How to safely use a 100V appliance in a home with 120V power.

Thread Starter

ta05960

Joined Apr 20, 2021
7
I want to use a 100V (Japanese) induction heating rice cooker in my house, but my house is 120V. The rice cooker's manual says that it is 100V, 15A, 1300W.
Would I be fine with a 1500W rated transformer or would I need something bigger?
 

crutschow

Joined Mar 14, 2008
26,969
I agree with Max.
A 15A transformer would be sufficient, but any transformer you can buy to do that will likely well exceed the cost of buying a new 120Vac cooker.
How much would a new one cost?
 

Thread Starter

ta05960

Joined Apr 20, 2021
7
Use a buck/boost transformer in buck mode, either way, a 1.5kva transformer is probably worth more than the cooker!
.
I agree with Max.
A 15A transformer would be sufficient, but any transformer you can buy to do that will likely well exceed the cost of buying a new 120Vac cooker.
How much would a new one cost?
The transformer I'm looking at is made in Japan, input 110-130V, output 100V, 1500W. I'm assuming this would be 15A?
What do I need to know regarding safety? I don't plan on keeping the rice cooker or the transformer plugged in for long periods of time, only when being used, which is probably once a day.
 

ronsimpson

Joined Oct 7, 2019
1,179
At digikey.com there are $200usd transformers. new

Next option is to get a used 2000 watt transformer that has a primary labeled "104V, 110V, 120V". So there are taps for several different voltages on the primary. You will connect the power line at 0V and 120V and the cooker to 0V and 104V. The secondary windings will not be connected.
 

Sensacell

Joined Jun 19, 2012
2,774
Speaking from experience.

Maybe not today, but soon, you will find yourself plugging the cooker into 120 and it will die.

I moved to Asia with a bunch of 120V appliances thinking that I would "just use a transformer" - but one by one - all the appliances got killed, it's just too easy to forget.
 

Thread Starter

ta05960

Joined Apr 20, 2021
7
Speaking from experience.

Maybe not today, but soon, you will find yourself plugging the cooker into 120 and it will die.

I moved to Asia with a bunch of 120V appliances thinking that I would "just use a transformer" - but one by one - all the appliances got killed, it's just too easy to forget.
I will not forget to use the transformer as the rice cooker would be my only 100V appliance...
I just need to know if it's "considered safe" to do this.
 

crutschow

Joined Mar 14, 2008
26,969
What do I need to know regarding safety? I don't plan on keeping the rice cooker or the transformer plugged in for long periods of time, only when being used, which is probably once a day.
You can leave the cooker plugged into the transformer as the cooker takes no power when off, and the transformer takes very little idle power when plugged in.
I just need to know if it's "considered safe" to do this.
Yes, quite safe, assuming the circuit has a proper circuit breaker at the mains panel.
 
if it's not too difficult put the transformer near the breaker box and run a 100V feed to the kitchen with the appropriate plug.
That transformer will be heavy. You would be better doing 240 to 100V. See https://acupwr.com/

I would not necessarily use that transformer mounted elsewhere.

This https://world-power-plugs.com/japan is like "Oops" too. I'd wire a plug that's totally different, e.g. a 120V twist lock. At least it would be different.

These https://toroid.com guys did a custom transformer for me in the 80's

Here https://www.larsonelectronics.com/p...r-120v-primary-100v-secondary-25-amps-50-60hz is somethig more appropriate to mount at the panel.

I'd be surprised if this https://www.larsonelectronics.com/p...5v-primary-96v-secondary-at-17-5-amps-50-60hz would not work.
 
Last edited:

crutschow

Joined Mar 14, 2008
26,969
Maybe not today, but soon, you will find yourself plugging the cooker into 120 and it will die.
As KISS noted, one way to prevent that would be to replace the device plug and transformer socket with one that won't plug into the 120V outlet, such as a 240V or 120V-20A types, or one of the European types.
 

Thread Starter

ta05960

Joined Apr 20, 2021
7
Yes, quite safe, assuming the circuit has a proper circuit breaker at the mains panel.
The Japanese made transformer I'm looking at states it is 100V, 1500W. I don't really see any other information about it other than:
  1. Ideal for using your Japanese products overseas
  2. If you want to use the transformer for more than an hour at a time, please make sure the transformer's capacity is 1.25x your appliance's rated wattage.
  3. Frequency will not be converted
  4. Both outlets can output at the same time, but please make sure output of both combined outlets is less than the maximum rated output.
  5. This transformer cannot be used in Japan.

This will be my first time using a transformer, do I need to know any particular safety tips and whatnot? It should be fine I kept the transformer on a plastic surface (table) right?
Additionally, my outlet is a Type B plug (with ground). The transformer and rice cooker are both type A, without grounds. Will this be an issue?
Also just to be sure, an induction heat cooker is not an inductive load right? Because some googling told me that inductive loads will need higher wattage ratings due to power factor or lag or something...

if it's not too difficult put the transformer near the breaker box and run a 100V feed to the kitchen with the appropriate plug.
That transformer will be heavy. You would be better doing 240 to 100V. See https://acupwr.com/

I would not necessarily use that transformer mounted elsewhere.
The transformer I'm looking at is "only" ~10 pounds. Would it be safe to keep the transformer on a plastic surface? I assume it wouldn't get that hot, right?
 

MaxHeadRoom

Joined Jul 18, 2013
22,823
You will also need to re-reference the earth ground conductor to one side of the secondary to replicate the grounded neutral.
You can make either secondary terminal a neutral.
You will then have two conductors at this terminal, one a neutral conductor, the other the ground.
 

crutschow

Joined Mar 14, 2008
26,969
an induction heat cooker is not an inductive load right?
Right.
The cooker takes the AC power, converts it to DC and then uses that to power the higher frequency (typically 25kHz-50kHz) induction unit.
Would it be safe to keep the transformer on a plastic surface? I assume it wouldn't get that hot, right?
Since I assume the cooker is only on for a relatively short time, I don't see that the transformer would get very hot.
 

Thread Starter

ta05960

Joined Apr 20, 2021
7
You will also need to re-reference the earth ground conductor to one side of the secondary to replicate the grounded neutral.
You can make either secondary terminal a neutral.
You will then have two conductors at this terminal, one a neutral conductor, the other the ground.
Could you elaborate? The transformer I'm looking at doesn't have a grounding port and neither does the rice cooker - both are type A plugs.
 

MaxHeadRoom

Joined Jul 18, 2013
22,823
If the cooker has a two pin plug then it means it is ungrounded, and does not require the earthed neutral, in that case, but does it conform to N.A. non grounded appliance standards?
 

Thread Starter

ta05960

Joined Apr 20, 2021
7
If the cooker has a two pin plug then it means it is ungrounded, and does not require the earthed neutral, in that case, but does it conform to N.A. non grounded appliance standards?
I have no clue as it's made for the Japanese domestic market...
Plenty of reviews (from Japanese expats in America/Europe) say these rice cookers work outside of Japan, but they are anecdotal accounts, and I doubt any of them are certified electricians.
 

Ian0

Joined Aug 7, 2020
1,863
Use a transformer with a 20V secondary at 15A, which would be 300VA. Put the secondary in series with the live supply to the cooker, wired so that it subtracts the 20V from the 120V supply.
 
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