Hi George, thanks very much for the reply and link.
It has me thinking some more. I know the washlets have 2 or 3 heaters: the seat, the bidet and sometimes an air fan. Of these, the seat and bidet heaters have different temperature settings. The air fan usually does not, although sometimes you can control the fan speed.
For the heated air fan, this is almost exactly like a hair dryer in design and function and thus has some pretty high risk of overheating with the higher voltages. Luckily I'm not interested in a model with a heated air fan.
For the seat and bidet, it depends how the temperature is controlled as to the risk...
If there is a some closed loop temperature controller than I have no worries about the effect with the higher voltage. This is because the heater power level (more accurately, likely the heater duty cycle) will be adjusted to keep the temperature constant and thus it will automatically compensate for voltage variation.
If the temperature is controlled by changing the heater duty using open loop control (no sensor, no feedback), then there is a big risk of having a too hot tushy! You're right back to the hair dryer analogy.
My personal opinion is the seat and bidet are closed loop control. I say this based on the following observations:
-despite the fact the water temperature varies seasonally, the bidet water is always just about body temperature. This would not be possible w/o CL control.
-despite the fact you can change the water spray pressure (and hence mass flow) during the spray event, the water temperature stays constant. This feat would also not be possible without CL control.
So I think the bidet is OK, low risk.
For the seat heater, this could be open loop:
-As a washlet designer, you could assume the person on the seat will be about 37degC. You could further assume there is not much heat rejection to the atmosphere through the un-seated part of the seat. Thus, the energy you put into the heater should mostly go to the person. In this case, three different fixed power levels would conver the range of comfort quite nicely w/o the complexities of CL control. I guess it depends on the thermal design of the seat (unknown).
-However, based on personal experience in winter time using a non-heated stand-alone bathroom (~0degC air temperature), the seat was still the perfect temperature, even on the low or medium setting. Thus despite the fact the air (and porcelain toilet) were much colder, the seat was still equally warm on the same low/mid setting.
Thus, if the setting was the same and the seat temperature was the same even though the air temperature was radically different, I am assuming the seat heater must be compensating (also be CL control).
Plus, if you goto Toto's US washlet website (www.cleanishappy.com), I learned the seat is making "adjustments" 100times a second. This sure sounds like a microcontroller at work doing CL control!
If there is a micro, it has to have an AC-DC converter. Usually these are able to handle a wide range of input voltages with no impact to the output DC voltage and hence no impact to the micro.
So, overall I think the risk is pretty low.
I'd sure love to find out exactly how these washlets work or talk to someone who has done this before so I can confirm my assumptions.
I'm almost ready to pull the trigger, buy one and report to the world the results (when I move back to the US in a few weeks!)
Feedback welcomed and appreciated...