[time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-Jun/date.html

We finally got in the Panasonic thermal fuses for the HP10811 and have
a few extra.  They will either plug in or solder.  Contact me if you
need one.

πθ°μΩω±√·Γλ
WB0KVV

-- Forwarded message --
From: Van Horn, David 
Date: Thu, May 11, 2017 at 7:01 PM
Subject: Re: [time-nuts] HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement 

The original article was from Kodiak consulting.  Good thing I saved a copy.
Thanks for the link to this one.
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Jeremy Nichols]

I had a vaguely similar situation with a pressure switch for the pump in my
home's water supply. The electrical contacts in the pressure switch have to
handle about 10 Amps at 250 Volts (our line voltage is on the high side).
Over the years, the contacts burn and become "ohmic" contacts, gradually
increasing in resistance. Early one morning the contacts finally got so
resistive they couldn't pass enough current to start the pump. Since the
water pressure never came up, the switch never shut off. It got hotter and
hotter and finally burst into flame. I found out about it at 4:00 AM when a
smoke alarm woke me. An extinguisher was sufficient to dowse the flames
although the local fire fighters were called as a precaution, me being
still half asleep. When I replaced the pressure switch, I added a thermal
fuse as protection should that problem ever recur.

Jeremy



On Thu, May 11, 2017 at 4:04 PM Donald E. Pauly <trojancow...@gmail.com>
wrote:

> https://www.febo.com/pipermail/time-nuts/2017-May/date.html
>
> This is the third report of an open thermistor which would have
> resulted in a fire in an HP10811 oven.  There are a dozen other
> problems that could cause such a fire.  See
> http://gonascent.com/papers/hp/hp10811/thermal.jpg .  The leads are
> long enough that they can be soldered quickly without a heat sink if
> the socket is to be replaced for better reliability.  A hemostat can
> also be used to heatsink the leads one at a time.  We have the 108° C
> fuse which is prone to nuisance blows.  HP has superceded it with a
> 125° C version.  Panasonic seems to make a direct replacement.  It is
> stocked by Digikey for under a dollar.  I can find no reports of a
> nuisance blow of the 125° version of the thermal fuse in a HP10811.
> All nuisance blows seem to be in the 108° version.
>
> In the 1970s, many consumer electronic products with 60 cps power
> transformers had a thermal fuse inside them.  I bought a Sony real to
> real stereo tape deck which was not working with that problem.  It was
> a nuisance blow since no problems existed in the tape deck.  I
> installed a fine gauge piece of solder since the fuse was close to
> 180° C.  I used it for over two years with no problems.
>
> Later model switching power supplies have windings of several volts
> per turn.  Shorts in these transformers will blow the fuse or destroy
> the switching transistors.  A 60 cps transformer operates at a small
> fraction of a volt per turn. A few shorted turns in a will not draw an
> excessive primary current but merely causes a hot spot.  The hot spot
> will grow as additional turns short.  Line current will not be greatly
> excessive even as the transformer heats up.  It can catch fire well
> before the fuse blows.
>
> I saw a living room that caught fire because of a 60 cps transformer
> in a stereo receiver.  The line breaker never tripped.  But for the
> grace of G-d, the house would have burnt down.  A thermal fuse in the
> transformer would have prevented several thousand dollars of damage.
> That would have paid for over a thousand thermal fuses.
>
> πθ°μΩω±√·Γλ
> WB0KVV
>
> ---- Forwarded message --
> From: David G. McGaw <david.g.mc...@dartmouth.edu>
> Date: Wed, May 10, 2017 at 8:20 PM
> Subject: Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse
> To: Discussion of precise time and frequency measurement <
> time-nuts@febo.com>
>
> I too have had a fuse open up due to a failed thermistor in a HP10811.
>
> David N1HAC
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Van Horn, David]

There's an excellent article out there on the web called "Low Voltage, the 
incompetent ignition source"  I highly recommend a read. 
I dealt with a case like this a couple years ago.  Failed fet in an H bridge 
caused a fault which the brick SMPS picked up as a short, and went into 
"hiccup" mode on.
The energy delivered in "hiccup" mode was about 1W average, and that was 
enough, after several hours, to cause ignition and sustained flame on the PCB.

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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

This is the third report of an open thermistor which would have
resulted in a fire in an HP10811 oven.  There are a dozen other
problems that could cause such a fire.  See
http://gonascent.com/papers/hp/hp10811/thermal.jpg .  The leads are
long enough that they can be soldered quickly without a heat sink if
the socket is to be replaced for better reliability.  A hemostat can
also be used to heatsink the leads one at a time.  We have the 108° C
fuse which is prone to nuisance blows.  HP has superceded it with a
125° C version.  Panasonic seems to make a direct replacement.  It is
stocked by Digikey for under a dollar.  I can find no reports of a
nuisance blow of the 125° version of the thermal fuse in a HP10811.
All nuisance blows seem to be in the 108° version.

