Rice Cooker

[nLite]

Hi there, first post here. So I have this Hello Kitty rice cooker that I've only used twice, and both times it failed on me. Both times, it failed when the rice was *almost* ready - like 3 more minutes would have been perfect. The indication that the unit stopped working was that the LED lights on the front (for "Keep Warm" and "Cook") shut off. The first time it failed, I opened the unit and replaced the the thermal fuse with the same temperature rated fuse (140 Celcius) after verifying that it wasn't conductive. I haven't opened the unit after the second failure, but I suspect it's due to the same reason.

The thermal fuse is wrapped in an insulating tube, which is held away from the cooking chamber by a metal bracket. I've considered simply replacing the thermal fuse one that breaks at a higher temperature, but I feel like this might be a fire hazard. Does anyone have any ideas on what's going on or how to troubleshoot this problem safely?

Edit:
The 2nd thermal fuse is indeed non-conductive.

 

[(*steve*)]

The *BEST* advice is to take it back from where you bought it from and get it replaced.

Alternatively (if you have already voided your warranty)

Show us the thermal fuse.

An open circuit thermal fuse is indicative of failure.

You are right that replacing it with a higher temperature one is asking for trouble.

 

[nLite]

Unfortunately, the rice cooker was gifted about half a year ago so replacement/return wasn't an option. I also didn't want to go through the warranty process because I couldn't find a website for the company that made the rice cooker. At the time, it seemed like replacing the fuse was the easiest option.

Here you can see the white insulator that encases the fuse and the bracket that holds it away from the cooking chamber.

Here is the insulator and the fuse. The black residue on the fuse is from electrical tape. Also, there is duct tape on the insulator because I had to cut it open to get the fuse out the first time.

If it helps, on the fuse is written: "142ºC / 10 A / JET 250V~ / C1112 / SEFUSE / SF193E"

 

[KrisBlueNZ]

There's quite a bit of discoloration around the earth connection.

Is the cooker actually overheating? Does the water boil in it?

Does it have a thermostat? Has that failed?

Is it rated for the correct AC mains voltage?

 

[nLite]

During the two times that I used it, large amounts of steam escape through the top vent as you would expect from rice cookers. So it does seem that water boils.

I'm a little inexperienced when it comes to these things so I don't know how to identify a thermostat. Here's a picture of the entire bottom

Also, the rating appears to be 250 V~. I live in U.S. so maybe this is the problem?

 

[KrisBlueNZ]

We've got a rice cooker and it doesn't boil. It doesn't really make steam either.

I can't identify it in that picture either, but you may be able to find it through a process of elimination.

It will be attached to the metal so it can monitor the temperature, and it will have two contacts, and two wires going to it.

It's not the heating element, and it's not the switch that's activated by the plunger through the centre.

It may have two heaters - one to keep the rice warm. I'm not sure. See if you can figure it out. Someone else here can probably help too.

 

[nLite]

I can only find two places where a pair of wires connect to the chamber. One is through the galvanized plate, and the other is through the prongs protruding behind the plunger.

It does have two settings: Warm and Cook.

I know the resistances are probably way off, but I sketched up a circuit diagram to be thorough. The switch being open corresponds to Warm mode, and closed corresponds to Cook mode. "Plate" is the galvanized plate, "Prongs" are the prongs behind the plunger, and the three 1k resistors represent the front indicator.

 

[KrisBlueNZ]

I don't think that circuit diagram is going to be of any use.

Can you take a photo looking almost directly at the underside of the bowl, add numbers to the photo for every item, and make a list that has the numbers, and for each number, everything you can tell us about that item in the photo. That might help.

 

[CocaCola]

These exact rice cookers can be had brand new at Target for $30 and I saw them for I believe on sale for $15 just a few months ago... They had an entire end cap full of Hello Kitty cooking gadgets on sale so it caught my eye, so I gave it a second glance as cheap kitchen gadgets even in pink are sometimes worth the money Personally I wouldn't spend a great deal of time trying to fix it...

