Thermal Fuse

[mgookin]

Appliances with heaters or timers (or both) are notorious for starting fires, often when not even in use.

Either 60 Minutes or Dateline did a laboratory test back in the 80's or 90's which set up dozens of (maybe 100) coffee makers. Several caught fire without even being in use, just sitting there on a counter.

Having 2 fuses in series provides greater assurance that the circuit will open upon the presence of excess heat as someone previously stated.

 

[ATSman]

Time Clock Solution

Time Clock Solution

Appliances with heaters or timers (or both) are notorious for starting fires, often when not even in use.

Either 60 Minutes or Dateline did a laboratory test back in the 80's or 90's which set up dozens of (maybe 100) coffee makers. Several caught fire without even being in use, just sitting there on a counter.

Having 2 fuses in series provides greater assurance that the circuit will open upon the presence of excess heat as someone previously stated.

That is why I have my coffee maker plugged into a time clock set on an hour window to limit the time that power is delivered to the plug. Problem solved

 

[Tony S]

Sorry, I made a bit of a mess of my last post

Two fuses diametrically opposed makes sense with US domestic supplies. That said, it wouldn’t make sense in the UK.

 

[steve66]

Thermal fuses are supposed to be one time use items, like a regular fuse. But I can testify that they a large percentage of them will remake contact after they cool down. (Just taking a wild guess from my own personal experience, I'd say maybe of 10% of tripped thermal fuses will do this.)

Not good for an appliance like a coffee pot that will start heating again as soon as the fuse remakes contact. It could just cycle on and off over and over again, and thermal fuses were never intended to open and close over and over again, so its hard to tell what could happen.

So I'd say the belt and suspenders approach of using 2 in series makes sense.

 

[Haji]

I see there is a colored end to each element and they appear to be connect 'back to back'.

I noticed that also. I didn't know that T-fuses had 'polarity', but there must be some reason to have one of each direction installed.

The coloring i.e the color code gives size of the fuse, tolerance etc that explains the back to back connection, IMO.

 

[Haji]

No I am addressing it to you, you made some claims I am wondering if you can back them up.

See the post below for information. So not to mess up the posts and then close the thread quoting wrong reasons as usual.:happyno:

I can.

Bunn coffee makers are set up that way. Here is a pic of the thermal fuse replacement kit:

 

[meternerd]

Short story....worked in an electric nuclear test tech shop. We had a coffee maker that quit working....BIG panic. I was the local "fix it" guy, so they begged me to get it working again. Aha! This little silver thingy is open circuited. I'll just jumper it out. Good to go. 15 minutes later, smoke alarms went off....coffee maker was melted and on fire. But boy was the coffee hot! They're there for a reason!

 

[Tony S]

Two fuses diametrically opposed makes sense with US domestic supplies. That said, it wouldn’t make sense in the UK.

A clue;

Have a look how a thermal fuse is constructed and its operation under fault. Then you may get my cryptic comment about US and UK supplies ;-)

 

[K8MHZ]

A clue;

Have a look how a thermal fuse is constructed and its operation under fault. Then you may get my cryptic comment about US and UK supplies ;-)

I have. What I saw was a fusible material and a small spring that would let go and open when the material melted.

I still don't see how that's an explanation. The belt and suspenders approach due to 'hanging' fuses (I have seen that happen with regular current fuses) makes more sense to me.

Please explain. Enquiring minds want to know.

 

[Tony S]

If you read deeper then you will find they are polarity rated.

 

[Little Bill]

Ok, full disclosure!

The coffee pot is mine and yes I worked on it!:happyyes:

It is indeed a Bunn coffee maker and the fuses look just like the photo posted a few posts back. Well except mine do not have colored ends. I guess white is a color so that may not be true.

Anyway I just wanted to know why the two fuses were in series. It kind of makes sense that one is a back up. What I don't understand is why one of mine blew.
We were gone on vacation last week and I unplugged the unit because I didn't feel comfortable leaving it sitting there heating water the whole time we were gone. I wasn't sure how much of the water would evaporate leaving the heater cooking away with little to no water.

When we got back I decided to run a pot of water through it to flush out the water that had been sitting there for a week. I didn't even turn it on I just poured in the water which forces out the water in the reservoir. The next morning I turned it on and let it sit for a while then made a pot of coffee. When I went to check on it I noticed the light for the hot plate/warmer wasn't on. Also the liquid that was supposed to be coffee was cold. I felt of the tank and it was cold so I knew it wasn't working.

I then took it apart and found the open fuse. Since I could see no reason for having two in series I just cut out the bad fuse and crimped the leads together, basically letting the remaining fuse be the protector. It's been heating all week since then and no problems yet.
The fuse appeared to blow/open as soon as the unit was turned on not after it had heated up. So I don't know what happened to it.
I'm just going to let it run and see what happens. If the remaining fuse blows I will put two back in like it was.

 

[mgookin]

Ok, full disclosure!

The coffee pot is mine and yes I worked on it!:happyyes:

It is indeed a Bunn coffee maker and the fuses look just like the photo posted a few posts back. Well except mine do not have colored ends. I guess white is a color so that may not be true.

Anyway I just wanted to know why the two fuses were in series. It kind of makes sense that one is a back up. What I don't understand is why one of mine blew.
We were gone on vacation last week and I unplugged the unit because I didn't feel comfortable leaving it sitting there heating water the whole time we were gone. I wasn't sure how much of the water would evaporate leaving the heater cooking away with little to no water.

When we got back I decided to run a pot of water through it to flush out the water that had been sitting there for a week. I didn't even turn it on I just poured in the water which forces out the water in the reservoir. The next morning I turned it on and let it sit for a while then made a pot of coffee. When I went to check on it I noticed the light for the hot plate/warmer wasn't on. Also the liquid that was supposed to be coffee was cold. I felt of the tank and it was cold so I knew it wasn't working.

I then took it apart and found the open fuse. Since I could see no reason for having two in series I just cut out the bad fuse and crimped the leads together, basically letting the remaining fuse be the protector. It's been heating all week since then and no problems yet.
The fuse appeared to blow/open as soon as the unit was turned on not after it had heated up. So I don't know what happened to it.
I'm just going to let it run and see what happens. If the remaining fuse blows I will put two back in like it was.

Fuse was old & tired? How old is this coffee maker?

 

[K8MHZ]

I think for 9 bucks I would get the OEM pair and put them in with the supplied crimps.

Google has a bunch of stuff about GE and Bunn coffee makers overheating and starting fires.

If I were your neighbor, I would buy you the correct parts and even install them for you. I have put T-fuses in lots of stuff over the years. You don't just use any old crimp connector. The right ones are hard to get. The kits come with the connectors already on the fuses.

If the remaining fuse blows, you have more than fuse problems to worry about, I fear. Still, 9 bucks is cheap insurance. If the OEM fuses blow, you have a fire hazard on your hands that the fuses likely mitigated.