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April 6, 2012

Modifying A Hamilton Beach Single-Cup Coffee Maker To Make Real Coffee

Hamilton Beach single cup coffee maker

Hamilton Beach single cup coffee maker

In my quest to make our coffee drinking more coffee-efficient, I recently purchased a single-cup coffee machine by manufacturer Hamilton Beach, when it was on sale for $49.95 at Canadian Tire. Unfortunately, after some testing, I found that this coffee maker made coffee far too weak for my taste, even using its “bold” setting. It was forcing water through the wire mesh filter system at too high a flow rate. Here’s the modification that I did to it to cause it to make better coffee.

First, the short story. This coffee maker is driven by electronics that use the SN8P2501BPB microprocessor, on the main circuit board inside it. I didn’t see any way to change its timing or output power from any programming means that I could easily access, but I found that simply by effectively chopping the applied power to the heater element in half using a series 1N4142 diode with the heater element (many other diode substitutes would also work), the end result was exactly the much stronger coffee that I desired, without needing to increase the amount of coffee grinds used per serving. A wonderfully easy mod that did the job.

Next, here are some details and pictures of how to do this modification. As you probably already realize, the purpose of the series diode that you will be inserting is to effectively chop out half the applied AC duty cycle. That IN4142 diode I used had a reverse voltage rated at 400V and a max forward current of a few amps. I was a bit leery of the current rating but I tried it anyway since I had it onhand within my parts bins. First, unplug the unit, remove all the filters, and drain any remaining water in the system by inverting the coffee maker over a sink. Then, with the unit on its side on a workbench surface (maybe put an old towel underneath to prevent marring the external finish on the machine) remove the 4 screws in the base.

Coffee Maker Base

Coffee Maker Base

3 of those screws are Philips screws, but the fourth was a weird slotted-head screw but with a barrier in the middle to make it hard to remove. Much as with this earlier repair of a toaster, this was likely intended to prevent users from dis-assembling the thing, but I am not easily foiled. I used an old standard screwdriver and light taps on the screwdriver with a hammer to rotate that screw out far enough that I could grab it with pliers and turn it the rest of the way out. Ha! Had I been in less of a hurry for caffeine, I probably would have used a more elegant solution, such as sawing a notch in an old standard blade screwdriver to fit the screwy anti-tamper screw.

The Anti-tamper Screw

The Anti-tamper Screw

With the bottom cover removed, I could see inside easily. After removing several more Philips-head self-tapping screws, I could access the circuit board with the microprocessor on it. I had to take out one more screw to access the board for soldering.

coffee maker internals

coffee maker internals

Per the picture below, the white lead soldered into the board in the upper right in the photo, going to the heater assembly, looked like a good candidate for inserting the series diode that I wanted to use to chop the power to the heater in half. I desoldered that lead, soldered one lead of the diode in its place on the board, and soldered the previously-removed heater wire to the other lead of the diode. Prior to doing that, I had slipped some heat shrink tubing over the lead. After completing the soldering, I slid that tubing back down over the solder connection to the diode. Note that this connection is well away from the heater when in use; the solder connection and the heat shrink are not exposed to much heat during operation.

coffee maker circuit board

coffee maker circuit board

After careful reassembly, I tested out the modded coffee maker. Success! Real, strong coffee. I now use either the “Regular” or “Bold” setting on the coffee maker, and while that now takes a bit longer than before the mod to brew a cup, I much prefer the minor wait over the feeble coffee that this machine made out of the box. With the mod, for tall cups, you might find that in “Regular” mode, the machine shuts off a bit early, but you can just hit the Regular button again to complete the brewing. That post-mod problem doesn’t seem to occur for “Bold”.

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