Inside a Chinese electrically heated lunch / bento box.

A rather odd device that leaves me wondering how many people use these to heat their meals at work on a daily basis. My first thought was about the risks of holding food at a medium temperature for long periods of time, particularly the common food poisoning villains like rice, pasta and potato. But used properly this unit does seem to bring the food to a high enough temperature to limit that risk. The instructions do suggest adding a small amount of water before heating, and I guess that may be to allow the steam to couple the heat throughout the food.
My test was perhaps a bit unfair in that I put a high mass of water in the unit. With a portion of loose food the heating time would be much faster, and especially so in a warmer environment. Yes, I do keep my home at a really low temperature in winter. I prefer a cool dry environment to a hot stuffy one.
Electrically this unit is very simple. Just a couple of self regulating PTC (Positive Temperature Coefficient - resistance rises as they get hotter) heating elements on an aluminium heat spreader. At plug in if the unit is very cold the current will peak at about 3A on a 240V supply before rapidly falling to a power dissipation of about 40W (20W per element). When it reaches its highest temperature the current drops to a passive level determined by the cooling effect of the external environment.
I suppose that something like this could also have other uses than heating food. It could also be used for various workshop applications where it's useful to heat something slightly before use.
One thing worthy of note is that the figure-8 cable supplied is copper coated aluminium, so it's possibly worth swapping it for a better locally sourced cable.
Here's a generic eBay search link to these type of units. You'll have to substitute your local voltage in the search box:-
https://www.ebay.com/sch/i.html?_from=R40&_nkw=electric+lunch+bento+box&_sacat=0&LH_TitleDesc=0&LH_BIN=1&_sop=15

I plugged this 220V unit into a 110V supply and it still stabilised at 40W so it may be capable of a wide voltage range. But I've not tested that under actual food heating conditions.

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Видео Inside a Chinese electrically heated lunch / bento box. канала bigclivedotcom