (eg, mothers sewing machines) that couldn't be easily replaced.Out of curiosity, I was now checking the prices of these things to get an estimate of how much it would cost, and what we want to take with us and what would be easier to just buy new. To my surprise, you can find 20-30 USD adapters that claim 2 kW output power - much cheaper than the 150 bucks I remember for a single 1 kW transformer, and it's the size of a simple power brick!Does anyone have any experience with them? Are these things safe? Do they work? Do they destroy electronic devices through high ripple?

author: soldar
author_rank: Super Contributor
timestamp: November 03, 2023, 10:09:45 am
content: You have to be very careful because it depends on the type of device. For some devices, like resistors, RMS is what counts; for other devices, like rectifier-capacitor, peak voltage is what counts, others may be sensitive to frequency.In general terms, you are moving from 230V 50Hz land to 120 V 60Hz split phase land so you can probably have access to 240V 60Hz.Each device has to be considered individually.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: November 03, 2023, 10:15:21 am
content: Quote from: soldar on November 03, 2023, 10:09:45 amWell, yes, obviously, but I am expecting a device that is advertised as a US-to-EU mains converter to output a nice 230-ish volt sinewave. Is this not a valid assumption? I hadn't thought about the frequency, but outside of a mains-locked clock and old-school motors, I can't imagine many that currently use the frequency.

author: tggzzz
author_rank: Super Contributor
timestamp: November 03, 2023, 10:22:38 am
content: Quote from: TheUnnamedNewbie on November 03, 2023, 10:15:21 amKey phrase: "modified sine wave", especially in conjunction with inverters and UPSs.In theory transformers and other PSU components might be sensitive to 50/60Hz, but suspect that isn't a major issue in practice.

author: tooki
author_rank: Super Contributor
timestamp: November 03, 2023, 10:35:15 am
content: Quote from: TheUnnamedNewbie on November 03, 2023, 09:38:40 amA few thoughts:1. Those $30, 2kW converters are almost certainly step-down converters to use 120V appliances on 230V outlets.2. Those $30, 2kW converters aren’t transformers, they simply work as fixed-output dimmer circuits that chop off part of the sine wave to reduce the effective voltage. That’s why they’re only for resistive loads.3. Practically all of your valuable gadgets (computers, phone chargers, etc) will be world-voltage already, requiring only a different plug. The real exceptions are household appliances. But those are rarely worth bringing anyway, and often use enough power that you’d need a large, heavy step-up transformer to use them — a transformer that would probably cost more than a new appliance. Just buy a new toaster and microwave when you arrive.4. You could, in theory, use the 240V normally used for the stove and clothes dryer. You’d probably need to build your own adapter cables to do this, plus an electrician to install such an outlet where you need it. Realistically, only doable if you own the house.In a nutshell, you’ll probably find that fewer devices need voltage conversion than you expect, and that of the ones that do, it’s unlikely to make sense to bring it along to begin with.

author: AVGresponding
author_rank: Super Contributor
timestamp: November 03, 2023, 10:35:42 am
content: Any "2kW" converter at that price point is going to be utter trash, will be a switcher and not a transformer, with an output that has never been anywhere near a sine wave, and will probably die if you try to load it over 200W or so.

author: tooki
author_rank: Super Contributor
timestamp: November 03, 2023, 10:43:46 am
content: Quote from: tggzzz on November 03, 2023, 10:22:38 amBut who was talking about inverters or UPSes?!?The only 120<->230V converters that involve inverters are the ones expressly designed to convert line frequency as well, but those cost way more than $30. The $30 things the OP is inquiring about are basically fixed-output dimmers, probably just a triac circuit with fixed resistors instead of a potentiometer.

author: tom66
author_rank: Super Contributor
timestamp: November 03, 2023, 10:50:15 am
content: I've seen those cheap power converter (for 240V to 120V) before, and torn one apart -- it had a single diode in it. Which resulted in 240V power becoming half-wave rectified, and in the mind of the engineers who designed it in China, that was 120V. In fact, even for a heating element, it's still twice the rated power because V2* I.Using one of these power supplies destroyed a nice American coffee maker that a friend had imported over. A £20 purchase on Amazon killed a $600 espresso machine.For the other way around (120V -> 240V), I suspect they are just autotransformers, so are *probably* ok to use, but unlikely to withstand the 2kW rating they claim unless they are quite substantial.

author: tooki
author_rank: Super Contributor
timestamp: November 03, 2023, 11:10:52 am
content: Quote from: tom66 on November 03, 2023, 10:50:15 amThere aren’t any $30, 2kW step-up converters. The small $30 step-up converters are indeed small autotransformers suitable for 30-50W.Step-down converters often have two mode selectable by a switchs: a 2kW mode for heating appliances using the diode or triac, and the 30-50W mode for things that need actual AC.

