SWMBO went to make a pot of coffee with our Bunn coffeemaker and
reported to me that the water which flowed through the ground coffee was
cold.

I checked for the obvious and then drained the unit and took it down to
my basement shop for a look see.

I quickly found the problem was an open 141 degree C thermal fuse
mounted on top of the heater tank. That fuse was the first thing in
series with the hot side of the power cord and fed everything else in
the coffeemaker.

But, I was surprised to find that there wasn't just one thermal fuse
there but two identical ones in series, clamped to the top of the tank
within a millimeter of each other.

I resisted the temptation to bypass the open thermal fuse and was
pleased to find that the Radio Shack store a quarter mile from our home
stocked them. Fifteen minutes later I was back home with a new $1.99
thermal fuse, installed it and the Bunn was back in business.

But why does Bunn use TWO identical thermal fuses in series? Are those
little suckers so unreliable that they felt the need to use two in case
one of them failed to open when the tank temperature soared because of a
stuck thermostat?

My curious mind wants to know.

Thanks guys.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

Jeff Wisnia wrote:
SWMBO went to make a pot of coffee with our Bunn coffeemaker and reported
to me that the water which flowed through the ground coffee was cold.

I checked for the obvious and then drained the unit and took it down to
my basement shop for a look see.

I quickly found the problem was an open 141 degree C thermal fuse mounted
on top of the heater tank. That fuse was the first thing in series with
the hot side of the power cord and fed everything else in the coffeemaker.

But, I was surprised to find that there wasn't just one thermal fuse
there but two identical ones in series, clamped to the top of the tank
within a millimeter of each other.

I resisted the temptation to bypass the open thermal fuse and was pleased
to find that the Radio Shack store a quarter mile from our home stocked
them. Fifteen minutes later I was back home with a new $1.99 thermal
fuse, installed it and the Bunn was back in business.

But why does Bunn use TWO identical thermal fuses in series? Are those
little suckers so unreliable that they felt the need to use two in case
one of them failed to open when the tank temperature soared because of a stuck thermostat?

My curious mind wants to know.

Thanks guys.

Jeff


Could be a positioning strategy...

http://forum.allaboutcircuits.com/sh...ad.php?t=40819

the manufacturer of the coffe maaker is using a beltsand suspender approach to make certain they never cause a failure.

purchased in bulk the extra fuse likely cost under 25 cents

On 11/2/2013 9:36 PM, bob haller wrote:
the manufacturer of the coffe maaker is using a

belts and suspender approach to make certain they

never cause a failure.

purchased in bulk the extra fuse likely cost

under 25 cents

Cheaper than fire liability claims?

--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Sun, 03 Nov 2013 02:58:59 -0500, Stormin Mormon
wrote:

On 11/2/2013 9:36 PM, bob haller wrote:
the manufacturer of the coffe maaker is using a

belts and suspender approach to make certain they

never cause a failure.

purchased in bulk the extra fuse likely cost

under 25 cents

Cheaper than fire liability claims?
At the factory door in China, closer to $0.025.

On Sat, 2 Nov 2013 18:36:54 -0700 (PDT), bob haller
wrote:

the manufacturer of the coffe maaker is using a beltsand suspender approach to make certain they never cause a failure.

purchased in bulk the extra fuse likely cost under 25 cents

Probably more (I've been trying to something that cheap).

They're probably in series because they aren't very reliably and
lawyers are expensive.

Most probably.

In order for Bunn to sell that Coffee Maker in the USA, it has to make it past UL, or Underwriter's Laboratories. In Canada, it has to be approved by CSA, or the Canada Standards Association.

If Bunn comes to them with a coffee maker that has a single thermal fuse and says "We want to sell a million of these things in the USA", UL is going to think: "If that thermal fuse doesn't open to shut off power to the heating element if the thermostat sticks, then we have a potential fire. Even if only one in 100,000 thermal fuses fails to blow, we're still talking about 10 potential fires. For the few cents that a second thermal fuse costs, it buys a lot more security that power will be shut off to this thing if it gets too hot." After all, the chances of one thermal fuse not blowing are low, but the chances both won't blow are miniscule, and therefore worth the few cents that a second thermal fuse is gonna cost.

So, most probably UL told Bunn they wanted a second thermal fuse in that coffee maker just to be on the super safe side or Bunn designed it with two thermal fuses just to streamline the approval process.

On Sat, 02 Nov 2013 20:19:26 -0400, Jeff Wisnia
wrote:


I resisted the temptation to bypass the open thermal fuse and was
pleased to find that the Radio Shack store a quarter mile from our home
stocked them. Fifteen minutes later I was back home with a new $1.99
thermal fuse, installed it and the Bunn was back in business.

How did you attach the thermal fuse? I'm afraid to solder them, and I
seem to have nothing good with which to crimp them.

On Sun, 03 Nov 2013 01:33:46 -0400, micky
wrote:

On Sat, 02 Nov 2013 20:19:26 -0400, Jeff Wisnia
wrote:


I resisted the temptation to bypass the open thermal fuse and was
pleased to find that the Radio Shack store a quarter mile from our home
stocked them. Fifteen minutes later I was back home with a new $1.99
thermal fuse, installed it and the Bunn was back in business.

