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Cheap coffee maker

Discussion in 'Troubleshooting and Repair' started by Wiiman3893, Oct 8, 2017.

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  1. Wiiman3893

    Wiiman3893

    2
    1
    Oct 8, 2017
    We have a cheap coffee maker, and it appears the thermostat is bad. It will heat water but shuts off randomly, the switch is a basic KDS301 designed for 120-130 volts and 7 amps. I am unable to find that thermostat or similar for a reasonable price.

    Does anyone know of a cheap/durable replacements or work-arounds.

    Could I use a 250volt 10amp switch?
     
    irene likes this.
  2. hevans1944

    hevans1944 Hop - AC8NS

    4,706
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    Jun 21, 2012
    Maybe you are looking for the wrong part number. An uxcell KSD301, 250V, 10A, N.C. Temperature Controlled Switch that opens at 135C should work fine in a cheap coffee maker. It will trip open when the water reservoir boils dry and the temperature rises from 100C to 135C. Available here at Amazon.com for $4.89 and free shipping. Some soldering and mechanical work may be required to replace the defective thermostat.
     
  3. Wiiman3893

    Wiiman3893

    2
    1
    Oct 8, 2017
    Do you know of one with a manual reset? The thermostat is also the power switch. Or is there a different switch that would allow me to toggle it and let it go through 1 cycle, then shut off?
     
  4. hevans1944

    hevans1944 Hop - AC8NS

    4,706
    2,203
    Jun 21, 2012
    Sorry, I didn't thoroughly research this for you. And I also didn't realize that after the empty water reservoir of the coffee maker cools down, then the switch will close again and continuously cycle between on and off as it tries to heat up water in a dry reservoir... not a good feature.

    Yes, there is a switch that will allow you to toggle the coffee maker on by applying power, whereupon it will toggle itself off and remain off until power is removed, when the water reservoir boils dry. See link below to a self-hold thermal cutout switch. You could also add a relay to the coffee pot and wire it latch on until the thermostatic switch opens its latching circuit. Problem is, unless you can find a relay with 115 VAC coil and contacts to handle 10 A for practically no cost, that solution would probably cost more than a new cheap coffee pot. And you would have to find a way to mount the relay somewhere, probably in a small box external to the coffee pot. And you would need to mount a push-button switch on that box to actuate the relay initially to brew a pot of coffee. A real kludge, and probably ugly to boot.

    But I did find a datasheet on variations of this bi-metallic thermostatic switch, and one of the variations is for a manual reset. If you can find one of these it should work. A better alternative may be this self hold thermal cutout switch, which will open at the preset temperature, but in doing so it inserts a small heating resistor, located under the bi-metallic disk, in series with the coffee maker heater. The added resistance is large enough to limit the current through the coffee maker heater, so the heater cools off, but there will still be enough current through the small heating resistor to heat the bi-metallic disc, thus maintaining its contacts in the open position. The only way to reset the device is to remove power and allow the bi-metallic disk to cool down and close the circuit to the coffee pot heater again.

    You can read more about this stuff at the Calco website. They appear to have taken over manufacturing and distribution of the original Texas Instruments patented Klixon bi-metallic switch, whether as an authorized entity or an Asian rip-off doing business in Ohio I don't know. The TI patent has probably long since expired, and I doubt there were ever any grounds to renew it on the basis of improvements. It is basically two bi-metallic disks, slightly dome shaped, welded together that have two bi-stable positions that depend on temperature. TI would take a bowl full of these disks to trade shows and hand them out as freebie toys. You held them in your hand until they warmed up to body temperature, pressed the center of the disk to "snap" it to its other bi-stable position, then casually set it on a table, concave side down, and walked away. When it cooled off sufficiently, it would "snap" back to the other bi-stable position, jumping up several feet into the air while doing so. Lots of fun to watch the reaction from passersby! Too bad I didn't save a bunch of them from the 1970s trade shows I visited.

    BTW, cheap small appliances are almost never worth the time and cost to repair them. Peel off a few bux and go buy another cheap coffee maker instead.
     
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