But water boils at different temperatures. At my elevation water boils at 203.4˚ F. The sensor can not heat enough to make the pot think it needs to be cleaned.

I believe that in most home coffee makers, the expansion of water/steam as a result of heating is used to push the water from the bottom of the machine up to the top. The place where water is boiling is significantly above local atmospheric pressure - the pressure where water is heating is determined in part by the weight of the water above it and by any flow restrictions which slow that water down as it tries to make its way towards the bed of coffee grounds. I don't have any hard data, and perhaps I'm overestimating these effects, but I think the water boils at a higher temperature than your elevation would lead you to believe.

And if you consider the possibility of using a time base to measure how fast water boils, in America, some homes are running close to 110 VAC at the outlet while others (some of the places I've been) can measure 119 VAC. Given the difference in voltages, the wattages will vary enough to cause the so called sensors problems deciphering when it's time to be cleaned.

Sorry, just having a hard time believing there's a simple way for a pot to know when it's time to be cleaned.

It sounds like temperature, not time, is the determining factor in this system, so the small differences in voltage shouldn't impact performance of the cleaning light system.

 

-0.00189 x altitude + 212 ( ˚F ) is how you determine the boiling temperature at any given altitude. I'm at 4550 feet above sea level.

-0.00189 x 4550 = -8.5995
-8.5995 + 212 = 203.4˚F, the temperature water boils at that altitude. Since this is not a closed system there is no practical change in water pressure on the boiler. It takes 27 inches of water (column) to raise pressure one pound. (given that I'm in the US, the American Standard Measurement of atmospheric pressure at sea level is about 14.7 pounds, so one pound would represent about 1/15th of one "atmosphere", by no means anything other than an insignificant change in pressure) The tank in my boiler holds about 6 inches of water, so there's not a significant change in pressure (by weight). Given that one end of the boiler is directed to the coffee grounds, there's no rise in pressure. Pressure cookers work by raising the internal pressure so that the water actually gets hotter. If you've never seen a boiler explosion I'd suggest you google it - it's a very interesting and impressive watch. (mythbusters blew up a water heater a couple times) The point about a boiler explosion is that once the boiler begins to fail the pressure falls. The falling pressure causes the water to flash over to steam. The crack widens and the explosion cascades into a spectacular event. Since a coffee boiler is not a closed system - you're not going to have an explosion in your kitchen. The point I'm getting at is that there is no rise in pressure in the boiler, so I disagree that the pressure is any higher.

The most plausible explanation (and one I don't quite subscribe to) is the notion of a pump and the BEMF providing a measurement for when the plumbing is so encrusted with scale that it begins to restrict flow. Since coffee tastes like crap LONG before your pot gets THAT encrusted I tend not to accept that explanation either.

Bottom line, I don't think home coffee brewers have the sophistication to know when a brewer has been cleaned. Just like the filter reminder in my fridge that tells me it's time to change the filter in the drinking water system, I think the "Clean" light comes on after so much time. Just my opinion. And I've been wrong before, but this is my argument and for now I'm sticking to it. But I love the debate.

 

I don't believe coffee makers get that hot (boil). Bunn says the ideal temperature to Brew coffee is 195 degrees.

 

"Bottom line, I don't think home coffee brewers have the sophistication to know when a brewer has been cleaned. Just like the filter reminder in my fridge that tells me it's time to change the filter in the drinking water system, I think the "Clean" light comes on after so much time."

Tony, exactly, same here. However, on my fridge after I change the water filter my clean light stays on until I push the reset button. After I clean my coffee maker the clean light does not come back on. Crazy.

 

Just like the filter reminder in my fridge that tells me it's time to change the filter in the drinking water system, I think the "Clean" light comes on after so much time. Just my opinion. And I've been wrong before, but this is my argument and for now I'm sticking to it. But I love the debate.

Ok, I may be overestimating the pressure differentials within a coffee machine (you didn't discuss the back-pressure in the system as a result of flow restrictions through small orifices, but perhaps that too is a smaller contribution than I think at the low flow rates of a home coffee maker.)

Nevertheless, clearly the machine is sensing something:

However, on my fridge after I change the water filter my clean light stays on until I push the reset button. After I clean my coffee maker the clean light does not come back on. Crazy.

