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I'm trying to build a prototype for my own coffee machine. It'll have a container of water that will need to be boiled when a signal is sent by my arduino. The question is, what component should I use to handle this?

This is for a hackathon this upcoming weekend, so I don't mind it looking incredibly terrible. Some have recommended that I simply run a kettle through a relay controlled by an arduino, but my problem with that is I need the water to be inside a container that I'll be making, as it will need to be connected to some sort of stand. I was thinking I could take the kettle apart and isolate its heating element. Would this be ideal, or is there some component out there that will handle this?

Any suggestions and/or advice would be very much appreciated.

EDIT: An idea - What if I just connected a fully assembled kettle to a fuse, and used some sort of "pump" to retrieve the water in it? rather than creating my own container with a heating element that I would be able to drain with by opening a flap at the bottom.

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closed as unclear what you're asking by Joe Hass, Dave Tweed, Chetan Bhargava, Nick Alexeev, Matt Young Mar 6 at 13:03

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

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What kind of coffeemaker are you talking about? Are you aware that a "drip" type coffeemaker does not boil the water in a container as such? Instead, the water flows through a relatively narrow metallic tube in which a little bit boils at a time, driving it to the top of the grounds holder. –  Dave Tweed Mar 6 at 3:10
    
@DaveTweed Yes, i'm sure it's not close at all to how an actual coffee maker works. Like I said, this is for a hackathon, and the actual coffee maker isn't the highlight of the project, but the technology i'll be incorporating with the arduino that will go with the coffee machine. I just need something that can boil water and run it through some grinds. –  Byron S Mar 6 at 3:18
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Intel x86 CPU comes to mind. –  Kaz Mar 6 at 4:00
    
@Kaz Particularly a LGA775 P4 Prescott core. Those made for excellent space heaters! –  Shamtam Mar 6 at 5:18
    
Given you can buy an actual coffee maker brand-new for around £15 / $20, why not use one of those for that bit of hardware? –  John U Mar 6 at 11:11

3 Answers 3

up vote 3 down vote accepted

You should confine yourself to materials that are safe for contact with potable water, which rules out a bunch of possibilities.

One idea might be to cannibalize a rice cooker- they have a heater below the rice bowl and a spring-loaded thermostat. I've seen them as cheap as $8 at discount stores, but $15 might be more typical. They are designed to shut off when the liquid is gone and the temperature rises. Perhaps you could substitute your own (open) container for the rice bowl.

I do hope you're not planning to make a homemade pressurized boiler. If so, I will have nothing to do with it, and you should check your local laws and regulations about what kind of testing and approvals may be necessary.

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I was actually hoping to try something similar to what you suggested: take a preexisting heating element and incorporate that. I just need to find a way to heat up water within a simple metal container that will then be drained for a cup of coffee. However, i'm low on time and need an object in which the heating element will be easy to extract and work with –  Byron S Mar 6 at 3:09
    
Actually, looking at some photos, the element is not spring loaded, only the cutoff thermostat. You'd have to ensure contact with the element, so maybe it's not that good an idea. Kettles use an immersion element which might be more difficult to work with. Heck, I'd buy a cheap one of each tonight and rip them apart. –  Spehro Pefhany Mar 6 at 3:18
    
What do you think about a water pump shoved down a fully assembled kettle? instead of making my own container with a heating element. –  Byron S Mar 6 at 4:02
    
That could work. Maybe find a way to pump cold water in and force the hot out without it mixing too much, so the pump doesn't see the hot water. That's similar to the way my commercial Bloomfield coffee maker works (except the pump is you pouring a carafe of cold water into the top). –  Spehro Pefhany Mar 6 at 4:16
    
is it an issue for the pump to come in contact with the hot water? –  Byron S Mar 6 at 4:46

There are small aluminum coil heaters made to use with a coffee cup, even a plastic cup as long as there is water in it. They plug into the mains so control with a triac or relay.

Here is an example http://www.amazon.com/Travel-Immersion-Water-Heater-Voltage/dp/B000AXS0UE

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Two potential solutions come to my mind. By the way, both of these solutions obviously could not be powered by the signal, but would control some form of power switching such as a MOSFET.

  1. A thermoelectric module

    -These devices take DC current and produce a temperature difference across both sides. Typically used for cooling applications, but there are certainly some powerful enough to do heating as well. Since they produce a temperature gradient, typically the other side has to be held at/near a constant temperature. For instance in cooling applications, in order to keep the cold side as cool as possible, a heatsink must be added to the opposite side to remove heat, thus lowering its temperature, and moving the cool side further down the temperature scale. In a heating application, you will need to do the reverse, and warm up the side trying to become cold so the hot side can stay hot enough.

  2. A power resistor

    I don't have experience with using power resistors as heaters, but it certainly seems possible. You might need to do some rough calculations to determine the heat energy of a specific resistor, and the time it will take to heat your amount of liquid to the desired temperature.

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I wouldn't consider myself experienced enough to try the power resistor approach. And the concern I have with the thermoelectric module is the time it would take to install one. I have no experience with them, and installing a heatsink sounds complicated and time consuming. I will have 24 hours to build this entire coffee machine. Thank you for the input though. –  Byron S Mar 6 at 3:05
    
@ByronS Yes both of those potential solutions are things you would need to test beforehand to ensure they work as expected. If you do decide to explore either of those possibilities, neither of them are difficult devices to connect, even for a beginner to electronics. Thermoelectric modules are simple 2 wire devices that need to be connected to a constant voltage supply, and a heatsink wouldn't be needed. I probably wasn't clear enough but the usage of a heatsink is necessary when using a TEC module as a cooler. Since you are using it as a heater, your liquid acts as the heats sink. –  krb686 Mar 6 at 3:12

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