I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan

On 10/17/2013 4:55 PM, Dan wrote:
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan
Google doesn't seem to have any trouble finding it.
First hit.
Assume you fixed what blew it.

On 10/17/2013 5:31 PM, mike wrote:
On 10/17/2013 4:55 PM, Dan wrote:
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan
Google doesn't seem to have any trouble finding it.
First hit.
Assume you fixed what blew it.

No schmuck, the 1st hit is AMAZON selling the fuses. The next 99 on
that page are ALSO simply sellers.

Thanks so much for taking the time to be HELPFUL.

On 10/17/2013 5:56 PM, Dan wrote:
On 10/17/2013 5:31 PM, mike wrote:
On 10/17/2013 4:55 PM, Dan wrote:
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan
Google doesn't seem to have any trouble finding it.
First hit.
Assume you fixed what blew it.

No schmuck, the 1st hit is AMAZON selling the fuses. The next 99 on
that page are ALSO simply sellers.

Thanks so much for taking the time to be HELPFUL.

Ok, let me quote the amazon page for you.

QUALITY USA brand fuses!! Set of 5 pieces, T3.15AH250V, T3.15A 250V,
T3.15 H250V, T3.15A 250V, T3.15H250V cartridge CERAMIC fuses 5X20mm
(3/16" X 3/4"), 3.15A 250V, SLOW-blow (Time Delay)

And again with focus on the rating:
3.15A 250V

And again with just the amperage
3.15A
The A is for Amps.
That helpful enough for you?

"mike"

Ok, let me quote the amazon page for you.

QUALITY USA brand fuses!! Set of 5 pieces, T3.15AH250V, T3.15A 250V, T3.15
H250V, T3.15A 250V, T3.15H250V cartridge CERAMIC fuses 5X20mm (3/16" X
3/4"), 3.15A 250V, SLOW-blow (Time Delay)


** Got any idea what the letter "T" stands for ?

Hint - it ain't "time".



.... Phil

"Phil Allison" wrote in message ...


"mike"

Ok, let me quote the amazon page for you.

QUALITY USA brand fuses!! Set of 5 pieces, T3.15AH250V, T3.15A 250V, T3.15
H250V, T3.15A 250V, T3.15H250V cartridge CERAMIC fuses 5X20mm (3/16" X
3/4"), 3.15A 250V, SLOW-blow (Time Delay)


** Got any idea what the letter "T" stands for ?

Hint - it ain't "time".



.... Phil

How about T for tiny... like your dick!

On Thursday, October 17, 2013 at 8:29:15 PM UTC-5, Phil Allison wrote:
"mike"

Ok, let me quote the amazon page for you.

QUALITY USA brand fuses!! Set of 5 pieces, T3.15AH250V, T3.15A 250V, T3..15
H250V, T3.15A 250V, T3.15H250V cartridge CERAMIC fuses 5X20mm (3/16" X
3/4"), 3.15A 250V, SLOW-blow (Time Delay)


** Got any idea what the letter "T" stands for ?

Hint - it ain't "time".



... Phil

Hey, I know there is some joking around going on here (and some animosity, too apparently) but the "T" DOES actually stand for: "T = Time. Time Delay or Slow Blow.(Typically open between 100 and 300 ms @ ten times the rated current)"

Correct? Or am I missing something? BTW that comes from this google cached page:

http://webcache.googleusercontent.co...&ct=clnk&gl=us

I'm just trying to learn, I've got to replace that same damn fuse, and I'm frankly having a bitch of a time figuring out what's causing it to blow (it's the psu from a 32' flatscreen tv if that matters) Replaced a bunch of bad caps, and it powers up for about 3 seconds with a nice picture, and then bam blown fuse. Does rogaine help for hair regrowth that you pulled out yourself lol?

Ok, let me quote the amazon page for you.

QUALITY USA brand fuses!! Set of 5 pieces, T3.15AH250V, T3.15A 250V,
T3.15 H250V, T3.15A 250V, T3.15H250V cartridge CERAMIC fuses 5X20mm
(3/16" X 3/4"), 3.15A 250V, SLOW-blow (Time Delay)

Yeah, I saw that. It also says "You will receive 5 fuses and they can
be either of these marking: T3.15AH250V, T3.15A 250V, T3.15 H250V,
T3.15A 250V, T3.15H250V." Not being a fuse expert, I don't know that
these are all in fact interchangeable, and I thought perhaps it might be
better to clarify the rating numbers with someone who's NOT trying to
'sell me something'.


And again with focus on the rating:
3.15A 250V

And again with just the amperage
3.15A
The A is for Amps.
That helpful enough for you?


That's what I was looking for. That wasn't so hard, now was it? I
guess I'll leave it to you and your shrink to determine why you didn't
simply give that info to begin with, and instead felt the need to make a
total stranger feel stupid for asking a legitimate question in an
appropriate forum. My guess would be low self esteem, but check Amazon,
I bet they have a self-help book on it.

Dan wrote:
Ok, let me quote the amazon page for you.

