Transformers: Running Japanese electronics safely in the US

While most Japanese electronics use a two prong plug compatible with US outlets and are designed to run at the same frequency of 60hz we use, they typically are not designed to handle 120v since Japan’s electrical grid runs at 100v. Plugging Japanese electronics into a 120v outlet ranges from mostly harmless (e.g. Super Famicom) to a very bad idea (a toaster). Just how much does that additional 20 volts strain the wiring? When calculating power, voltage is squared, so it is not a 20% increase but a 44% increase (120x120=14,400 vs 100x100=10,000).

How do transformers solve this issue?

Transformers feature two coils of wires - a primary coil and a secondary coil. The two coils have a different number of loops and are close to each, but not touching. Using electromagnetic induction, the power is transfered from one higher voltage coil to the lower voltage coil, outputting safe 100v power for Japanese electronics.

How many watts should my transformer support?

You should avoid getting a unit rated at the exact same power as the electronic device you’re trying to run, as there’s a higher risk of blowing the fuse. There should be at least 10% headroom; closer to 20-30% is ideal, especially for Chinese-manufactured units.

What transformers are available?

Nissyo offers multiple Japanese-manufactured step-down transformers, mainly the NDF-550U 550w and NDF-1500U 1500w (no longer available on Amazon) that have been powering kotatsu heaters and other Japanese appliances in the US for decades. They certainly look like it, too, only being offered beige. However, they’re a great option because of their compact size, buy it for life reliability, and screw mount feet. The 550w version takes up just 35 cubic inches, almost 3 times smaller than other manufacturers’ 500w options. The 1100w takes up 75 cubic inches and 1500w takes up an impossible 91 cubic inches of space while cramming in two plugs, which is still smaller than Chinese manufacturers’ 500w options.

I’m not sure why Amazon removed the NDF-1500U from their catalog as of January 2025. Now, the best way to purchase in the US is from eBay. The NDF-550U is around $90 on eBay, NDF-1100u goes for $110, and the NDF-1500U goes for around $120. Since these could conceivably last for a lifetime, unless size is at an premium it might make sense to go with NDF-1500U which has two plugs and at 1500 watts, can be used for almost any Japanese appliance.

PowerBright offers well-reviewed, economically-priced, Chinese-manufactured step-down transformers in various voltages. They are a bit chonky with 500w VC500J taking up 115 cubic inches and 1000w VC1000J taking up a massive 425 cubic inches of space. As of January 2025, the the 1000w is $63.

Umi offers beautiful modern-looking Chinese-manufactured transformers with digital displays and two 100v output outlets. Taking up just 100 cubic inches for the 500w version and 190 for the 1600w version, they are smaller than the PowerBright, but still much larger than Nissyo models. However, there are some reports of them outputting less than 100v, and failing. It’s also strange to use three prong output plugs when Japan does not use three prong outlets. Also, they are not cheap. The 500w version is $70 and the 1600w version is a whopping $130.

Zhengxi is a newer Chinese brand that like Umi offers modern looking models with digital displays, but larger and features only one output outlet (again, a three prong outlet for no reason). They claim to offer units that handle up to 3000w, but Zhengxi also says you need 25% headroom for wattage (for example, the 1000w unit can only handle 800w). Despite this, users report even 705w overloading the 1000w unit. Avoid.

VGT appears similar to PowerBright at first glance, but bad reviews point to the unit failing when used within spec (as opposed to the obvious user errors on the few bad reviews for the PowerBright). Avoid.

EDITOR’S Pick: Go with the Nissyo units as they have over half a century of usage and no common failures. They are the smallest, and with their screw mounts, they can mount under a kitchen cabinet or wherever you need to it to. If you’re on a budget and don’t mind the size, the PowerBright units seem to work fine.