More Rice Cooker Failures
 

I've worked my way through four rice cookers, two different brands, in
as many months. The failure mode is consistent - the cooker cooks the
rice, and then fails when it goes into the mode where it keeps the rice
warm.

In each case, it seems that the temperature sensitive fuse has blown.

I'm in Australia, where the nominal mains voltage is 240V, but I
actually get more like 250V. I'm trying to figure out whether this can
really explain these multiple failures. The warming mode involves having
an extra component in series with the heating element. I speculate that
it is a capacitor, though if it is, its value is less than my multimeter
will measure.

Anyone have any thoughts on whether these things really run so close the
edge in warming mode that a 4% overvoltage can kill them?

Sylvia.

Check the power label on the cooker to make sure that it is rated for your
mains line voltage and mains frequency.

Contact the dealer who sold you the rice cookers and tell them about the
problem you are having.

--

Personally, I would prefer to use a good old fashioned pot on the stove to
cook my rice. It is usually much less of a problem this way...

--

JANA
_____


"Sylvia Else" wrote in message
u...
I've worked my way through four rice cookers, two different brands, in
as many months. The failure mode is consistent - the cooker cooks the
rice, and then fails when it goes into the mode where it keeps the rice
warm.

In each case, it seems that the temperature sensitive fuse has blown.

I'm in Australia, where the nominal mains voltage is 240V, but I
actually get more like 250V. I'm trying to figure out whether this can
really explain these multiple failures. The warming mode involves having
an extra component in series with the heating element. I speculate that
it is a capacitor, though if it is, its value is less than my multimeter
will measure.

Anyone have any thoughts on whether these things really run so close the
edge in warming mode that a 4% overvoltage can kill them?

Sylvia.

Sylvia Else wrote:
: I've worked my way through four rice cookers, two different brands, in
: as many months. The failure mode is consistent - the cooker cooks the
: rice, and then fails when it goes into the mode where it keeps the rice
: warm.

: In each case, it seems that the temperature sensitive fuse has blown.

: I'm in Australia, where the nominal mains voltage is 240V, but I
: actually get more like 250V. I'm trying to figure out whether this can
: really explain these multiple failures. The warming mode involves having
: an extra component in series with the heating element. I speculate that
: it is a capacitor, though if it is, its value is less than my multimeter
: will measure.

: Anyone have any thoughts on whether these things really run so close the
: edge in warming mode that a 4% overvoltage can kill them?

: Sylvia.

The keep warm rice cookers I've seen use a secondary warming coil separate
from the main cooking coil. I would doubt the extra component is a
capacitor, maybe thermal fuse. Is there continuity in the heating circuit?
Its possible the overvoltage could have blown a thermal fuse, it all
depends on how much margin was used when selecting the fuse.

wrote:

Sylvia Else wrote:
: I've worked my way through four rice cookers, two different brands, in
: as many months. The failure mode is consistent - the cooker cooks the
: rice, and then fails when it goes into the mode where it keeps the rice
: warm.

: In each case, it seems that the temperature sensitive fuse has blown.

: I'm in Australia, where the nominal mains voltage is 240V, but I
: actually get more like 250V. I'm trying to figure out whether this can
: really explain these multiple failures. The warming mode involves having
: an extra component in series with the heating element. I speculate that
: it is a capacitor, though if it is, its value is less than my multimeter
: will measure.

: Anyone have any thoughts on whether these things really run so close the
: edge in warming mode that a 4% overvoltage can kill them?

: Sylvia.

The keep warm rice cookers I've seen use a secondary warming coil separate
from the main cooking coil. I would doubt the extra component is a
capacitor, maybe thermal fuse. Is there continuity in the heating circuit?
Its possible the overvoltage could have blown a thermal fuse, it all
depends on how much margin was used when selecting the fuse.

Now that I have yet another new one to play with, it appears this extra
component is a resistor of some sort - apparently it also burned out
when the rice cooker failed. Its resistance, when cold, is 1.2K.

This is what it looks like. The ruler is in centimetres, so this
component is about 2.5 inches long.

http://members.optushome.com.au/sylviae/resistor.jpg

The restance of the main heating coil, when hot, would have to be about
140 Ohms (given that it's rated at 400W at 240V).

The main heating coil remains in circuit in warming mode, in series with
the other component, but clearly, given its resistance, it will be
dissipating little heat. I think it's done that way simply to avoid
needing a double throw switch - it reduces the cost a bit. The other
component is mounted on the heating plate, so it would be providing most
of the heat for warming.

The failed component had some discolouration, but given that this new
one has probably never been heated up, it's hard to know whether the
discolouration means anything.

If the average punter knew how these things are put together....

Sylvia.