In the 1970s, many consumer electronic products with 60 cps power
transformers had a thermal fuse inside them.  I bought a Sony real to
real stereo tape deck which was not working with that problem.  It was
a nuisance blow since no problems existed in the tape deck.  I
installed a fine gauge piece of solder since the fuse was close to
180° C.  I used it for over two years with no problems.

Later model switching power supplies have windings of several volts
per turn.  Shorts in these transformers will blow the fuse or destroy
the switching transistors.  A 60 cps transformer operates at a small
fraction of a volt per turn. A few shorted turns in a will not draw an
excessive primary current but merely causes a hot spot.  The hot spot
will grow as additional turns short.  Line current will not be greatly
excessive even as the transformer heats up.  It can catch fire well
before the fuse blows.

I saw a living room that caught fire because of a 60 cps transformer
in a stereo receiver.  The line breaker never tripped.  But for the
grace of G-d, the house would have burnt down.  A thermal fuse in the
transformer would have prevented several thousand dollars of damage.
That would have paid for over a thousand thermal fuses.

πθ°μΩω±√·Γλ
WB0KVV

 Forwarded message --
From: David G. McGaw <david.g.mc...@dartmouth.edu>
Date: Wed, May 10, 2017 at 8:20 PM
Subject: Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>

I too have had a fuse open up due to a failed thermistor in a HP10811.

David N1HAC
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[ewkehren via time-nuts]

Having  had a fan failure on a well insulated Rb we use a temperature sensor 
also used for compensation in to a PIC to shut down the systemBert Kehren

Sent from my Galaxy Tab® A
 Original message From: "David G. McGaw" 
<david.g.mc...@dartmouth.edu> Date: 5/10/17  11:20 PM  (GMT-05:00) To: 
Discussion of precise time and frequency measurement <time-nuts@febo.com> 
Subject: Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse 
I too have had a fuse open up due to a failed thermistor in a HP10811.

David N1HAC


On 5/10/17 7:43 PM, Dan Rae wrote:
> As I reported the last time this subject came up, or maybe the time 
> before, the only time I had an open thermal fuse was in a 10811 that 
> had an open thermistor.  I was able to replace that and get the OCXO 
> working, but if the fuse had been replaced with a wire link I'm sure 
> the entire oven would have been toast.
>
> There have been two types of fuse fitted, all I those have are the 
> type that can be fitted with the plug in axial panasonic type, less 
> than a dollar from Digikey.  The older ovens had a different type but 
> I imagine it's similarly easy to replace.
>
> All my 10811s have the higher temperature Panasonic fuse fitted and I 
> sleep well at night...
>
> Dan
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[David G. McGaw]

I too have had a fuse open up due to a failed thermistor in a HP10811.

David N1HAC


On 5/10/17 7:43 PM, Dan Rae wrote:
As I reported the last time this subject came up, or maybe the time 
before, the only time I had an open thermal fuse was in a 10811 that 
had an open thermistor.  I was able to replace that and get the OCXO 
working, but if the fuse had been replaced with a wire link I'm sure 
the entire oven would have been toast.


There have been two types of fuse fitted, all I those have are the 
type that can be fitted with the plug in axial panasonic type, less 
than a dollar from Digikey.  The older ovens had a different type but 
I imagine it's similarly easy to replace.


All my 10811s have the higher temperature Panasonic fuse fitted and I 
sleep well at night...


Dan
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Hal Murray]

kb...@n1k.org said:
> The is related to safety (full time  power on). As it worked out, the fuse
> did not help them in that respect. The Fed’s still ruled the gear had to be
> shut off at night. 

Could you please say more...

Does that mean unplugging gear with always-on OCXOs?  Or dumping the main 
power to the lab when the lights are turned off?


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Richard (Rick) Karlquist]

The view from inside HP when I worked with the people
who designed and built the 10811 some 35-40 years ago
was that:

1.  10811 ovens rarely fail.

2.  When they do fail, it is rarely because the oven
runs away.  I know I have never encountered a runaway.
No one at HP had a "trophy" on their desk of a runaway
10811.  People tend to collect stuff like that.  One
engineer did have a 10811 with a 45 caliber bullet
fired through it (long story).

3.  From a business perspective, a failure is a failure
and so there is no business reason to have a fuse.

4.  Because the fuse could not be soldered in, it had
to be socketed, and the socket failures exceeded any
oven runaways by a good margin.  Therefore, it made
the "failure rate" worse.  That is all that matters to
the bean counters.