author: soldar
author_rank: Super Contributor
timestamp: November 03, 2023, 11:14:06 am
content: Quote from: TheUnnamedNewbie on November 03, 2023, 10:15:21 amIf frequency is not an issue then you will have 240V 60Hz available directly at the panel.

author: wraper
author_rank: Unknown
timestamp: November 03, 2023, 11:21:39 am
content: You need autotransformer for (usually high power) devices which require 230V like Ktettle, coffee machine and similar. Be aware that power that US sockets are rated for way less power than in EU. Devices that use SMPS most likely can work from 120V to begin with. Like phone chargers, PC/laptop PSU, TV and similar.

author: soldar
author_rank: Super Contributor
timestamp: November 03, 2023, 11:45:25 am
content: Quote from: tom66 on November 03, 2023, 10:50:15 amI have a 30 year old Radio Shack Archer 273-1404 triac converter which allows the use of 120V heating appliances with 220 V. It is basically a dimmer type control but what is interesting is the trigger circuit which is not the usual delay type but is triggered by a capacitor and the wave falling from the top. So it is essentially impossible to fire too soon because the wave has to fall a certain amount for it to trigger. It is quite clever.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 03, 2023, 12:44:41 pm
content: For the case of converting 120V to 240V, one could voltage doubler rectify the 120V, then generate a 120V modified sine which is 180 degrees out of phase so it adds to the original 120V. The resulting waveform quality would be in between pure sine and modified sine.

author: rstofer
author_rank: Super Contributor
timestamp: November 03, 2023, 09:08:26 pm
content: If you just buy replacement gadgets (coffee maker, etc) you might consider donating them to one of the larger charities (Salvation Army, Good Will, etc) and see if the tax deduction helps. Or advertise them in the ex-pat community, some newcomer will need them for the same reason.

author: bdunham7
author_rank: Super Contributor
timestamp: November 03, 2023, 09:17:28 pm
content: Quote from: TheUnnamedNewbie on November 03, 2023, 09:38:40 amDo you have a link to one of these devices? I can't imagine what would be worth all the trouble of doing this adapting--you're not going to get enough power to run your 3kW kettle unless you tap directly into a panel or unplug a clothes dryer. Most other devices just need a connective adapter and will work on 120VAC. Those that don't can be replaced cheaply. If you really did have a need to run anything on 240VAC, just get an actual transformer--they aren't that terribly expensive in a reasonable capacity (not 2kW).

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 04, 2023, 08:55:20 pm
content: For cheap? Use the 240V already in the building. Sometimes you find a place with a 240V air conditioner socket (15-20A) already installed. Or if you're comfortable assembling such things buy a sub panel and plug it into the stove or dryer socket (240V 30 or 50A) and install a 15A two pole breaker to give a 240V 60Hz split phase supply to a socket of your choice. Note that in an apartment you sometimes get 2/3 of a 208Y 3 phase supply so you'll have 208V and not 240.

author: TimFox
author_rank: Super Contributor
timestamp: November 04, 2023, 10:19:57 pm
content: A quick look at Mouser finds several "regular" transformers capable of 120 V in and 240 V out, rated at 1 kVA.The price in single-unit quantity ranges from about $150 to $200 US.

author: AVGresponding
author_rank: Super Contributor
timestamp: November 05, 2023, 09:33:10 am
content: Quote from: BrokenYugo on November 04, 2023, 08:55:20 pmUK/EU devices are designed to work with a power supply that has the neutral bonded to the earth at the installation source. US 240V is split phase and there is no earth-neutral bond in this case. Itmightbe ok, or it might cause problems, ie with the mains input filtering. Proceed with care and caution if you choose to do this.

author: wraper
author_rank: Unknown
timestamp: November 05, 2023, 09:55:07 am
content: Quote from: AVGresponding on November 05, 2023, 09:33:10 amIt's a total no issue. EU devices that are earthed are just supposed to be earthed, nothing to do with neural bonded to earth. Plugs/sockets are not polarized so neutral can be on either of prongs. Not to say Norway uses IT earthing system.

author: forrestc
author_rank: Unknown
timestamp: November 05, 2023, 09:55:53 am
content: Have you taken an inventory of what you might want to take with you that is actually 240V only?I think you might be surprised how much stuff is actually 120/240V already and won't need a voltage converter. All you'll need is either an adapter or a replacement cord. Sometimes you'll find an older external power supply which is 240V only, but you can often just swap it for a similar universal voltage unit.Others have suggested options for powering 240V-only stuff in the USA. I'd suggest doing that only as a last resort.

