Help with thermal fuse specs?

D

DaveC

Guest
Found a white, square, 2-lead device located in a small transformer, under
the insulation tape, soldered in series with the primary winding of a
120v/12v small transformer in a wall-wart power supply. It is open (no
infinite cont.)

It has these markings:

M20
Tf (that's T sub-f) 115 deg C
11F

It is a little smaller than a TO-220 package (no tab heat sink, 'tho).

What is this? I presume it is thermal cutout or fuse of some kind. What specs
do I need to know to replace it with kind unit?

Can anyone cross this number to a current product?

Thanks,
--
DaveC
me@privacy.net
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On Sun, 14 Dec 2003 23:09:53 -0800, DaveC wrote
(in message <0001HW.BC029E4100B94443F0080600@news.individual.net>):

It is open (no infinite cont.)
Click to expand...
Of course, this should say "infinite continuity."
--
DaveC
me@privacy.net
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DaveC wrote:

On Sun, 14 Dec 2003 23:09:53 -0800, DaveC wrote
(in message <0001HW.BC029E4100B94443F0080600@news.individual.net>):

It is open (no infinite cont.)

Of course, this should say "infinite continuity."
--
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group
Click to expand...
Of course, it should REALLY say "infinite resistance"
or "no continuity".

ARM ;-)
 
On Mon, 15 Dec 2003 9:22:46 -0800, Alan McClure wrote
(in message <3FDDEDE5.9EA70EC1@gwis.com>):

Of course, this should say "infinite continuity."

Of course, it should REALLY say "infinite resistance"
or "no continuity".
Click to expand...
Blast and damn those early-morn posts!
--
DaveC
me@privacy.net
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On Sun, 14 Dec 2003 23:09:53 -0800 DaveC <me@privacy.net> wrote:

Found a white, square, 2-lead device located in a small transformer, under
the insulation tape, soldered in series with the primary winding of a
120v/12v small transformer in a wall-wart power supply. It is open (no
infinite cont.)

It has these markings:

M20
Tf (that's T sub-f) 115 deg C
11F

It is a little smaller than a TO-220 package (no tab heat sink, 'tho).
Click to expand...
It certainly sounds like a 115C thermal fuse, but all the ones I've
ever seen were cylindrical, about the size of a 3A diode, but with a
metal shell and axial leads. One lead insulated.

I used to be able to buy replacements at Radio Shack, but I believe
NTE sells a wider assortment.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
 
On Mon, 15 Dec 2003 20:14:50 -0800, Jim Adney wrote
(in message <901ttv4ms33p25fmanriq1s9devlcka196@4ax.com>):

I used to be able to buy replacements at Radio Shack, but I believe
NTE sells a wider assortment.
Click to expand...
Yeah, I got an NTE replacement. It is larger, and cylindrical, as you say.
But there was room, and after ruining one by soldering it in without using a
heat sink (Doh!!), I successfully installed one. Works fine, now.

Thanks,
--
DaveC
me@privacy.net
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Please reply in the news group
 
"Jim Adney" bravely wrote to "All" (15 Dec 03 22:14:50)
--- on the heady topic of "Re: Help with thermal fuse specs?"

JA> From: Jim Adney <jadney@vwtype3.org>
JA> On Sun, 14 Dec 2003 23:09:53 -0800 DaveC <me@privacy.net> wrote:

Found a white, square, 2-lead device located in a small transformer, under
the insulation tape, soldered in series with the primary winding of a
120v/12v small transformer in a wall-wart power supply. It is open (no
infinite cont.)

It has these markings:

M20
Tf (that's T sub-f) 115 deg C
11F

It is a little smaller than a TO-220 package (no tab heat sink, 'tho).
Click to expand...
JA> It certainly sounds like a 115C thermal fuse, but all the ones I've
JA> ever seen were cylindrical, about the size of a 3A diode, but with a
JA> metal shell and axial leads. One lead insulated.

Yes, I've seen square thermal fuses...

.... You may be a tech if you're entertained by a 6-pack and sparking HV.
 
On Mon, 15 Dec 2003 22:05:45 -0800 DaveC <me@privacy.net> wrote:

But there was room, and after ruining one by soldering it in without using a
heat sink (Doh!!),
Click to expand...
BTDT

Isn't it amazing how quickly they respond to temperature? ;-)

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
 
Short the "thermal" fuse and wire in a conventional one.
These fail because of repeated transformer currents on switch on.
Use an appopriate value fuse.
 
"GPG" <peg@slingshot.co.nz> wrote in message
Short the "thermal" fuse and wire in a conventional one.
These fail because of repeated transformer currents on switch on.
Use an appopriate value fuse.
--------------------------------------
Click to expand...


GPG:
Not really a good plan......
........a conventional fuse will not provide over-temperature protection and
fire hazard prevention.
The thermal cut-out fails not because of "repeated transformer currents on
switch on" but rather because of over-temperature due to the windings in the
transformer over-heating.
Usually the thermal cut-outs, in addition to the temperature rating, have a
CURRENT rating well in excess of the transformer application..... 2 amps
for the small thermal cut-outs and 10 amps for the "common" ones available
from Radio Shack, NTE, ECG, etc.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
---------------------------
 
"GPG" <peg@slingshot.co.nz> wrote in message
news:62069f15.0312170333.5a591f60@posting.google.com...
Short the "thermal" fuse and wire in a conventional one.
These fail because of repeated transformer currents on switch on.
Use an appopriate value fuse.
Click to expand...
Exactly how will this protect the winding against over-temperature
conditions? What is an "appropriate value"? Have you run the UL temperature
tests to confirm the effectiveness of your recommendation? Modifications
such as this are not a good idea.

Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
 
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