How did you attach the thermal fuse? I'm afraid to solder them, and I
seem to have nothing good with which to crimp them.

Soldering is no problem. Be quick, with a hot iron.

wrote:
On Sun, 03 Nov 2013 01:33:46 -0400, micky
wrote:

On Sat, 02 Nov 2013 20:19:26 -0400, Jeff Wisnia
wrote:


I resisted the temptation to bypass the open thermal fuse and was
pleased to find that the Radio Shack store a quarter mile from our home
stocked them. Fifteen minutes later I was back home with a new $1.99
thermal fuse, installed it and the Bunn was back in business.

How did you attach the thermal fuse? I'm afraid to solder them, and I
seem to have nothing good with which to crimp them.

Soldering is no problem. Be quick, with a hot iron.

Yep, that's just what I did.

I thought about using a pair of long nosed pliers with a rubber band
around the handles as a heat sink between the solder point and the fuse
body, but didn't bother.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

On Sun, 03 Nov 2013 12:00:42 -0500, Jeff Wisnia
wrote:

wrote:
On Sun, 03 Nov 2013 01:33:46 -0400, micky
wrote:

On Sat, 02 Nov 2013 20:19:26 -0400, Jeff Wisnia
wrote:


I resisted the temptation to bypass the open thermal fuse and was
pleased to find that the Radio Shack store a quarter mile from our home
stocked them. Fifteen minutes later I was back home with a new $1.99
thermal fuse, installed it and the Bunn was back in business.

How did you attach the thermal fuse? I'm afraid to solder them, and I
seem to have nothing good with which to crimp them.

Soldering is no problem. Be quick, with a hot iron.

Yep, that's just what I did.

I thought about using a pair of long nosed pliers with a rubber band
around the handles as a heat sink between the solder point and the fuse
body, but didn't bother.

If you've got the space to do that, they work fine. Forceps are the
perfect tool for this. For $5 at Harborfrieght, can't go wrong.
Harborfrieght is good for some things.

On Sun, 03 Nov 2013 12:00:42 -0500, Jeff Wisnia
wrote:

wrote:
On Sun, 03 Nov 2013 01:33:46 -0400, micky
wrote:

On Sat, 02 Nov 2013 20:19:26 -0400, Jeff Wisnia
wrote:


I resisted the temptation to bypass the open thermal fuse and was
pleased to find that the Radio Shack store a quarter mile from our home
stocked them. Fifteen minutes later I was back home with a new $1.99
thermal fuse, installed it and the Bunn was back in business.

How did you attach the thermal fuse? I'm afraid to solder them, and I
seem to have nothing good with which to crimp them.

Soldering is no problem. Be quick, with a hot iron.

Thanks.

Yep, that's just what I did.

I thought about using a pair of long nosed pliers with a rubber band
around the handles as a heat sink between the solder point and the fuse
body, but didn't bother.

Thanks. I have a little set of 5 heat sinks, spring clips in two
sizes, one with the jaws bent 90^, and a fifth one with a metal clad
magnet connected to it. I also have forceps that I got at a
hamfest. But it sounds like I can do without all that if I'm quick,
and I'm quick if I try to be.
Jeff

On Saturday, November 2, 2013 5:19:26 PM UTC-7, Jeff Wisnia wrote:

SWMBO went to make a pot of coffee with our Bunn coffeemaker and
reported to me that the water which flowed through the ground coffee was
cold.

I quickly found the problem was an open 141 degree C thermal fuse
mounted on top of the heater tank. That fuse was the first thing in
series with the hot side of the power cord and fed everything else in
the coffeemaker.

But, I was surprised to find that there wasn't just one thermal fuse
there but two identical ones in series, clamped to the top of the tank
within a millimeter of each other.

They probably used 2 thermal fuses in series to avoid the problem GE
had with many of its drip coffee makers produced from 1976-1984
causing house fires when their single thermal fuse failed to melt:

http://www.cpsc.gov/en/Recalls/1991/...A-Fire-Hazard/

soldering thermal fuses leads to premature failure. it stresses the fuses.

I service roll laminators for a living, one manufacturer had mass thermal fuse failures, traced back to soldering them.

there are crimp connectors made just for thermal fuses

On Sun, 3 Nov 2013 09:13:29 -0800 (PST), bob haller
wrote:

soldering thermal fuses leads to premature failure. it stresses the fuses.

I service roll laminators for a living, one manufacturer had mass thermal fuse failures, traced back to soldering them.

there are crimp connectors made just for thermal fuses

Thanks!

On Saturday, November 2, 2013 at 7:19:26 PM UTC-5, Jeff Wisnia wrote:
[...]
But why does Bunn use TWO identical thermal fuses in series? Are those
little suckers so unreliable that they felt the need to use two in case
one of them failed to open when the tank temperature soared because of a
stuck thermostat?

My curious mind wants to know.


I suspect they are so cheap that it makes sense to use several
since they each detect heat only in one very small location. Plastic
appliances are quite a fire risk and can turn into balls of flame.