Fuses, Am I That Stupid ?...

[Phil Allison]

Ralph Mowery wrote:

==================

The $ 1000 device has already failed when the fuse blows. The fuse is
really to protect the wiring going to the device. A fuse may prevent
major damage to the devise it is wired to. Such as in a power supply
part of the device a capacitor may short and the fuse may protect the
power transformer.

The common mistake about fuses is that it is to protect the device, but
it is really they are to protect the wiring and the power supply that is
feedig the device.

Without a fuse, the wires could get hot enough to cause a fire.

** Supply line fuses limit damage to the following circuitry - particularly steel core transformers and other heat sensitive parts. Internal supply wiring should be and normally IS adequate to trip external breakers without burning up.

That makers specify a correct supply fuse to fit tells you it is not just for cable protection. However, the biggest mistake is to think user replaceable fuses actually protect anything.



...... Phil

 

[Pimpom]

On 8/19/2020 7:11 PM, Phil Allison wrote:

Pimpom wrote:

==============


I use what I can get here and the 3-5 cent (US) fast-blow fuses I
normally stock are often crudely constructed. But they behave as
expected in the few tests I\'ve done as well as in practical
products. They take several seconds to blow at the rated current
and quickly at 2x.


** No fuse should blow at the rated current.

Cos the Amp rating is for the max holding value.

Slow acting ( ie T for trage ) types open at current levels not much above their rating, given enough time.


..... Phil

I stand corrected. I just looked up some current datasheets and
it\'s hours at 100% and several secs at 200%. I haven\'t updated
myself and was thinking of some mfr\'s data and my own test from
long ago which were around 30 secs at 100% and 1 sec at 200%.

 

[Michael_A_Terrell]

legg wrote:

On Tue, 18 Aug 2020 02:26:12 -0700 (PDT), Jeff Urban
jurb6006@gmail.com> wrote:

3AG is a series of glass bodied low voltage fuses.
(Automotive Glass)

Automotive fuses were SFE, until they switched to those plastic,
plug in type. They were rated for 32VDC maximum, and they got longer as
the current rating went up, to prevent you from putting in a much larger
fuse. Our shop used to stock over 250 series and values of fuses,
including the Belfuse chemical fuses.




--
Never piss off an Engineer!

They don\'t get mad.

They don\'t get even.

They go for over unity! ;-)

 

[ohg...@gmail.com]

On Thursday, August 20, 2020 at 3:27:13 AM UTC-4, terrell....@gmail.com wrote:

legg wrote:
On Tue, 18 Aug 2020 02:26:12 -0700 (PDT), Jeff Urban
jurb...@gmail.com> wrote:

3AG is a series of glass bodied low voltage fuses.
(Automotive Glass)
Automotive fuses were SFE, until they switched to those plastic,
plug in type. They were rated for 32VDC maximum, and they got longer as
the current rating went up, to prevent you from putting in a much larger
fuse. Our shop used to stock over 250 series and values of fuses,
including the Belfuse chemical fuses.
--

Uh oh! You did *not* call them \"chemical\" fuses!!! Standby...

 

[Michael_A_Terrell]

ohg...@gmail.com wrote:

On Thursday, August 20, 2020 at 3:27:13 AM UTC-4, terrell....@gmail.com wrote:
legg wrote:
On Tue, 18 Aug 2020 02:26:12 -0700 (PDT), Jeff Urban
jurb...@gmail.com> wrote:

3AG is a series of glass bodied low voltage fuses.
(Automotive Glass)
Automotive fuses were SFE, until they switched to those plastic,
plug in type. They were rated for 32VDC maximum, and they got longer as
the current rating went up, to prevent you from putting in a much larger
fuse. Our shop used to stock over 250 series and values of fuses,
including the Belfuse chemical fuses.
--


Uh oh! You did *not* call them \"chemical\" fuses!!! Standby...

That\'s what they are. The fuse element is coated with a chemical
that burns as soon as it reaches its critical temperature to ensure that
it opens quickly. They were use in the cathodes of Horizontal output
tubes, and some solid state circuits. They are very fast opening fuses,
and similar to the 7200V fuses used by utilities, except they use
gunpowder to quench the plasma. Both methods can run right below their
critical temperature without opening. Once any part of the element
reaches critical temperature, it opens. No sagging fuse elements that
change their fusing current from running too hot without opening. I\'ve
seen some AGC fuses where it had melted, and drooped to the glass
without opening.

--
Never piss off an Engineer!

They don\'t get mad.

They don\'t get even.

