Why did this happen? (electrical)

We bought some transformers in Japan to use here in the US. Thus far, everything works fine (stereo, hair dryer, etc.)–until today.

BTW, Japan’s electricity is 100 V everywhere, 50 Hz in the east and 60 Hz in the west (yes, that’s weird that it is different in two regions in such a small country). At any rate, the electricity is pretty similar to that of the US, and the plug size is the same.

Today, however, we plugged our rice cooker into the transformer and it made a werid buzzy/electricity sound. Nor would it work at all–press a button, nothing.

But when we just plugged it into the wall, it worked fine. We made rice, tasted great.

Two questions:

  1. Why was it different with the rice cooker? (For the record, the wattage of the cooker was below that of the transformer.)

  2. Will the 110 V electricity we have in the US eventually fry out the cooker, which was designed for 100 V?

Thanks for your help!

IANAERCE (I am not an electric rice cooker expert), but I suspect that the cooker’s power requirements exceed the transformer’s rated power. Are the transformer and/or cooker labeled with their specs?

A. What is the rated maximum wattage for the transformer(s)?

B. What is the rated maximum wattage for the rice cooker?

If B > A then you have a problem.

There are basically three techniques used to change voltage in foreign travel adapters. One way is to use a transformer to step up or step down the voltage to the required level. This is fine for smaller devices which don’t use a lot of power. But, for high-power devices like hair dryers and curling irons, transformers at power-line frequencies become large and heavy. To make adapters for these devices, one of two methods is normally employed. If the voltage only needs to be stepped down, then it is possible to simply chop off the input voltage at the required output level. One of the biggest problems with this is that it creates an abrupt change in current flow, similar to a square wave, which doesn’t play nicely with heavily inductive loads, like transformers and large motors. Things like heating appliances and light bulbs–almost purely resistive loads–don’t mind this too much, but most electronics won’t work properly, or at all. To solve both of these problems, another type basically uses a switching power supply. Some of these can provide a nice smooth sinusoidal output, which makes everything happy, but this costs money. Some less expensive units instead output what is called a pseudo-sine, or stepped square wave–some automotive DC-to-AC inverters do this, as well. This waveform closely approximates the RMS and peak voltage values of a sine wave closely enough so that most things work fine with it. But not everything. If I had to guess, I’d say your Japanese voltage converter is of this latter type, and your rice cooker is one of those things that choke on a pseudo-sine wave power input. If the transformer in question is rated at around 1 kW or more, but is not particularly heavy or bulky, then it’s a good bet this is the problem.

Hi again. It’s 1.5 kW, and the wattage is more than that of the cooker (which is 1,210).

We purposely got what we thought were good transformers, and the guy at the store helped us. They are, in fact, pretty big and bulky.

I have the thing plugged into a surge strip and then my high-end Denon amp and record player plugged into that–no problems.

Also, the weird buzzing sound was coming from the transformer itself, almost as if the flow of electricity was being blocked or something.

Any further ideas?


A voltmeter would be helpful here. Do you have one?

Also, try plugging the transformer directly into the wall outlet, then plugging the rice cooker directly into that, with nothing else connected.