If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#136
|
|||
|
|||
Problem of using fuses for hardware protection is their very
wide range of 'protection'. To appreciate the problem, learn about the well understood I^2t curve. For example, semiconductor devices will fail in microseconds. A microseconds transient that exceeds the fuse current ratings by factors of tens will not even blow the fuse. The fuse takes tens of milliseconds (or longer) to blow. Fuse only blows long after damage has occurred. Fuses will do better on equipment that can take massive overcurrent for a long times, such as large motors. Review the numbers. For example, a 20 Amp fuse for automotive protection would conduct 100 amps for 0.5 seconds before opening. Or 40 amps for 9 seconds. And this assumes ambient temperature is constant. The fuse must be sized to not blow also at over 100 degrees F. However the same fuse will now require 10% or more current to blow in winter temperatures. Then there are waveforms for that overcurrent. Then the manufacturer recommends adding another 20% margin of safety. We have assumed an ideal overcurrent - a square wave. That 100 amps might take twice as long to trip a 20 amp fuse if current only averages 100 amps but really peaked at 200+ amps. Variations mean that sizing a fuse for hardware protection becomes difficult if not impossible. This 20 amp fuse would be selected typically for loads that may peak around 10 amps or less just to avoid nuisance tripping. And yet a 100 amps short circuit is required could make the fuse open in less than one second. IOW the fuse of for protection after damage has occurred. For UL approval, a fuse must open at 135% of rated power within one hour. It must open within 2 minutes is the overcurrent is 200%. That means to protect a 1 amp load, the two amp fuse (the smallest selected so as to avoid most nuisance tripping) would conduct 4 amps through the protected appliance for minutes. Or 10 amps for 0.1 seconds. Ten times more current through a 1 amp item - where is the hardware protection? Does not exist. Fuses were not for hardware protection. Fuses are installed first and foremost for human safety. These are numbers. Others are invited to demonstrate knowledge of numbers rather than post "horse****", "lamer", and other technical facts. Fuses are excellent at stopping wire fires. The standard 20 amp electric wire should handle hundreds of amps without damage (and fire). Long enough for a fuse to eventually open. But fuses are woefully insufficient at avoiding appliance damage. That I^2t curve, well understood by those with basic electrical background, demonstrates the problem. Time even tens of milliseconds for faster fuses is woefully too long to protect electronics - such as a power supply. Fuses don't even claim to protect appliances. Fuses are installed to blow after a failure has happened. After current well exceeds what is normal rated consumption. The fuse provides human protection after damage has occurred. Above numbers demonstrate that fact. Numbers rather than insults demonstrate that fuses do not protect hardware. Fuses blow after damage has occurred; for human safety. Richard Urban wrote: I want the fuse to blow before damage to the hardware occurs. If the fuse is sized for the hardware's optimal current draw, that is what will happen. Then the hardware can be electrically repaired, the fuse replaced and the machine is again happy. By the way, I have repaired thousands of machines over the years that have blown fuses. With few exceptions they were all repairable and never again blew another fuse. And I am happy to say that no one died in the process. I guess the fuse saved their lives! That is great, but I still fuse to protect the equipment. |
Ads |
#137
|
|||
|
|||
Problem of using fuses for hardware protection is their very
wide range of 'protection'. To appreciate the problem, learn about the well understood I^2t curve. For example, semiconductor devices will fail in microseconds. A microseconds transient that exceeds the fuse current ratings by factors of tens will not even blow the fuse. The fuse takes tens of milliseconds (or longer) to blow. Fuse only blows long after damage has occurred. Fuses will do better on equipment that can take massive overcurrent for a long times, such as large motors. Review the numbers. For example, a 20 Amp fuse for automotive protection would conduct 100 amps for 0.5 seconds before opening. Or 40 amps for 9 seconds. And this assumes ambient temperature is constant. The fuse must be sized to not blow also at over 100 degrees F. However the same fuse will now require 10% or more current to blow in winter temperatures. Then there are waveforms for that overcurrent. Then the manufacturer recommends adding another 20% margin of safety. We have assumed an ideal overcurrent - a square wave. That 100 amps might take twice as long to trip a 20 amp fuse if current only averages 100 amps but really peaked at 200+ amps. Variations mean that sizing a fuse for hardware protection becomes difficult if not impossible. This 20 amp fuse would be selected typically for loads that may peak around 10 amps or less just to avoid nuisance tripping. And yet a 100 amps short circuit is required could make the fuse open in less than one second. IOW the fuse of for protection after damage has occurred. For UL approval, a fuse must open at 135% of rated power within one hour. It must open within 2 minutes is the overcurrent is 200%. That means to protect a 1 amp load, the two amp fuse (the smallest selected so as to avoid most nuisance tripping) would conduct 4 amps through the protected appliance for minutes. Or 10 amps for 0.1 seconds. Ten times more current through a 1 amp item - where is the hardware protection? Does not exist. Fuses were not for hardware