Question is the heating element actually shutting off prematurely from overheat or is the 'weight' sensor shutting it off prematurely?

In other words if you add a little more water will it will cook a little bit longer?

If you can set the thing on an elevated platform with the bottom off (do it safe) you can monitor the weight trigger, if that trigger is what is kicking it into 'warm' mode then it's working properly...

 

[KrisBlueNZ]

CC, I think the problem is that the thermal fuse is opening because it gets too hot.

I assumed this would be caused by a failed thermostat, because of the discoloration, the fact that it boils the water and produces steam, and the fact that a 142 degrees Celsius thermal fuse is popping.

But it may not actually have a thermostat. Perhaps it is staying in "cook" mode and not switching to "keep warm" mode after a certain amount of time, and in cook mode, it eventually overheats. I kind of doubt this but it's possible I guess.

AFAIK the weight sensor in the middle doesn't switch it between cook and warm modes. At least, the rice cooker we have doesn't work that way.

What does the user manual say about cook and warm modes? Can you scan the whole thing?

 

[nLite]

Unfortunately I'm not at home so I can't take another picture at the moment. Also the week is starting so I apologize in advance if my replies start to slow down. Thank you guys for your input so far, though.

1. Port for electrical plug. Has three prongs. Rated 10A, 250V (see pic above)
2. Switch for Cook and Warm modes. The switch is closed when the two copper tangs to the right come into contact. Warm mode: open, Cook mode: closed.
3. Pair of prongs. When in operation, the prong to the right is closest to the thermal fuse.
4. Plunger. Not really sure how it works at the moment, but I'll update on this when I get home. It seems to work in conjunction with the switch (2) though.
5. Front panel. Has two LEDs for Warm and Cook mode, and a resistor. Above it is the control bit for the switch.
6. Galvanized plate. Not really sure what to say about this besides that it's held onto the chamber by a screw.
7. Outside of cooking chamber. It's a smooth piece of metal that's encasing the actual cooking chamber, which looks like it's coated in wrinkly tin. Again, not much to say about this besides the discoloration around the three screws that hold the casing to the actual cooking chamber (the last one is hidden behind the switch.

CC, since I don't have a spare fuse on hand, I can't do any live tests without skipping out on the fuse or potentially sacrificing a new fuse. Maybe a detail that I probably should have taken note of is whether the switch was set to Cook or Warm when I noticed that it failed.. I really can't remember. What I can do is figure out how the plunger operates in conjunction with the switch and how having a weighted rice bowl inside affects this.

Kris, unfortunately I do not have a manual. I most likely threw it away (bad idea now I know). This is actually the reason why I'm designating a place for all my manuals from now on.

 

[KrisBlueNZ]

That's exactly what I asked for and you've done a good job, so I'm really sorry to say that it's not enough to enable me to understand how it all works. Perhaps another photo looking nearly straight at the bottom would help.

Also, close-ups of the switch stack (2) from several angles might help.

Actually I was hoping that someone else here would have prior experience with rice cookers and would be able to identify and describe the parts.

It looks like the switch stack (2) is tied in with the cook/warm switch (that's actuated from the outside, via the bent metal arm to the left of the switch stack), AND the plunger, which is actuated by the weight of the rice bowl, correct?

Perhaps the thermostat is incorporated into the switch stack as well...

I'm interested in (6). I thought it might be the keep-warm heater. What do you think? If it is, perhaps heat from it is conducted through the screw and into the bottom of the heating bowl.

Is the visible metal (7) the underside of the bowl that the rice holder sits on, or is there another bowl inside the (7) metal with an insulating layer between them?

Have you identified the two connections for the main heating element?

You could try Googling the model number; the user manual may be available for download.

 

[(*steve*)]

Actually I was hoping that someone else here would have prior experience with rice cookers and would be able to identify and describe the parts.

Only from use of them.

