Thermal fuses....why do coffee makers use two in series?

[nevetslab]

Where did you get the hose and what kind?

McMaster-Carr, stk # FC-28492790 Silicone Rubber Hi Temp tubing, 3/8" ID x 1/2" OD

I found one morning, upon making a fresh pot, there was only a little bit of coffee in the pot, then noticed the lake of water all over the top of the filing cabinet, and a growing puddle on the floor.

[nevetslab]

Just for your information...

Before I retired, one of my responsibilities as an electrical engineer was protecting my large, wealthy corporation from insurance companies who wanted to blame us for fires to get their settlement money back, or attorneys for bad electricians trying to shift the blame off of their clients.
I would investigate the site where the damage occurred and then when all of the suspicious evidence was gathered we would meet in a lab somewhere to do the forensics.

Guess what were the number one devices, by far, that lined the shelves in all these labs where all of the evidence from different fires was stored.
Yes, coffee makers, especially the same kind shown in your pictures. Row after row of them. (space heaters were number two)

I never lost a case, but the coffee maker guys did in the past. That is why you see so many thermal cutoffs. You really should either remember to turn it off or at least put it on a 24 hour timer.
By the way, you could turn it off after it brews and microwave it when you want to drink it. It tastes better that way, unless you are one of those people who like it well done.

Steve

I'm not surprised. My previous coffee maker was a Krups, whose thermal fuses both opened, one being a 216 deg C, the other a 240 deg C. Replaced them both, had to do that twice, and after the second time, when it stopped working, the hot plate had melted down into the base of the maker, again opening up the thermal fuses.

You make a good point, putting this on a timer. I'd make that a 10-12 hr setting, resetting every morning, and, if I forget when leaving for the day, it would shut off shortly. While there is ONE microwave oven in the building, it's at the opposite end and upstairs. Not convenient. As it is, I only pour half a cup, get a few sips of it, then by the time I go to sip again, it's cooled off, and gets poured back into my pot for another shot of half a cup. The pot sits right next to my computer at the front of the small filing cabinet, so quite convenient. I'll fetch a timer, though......like that idea.

[J M Fahey]

Well, my shop and half my home burnt because I forgot to turn OFF my homemade speaker glue drying oven, capable of curing 12 x 10" or 6 x 12" speakers in a single sitting.
I have only myself to blame

Since then and actually in this very moment I cure epoxy on a hot plate, 2 meters away from my speaker assembly/reconing bench, in smaller 2 x 15" / 3 x 12" / 4 x 8" or 10" batches.

And if I am not in the room I turn it OFF, period.

In any case I am not selling that many of them

[Bill Moore]

I have a Proctor Silex timer assy from a long dead coffee pot, installed into a RS box with a short extension cord in, and out, starts the coffee whenever you tell it. When I do need to replace a coffee pot, I buy the one without a timer!
It only stays on for 2 hours, so if I forget, it's OK, if you need to keep it going, switch off and then on, good for another two hours.

[The Dude]

I drink more coffee than is probably legally allowed. So, I have a shelf of coffee pots in rotation. When one stops working, I grab another. Then, fix the broken one and put it back in "stock". It's good to have spares.

[J M Fahey]

So you justify having a house or room filled to chest height with dead stuff which "can" be useful one day?.
I see, I see.
I mean, I see I can invite you inside my home

I have the faint suspicion I might also invite a few others from around here

[g1]

It helps to have some out-buildings that you can also try to fill up.

[nevetslab]

Well, my shop and half my home burnt because I forgot to turn OFF my homemade speaker glue drying oven, capable of curing 12 x 10" or 6 x 12" speakers in a single sitting.
I have only myself to blame

Since then and actually in this very moment I cure epoxy on a hot plate, 2 meters away from my speaker assembly/reconing bench, in smaller 2 x 15" / 3 x 12" / 4 x 8" or 10" batches.

And if I am not in the room I turn it OFF, period.

In any case I am not selling that many of them

OUCH!!!!!! I've been lucky in that regard all of my technical career. I did loose all of my stored belongings back in the mid-70's when the company's PCB fabrication equipment was left on and burnt up half the building and ruined a close friend's wood shop assets in that fire. My loss in that fire wasn't so significant....mostly lost my oboe sheet music, band's lyric sheets and a 0-450V 200mA Lambda Tube Power Supply. These days, other then the occasional forgetfulness with the coffee maker being left on, all but my Topaz 5kVA isolation xfmr remains turned off. It is at least on a breaker, and is barely warm to the touch on it's core. 240VAC input, 120VAC output, feeds my 30A 0-140VAC Variac/Power Analyzer. So, actually the input to that variac is on, as is a 0-140V 20A GR Variac, on a separate breaker.

[Uzziah]

Noob here, at least to this forum. Joined and posting because I sense some kindred spirits here…

The wife has an old 4-cup Mr Coffee that suddenly quit working. It has the two thermal cutoff fuses in series, in this case SF-214E, 10A 250V.

Other than a poorly-designed part of the swing-out filter basket, it has been very reliable and helps keep me from drinking too much coffee.

This morning the light came on as usual, but the heating element didn’t, so no brewing, of course. Tossing a meter across the fuses revealed that both of them were open. Both are tied together between the resistor and the load.

My first thought was to replace them, but then I started wondering what the odds were that both of them would blow in the usual course of events? Seems like the more typical thing would be that one fails just before the other, and once it blows, the load is gone so the other survives. With them both blowing simultaneously it almost seems like there’s something greater that has failed, so that if I take the time to fix it, they’ll probably both blow again right away.

I’m definitely a fix-it guy, but at the same time I would just as soon retire this one and start using the 12-cup we have in the garage (“for when company comes”). Plus if I tell the wife I can replace the fuses and it just blows them right away, she’ll ask me why I told her I could fix it, why I wasted the time and money on it, etc.

Thoughts? Opinions?

[The Dude]

They use 2 because it's cheaper to meet UL specifications with two lower cost devices than a single more expensive device. There are exceptions, of course, but this is my experience. My views on this have changed since my last post. I've tried multiple times to replace those thermal cutoffs and they don't usually last long. I've not explored why. It could be the thermal switch that controls temperature does not open. It could be a partially shorted heat element, etc. Regardless of why, I just don't bother anymore. I'll just go buy another cheap coffee maker. That said, if you have a more expensive coffee maker that you like, it might be worth a shot. You might try heating up the thermal switch with a heat gun and see if it opens before firing up. If the switch sticks on, the temp will run away and likely blow the fuses again. I just go buy another 15 dollar coffee maker at Wallyworld.