protection. Fuses are installed first and foremost for human safety. These are numbers. Others are invited to demonstrate knowledge of numbers rather than post "horse****", "lamer", and other technical facts. Fuses are excellent at stopping wire fires. The standard 20 amp electric wire should handle hundreds of amps without damage (and fire). Long enough for a fuse to eventually open. But fuses are woefully insufficient at avoiding appliance damage. That I^2t curve, well understood by those with basic electrical background, demonstrates the problem. Time even tens of milliseconds for faster fuses is woefully too long to protect electronics - such as a power supply. Fuses don't even claim to protect appliances. Fuses are installed to blow after a failure has happened. After current well exceeds what is normal rated consumption. The fuse provides human protection after damage has occurred. Above numbers demonstrate that fact. Numbers rather than insults demonstrate that fuses do not protect hardware. Fuses blow after damage has occurred; for human safety. Richard Urban wrote: I want the fuse to blow before damage to the hardware occurs. If the fuse is sized for the hardware's optimal current draw, that is what will happen. Then the hardware can be electrically repaired, the fuse replaced and the machine is again happy. By the way, I have repaired thousands of machines over the years that have blown fuses. With few exceptions they were all repairable and never again blew another fuse. And I am happy to say that no one died in the process. I guess the fuse saved their lives! That is great, but I still fuse to protect the equipment. |
#138
|
|||
|
|||
Well again Leythos uses words to demonstrate the quality of
his technical knowledge. But Leythos, you might learn something. Numbers are posted elsewhere in this thread. Numbers. Remember those things you post insults to avoid? You only stand by insults. As usual, insults remain your only technical fact. Numbers? Do you know any good numbers? Meanwhile for the benefit of others more interested in reality, linear supplies routinely included current fold back limiting even 35 years ago. For others, numbers for fuses are provided in another post to Richard. Numbers that demonstrate why fuses cannot protect electronic appliances. Leythos wrote: I stand by my statement - you are really a lamer and troll. Not all power supply units are designed to protect their circuits against a dead short, not all are designed to handle over-current conditions. Sure, many of the nicer ones are, but you seem to have very limit scope of contact with the real world. Heck, we still had power circuits in F14 control systems that were fused 10 years ago - so much for your 35 years. Oh, and as late as the early 90's there were many non-switching PSU's in use in a varied number of devices. You need to get off your small minded, limited experience, little bit of knowledge, and learn that you don't seem to know jack-shot about a lot of think kid. |
#139
|
|||
|
|||
Well again Leythos uses words to demonstrate the quality of
his technical knowledge. But Leythos, you might learn something. Numbers are posted elsewhere in this thread. Numbers. Remember those things you post insults to avoid? You only stand by insults. As usual, insults remain your only technical fact. Numbers? Do you know any good numbers? Meanwhile for the benefit of others more interested in reality, linear supplies routinely included current fold back limiting even 35 years ago. For others, numbers for fuses are provided in another post to Richard. Numbers that demonstrate why fuses cannot protect electronic appliances. Leythos wrote: I stand by my statement - you are really a lamer and troll. Not all power supply units are designed to protect their circuits against a dead short, not all are designed to handle over-current conditions. Sure, many of the nicer ones are, but you seem to have very limit scope of contact with the real world. Heck, we still had power circuits in F14 control systems that were fused 10 years ago - so much for your 35 years. Oh, and as late as the early 90's there were many non-switching PSU's in use in a varied number of devices. You need to get off your small minded, limited experience, little bit of knowledge, and learn that you don't seem to know jack-shot about a lot of think kid. |
#140
|
|||
|
|||
Woww. Such hate. Such acidity even to a little humor. Are
you sure your name is not Leythos? Lighten up, son. Richard Urban wrote: Boy, you do have a one track mind. Perchance did you screw up years ago while you were learning and severely cause injury, or worse, to someone! That would explain it. "w_tom" wrote in message ... Good show. Thanks to powers that be (ie Mickey Mouse), you can now demand royalties for something like seventy five years - unless someone with deep pockets decides to sue. But then that is a different 'human safety' issue using different protection devices. Richard Urban wrote: Hey! That phrase was copyrighted. You may send your check to..................... (-: |
#141
|
|||
|
|||
Woww. Such hate. Such acidity even to a little humor. Are
you sure your name is not Leythos? Lighten up, son. Richard Urban wrote: Boy, you do have a one track mind. Perchance did you screw up years ago while you were learning and severely cause injury, or worse, to someone! That would explain it. "w_tom" wrote in message ... Good show. Thanks to powers that be (ie Mickey Mouse), you can now demand royalties for something like seventy five years - unless someone with deep pockets decides to sue. But then that is a different 'human safety' issue using different protection devices. Richard Urban wrote: Hey! That phrase was copyrighted. You may send your check to..................... (-: |
#143
|
|||
|
|||
In article , says...
