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Topic: Alpenrost death, part II (13 msgs / 339 lines)
1) From: Gak
Thanks to all those who struggled with me to determine if the transformer
was the problem.  To those who argued that it seemed unlikely- take a bow.
I ordered a new transformer (a $2.49 investment!) and quickly discovered
that it didn't help.  What I didn't realize until I looked harder was that
the power in splits off before going to the transformer.  Power from wall,
yes.  Power to xfmr, no.  Once I realized that, it was easy to trace the
real problem: thermal fuse.  It's hidden up under one of the sides of the
unit, away from everything else.
Tomorrow I head to radio shack, as their website indicates that they have a
141C thermal fuse to replace the 142C fuse that blew.
Can anyone tell me if there's an issue replacing a 10A thermal fuse with a
15A one?  For a thermal fuse, I can't see it making a difference.
Thanks again for the assistance - I'll report in if I get the monster back

2) From: Rick Farris
Garrik said:
with a 15A one?
I poked around the web a little bit and found this page:http://www.elcut.com/glossary.htmlwhich includes this entry: 
Rated Current : The allowable maximum current which a Thermal Cutoff
Fuse is able to carry. 
I'd say you're fine.
-- Rick

3) From: jim gundlach
I would have to disagree.  The thermal fuse breaks the circuit when the 
temperature reaches the critical point.  There are other electrical 
fuses that break the circuit when too much electricity flows causing a 
potential fire.  They put the 10 amp thermal fuse in because that is 
all that was needed and was cheaper than the 15 amp that Garri can find 
locally.  Using the higher amp thermal fuse is just like using heaver 
wire than necessary.  It is more expensive, especially if you are 
making a lot of them, but it is not like putting in a higher capacity 
electrical fuse.
Jim Gundlach
On Dec 3, 2003, at 1:42 PM, John Cramer wrote:

4) From: John Cramer
Replacing a 10amp with a 15amp can create a fire hazard.
It'll take more amperage til it cuts off than some other 
part(s) can carry easily. It/They can heat up and start a
Gak wrote:

5) From: miKe mcKoffee

6) From: Johnny Kent
FWIW: Isn't the 'thermal' part of the 'thermal fuse'  that it melts (and so
opens the circuit)
at the rated fusing current (which varies but is often 1.5 to 2 times the
rated working current).
So going to 15A is not wise unless you know what you are doing.
It 's the ambiguity of the term 'thermal fuse' but since the rating is amps
not degrees
 that would indicate a regular fuse that melts when too much current passes
for long enough.

7) From: john roberts
The ampere rating is related to it's ability to safely carry and/or break a
certain current. The actual temperature at which it trips will be specified
independent of that.
I can't imagine any problem from substituting a higher current capacity part
as long as it is physically similar in size and will fit in the same
location. If it is physically larger and touches other parts it didn't
before, conducted heat transfer either toward or away from it could alter
the trip behavior.
There may be some confusion with "Thermal Circuit Breakers", a class of
current interrupters that are in fact rated in amperes where such a
substitution would be inappropriate. In their case the "thermal" refers to
the actual mechanism that opens the switch and while they will vary somewhat
with ambient temperature, current is the dominant mechanism.
To further add confusion there is such a thing as a thermal fuse that is
self resetting when it cools, but even then they are commonly called
resettable thermal "fuses".
I hope this adds more clarity than confusion. Proper use and maintenance of
safety componentry is important.

8) From: miKe mcKoffee
No no no. A thermal fuse is rated in temperature C and/or F to blow at a
given ambient temperature. PLUS current rating for desired application
tolerances. An extension cord has an amperage rating, does that mean it's a
fuse? Thermal fuses are not designed as a current protection device, they
are a temperature protection device. Same type of things used in clothes
dryers to protect against over heating and burning clothes... open your
phone book, pick up your phone tomorrow and call an electrician or better
yet appliance repair person to verify if you wish. MM

9) From: Johnny Kent
Well that's definitive then. :)
In which case I agree with the original poster it doesn't matter
if you up the current rating since its over-temperature that's being
protected against.  J

10) From: Rick Farris
John writes:
And you're still wrong.  A thermal fuse opens when it gets too hot, not
when it passes too much current.  The current rating on a thermal fuse
is simply the amount of current it is capable of safely carrying, not
the current at which it opens.  
The word "thermal" in "thermal fuse" is significant, it means that
you're dealing with an entirely different device than the one of which
you are thinking.
-- Rick

11) From: Rick Farris
Jonny added:
No.  That's a description of a NON-thermal fuse.  A NON-thermal fuse
opens when it's rated current (actually, as you mentioned, usually
somewhere beyond it's rated current) passes through it.  
A THERMAL fuse, on the other hand, opens when it's THERMAL TEMPERATURE
rating is exceeded.
The reason thermal fuses have a current rating is because of this:
Suppose that you are trying to protect a 5-horsepower motor from
overheating.  Such a motor would (off-the-cuff here) draw forty or fifty
amps.  Because a thermal fuse is in the path of the current supplied to
the motor, it, too, would have to be able of carrying that 50-amp load.
That means that it would have to be physically large, perhaps the size
of, say, a shotgun shell.
Now, consider the opposite case; where you're trying to protect a little
popcorn-popper fan motor.  There you're working with a maximum current
of less than 10 amps, so the fuse itself can be smaller.  You could just
have a one-size-fits-all shotgun-shell sized thermal fuse, or you could
make a series of thermal fuses, each working at a different rated
current, and sized appropriately for the expected load.
But all of them: 100-amp, 50-amp, 40-, 30-, 20-, and 10-amp would blow
at the same temperature.
-- Rick

12) From: John Cramer
Listen to yourself. "Using the higher amp thermal fuse is 
just like using heaver wire than necessary." Using a
heavier wire means it'll carry more electricity through to
some parts that may not be able to handle it. My warning
jim gundlach wrote:

13) From: John F. Coffey
Interesing discussion.  Ummm is not the purpose of a THERMAL FUSE to 
fail when the temp reachs and exceeds a give temp ??
If that is the case... I can see where replacing a fuse with one that 
is 50 degrees higher in cutoff is a problem.
I can see where replacing a fuse with a lower amp rating would be a problem ..
But I can't see a case where replacing a THERMAL fuse with the SAME 
THERMAL rating and a HIGHER AMP rating would be a problem.
To me the key word here in this fuse scenario is THERMAL. No where 
did anyone say anything about changing the THERMAL rating of the 
Just my 2 cents worth .. which isn't worth much ...

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