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I moved to an old apartment where the energy output is, in practice, between 130v and 140v (should be 127v max in an ideal world), and I have a 220v (not 240v) washing machine which was intended to be plugged to a 110v-220v transformer. The energy company will likely either not solve anything, or take a while to do so. I'm considering buying an external voltage regulator, but it is not cheap, so I tried finding among my machine's specs its voltage range/tolerance and I failed. The machine is a Samsung WD11A 220v. I have a 110v-220v transformer that gives around 265v in this situation (having already blown another 220v washing machine).

Is there anywhere I can find this specific information, or can it be inferred somehow (some standard I'm not aware of)? Does someone have any suggestion for the whole situation?

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    I would expect most single voltage label machines to have a -/+ 10 or 15% range(safe) and might be okay at a bit more.
    – crip659
    Dec 6, 2023 at 15:59
  • Are you in the US? The standard here is +/- 5% so up to 252 is allowed. The age of the apartment has nothing to do with it, the voltage is provided by the utility.
    – KMJ
    Dec 6, 2023 at 16:02
  • @crip659 yeah. that's the general information i have. which means my machine would be fine at 242v. 255v~ optimistically. but i get 265v from my transformer, given the untransformed output is already high Dec 6, 2023 at 16:06
  • @KMJ Brazil. And I believe so. But, somehow, the voltage is abnormally high (and it is not that high at, like, the building next door) Dec 6, 2023 at 16:08
  • @PedroV.G. It's a bit different here in the UK, but with houses (as opposed to apartments) and 3-phase distribution, I'd wonder about the voltage next door but 2. They'd be on the same phase. I suspect that the 3-phase transformer serving a few houses is unevenly loaded between phases and the taps were adjusted for all based on the most loaded phase. Or your phase used to have a big continuous load on it but no more
    – Chris H
    Dec 6, 2023 at 19:48

3 Answers 3

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I think you're doing it the hard way.

Areas which are 127V nominal, choose that voltage for a very specific purpose: when you configure your power supply as 3-phase "wye", with 127V any phase to neutral, that means your phase-phase voltage is 220V. So this arrangement is universal - depending on how you tap it, you get 127V, which plays well with North American 120V appliance, and also, from the same transformer, 220V, which plays well with European 230V and North American 240V appliances.

So, 220V is in your service panel or pole top waiting for you to have an electrician tap it. You can stop using the transformer and run it direct on utility 220V. It's probably a little high of 220V, probably 230-235V, but that is fine.

Or not.

One way that 3-phase installations can fail is called a "Lost Neutral". The three hot-neutral phases are no longer the voltage they're supposed to be, and wander all over the place, high and low. Adding a load will cause the voltage to drop. In that scenario, hot-hot loads that are 220V will be unaffected.

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  • That's if they get 3 phases to the service panel of course. It's not routine here, and is a very expensive option even after you've paid for the road to be dug up - which means the utility company. But it's a good solution.
    – Chris H
    Dec 7, 2023 at 9:28
  • @ChrisH OP's situation is typical for large apartment buildings in the US. This is because the power company wants the load split over 3 phases, there are 3 phase loads in the building like elevators and water booster pumps, and perhaps there's a business on the ground floor that wants 3 phase power.
    – user71659
    Dec 8, 2023 at 0:58
  • @ChrisH 2 phases would suffice. Dec 8, 2023 at 3:14
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    @Harper-ReinstateMonica technically yes, but 2-phase supply never happens here. It's 1 or 3. Does it happen where you are?
    – Chris H
    Dec 8, 2023 at 7:10
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    @ChrisH You are implying that all 3 phases would be needed to power a 220V single-phase load. I am saying 2 of 3 phases would suffice. You just were aware of an info-nugget that "literal, 90 degree 2-phase power is extremely rare" and jumped on that. Here's another info-nugget: In NYC and dense apartments provided 3-phase by the utility; they use 120/208V specifically so they can use cheap split-phase consumer service equipment instead of 3-phase arcana. I suspect it's done at OP's home country as well; that being the entire point of choosing 127/220V as a supply voltage. Dec 8, 2023 at 19:49
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I assume your 110-220V transformer is an autotransformer as it uses less copper and you don't need isolation. Autotransformers do exist with the ability to select the taps on the input and/or output, changing the ratio slightly, and you can also get variable transformers (example manufacturer) that would allow you to fine-tune.

There may even be a service that can rewind your existing transformer for lower output voltage. The difficulty here is that they'd need to remove about 1/6 of the turns to get from 265V to 220V, and that means knowing how many turns there are to start with.

It would be possible experimentally to measure the voltage on the output, remove several turns, reconnect, remeasure, and calculate the number of turns still to be removed. I'd consider doing it myself on little transformers, maybe even for mains use, but I have experience of mains work. This wouldn't be a job for an electrician but again would be something a transformer/motor/coil winding company could do - if you can find one that still exists.

A mains-input inverter with variable output voltage might be cheaper; I've only used them in 3-phase when we also needed to change the frequency. This Mitsubishi is getting close but not quite right as the output current is too low, you're also right on the edge of the input envelope on this and many other models, as 200-240V ± 10% (or +10% -15%) is common, giving max 264V.

One thing that won't work is adding a series resistance. The load is too variable for that. If you calculate what you'd need at maximum current with the element on, you'll have too much when it's just driving the logic parts or even the motor.

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  • Not a straightforward solution I'm afraid, barely an answer, but some pointers at least
    – Chris H
    Dec 6, 2023 at 16:38
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First: to answer the question you asked, there's no standard way to find the voltage tolerance of an appliance. They will all be good for 5% variance as that's the grid standard in many places, but anything past that is going to be down to the makeup of the device. Some devices can run all the way up to 290V or so, which is the highest possible voltage for 277V service. Others which are rated for 220V or 230V might only tolerate 242V as it's 230V+5%.

As mentioned in the other answer, this is a situation where an autotransformer can work. There's a specific class called a 'boost-buck' transformer. They are often used in the US when you have a 240V load that needs to run on a 208V supply or vice-versa. Thankfully the 32V drop turns out to be perfect for what you're looking to do. I'd start hunting for one as industrial surplus. Even if you have to buy one new, they can be relatively reasonable in cost for large loads. One manufacturer makes a 25A capable unit that sells new for under $400 right now (2023).

Another option is to look for a 120V to 208V transformer instead of your 120V to 240V one. Since it has a lower ratio, it will turn the 140V you are getting into 243V, perfectly in the range for normal '220V' nominal rated equipment. Unfortunately these are probably quite a bit more expensive. If you can find a 208V to 120V transformer, you can use it 'backwards' to accomplish what you are looking to do.

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  • Nice ideas. I'd forgotten about 208V because it's really uncommon here. Note to the OP: if you use a 208-120V transformer backwards, be sure to change the connectors on that rather than making adaptor leads. You don't want live pins sticking out of anything
    – Chris H
    Dec 6, 2023 at 19:43
  • There's a lot of hardware out there for converting between 208V and 240V, and it's all pretty efficient too. I was looking for a single transformer solution though, which is what got me to the 120-208V option. High quality 208V to 120V step-down transformers are relatively common in data center environments, so used ones should be around.
    – KMJ
    Dec 6, 2023 at 20:57
  • but not in 230V-land, where I am. Our 3-phase is 400-415V (phase-to-phase). I did once have to deal with a 208V 3-phase water cooler for a laser. We had no end of trouble getting power for that
    – Chris H
    Dec 6, 2023 at 21:36
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    That would explain why 208V hardware doesn't come to mind for sure.
    – KMJ
    Dec 6, 2023 at 22:08

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