Well again Leythos uses words to demonstrate the quality of his technical knowledge. But Leythos, you might learn something. Numbers are posted elsewhere in this thread. Numbers. Remember those things you post insults to avoid? You only stand by insults. As usual, insults remain your only technical fact. Numbers? Do you know any good numbers? Meanwhile for the benefit of others more interested in reality, linear supplies routinely included current fold back limiting even 35 years ago. For others, numbers for fuses are provided in another post to Richard. Numbers that demonstrate why fuses cannot protect electronic appliances. And again you miss a lot, you miss small 24VDC PSU's, the fused circuits to cover overload on amps, the fuses on all sorts of hardware. I got news for you - fuses don't just protect LARGE MOTORS, they protect a entire range of devices that you ignore due to your complete lack of understanding anything posted in any Usenet group you participate in. What part of numbers for power supply units that HAVE FUSES did you miss - there are hundreds of sites in that google search I presented you with that you seem to have missed. Oh, and no one uses Fuses for microsecond protection of anything - everyone already knows that fuses are slow devices, even fast acting fuses are slow. Heck, I even have old Radio's that have 1A or 2A fuses in them to protect the power output from simple transistors used in the regulator circuits - but I'm sure you will tell me that those only blow after the unit is damaged, even though I've replaced them, without replacing anything else, and the units still work after more than 20 years. So, come on, tell us again how fuses only protect damaged devices from injuring people. You lost all credibility when you started your BS this time. -- -- remove 999 in order to email me |
#144
|
|||
|
|||
Fuses in that radio would be required by the UL so that it
does not kill someone. If fuses are routinely blowing, then fuses are too small - nuisance tripping. That too demonstrated in another post with numbers. To protect electronics, a fuse must blow in microseconds. But again, you damn the numbers. You know better because undersized fuses in a Radio are nuisance tripping. That alone is sufficient proof of what? Next you will claim a UPS provides protection that even its manufacturer does not claim. Why? Your speculation, as ususal, is proof enough. Numbers be damned. For others, numbers are provided elsewhere. Fuse takes numerous seconds or minutes to protect from an overload. But after damage has occurred, the higher current will quickly open the fuse - to protect human life. Leythos wrote: And again you miss a lot, you miss small 24VDC PSU's, the fused circuits to cover overload on amps, the fuses on all sorts of hardware. I got news for you - fuses don't just protect LARGE MOTORS, they protect a entire range of devices that you ignore due to your complete lack of understanding anything posted in any Usenet group you participate in. What part of numbers for power supply units that HAVE FUSES did you miss - there are hundreds of sites in that google search I presented you with that you seem to have missed. Oh, and no one uses Fuses for microsecond protection of anything - everyone already knows that fuses are slow devices, even fast acting fuses are slow. Heck, I even have old Radio's that have 1A or 2A fuses in them to protect the power output from simple transistors used in the regulator circuits - but I'm sure you will tell me that those only blow after the unit is damaged, even though I've replaced them, without replacing anything else, and the units still work after more than 20 years. So, come on, tell us again how fuses only protect damaged devices from injuring people. You lost all credibility when you started your BS this time. -- -- remove 999 in order to email me |
#145
|
|||
|
|||
Fuses in that radio would be required by the UL so that it
does not kill someone. If fuses are routinely blowing, then fuses are too small - nuisance tripping. That too demonstrated in another post with numbers. To protect electronics, a fuse must blow in microseconds. But again, you damn the numbers. You know better because undersized fuses in a Radio are nuisance tripping. That alone is sufficient proof of what? Next you will claim a UPS provides protection that even its manufacturer does not claim. Why? Your speculation, as ususal, is proof enough. Numbers be damned. For others, numbers are provided elsewhere. Fuse takes numerous seconds or minutes to protect from an overload. But after damage has occurred, the higher current will quickly open the fuse - to protect human life. Leythos wrote: And again you miss a lot, you miss small 24VDC PSU's, the fused circuits to cover overload on amps, the fuses on all sorts of hardware. I got news for you - fuses don't just protect LARGE MOTORS, they protect a entire range of devices that you ignore due to your complete lack of understanding anything posted in any Usenet group you participate in. What part of numbers for power supply units that HAVE FUSES did you miss - there are hundreds of sites in that google search I presented you with that you seem to have missed. Oh, and no one uses Fuses for microsecond protection of anything - everyone already knows that fuses are slow devices, even fast acting fuses are slow. Heck, I even have old Radio's that have 1A or 2A fuses in them to protect the power output from simple transistors used in the regulator circuits - but I'm sure you will tell me that those only blow after the unit is damaged, even though I've replaced them, without replacing anything else, and the units still work after more than 20 years. So, come on, tell us again how fuses only protect damaged devices from injuring people. You lost all credibility when you started your BS this time. -- -- remove 999 in order to email me |
#146
|
|||
|
|||
In article , says...