author: tridac
author_rank: Regular Contributor
timestamp: November 05, 2023, 12:31:47 pm
content: Anyone who claims 1Kw for $30 must have a bridge to sell you. Perhaps just a simple phase control, or a diode in series with the line, with a nasty output waveform, which could damge equipment. Steer well clear and check out Ebay for a s/hand isolation transformer, the only economic way to do that safely. If you are a dab hand with electronics, another solution might be to find a s/hand yellow case building site transformer, 240 to 115 volts, and use it in reverse, being careful to disconnect the 115v side center tap earth. Foolhardy to take risks with electrical safety...

author: wraper
author_rank: Unknown
timestamp: November 05, 2023, 02:07:01 pm
content: Quote from: tridac on November 05, 2023, 12:31:47 pmYou want autotransformer. Or somewhat worse regular transformer with center tap in primary that you can use as autotransformer. Isolation transformer will be at least 2x the size of autotransformer for the same power.

author: AVGresponding
author_rank: Super Contributor
timestamp: November 05, 2023, 07:48:37 pm
content: Quote from: wraper on November 05, 2023, 09:55:07 amI doubt very much that you would be prepared to take legal responsibility for that statement. Just because you are unaware of a case doesn't mean they don't exist.

author: Gregg
author_rank: Super Contributor
timestamp: November 05, 2023, 08:34:42 pm
content: If you have the common US 240-120V center tap grounded neutral power available, an industrial transformer like thishttps://www.ebay.com/itm/385206481442would suit your purposes because it can be wired for isolation of the secondary 240V so that you can ground one side and call it neutral. Inrush protection may be needed depending on your circumstances and proper fuses and or circuit breakers should be used.

author: tom66
author_rank: Super Contributor
timestamp: November 05, 2023, 08:58:54 pm
content: I have given thought to the idea of importing a 3kW British kettle to the States if I ever were to emigrate there. I'd have a sparky install a NEMA 14-30, or whatever is legal, in the kitchen, and then wire the kettle to the right plug for this. I'd need to take care to find a kettle that isolated both live and neutral of course, given the split phase 240V compared to our single phase here, but it feels workable!

author: wraper
author_rank: Unknown
timestamp: November 05, 2023, 11:06:05 pm
content: Quote from: AVGresponding on November 05, 2023, 07:48:37 pmI doubt you are prepared to use logic. Any earthed mains powered device that is legally sold in EU must tolerate full mains voltage between earth connection and either of prongs as plugs are not polarized. Implying there is safety hazard if you halve that voltage makes no sense. And again, Norway uses the same sockets/plugs and has IT earthing system where neutral is not connected to earth.EDIT: And if something like that exists, it should have never passed safety tests to begin with as both wires must be treated as live.

author: wraper
author_rank: Unknown
timestamp: November 05, 2023, 11:17:45 pm
content: Quote from: Gregg on November 05, 2023, 08:34:42 pmOr you use autotransformer and make direct use of existing earth and neutral connections without doing any shenanigans.

author: tridac
author_rank: Regular Contributor
timestamp: November 09, 2023, 01:45:52 pm
content: Sure, an auto would be smaller for the power, but an isolation transformer would perhaps be safer for someone not familiar with electrical systems...

author: wraper
author_rank: Unknown
timestamp: November 09, 2023, 05:18:27 pm
content: Quote from: tridac on November 09, 2023, 01:45:52 pmPreventing GFCI from tripping is not safer. The suggestion from Gregg of connecting "neutral" output wire from isolation transformer to earth is the dumbest. Since output won't be floating, you can get electrocuted form touching "live" wire and anything that is earthed but GFCI in electrical box won't have any clue that something gone wrong.

author: BrokenYugo
author_rank: Super Contributor
timestamp: November 09, 2023, 06:38:06 pm
content: Quote from: AVGresponding on November 05, 2023, 09:33:10 amWhat hazardous situation do you envision? The power is earth/neutral bonded, heavily, around me with a ground rod every house (I think modern code is 2 per building with #8 wire) and a wire running down every pole, all bonded together, the earth is just connected at the center tap of the pole transformer 240V winding feeding the building instead of one end. In a mains filter the Y caps to earth would see less stress only having 120V across each rather than 240V across one.The big gotcha that does come to mind now is RCD/GFCI protection on 240V circuits in the US is uncommon, the breakers are available albeit expensive and probably special order for 15A. Also don't trust a non contact voltage probe around split phase, mine (old and cheap) only triggers on split phase cables sporadically, I guess because it's sort of balanced power with no neutral load, so it radiates less?

author: AVGresponding
author_rank: Super Contributor
timestamp: November 10, 2023, 03:00:46 pm
content: Quote from: BrokenYugo on November 09, 2023, 06:38:06 pmAt no point did I specify "hazardous" as a potential situational outcome, though I suppose that's possible too. I said it "might cause problems" and that's what I meant. Some devices you might wish to connect will have mains status detection and might well see the neutral being 120V away from earth as a supply problem and not function as you intend them to.