Reading through the manual for the machine it specifically says that after a cleaning cycle, if it was effective the light will stay off, but if it wasn't effective the light will come on again telling you it needs more cleaning. So, the machine is clearly sensing something related to scale build up. It may be true that this feature wouldn't trigger at the right level at high elevations, but it's clearly more than a timer like the ones for filter changes.

I've got to run out the door for work now, but I'll be back with more shortly...

 

I don't believe coffee makers get that hot (boil). Bunn says the ideal temperature to Brew coffee is 195 degrees.

Typical home drip brewers work differently than commercial brewers and a very small number of home brewers from Bunn, Bonavita, and a few others.

Bunns have a tank full of water that is heated to the desired temperature, regulated by a thermostat. When you add water, the cold water you've added displaces the already-hot water which is forced through a shower head and through your coffee grounds. This is the essence of most office and restaurant coffee brewers until fairly recently as well.

In typical home coffee makers, there is no hot water until you start brewing. Then, the boiling of a very, very small amount of water is used to force water through a skinny tube to the top of the machine. The machine can't function without boiling water. Because of this you can't control temperature, which is a shame.

Small differences in brew temperature make big differences in flavor (195-205F is generally considered the ideal range, but within that range it's personal preference, and different coffees taste better at different temperatures.) On commercial machines and the few comparable home machines, you can fine tune temperature to suit your tastes, but with a typical home coffee maker, there's nothing you can do to change the brew extraction temperature.

The link below provides a really good description of how typical home coffee makers work:

https://home.howstuffworks.com/coffee-maker1.htm

 

As for temperature sensing to detect a scaled up heating element, it makes perfect sense:

When a heating element is immersed in water, the heating element can only get so hot. Convection currents keep the water moving, and boiling water off as steam prevents the water touching the element from getting significantly above the boiling point. As such, the outer surface of the element is limited to very close to the boiling point.

The thermal resistance of the materials in the heating element determine the temperature gradients from the outer surface to the resistive coil inside the element. An equilibrium is quickly reached with the internal temperature of the element limited to some predictable temperature above the boiling point.

If you run out of water, the cooling effect of ambient air is much less effective, the outer surface of the element can continue heating well above the boiling point, and the internal temperature of the element can rise as well, often with disastrous consequences.

Similarly, if you cover the outside of the immersed element with scale buildup, it acts as an insulator. The outside of the scale buildup is limited to near the boiling point, but now there's a temperature gradient across the thickness of the scale buildup, so the element itself gets hotter before the water boils. If you let the scale get thick enough, this too will cause an element to overheat to the point of failure. These are even more fun than the dry tank failures! (really, I've got lots of souvenirs from my coffee tech days - these things make abstract art sculptures sometimes when they fail!)

The physical layout will be different in a home coffee maker than in a commercial brewer's immersed element, but the effect of scale build up as an insulator, and the increased temperature gradients between water temperature and heating element temperature will still exist. If they have sensors or switches placed in a way to detect rising element temperature relative to rising water temperature, they can detect scale buildup.

 

Been following this, but not any kind of"expert". Couldn't the cleaning sensor be a simple as two electrodes a set distance apart? When the pot is clean, the water would allow a certain amount of current to flow between the electrodes. When the pot is"scaled up", in need of cleaning, that current is less than is normally expected, turning on the 'clean' light. If on the next cycle of use it reads the proper current, light goes off. If not light stays on.

This could be proven by using deionized/distilled water with a clean pot. Since distilled water dosen't have the minerals in it to conduct as well as tap water, using it 'should', by my theory, turn the clean light on. And to be honest it is just my theory of this.

 

on my fridge after I change the water filter my clean light stays on until I push the reset button. After I clean my coffee maker the clean light does not come back on. Crazy.

Not sure, but your clean light ? ? ? is it a button you push to put it through a clean cycle?

Honestly, this whole thing is somewhat beyond my experience and knowledge. Best I can offer is an opinion based on rational thought and reason. But sometimes that fails me. Sometimes I sound like a fool. Oh well. When I'm wrong - I own it. Bottom line here on this thread - I don't know why your light seems to come on when you cancel it time and again but doesn't come back on after you've cleaned it. I THINK that's kind of what you said. So the little microprocessor that's probably in there can be smart enough to monitor buttons and when you cancel the light versus when you put it through a clean cycle.

