Black and Decker 5-Cup Coffee Maker

A coffee machine for the home kitchen can get very fancy, but not this one. This was the lowest-end, simplest, least expensive model DCM600B available at the store that day many years ago. I’m curious how simple a coffee maker can be inside. As the entry-level product, every expense would have been spared, and I hope to see some engineering creativity to reach that cost-optimized goal.

From the top, there is only one visible fastener. A Philips-head screw in the water reservoir.

With it removed, we can see majority of the path for boiling hot water.

  1. Hot water is pumped up through this pipe.
  2. Which then makes it through this bend in the lid.
  3. Exits here to dribble onto coffee grounds.
  4. Held inside a coffee filter sitting in this cup. Water filters through the coffee grounds, through the filter, out through the hole in the center of this cup.
  5. Which drips into the carafe.

Bottom view with model number DCM600B visible. The power cord was cut some time ago. I no longer remember the reason why, but it is quite apparent past me wanted to ensure there would be no further use.

Two fasteners are visible from the bottom. The first surprise was that nonstandard fasteners were used, I had expected generic screws in the interest of cost.

My screwdriver bit that matched this screw was labeled CR-V 6.

The second surprise was that no screws were hidden under rubber feet. Once the two visible nonstandard screws were removed, the bottom cover flipped open. There were some grates in that bottom cover to release any liquid that might enter this enclosure. There was also a dam that protected electric wire from such liquid.

Judging by residue and this corroded screw, that seepage draining provision came in handy.

I would not have been surprised if the power switch merely wired power directly to a heating element. The machine is actually slightly more sophisticated than that, but not by much.

Removing a few things allowed some untangling of the wire. One end of the power cable is connected to a black wire, presumably ground, connected to one end of the horseshoe-shaped heating element. The other end is connected to a red wire that led to the power switch, which connects it to a blue wire connected to the other end of the heating element via three components. I don’t know what these components are, but the first of these three in series is clamped to the heating tube. Functionally, I infer they sense temperature and would open the circuit when things get too hot, and close the circuit once things cooled down. Such a circuit would implement the “keep coffee warm” feature.

The item clamped to the heating tube is presumably a temperature sensor. It has the following markings:

1504
T3/33
125V10A
150

There is very low resistance across the two terminals at room temperature. I heated it up with the most convenient heat source, which was my heat shrink tube hot air gun. The measured resistance did not appreciably rise as I heated it up, nor did it go open circuit. But I doubt this hot air gun pushed the device to water boiling temperature, so the results are inconclusive. I don’t have the equipment to test electronics behavior at different temperatures, the only thermometers I have are for measuring human fevers and for kitchen baking.

While brewing coffee, water from the reservoir would keep the heating element from getting too hot. Hot water would boil and expand. How did the machine ensure that such water would be sent through coffee grounds instead of back to the reservoir? This cheap and simple ball check valve is the answer. It would not have been a perfect seal, allowing some water back into the reservoir, but it’s good enough for the job.

Disassembled components from the bottom.

I admire the simplistic efficiency of this machine’s design. Here’s a final example: this machine has capacity for five cups of water. How do we prevent the user from overfilling? I would have guessed float sensors and maybe an overflow valve. The design team didn’t need any of that complexity, they cut two holes in the water reservoir to drain excess water out to the kitchen countertop. Problem solved!

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