5.  The one and only reason it was in there at all
was the concern about toxic gases being released from
the foam.  Even without a runaway, foams tend to have
a "slow burn" and outgas "stuff" all the time.  Various
foams were evaluated to balance that issue with thermal
resistance and with the big issue with foam which is
mechanical fatigue.  This is similar to the wear out
of foam mattresses.

What should have been done with the thermal fuse would
have been to put crimp lugs on the leads and attach
the crimp lugs with screws.  However, there was no space
for all that stuff.

Rick N6RK


On 5/10/2017 4:43 PM, Dan Rae wrote:

As I reported the last time this subject came up, or maybe the time
before, the only time I had an open thermal fuse was in a 10811 that had
an open thermistor.  I was able to replace that and get the OCXO
working, but if the fuse had been replaced with a wire link I'm sure the
entire oven would have been toast.

There have been two types of fuse fitted, all I those have are the type
that can be fitted with the plug in axial panasonic type, less than a
dollar from Digikey.  The older ovens had a different type but I imagine
it's similarly easy to replace.

All my 10811s have the higher temperature Panasonic fuse fitted and I
sleep well at night...

Dan
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Dan Rae]

As I reported the last time this subject came up, or maybe the time 
before, the only time I had an open thermal fuse was in a 10811 that had 
an open thermistor.  I was able to replace that and get the OCXO 
working, but if the fuse had been replaced with a wire link I'm sure the 
entire oven would have been toast.


There have been two types of fuse fitted, all I those have are the type 
that can be fitted with the plug in axial panasonic type, less than a 
dollar from Digikey.  The older ovens had a different type but I imagine 
it's similarly easy to replace.


All my 10811s have the higher temperature Panasonic fuse fitted and I 
sleep well at night...


Dan
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Bob kb8tq]

 Hi

Unless you believe that HP’s quality was poor, the experience of the rest of 
the OCXO
business is likely relevant. In `~50 years of designing OCXO’s the only one I 
have ever
seen are the HP units. Nobody else does that. Based on return rates, the number 
of 
“runaway ovens” is negligible over a 30 year period. The is related to safety 
(full time 
power on). As it worked out, the fuse did not help them in that respect. The 
Fed’s still
ruled the gear had to be shut off at night.

Bob


> On May 10, 2017, at 5:34 PM, Donald E. Pauly <trojancow...@gmail.com> wrote:
> 
> https://www.febo.com/pipermail/time-nuts/2017-May/date.html
> 
> The poster at 
> http://www.simonsdialogs.com/2016/09/a-thermal-fuse-and-hp-10811-60111-repair/
> reported that the thermal fuse saved an oscillator from destruction
> when a thermistor opened.  HP made thousands of these which sold for
> $800.  If a large portion failed it would have been addressed.  They
> raised the temperature of the thermal fuse to reduce nuisance blows.
> I say that nuisance blows equal to real blows are worth the trouble.
> You may be getting oscillators on the surplus market or eBay which
> have a higher proportion of nuisance blows.
> 
> πθ°μΩω±√·Γλ
> WB0KVV
> 
> From: Mike Feher <mfe...@eozinc.com>
> Date: Tue, May 9, 2017 at 9:10 PM
> Subject: Re: [time-nuts] Fwd:  HP10811 Oscillator Thermal Fuse
> To: Discussion of precise time and frequency measurement <time-nuts@febo.com>
> 
> Respectfully I disagree. I have totally shorted out numerous
> oscillator’s fuses with no problems. The design of those thermal fuses
> makes them vulnerable to opening just due to years of use without
> problem, in any of the electronics. My shorted out oscillators still
> work. Ideally, if handy, it is easy enough to replace them if one is
> available. They just plug in. If there is a thermal runaway, that
> caused the opening, to me that implies that there are other issues.
> Regards – Mike
> 
> Mike B. Feher, N4FS
> 
> 89 Arnold Blvd.
> 
> Howell, NJ, 07731
> 
> 848-245-9115
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[time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

The poster at 
http://www.simonsdialogs.com/2016/09/a-thermal-fuse-and-hp-10811-60111-repair/
reported that the thermal fuse saved an oscillator from destruction
when a thermistor opened.  HP made thousands of these which sold for
$800.  If a large portion failed it would have been addressed.  They
raised the temperature of the thermal fuse to reduce nuisance blows.
I say that nuisance blows equal to real blows are worth the trouble.
You may be getting oscillators on the surplus market or eBay which
have a higher proportion of nuisance blows.