Fuses in that radio would be required by the UL so that it does not kill someone. If fuses are routinely blowing, then fuses are too small - nuisance tripping. That too demonstrated in another post with numbers. There you go assuming you know why they blew, and that they blew many enough times to mean they were too small for the reason they were installed. Fuses that have blown 3 times in 20 years is not significant in some circuits, but I don't expect you to have any experience in that area either. To protect electronics, a fuse must blow in microseconds. But again, you damn the numbers. You know better because undersized fuses in a Radio are nuisance tripping. That alone is sufficient proof of what? Next you will claim a UPS provides protection that even its manufacturer does not claim. Why? Your speculation, as ususal, is proof enough. Numbers be damned. You've got to be kidding - many devices can take minutes of excessive load without being damaged, some hours, you really have never worked with electrical devices of a varied nature - have you? For others, numbers are provided elsewhere. Fuse takes numerous seconds or minutes to protect from an overload. But after damage has occurred, the higher current will quickly open the fuse - to protect human life. Again, you miss the mark - fuses do take time to open, some open in milliseconds, some open in seconds, some longer, but since you've not posted any specific fuse and the load you are suggesting, we can't really suggest if the fuse blows quickly or slowly. If I draw 1.05A on a 1A fuse it may never blow, or it may blow after minutes, but if I draw 1.7A on it, it's going to blow quickly - even though all of the devices in the rest of the circuit could handle the load for several minutes without damage - the idea is that the fuse blows as quickly as needed to protect the circuit and it's parts. Ever hook a multimeter to a 600V line on the wrong setting? The little 315MA fuse blows in less than a millisecond (I would have to guess), but there is no damage to the device, and the foil on the circuit board would vaporize before damage to human, so there was no reason to have it there to protect the human, it was there to protect the foil traces on the circuit board or other components inside the multimeter. None of these REAL examples have anything to do with protecting a HUMAN, it's about protecting the device. -- -- remove 999 in order to email me |
#147
|
|||
|
|||
In article , says...
Fuses in that radio would be required by the UL so that it does not kill someone. If fuses are routinely blowing, then fuses are too small - nuisance tripping. That too demonstrated in another post with numbers. There you go assuming you know why they blew, and that they blew many enough times to mean they were too small for the reason they were installed. Fuses that have blown 3 times in 20 years is not significant in some circuits, but I don't expect you to have any experience in that area either. To protect electronics, a fuse must blow in microseconds. But again, you damn the numbers. You know better because undersized fuses in a Radio are nuisance tripping. That alone is sufficient proof of what? Next you will claim a UPS provides protection that even its manufacturer does not claim. Why? Your speculation, as ususal, is proof enough. Numbers be damned. You've got to be kidding - many devices can take minutes of excessive load without being damaged, some hours, you really have never worked with electrical devices of a varied nature - have you? For others, numbers are provided elsewhere. Fuse takes numerous seconds or minutes to protect from an overload. But after damage has occurred, the higher current will quickly open the fuse - to protect human life. Again, you miss the mark - fuses do take time to open, some open in milliseconds, some open in seconds, some longer, but since you've not posted any specific fuse and the load you are suggesting, we can't really suggest if the fuse blows quickly or slowly. If I draw 1.05A on a 1A fuse it may never blow, or it may blow after minutes, but if I draw 1.7A on it, it's going to blow quickly - even though all of the devices in the rest of the circuit could handle the load for several minutes without damage - the idea is that the fuse blows as quickly as needed to protect the circuit and it's parts. Ever hook a multimeter to a 600V line on the wrong setting? The little 315MA fuse blows in less than a millisecond (I would have to guess), but there is no damage to the device, and the foil on the circuit board would vaporize before damage to human, so there was no reason to have it there to protect the human, it was there to protect the foil traces on the circuit board or other components inside the multimeter. None of these REAL examples have anything to do with protecting a HUMAN, it's about protecting the device. -- -- remove 999 in order to email me |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
24/7 | Carl G | General XP issues or comments | 23 | February 22nd 05 06:39 PM |
Power User Accts: strange behaviours | Danor | Security and Administration with Windows XP | 0 | February 22nd 05 12:09 AM |
When electricity goes off suddenly does it damage my windows XP installation? | dev | General XP issues or comments | 52 | December 31st 04 02:24 AM |
on or off | Happy | The Basics | 11 | December 2nd 04 10:27 PM |
Not a problem, Dell shuts down faster using the POWER OFF button | anon | General XP issues or comments | 17 | October 20th 04 01:42 PM |