It appears to me that they maintain a higher power until the temperature rises above 100C (indicating that all the water has been absorbed) then they switch to a lower heat setting.

That fits with how they operate, but the actual temperature is conjecture. They certainly don't vigorously boil, it's more like a slow simmer.

 

[Miguel Lopez]

That kind of cooker does not use a thermostat. When the main switch opens, due to the demagnetization of the magnet inside the middle piece, it simply add a resistor in series , which you can see in the picture (the flat square piece No.6). That's how it keeps the rice warm.

In Cuba we usually "bridge" the fuse as there is not spares, but don't take this advice, as I understand it could be dangerous.

There should be a plate in the cooker body, indicating the nominal mains value, which might not be the one you showed in the mains plug.

 

[Miguel Lopez]

Looking again to the picture, it seems as in this cooker should be used for a long time before to be gifted to you, cause the screws which holds the heating resistance to the chasis show evidence of continous heating. Even the paint is lifted off from the metal surface.

 

[KrisBlueNZ]

Thanks Miguel. That explains a lot.

 

[(*steve*)]

When the main switch opens, due to the demagnetization of the magnet inside the middle piece

Ah! so that's the function of that middle bit. I knew it was something to do with the sensing of temperature, but I didn't realise how.

 

[nLite]

I messed around with the plunger and this is what I found. Maybe this is or isn't normal rice cooker behavior:
1. When the plunger is not depressed, attempting to switch from Warm to Cook will just go back to Warm.
2. When the plunger is depressed all the way, switching from Warm to Cook will lock the switch into Cook mode. Only when the pressure on the plunger is released past the level of the bowl seating will the switch release back into Warm mode.
3. When a weighted bowl is placed into the cooker and the mode switched to Cook while the top is open, the switch stays in Cook mode. When the weight (glass bottle) is removed), the switch stays in Cook mode.
4. When an empty bowl is placed in the cooker and the top is closed, switching to Cook locks into Cook mode. Opening the top quickly releases the switch back to Warm, and opening slowly leaves it in Cook.

Here are some more pictures as requested:
Switch stack (2) from the front: http://i.imgur.com/3Efv8x6.jpg
Switch stack from the top: http://i.imgur.com/HDcjRnb.jpg
Switch stack from the side: http://i.imgur.com/NCa71n9.jpg
Top view of underside: http://i.imgur.com/nGai1ol.jpg
Close up of the rating near the plunger, says 500 W and 120 V:
http://i.imgur.com/kaUkHxk.jpg

 

[Miguel Lopez]

Ah! so that's the function of that middle bit. I knew it was something to do with the sensing of temperature, but I didn't realise how.

Yes, that's how it works. While the bowl contains water, temperature never goes higher than 100°C, but when all water has gone, temperature increases quickly and the magnet inside the middle piece (No.4) losses its magnetic properties and then the main switch is released to Warm position.

When the plunger is not depressed, attempting to switch from Warm to Cook will just go back to Warm.

That's OK

2. When the plunger is depressed all the way, switching from Warm to Cook will lock the switch into Cook mode. Only when the pressure on the plunger is released past the level of the bowl seating will the switch release back into Warm mode.

That's OK too. The plunger has a spring inside which de-attach the magnet when the cooking bowl is removed. The spring is more powerful than the magnet.

When a weighted bowl is placed into the cooker and the mode switched to Cook while the top is open, the switch stays in Cook mode. When the weight (glass bottle) is removed), the switch stays in Cook mode.

That is good too.

4. When an empty bowl is placed in the cooker and the top is closed, switching to Cook locks into Cook mode. Opening the top quickly releases the switch back to Warm, and opening slowly leaves it in Cook.

That's OK. It is thought to work with rice inside, and never use it empty

So, I think your cooker is working OK. Try to measure current leakage between the cooking resistance and chassis (with a neon indicator). You can also "bridge" the thermal fuse a make a test (call the firemen first, just in case )

Hope this help.