πθ°μΩω±√·Γλ
WB0KVV

From: Mike Feher <mfe...@eozinc.com>
Date: Tue, May 9, 2017 at 9:10 PM
Subject: Re: [time-nuts] Fwd:  HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>

Respectfully I disagree. I have totally shorted out numerous
oscillator’s fuses with no problems. The design of those thermal fuses
makes them vulnerable to opening just due to years of use without
problem, in any of the electronics. My shorted out oscillators still
work. Ideally, if handy, it is easy enough to replace them if one is
available. They just plug in. If there is a thermal runaway, that
caused the opening, to me that implies that there are other issues.
Regards – Mike

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell, NJ, 07731

848-245-9115
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Re: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Mike Feher]

Respectfully I disagree. I have totally shorted out numerous oscillator’s fuses 
with no problems. The design of those thermal fuses makes them vulnerable to 
opening just due to years of use without problem, in any of the electronics. My 
shorted out oscillators still work. Ideally, if handy, it is easy enough to 
replace them if one is available. They just plug in. If there is a thermal 
runaway, that caused the opening, to me that implies that there are other 
issues. Regards – Mike  

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell, NJ, 07731

848-245-9115

 

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Donald E. Pauly
Sent: Tuesday, May 09, 2017 9:49 PM
To: time-nuts; Donald E. Pauly
Subject: [time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

 

 <https://www.febo.com/pipermail/time-nuts/2017-May/date.html> 
https://www.febo.com/pipermail/time-nuts/2017-May/date.html

 

I disagree about permanently jumpering the thermal fuse.  The oscillator is 
rated down to -55° C and the oven can maintain 82° C at that temperature.  This 
is a 137° C rise.  It is likely capable of more heat than that.  At 25° C, it 
would therefore be able to reach at least 25+137=162° C.  This is near solder 
melting temperature and would quickly cook the components.  It is rated to work 
at 71° which would give a temperature of 208° C and do serious damage.  That 
thermal fuse is very important.  There are a dozen failures which could result 
in a thermal runaway.

 

This web page discusses the fact that a thermal fuse should be 30° C above 
normal operating temperature to prevent nuisance blows.

 
<http://www.simonsdialogs.com/2016/09/a-thermal-fuse-and-hp-10811-60111-repair/>
 http://www.simonsdialogs.com/2016/09/a-thermal-fuse-and-hp-10811-60111-repair/

HP originally used a 26° C margin and later changed it to a 33° margin.  This 
explains the frequent failures.  This poster used the wrong type of fuse but 
the correct type is commercially available.

 

πθ°μΩω±√·Γλ

WB0KVV

 

-- Forwarded message --

From: Bob kb8tq < <mailto:kb...@n1k.org> kb...@n1k.org>

Date: Mon, May 8, 2017 at 6:07 PM

Subject: Re: [time-nuts] HP10811 Oscillator Thermal Fuse

To: Discussion of precise time and frequency measurement < 
<mailto:time-nuts@febo.com> time-nuts@febo.com>

Cc: "Donald E. Pauly" < <mailto:trojancow...@gmail.com> trojancow...@gmail.com>

 

Hi

 

You will get a lot of diversity of opinion on the topic of the thermal fuse on 
the 10811. My feeling is that they are a nuisance and contribute very little to 
the design. I’d just short it out and move on. In the era of failure prone 
heater transistors or faulty thermistors, the fuse may have made sense. That 
era ended before the

10811 went into production.

 

Bob

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[time-nuts] Fwd: HP10811 Oscillator Thermal Fuse

[Donald E. Pauly]

https://www.febo.com/pipermail/time-nuts/2017-May/date.html

I disagree about permanently jumpering the thermal fuse.  The
oscillator is rated down to -55° C and the oven can maintain 82° C at
that temperature.  This is a 137° C rise.  It is likely capable of
more heat than that.  At 25° C, it would therefore be able to reach at
least 25+137=162° C.  This is near solder melting temperature and
would quickly cook the components.  It is rated to work at 71° which
would give a temperature of 208° C and do serious damage.  That
thermal fuse is very important.  There are a dozen failures which
could result in a thermal runaway.

This web page discusses the fact that a thermal fuse should be 30° C
above normal operating temperature to prevent nuisance blows.
http://www.simonsdialogs.com/2016/09/a-thermal-fuse-and-hp-10811-60111-repair/
HP originally used a 26° C margin and later changed it to a 33°
margin.  This explains the frequent failures.  This poster used the
wrong type of fuse but the correct type is commercially available.

πθ°μΩω±√·Γλ
WB0KVV

-- Forwarded message --
From: Bob kb8tq 
Date: Mon, May 8, 2017 at 6:07 PM
Subject: Re: [time-nuts] HP10811 Oscillator Thermal Fuse
To: Discussion of precise time and frequency measurement 
Cc: "Donald E. Pauly" 

Hi

You will get a lot of diversity of opinion on the topic of the thermal
fuse on the 10811. My feeling is that they are a nuisance and
contribute very little to the design. I’d just short it out and move
on. In the era of failure prone heater transistors or faulty
thermistors, the fuse may have made sense. That era ended before the
10811 went into production.

Bob
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