They go for over unity! ;-)

 

[server]

On Thursday, 20 August 2020 08:20:49 UTC+1, Pimpom wrote:

On 8/19/2020 7:11 PM, Phil Allison wrote:
Pimpom wrote:

==============


I use what I can get here and the 3-5 cent (US) fast-blow fuses I
normally stock are often crudely constructed. But they behave as
expected in the few tests I\'ve done as well as in practical
products. They take several seconds to blow at the rated current
and quickly at 2x.


** No fuse should blow at the rated current.

Cos the Amp rating is for the max holding value.

Slow acting ( ie T for trage ) types open at current levels not much above their rating, given enough time.


..... Phil

I stand corrected. I just looked up some current datasheets and
it\'s hours at 100% and several secs at 200%. I haven\'t updated
myself and was thinking of some mfr\'s data and my own test from
long ago which were around 30 secs at 100% and 1 sec at 200%.

There are fuses that pop at 100% rating, but the great majority of types carry 100% indefinitely.


NT

 

[ohg...@gmail.com]

On Thursday, August 20, 2020 at 5:42:03 PM UTC-4, terrell....@gmail.com wrote:

ohg...@gmail.com wrote:
On Thursday, August 20, 2020 at 3:27:13 AM UTC-4, terrell....@gmail.com wrote:
legg wrote:
On Tue, 18 Aug 2020 02:26:12 -0700 (PDT), Jeff Urban
jurb...@gmail.com> wrote:

3AG is a series of glass bodied low voltage fuses.
(Automotive Glass)
Automotive fuses were SFE, until they switched to those plastic,
plug in type. They were rated for 32VDC maximum, and they got longer as
the current rating went up, to prevent you from putting in a much larger
fuse. Our shop used to stock over 250 series and values of fuses,
including the Belfuse chemical fuses.
--



Uh oh! You did *not* call them \"chemical\" fuses!!! Standby...

That\'s what they are. The fuse element is coated with a chemical
that burns as soon as it reaches its critical temperature to ensure that
it opens quickly. They were use in the cathodes of Horizontal output
tubes, and some solid state circuits. They are very fast opening fuses,
and similar to the 7200V fuses used by utilities, except they use
gunpowder to quench the plasma. Both methods can run right below their
critical temperature without opening. Once any part of the element
reaches critical temperature, it opens. No sagging fuse elements that
change their fusing current from running too hot without opening. I\'ve
seen some AGC fuses where it had melted, and drooped to the glass
without opening.
--

We all know the Belfuse fuses were chemical fuses except for just *one* group contributor who is *never* wrong and said they aren\'t chemical fuses...

 

[Michael_A_Terrell]

ohg...@gmail.com wrote:

On Thursday, August 20, 2020 at 5:42:03 PM UTC-4, terrell....@gmail.com wrote:
ohg...@gmail.com wrote:
On Thursday, August 20, 2020 at 3:27:13 AM UTC-4, terrell....@gmail.com wrote:
legg wrote:
On Tue, 18 Aug 2020 02:26:12 -0700 (PDT), Jeff Urban
jurb...@gmail.com> wrote:

3AG is a series of glass bodied low voltage fuses.
(Automotive Glass)
Automotive fuses were SFE, until they switched to those plastic,
plug in type. They were rated for 32VDC maximum, and they got longer as
the current rating went up, to prevent you from putting in a much larger
fuse. Our shop used to stock over 250 series and values of fuses,
including the Belfuse chemical fuses.
--



Uh oh! You did *not* call them \"chemical\" fuses!!! Standby...


That\'s what they are. The fuse element is coated with a chemical
that burns as soon as it reaches its critical temperature to ensure that
it opens quickly. They were use in the cathodes of Horizontal output
tubes, and some solid state circuits. They are very fast opening fuses,
and similar to the 7200V fuses used by utilities, except they use
gunpowder to quench the plasma. Both methods can run right below their
critical temperature without opening. Once any part of the element
reaches critical temperature, it opens. No sagging fuse elements that
change their fusing current from running too hot without opening. I\'ve
seen some AGC fuses where it had melted, and drooped to the glass
without opening.
--

We all know the Belfuse fuses were chemical fuses except for just *one* group contributor who is *never* wrong and said they aren\'t chemical fuses...

What he doesn\'t know would fill entire libraries. I\'ll bet that he\'s
never heard of a Klystrode, either. They replaced Klystrons in high
power TV transmitters, but they wer more efficient so the station\'s
power bill was lower. the 5MW UHF site that I maintaining had a $45,000
per month electric bill. It would have been about 15 to 20% lower if it
used Klystrodes.


--
Never piss off an Engineer!

They don\'t get mad.

They don\'t get even.

They go for over unity! ;-)