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Modding rice cooker to increase "keep warm" temperature - bad idea?

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unturned3:
My rice cooker's "keep warm" function holds the temperature at roughly 50˚C, and I'd like to increase it to around 60˚C.

After a bit of searching, it seems like the "keep warm" function is implemented by placing a thermistor (with positive temperature coefficient) in series with the heating element.

The thermistor is a "coil" of resistive wire wrapped around mica sheets. I inserted a length of copper wire underneath a section of the coil, essentially shorting it out, decreasing the effective length (and thus the resistance) of the wire.

The cooker has been running continuously for the past hour or so, holding the temperature at about 64˚C. I did notice that the "coil" in the thermistor is glowing red hot though. Is this a bad idea? Are such wire-wound thermistors meant to glow in normal operation?

moffy:
To me it looks like the PTC is resistance wire, like in a toaster, whose resistance increases because it gets so hot, glowing like a filament light bulb. If you have shorted out a section of the resistor then the current through the remaining section will be higher than previously quite possibly leading to premature failure. Not recommended, it could also lead to a fire within the device.

Whales:
The whole cooker unit is designed to run hotter than that in the cooking (non-keep-warm) phase, so presumably your concerns should be localised to near that modified part.  It looks like it's made of mica (like an electric toaster element) but beyond that I don't know.  How brightly did it glow before the mod?  Is it possible to recreate that? 

amyk:
In the case of incandescent lights, lifetime is inversely proportional to the sixteenth power of voltage. I'm not sure how much that applies to this, but I'd expect it to burn out sooner.

thm_w:
I'm confused, how did you determine there is a PTC? Are you showing it in the photo? To me it just looks like a nichrome heating wire as moffy says.


--- Quote from: Whales on September 25, 2023, 11:56:07 pm ---The whole cooker unit is designed to run hotter than that in the cooking (non-keep-warm) phase, so presumably your concerns should be localised to near that modified part.  It looks like it's made of mica (like an electric toaster element) but beyond that I don't know.  How brightly did it glow before the mod?  Is it possible to recreate that?

--- End quote ---

Is the "keep warm" heater the same as the cooking heater though? OP: I assume there are two separate heaters in this thing?
I agree I would go back to the unmodified state and take measurements there first.

If there are two heaters and this is only used for keep warm, the "correct" mod would be to add more heater filament in parallel with the existing heater. This way you know that the filament won't be overloaded. But even then.. I don't know if I would consider it if I can find another cooker for cheap. Apparently to be safe for extended time periods, keep warm should be at 60C, as you are aiming for.

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