In article ,
Bill Turner wrote:

On 24 Nov 2003 22:50:40 -0800, (Jason Hsu) wrote:

Can the 1W-51 ohm resistors handle this 50 RF volts 0-peak (about 50W
PEP) for .007 sec? 50W over .007 seconds is .35 Joules. .35W for 1
second is also .35 Joules, which a 1W resistor should have no trouble
handling. Can the resistors be damaged during that .007 seconds?

__________________________________________________ _______

You really need to ask the manufacturer of the resistor. They are well
aware of the problem - if you get to the right person.

Having said that, here is a generalization: If the resistor's element
is a solid block of material, such as in a carbon composition type, it
will have very good pulse power ratings. On the other hand, if the
element is a film, it may develop tiny hot spots during pulsing and
eventually fail.


Many years ago I analyzed a problem with resistors which were
discoloring in the field. This involved two identical circuits with
identical singal inputs. In one circuit, a resistor kept turning brown
over time, in the other it did not. We were getting field returns as a
result of troubleshooting that focused on the brown resistors.

What was the difference? The resistor which did not discolor was resting
on two metal traces which ran under it, the one which discolored, was
resting on the PCB. That tiny amount of heatsinking provided by the
traces was the difference. Obviously, the circuit needed to be
redesigned, but it worked great on the breadboard when it went into
production.

Al

--
There's never enough time to do it right the first time.......

Al wrote:

In article ,
Bill Turner wrote:


On 24 Nov 2003 22:50:40 -0800, (Jason Hsu) wrote:


Can the 1W-51 ohm resistors handle this 50 RF volts 0-peak (about 50W
PEP) for .007 sec? 50W over .007 seconds is .35 Joules. .35W for 1
second is also .35 Joules, which a 1W resistor should have no trouble
handling. Can the resistors be damaged during that .007 seconds?

________________________________________________ _________

You really need to ask the manufacturer of the resistor. They are well
aware of the problem - if you get to the right person.

Having said that, here is a generalization: If the resistor's element
is a solid block of material, such as in a carbon composition type, it
will have very good pulse power ratings. On the other hand, if the
element is a film, it may develop tiny hot spots during pulsing and
eventually fail.



Many years ago I analyzed a problem with resistors which were
discoloring in the field. This involved two identical circuits with
identical singal inputs. In one circuit, a resistor kept turning brown
over time, in the other it did not. We were getting field returns as a
result of troubleshooting that focused on the brown resistors.

What was the difference? The resistor which did not discolor was resting
on two metal traces which ran under it, the one which discolored, was
resting on the PCB. That tiny amount of heatsinking provided by the
traces was the difference. Obviously, the circuit needed to be
redesigned, but it worked great on the breadboard when it went into
production.

The resistor should never have been run at that close to its maximum
dissipation to begin with. That's a lack of what they call a
conservative design.

Al



--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
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My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 at hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
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Watson A.Name \"Watt Sun - the Dark Remover\" wrote:



The resistor should never have been run at that close to its maximum
dissipation to begin with. That's a lack of what they call a
conservative design.

That's exactly right-and this story about "it worked right during
production testing" points up the fact that the price you pay for
misapplying a component is extended in-house testing designed at a
higher skill level than the usual application engineer possesses.

In article ,
mentioned...


Watson A.Name \"Watt Sun - the Dark Remover\" wrote:



The resistor should never have been run at that close to its maximum
dissipation to begin with. That's a lack of what they call a
conservative design.

That's exactly right-and this story about "it worked right during
production testing" points up the fact that the price you pay for
misapplying a component is extended in-house testing designed at a
higher skill level than the usual application engineer possesses.

I worked for a small company that was owned by a conglomerate. The
conglomerate said that they'd never use any of our equipment that were
in a blue case. Which, since almost everything was in a blue case...