Hope you get a satisfactory answer. I'll be watching, but probably not adding much if anything more here. For now - Merry Christmas. Only 24 shopping days left.

 

"Not sure, but your clean light ? ? ? is it a button you push to put it through a clean cycle?"

Tony, the only thing the "clean button" does on my Cuisinart is shut off the light. Ill wait till it comes on next time and monitor it more closely.

 

As for temperature sensing to detect a scaled up heating element, it makes perfect sense:

When a heating element is immersed in water, the heating element can only get so hot. Convection currents keep the water moving, and boiling water off as steam prevents the water touching the element from getting significantly above the boiling point. As such, the outer surface of the element is limited to very close to the boiling point.

The thermal resistance of the materials in the heating element determine the temperature gradients from the outer surface to the resistive coil inside the element. An equilibrium is quickly reached with the internal temperature of the element limited to some predictable temperature above the boiling point.

If you run out of water, the cooling effect of ambient air is much less effective, the outer surface of the element can continue heating well above the boiling point, and the internal temperature of the element can rise as well, often with disastrous consequences.

Similarly, if you cover the outside of the immersed element with scale buildup, it acts as an insulator. The outside of the scale buildup is limited to near the boiling point, but now there's a temperature gradient across the thickness of the scale buildup, so the element itself gets hotter before the water boils. If you let the scale get thick enough, this too will cause an element to overheat to the point of failure. These are even more fun than the dry tank failures! (really, I've got lots of souvenirs from my coffee tech days - these things make abstract art sculptures sometimes when they fail!)

The physical layout will be different in a home coffee maker than in a commercial brewer's immersed element, but the effect of scale build up as an insulator, and the increased temperature gradients between water temperature and heating element temperature will still exist. If they have sensors or switches placed in a way to detect rising element temperature relative to rising water temperature, they can detect scale buildup.

I think your on to something here. I would like to tear that sucker apart.

 

@ebeowulf17 Populr Mechanics did a recent review and teardown of the Mocamaster. http://www.technivorm.com/ It's unlike most coffee makers in many ways. They created a design long ago and it's the same one being produced today. Not a bew Coffee maker a year sort of thing.

Take a Shop-Vac. What can really be different? I have a small one (Model 500) that's like 40 years old. I could still get a motor assembly for it, It's more like a tip-and-tell, but I like it because it's small. Only about 5 gallons. The filters fit, today's attachments fit. Stupid #1: The center of gravity is off especially with a long skinny hose (designed for power tools). So, you pull on the hose, the canister tips and spills it;s contents, I upgraded the latch, so that's fixed. The hose/wand is basically one piece so the straight portion is molded onto the hose which does detach from the base. It leaves at the standard 2.5" diameter or so, but the plug-in hose abruptly makes a 90 degree angle and this big stuff catches there. I use a straight longer hose now which does make it easier to tip.

There is a removeable foam filter for dry stuff and a big ball check valve for when it tips.

One drawback is that the motor assembly and deck are all one piece with impossible to replace brushes. The replacement deck broke after a few months. A loose wire (spot welded). It really didn't have enough slack.

The new stuff may have five extending legs instead of 4, better filters, and even allow a power tool to plug into it. When the power tool turns on, the vacuum cleaner does too.

What would help is a brush monitor that detects brush wear like the Bosch Demolition hammers use. If the light comes on, you might have about 10 hrs left before the unit needs to have them replaced. The tool will stop until the brushes are replaced.

For those that don't know, Bosch has re-build manuals. I rebuilt mine without the manual. I had to ask a shop ( I used a rental store) to remove the chuck for me.

Fixing stuff isn't an option any more. A can-opener has to be replaced because all it needs is a cutting blade.

They use a connical drip tube to extract the flavor from the coffee. They claim that the earlier drips (vertical) are different than the lower portion The heating chambers are copper. They make a distinction between those you like their coffee black and those that a cold creamer. The keep warm temperature is higher.

It was a really cool description for nerds. I can't really drink coffee anymore. I get headaches most of the time. It is coffee brand specific and it's most coffees. Ironically, 7-11 coffee can sometimes make a migraine better. Dunkin Donuts coffee is really bad. Before Dunkin donuts bought M. Donut, I could drink Mr. Donut's coffee.