I bought the 500VA VT-500J transformer for use with a 100V 495W Zojirushi rice cooker (Japan Model), for use in the USA. In short - the transformer works and is decent for the price, but be well aware of the ratings (for example, without cooling, the transformer in this 500VA rating is likely only good for 100-125VA continuous!). As an electrical engineer, I work with power systems daily. I have worked with proper 500VA-rated transformers and they are significantly larger, typically weighing in at about 7kg. The transformer inside this as you can see is very small, about 1.5kg, and likely rated for no more than 100VA continuous operation. This is evident in the small-text the manufacturer is recommending, since they do say (in customer feedback in the comments section) to leave a 4x margin. Meaning this '500VA' transformer is in fact, more like a 125VA-continuous transformer. However, for the price (about $35), and keeping in mind that I'll be reviewing this as a 125VA unit (instead of a 500VA unit), it's decent. Construction is good sheet metal with a very nice powder coat finish. It operates in both 100 to 120V step-up and 120 to 100V step down operation (default). Soldering inside was OK, wires used were cheap but OK 22AWG PVC, and grounding was properly done with a locking washer and crimped terminal. Quick measurement for voltage conversion - 122.7VAC input gave me 104.0VAC output with no load - good enough. If I claim that the transformer is only 125VA, why am I using it for my 495W rice cooker? While a transformer of this size is only good for 100+VA continuous operation, it can operate at higher power levels for short periods of time. The limits are (1) thermal and (2) transformer saturation. In order to make this 'work' for my rice-cooker, I did some measurements and found that my particular rice cooker only turns on its heating element (which when it does, does draw about 500W) for fairly short periods of time (10s of seconds), before turning it on and off. As a result, the total average duty cycle is low. I also found the transformer performance to be acceptable at full load. Now we're left with thermals. To mitigate this, I added my own 120VAC fan on top of the transformer box. The unit draws just over 4A from my 120VAC outlet, so I kept the 5A fuse. I've run this box with my rice cooker many times now with no issues. Regardless, I am doing so knowing that I'm pushing the transformer to its saturation limits and keeping in mind that the overall duty cycle of my rice-cooker is fairly low. In addition, I DO NOT recommend modifying this product in any way, unless you’re absolutely sure you know what you’re doing, and understand that it will void your warranty. I will certainly NOT recommend this though for any product that uses 500W continuous for any period of time. For that, you will need to buy the 2000VA model. However, for smaller products which draw a lot less power, this is an acceptable unit.