Anyway, we had problems with the 7805 regulators shutting down from
overtemp. They were mounted on the PCB with a small heatsink. So we
had to ECO them by adding a few inches of wire and bolting the 7805 to
the aluminum case, which soaked up plenty of heat. After that, no
more weird behavior.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 at hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@

Anyway, we had problems with the 7805 regulators shutting down from
overtemp. They were mounted on the PCB with a small heatsink.

Hi all,
overheating should not be neglected. In my professional life I
encountered a device made by a famous company, which had a 7805 on a
heatsink, a processor and several customer chips inside a tightly
closed plastic box. All was O.K. at power-up. I was called for service
after two days. The device was hot and really did not work. I let it
cool down and all was O.K. again - for next two days. I was forced to
remove the top cover of the box forever. The device has been working
for several years now.
Proper cooling seems to be a must.

BR from Ivan OK1SIP

Anyway, we had problems with the 7805 regulators shutting down from
overtemp. They were mounted on the PCB with a small heatsink.

Hi all,
overheating should not be neglected. In my professional life I
encountered a device made by a famous company, which had a 7805 on a
heatsink, a processor and several customer chips inside a tightly
closed plastic box. All was O.K. at power-up. I was called for service
after two days. The device was hot and really did not work. I let it
cool down and all was O.K. again - for next two days. I was forced to
remove the top cover of the box forever. The device has been working
for several years now.
Proper cooling seems to be a must.

BR from Ivan OK1SIP

On 2003-11-26, Watson A.Name - Watt Sun, Dark Remover wrote:
I worked for a small company that was owned by a conglomerate. The
conglomerate said that they'd never use any of our equipment that were
in a blue case. Which, since almost everything was in a blue case...

Anyway, we had problems with the 7805 regulators shutting down from
overtemp. They were mounted on the PCB with a small heatsink. So we
had to ECO them by adding a few inches of wire and bolting the 7805 to
the aluminum case, which soaked up plenty of heat. After that, no
more weird behavior.

It wasn't WG Security Products, was it? Doesn't sound like it. A while
back I got a used video quad that they had made, and the 7805 was mounted
like that. Also, the 7805 was blown.

-- uns

On 2003-11-26, Watson A.Name - Watt Sun, Dark Remover wrote:
I worked for a small company that was owned by a conglomerate. The
conglomerate said that they'd never use any of our equipment that were
in a blue case. Which, since almost everything was in a blue case...

Anyway, we had problems with the 7805 regulators shutting down from
overtemp. They were mounted on the PCB with a small heatsink. So we
had to ECO them by adding a few inches of wire and bolting the 7805 to
the aluminum case, which soaked up plenty of heat. After that, no
more weird behavior.

It wasn't WG Security Products, was it? Doesn't sound like it. A while
back I got a used video quad that they had made, and the 7805 was mounted
like that. Also, the 7805 was blown.

-- uns

In article ,
mentioned...


Watson A.Name \"Watt Sun - the Dark Remover\" wrote:



The resistor should never have been run at that close to its maximum
dissipation to begin with. That's a lack of what they call a
conservative design.

That's exactly right-and this story about "it worked right during
production testing" points up the fact that the price you pay for
misapplying a component is extended in-house testing designed at a
higher skill level than the usual application engineer possesses.

I worked for a small company that was owned by a conglomerate. The
conglomerate said that they'd never use any of our equipment that were
in a blue case. Which, since almost everything was in a blue case...

Anyway, we had problems with the 7805 regulators shutting down from
overtemp. They were mounted on the PCB with a small heatsink. So we
had to ECO them by adding a few inches of wire and bolting the 7805 to
the aluminum case, which soaked up plenty of heat. After that, no
more weird behavior.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 at hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@

Watson A.Name \"Watt Sun - the Dark Remover\" wrote:



The resistor should never have been run at that close to its maximum
dissipation to begin with. That's a lack of what they call a
conservative design.

That's exactly right-and this story about "it worked right during
production testing" points up the fact that the price you pay for
misapplying a component is extended in-house testing designed at a
higher skill level than the usual application engineer possesses.