Can PWM power a 12V rice cooker? - Page 1
Forum section: electronics / beginners

author: vanlife
author_rank: Newbie
timestamp: January 28, 2023, 02:48:13 pm
content: Hi all!I'm new here.Have a really basic 12V rice cooker.Want to be able to adjust the temperature and make soups in it.Could PWM damage the unit?Many thanks.

author: wasedadoc
author_rank: Super Contributor
timestamp: January 28, 2023, 03:18:06 pm
content: Perhaps you should explain whatyouthink PWM is.

author: ledtester
author_rank: Super Contributor
timestamp: January 28, 2023, 03:26:58 pm
content: How about attaching a temp sensor to the pot? Then you can applied power when you need heat and turn it off when the temp has been reached. A simple algorithm like checking the temp every 15 seconds should work fine (for instance, using a microcontroller) or you could use an analog temperature controller which implements hysteresis - there are a lot of off-the-shelf solutions available.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 28, 2023, 04:01:05 pm
content: +1 for on-off thermostat. Can be a mechanical one, or it can be a digital sensor, Arduino and four lines of code.

author: bdunham7
author_rank: Super Contributor
timestamp: January 28, 2023, 04:06:44 pm
content: Quote from: vanlife on January 28, 2023, 02:48:13 pmTo answer your question, if it is truly basic with no electronics or displays and just a heating element and perhaps a mechanical thermostat, then regulating its current via PWM is going to be fine. If it has a mechanical thermostat, then PWM won't really change the temperature it operates at until your duty cycle gets low enough that thermostat stops cycling. You would have to experiment with that.However, if it has an electronic timer you may have issues with PWM on the inputs. You'd have to provide the exact details of the unit and perhaps take a cover or two off and post pictures.

author: byte
author_rank: Contributor
timestamp: January 28, 2023, 04:19:42 pm
content: Quote from: vanlife on January 28, 2023, 02:48:13 pmOnly one way to find out!IMHO, PWM is probably not the best way to temperature control a rice cooker. If it's one of those induction rice cookers, just controlling power input with PWM and adjusting the duty cycle will not work. But if it uses a simple 12V resistive heating element, it should work in theory.Regardless, if you are thinking of controlling this with something like a 1KHz PWM signal from a micro controller, it's way overkill. The thermal mass of the cooker and food acts as an energy capacitor and doesn't require fast switching frequencies to maintain a constant temperature. There is a reason most cooking appliances are very dumb and use just a basic thermocouple or bimetal thermal switch to cycle the heating element on off over a period of many seconds or even minutes. You can hear this "clicking" on many rangetops and ovens.If you really want to computer control this DIY style, then I think just a relay and thermocouple tied to a microcontroller will be the most effective and simple option. That being said, if you want better temperature control accuracy and not huge swings in temperature, you will want to implement and tune a PID loop in your controller. If you are not familiar with control theory, it may be a little daunting at first but great stuff to know.Cheers

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 28, 2023, 04:26:04 pm
content: You really have a 12V rice cooker? Which make and model is it?

author: BillyO
author_rank: Super Contributor
timestamp: January 28, 2023, 06:02:02 pm
content: Quote from: BeBuLamar on January 28, 2023, 04:26:04 pmYeah, they are a thing.https://www.amazon.ca/Multi-function-Cooking-Heating-Keeping-Travel/dp/B01NCK6WBYIf the OP's is like this one it may have some simple electronics in it.Should do soup just fine the way it is though.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 28, 2023, 08:11:13 pm
content: Simple rice cooker doesn't have electronics. It has a thermoswitch that switch to keep warm when the temperature raises above boiling temperature. So if your if you put soup in there and use the PWM you can keep the temp below the boilting temp. Without doing anything the cooker will keep the soup at boiling temp until all the water evaporates.

author: BillyO
author_rank: Super Contributor
timestamp: January 28, 2023, 08:32:59 pm
content: I have a simple 120V rice cooker. Other than being a bit bigger than what I linked to it's basically the same. Has a "cook" button and a "warm" button. As you say, when it finishes cooking it goes to warm. However, warm is not 100C, it's 65C. It's perfectly fine for heating soup. Instead of pressing the cook button, I just press the warm button. I've not taken it apart (yet), but I imagine there is a $0.10 8-pin MCU in there somewhere along with a thermister and a triac. At least, that's the way I'd do it.

author: IanB
author_rank: Super Contributor
timestamp: January 28, 2023, 09:22:48 pm
content: Generally speaking the way rice cookers work is to boil the liquid inside until it dries up (the rice is cooked), and then turn the heat down.Really simple rice cookers have no electronics and use a simple magnetic thermostat to detect when all the liquid has boiled away. See the video below for an explanation, it is fascinating.I would say that such a simple device could readily be used for heating soup, and you would manually switch it to warm mode when your soup is hot enough. Since it has no electronics you could also regulate it with a phase control dimmer (mains) or a PWM dimmer (12 V DC). However, I am not sure what would be the point?If it is a fancy rice cooker with electronics inside (LCD display, beeping and fancy timers), then trying to apply power control from outside would not work. On the other hand, such a fancy rice cooker most likely already has a soup mode.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 29, 2023, 12:54:15 am
content: I have the Aroma cooker. It's 120VAC and if you want keep warm you push no button. Just plug it in. When you push the button it raise the power and boil the water. When the water is boiling the temp is 100C. When all the water evaporates the temp rises above 100C that is when it pops the button up and in the keep warm mode.

author: IanB
author_rank: Super Contributor
timestamp: January 29, 2023, 01:19:43 am
content: Quote from: BeBuLamar on January 29, 2023, 12:54:15 amHow long does it take to cook the rice (one portion, two portions, three portions, ...)?

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 29, 2023, 01:45:56 am
content: About 20 min. It doesn't make much of a different whether you cook a little or a lot. The only difference is the time for it to get to a boil as more rice you put more water. But once it boiled the remaining time is the same.

author: vanlife
author_rank: Newbie
timestamp: January 29, 2023, 03:32:09 pm
content: Thank you for all the great replies.I will give PWM a try and go from there...Thank you!