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### Course: Electrical engineering>Unit 9

Lesson 1: Household items

# What is inside a coffee maker?

In this video we explore what is inside a coffee maker, how it is made, and how it works. Created by Karl Wendt.

## Want to join the conversation?

• So is the thermal fuse one-use?

(Hey, that rhymes.)
• probably, yes. However the threshold for breaking it may be as close to a worst care scenario tempurature as possable (to avoid loss of the product). While buying a new coffie maker might help the company, hurting the customer certainly will not. hope this helps :)
• Could you provide a better explanation for the action that causes the heated water to rise in the tube? I always thought an internal check-valve would keep the heated water from returning to the reservoir, but apparently that is not the case.
• According to http://home.howstuffworks.com/coffee-maker3.htm,
•When you pour in cold water, it flows from the reservoir through the hole and into the orange tube.
•Then the water flows through the one-way valve, into the aluminum tube in the heating element and then partially up through the white tube. This all happens naturally because of gravity.
•­When you turn on the switch, the resistive heating element starts heating the aluminum tube and eventually the water in the tube boils.
•When the water boils, the bubbles rise up in the white tube. What happens next is exactly what happens in a typical aquarium filter: The tube is small enough and the bubbles are big enough that a column of water can ride upward on top of the bubbles.
•The water flows up the white tube and is dispersed to drip evenly on the waiting coffee grounds.

This explanation sees to make sense to me. I think the one way valve would be needed to make sure all of the water is consumed. If it could go up either tube, it would be difficult to empty the reservoir of all of the water. I may hve to check out one of my old ones to see if they have a one-way valve.

I also found this on how perculators work:
http://www.fantes.com/manuals/percolator.pdf
The tube is smaller in diameter than bubbles, so that each snugly-fitting bubble that passes through the tube will carry a bit of water above it along its upward journey.
As these continuous jets of water reach the top of the Pump Stem, they discharge onto the Spreader Cover, which helps disperse the water over the grounds underneath in a more uniform manner, and also keeps grounds from
splashing up.
• What are safety screws, and what makes them so safe?
• I'm not sure about the screws in the video because it's a little difficult to see, but typically they are flathead screws where the head is designed in such a way that when you turn the screwdriver clockwise (to tighten the screw), it engages the screw normally, but if you turn counter-clockwise (to loosen the screw), the screwdriver will slip out of the screw's head, making it impossible to turn. This way, it tightens like a normal screw, but can't be undone without a specialty tools. (see: http://en.foerch.com/documents/thumbs/-1642553479_20111511074942_800x800_Fit_0_0.png)

What makes it "safe" in this case, is that it prevents the customer from being able to open up the bottom of their coffee maker and either burn themselves on the heating element, or spill water on exposed electrical wires.
• How does the water go up the tube, doesn't gravity pull it down?
• Water doesn't go up the tube. STEAM goes up the tubes. On the reservoir side of the heating tube the steam is blocked by a trap in the tube. The liquid water always moves TOWARDS the heater coil until it has all been converted to steam and passed out to the pot. See above.
• What actually happens in a coffee maker when it has the water and coffee bean grounds it it and it's on? I have never opened a coffee maker when it was on, not to mention that I don't even touch coffee, I am 11! :) Does the water drip into the grounds, and does the coffee grounds "contaminate" the water making the water brown and bitter? and how does it get into the pitcher?
• It happens pretty much like you said! If you go to in the video, you see the part of the coffee maker where the filter goes. Inside of the filter you put the coffee grounds. The filter allows water (Actually, coffee at that point) to drip through, but keeps the grounds in the maker. There's a hole the freshly made coffee drips through that you can see, directly into the kettle below. So yes, hot water drips out onto the coffee grounds, soaks through them, dissolves much of the grounds (In the process picking up their flavor and color), and drips through filter and the hole into the kettle.
• Hi, may I ask if there is any resistor inside the circuits? Also, if possible can anyone show me how to draw the circuits? Thank you!
• does the nicronium heat the horse shaped U tube directly or the temperature controller ( having the bimettalic stip heats it ) ......... heat is basically generated by resistor in this case its the nicronium so how does heat flow from there ?
• how does the water comes back to the top of the coffee maker ?
(1 vote)
• When water is hot, it starts to expand. When it expands, it travels up the pipe. Do you see how narrow the circumference of the pipe is? In Physics, there is this thing where the size of a pipe affects how fast water flows. With thermal expansion and the circumference of the pipe water can defy gravity. Check out the Fluids and Thermodynamics sections under Physics on this website for more information. Hope that helps out!
• What will go wrong if there is no water in the reservoir?
• Nothing. This is a normal operating state for this coffee maker. Recall step one was to fill the reservoir. As the coffee is brewed the reservoir is emptied. The coffee maker then functions only to keep the base of the pot hot.

A better question is what happens when the thermostat fails. You can just see the thermostat at https://youtu.be/XQTIKNXDAao?t=615 it is hiding under the black clip just above the right thumb. Normally this device regulates the temperature by opening and closing the electrical circuit as described in the video. However, if it gets stuck in the closed position we are in trouble as the heater will get very hot. Hot enough to cause a fire.

This is where the failsafe devices kick in. If you look at the video at time https://youtu.be/XQTIKNXDAao?t=615 you will see two round devices suspended by wires in the middle of the heater coil. These are thermal fuses. If they overheat they “pop” thereby removing electricity to the coil. Normally these are one time devices. One failure of the thermostat causing an overheating event and the coffee pot is garbage.

Regards,

APD
(1 vote)
• Why is the power looped? And what is this process called?
• Hello Com212,

At we see the heating element separated from the plate that heats the coffee pot. The heater is in the look to the left. Observe the white gunk on the heater plate. This is thermally conductive material that ensures good heat transfer from the heater to plate.

The heater is a simple resistive element.