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Two ways to fry a component

M

Midnight Oil

Jan 1, 1970
0
Many components I have seen have 2 ratings on them: volts and amps. I
am guessing that they put these two ratings on there because there are two
ways to "break" the component:


1) The voltage rating indicates how much "push" or force you can apply to
the device before it breaks. Even if you have a small amount of current
flowing through the device, if you apply too much push, it will break.
Like a door in a house, even if there is just one person going through the
door, if they are a very strong person and they push too hard on the door,
the latch will snap.

2) The current rating. If you apply a safe amount of push (voltage), but
you have a lot of current going through the device, it will break in
another way. Like the doorway analogy. If you have a bunch of weak people
running through the door, there isn't a lot of pressure, so the latch
won't snap, but with the crowd rushing through, the doorway will break.


So, when hooking up a device in a circuit, you need to observe both
ratings. Like the doorway, you want to be sure that someone too strong
doesn't go through and break the latch, and you also want to be sure not
too many people go through at once and break the doorway down. Two
different scenarios.


Is my understanding correct?


- Jamie





The Moon is Waxing Crescent (18% of Full)
 
R

Ralph Mowery

Jan 1, 1970
0
Midnight Oil said:
Many components I have seen have 2 ratings on them: volts and amps. I
am guessing that they put these two ratings on there because there are two
ways to "break" the component:

Electronic devices may actually have 3 ratings that can 'break' them. If
too much voltage is applied the device will break down or arc over. Too
much current and the device melts. Also if the voltage and current are
under the limit but the product of them (watts) the device will melt. Most
simiconductors must get rid of the excess heat that is produced. That is
partly why the power devices are mounted on large heat sinks.
 
P

PeteS

Jan 1, 1970
0
There are lots of voltage and current ratings for parts.

There's usually a current rating per pin on connectors, (as well as a
voltage rating which does not refer to the same thing). On ICs, there
is usually a current and voltage rating on IO ports when used as an
output or an input (how much it can source or sink - current - and the
maximum voltage permitted on the pin as an input usually). There are
many, many other voltage and current ratings (to say nothing of power
ratings and derating information).

In many (most?) cases, the two are not referring to the same thing.

Your post is mixing things apparently out of context, and in
electronics, context can be everything.

Get a specific part and ask about it - all will be explained by the
usenet denizens :)

Cheers

PeteS
 
P

Peter Bennett

Jan 1, 1970
0
Many components I have seen have 2 ratings on them: volts and amps. I
am guessing that they put these two ratings on there because there are two
ways to "break" the component:


1) The voltage rating indicates how much "push" or force you can apply to
the device before it breaks. Even if you have a small amount of current
flowing through the device, if you apply too much push, it will break.
Like a door in a house, even if there is just one person going through the
door, if they are a very strong person and they push too hard on the door,
the latch will snap.

2) The current rating. If you apply a safe amount of push (voltage), but
you have a lot of current going through the device, it will break in
another way. Like the doorway analogy. If you have a bunch of weak people
running through the door, there isn't a lot of pressure, so the latch
won't snap, but with the crowd rushing through, the doorway will break.

For many components, the current rating is the current the device will
draw at the recommended voltage.

For switches, and relay contacts, the current rating is the maximum
current that the contacts should be asked to carry or switch.

For fuses, the current rating is the maximum current the fuse should
carry without blowing, and the voltage rating is the maximum voltage
that should appear across the fuse if it does blow. If you use a 32
volt fuse on a 120 V circuit, it is likely to arc for some time,
rather than blowing cleanly.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
 
J

Jasen Betts

Jan 1, 1970
0
Many components I have seen have 2 ratings on them: volts and amps. I
am guessing that they put these two ratings on there because there are two
ways to "break" the component:


1) The voltage rating indicates how much "push" or force you can apply to
the device before it breaks. Even if you have a small amount of current
flowing through the device, if you apply too much push, it will break.
Like a door in a house, even if there is just one person going through the
door, if they are a very strong person and they push too hard on the door,
the latch will snap.

2) The current rating. If you apply a safe amount of push (voltage), but
you have a lot of current going through the device, it will break in
another way. Like the doorway analogy. If you have a bunch of weak people
running through the door, there isn't a lot of pressure, so the latch
won't snap, but with the crowd rushing through, the doorway will break.
So, when hooking up a device in a circuit, you need to observe both
ratings. Like the doorway, you want to be sure that someone too strong
doesn't go through and break the latch, and you also want to be sure not
too many people go through at once and break the doorway down. Two
different scenarios.

Immagine a revolving door or turnstile, with too many people passing through
the people move so fast that the bearings overheat and the turnstile falls
off (failed device is short circuit) or the bearing seize up (failed device
is open circuit)

current damage (too many amps) is usually caused by the resistive
overheating of some part of the device.

voltage damage is typically caused by the insulation failing inside
the device and then either causing overheating or leaving a
permanent hole in the insulation so current flows where it shouldn't
Is my understanding correct?

pretty much

Bye.
Jasen
 
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