QUALITY USA brand fuses!! Set of 5 pieces, T3.15AH250V, T3.15A 250V,
T3.15 H250V, T3.15A 250V, T3.15H250V cartridge CERAMIC fuses 5X20mm
(3/16" X 3/4"), 3.15A 250V, SLOW-blow (Time Delay)

Yeah, I saw that. It also says "You will receive 5 fuses and they can
be either of these marking: T3.15AH250V, T3.15A 250V, T3.15 H250V,
T3.15A 250V, T3.15H250V." Not being a fuse expert, I don't know that
these are all in fact interchangeable, and I thought perhaps it might
be better to clarify the rating numbers with someone who's NOT trying
to 'sell me something'.


And again with focus on the rating:
3.15A 250V

And again with just the amperage
3.15A
The A is for Amps.
That helpful enough for you?


That's what I was looking for. That wasn't so hard, now was it? I
guess I'll leave it to you and your shrink to determine why you didn't
simply give that info to begin with, and instead felt the need to
make a total stranger feel stupid for asking a legitimate question in
an appropriate forum. My guess would be low self esteem, but check
Amazon, I bet they have a self-help book on it.

Is this the way YOU say thank you. Remind me no to respond to your posts.

On Thursday, October 17, 2013 5:56:12 PM UTC-7, Dan wrote:
On 10/17/2013 5:31 PM, mike wrote:

On 10/17/2013 4:55 PM, Dan wrote:

I need to replace a PSU fuse in an LCD monitor. The open fuse is

ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing

between the various markings. I understand the speed rating (T) and the

voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15

amps, or 15 amps? Did some searching, but all I can find are pages

trying to sell fuses, not any giving how to read the ratings.



TIA



Dan

Google doesn't seem to have any trouble finding it.

First hit.

Assume you fixed what blew it.



No schmuck, the 1st hit is AMAZON selling the fuses. The next 99 on

that page are ALSO simply sellers.



Thanks so much for taking the time to be HELPFUL.

A lot of nerve calling names when YOU'RE the who one can't read a fuse or even look it up. And what creative name will you have for me?

G²

"Dan" wrote in message
eb.com...
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages trying
to sell fuses, not any giving how to read the ratings.

TIA

Dan


This is an absolutely bog standard fuse size. It is 'T' rated, and 3.15 amps
nominal carrying capacity. That is a very common value and fuse type
(ceramic bodied) for the front end fuse in a typical LCD TV switch-mode
power supply. It is important that it is only replaced with a ceramic type,
as faults in this area can cause a glass fuse to explode. Which brings me to
why you are replacing this fuse. It is quite unusual for the fuse in this
position to fail for no reason. You will normally find that the PSU has
suffered a major front-end failure, which may be something quite
straightforward like a faulty bridge, but more often than not, a fuse-blower
will have a short circuit switching element - usually a FET - and along with
this, it will have various short circuit diodes, open circuit resistors, and
often a blown supervisor IC ...

If that should turn out to be the case, there are 'repair kits' available on
the 'net for most common makes and models. These will contain a number of
components, all of which need to be replaced, whether the originals seem to
be faulty or not. 99% of the time, fitting such a kit results in a fix. A
degree of skill and knowledge beyond the level of simple fuse replacement,
is however required to do the job, as some parts may be surface mount.

Alternatively, replacement power supply boards are often available
remarkably cheaply.

So, bottom line, by all means try a replacement fuse first. You may be lucky
and get away with it. But be prepared for your new fuse to fail immediately
.... :-\

Arfa

Arfa - Thanks for all the great info. What happened was my daughter
accidentally knocked the monitor on the floor when it was on, badly
banging the screen area. Oddly, it blew the ground fault interrupter
on that circuit, but also the internal fuse. The monitor is older,
probably not worth the more expensive repairs you suggest, but thanks
for passing on all the possibilities, I appreciate your help!

Dan

On 10/17/2013 5:37 PM, Arfa Daily wrote:


"Dan" wrote in message
eb.com...
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and
the voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps,
.15 amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan


This is an absolutely bog standard fuse size. It is 'T' rated, and 3.15
amps nominal carrying capacity. That is a very common value and fuse
type (ceramic bodied) for the front end fuse in a typical LCD TV
switch-mode power supply. It is important that it is only replaced with
a ceramic type, as faults in this area can cause a glass fuse to
explode. Which brings me to why you are replacing this fuse. It is quite
unusual for the fuse in this position to fail for no reason. You will
normally find that the PSU has suffered a major front-end failure, which
may be something quite straightforward like a faulty bridge, but more
often than not, a fuse-blower will have a short circuit switching
element - usually a FET - and along with this, it will have various
short circuit diodes, open circuit resistors, and often a blown
supervisor IC ...

If that should turn out to be the case, there are 'repair kits'
available on the 'net for most common makes and models. These will
contain a number of components, all of which need to be replaced,
whether the originals seem to be faulty or not. 99% of the time, fitting
such a kit results in a fix. A degree of skill and knowledge beyond the
level of simple fuse replacement, is however required to do the job, as
some parts may be surface mount.

Alternatively, replacement power supply boards are often available
remarkably cheaply.

So, bottom line, by all means try a replacement fuse first. You may be
lucky and get away with it. But be prepared for your new fuse to fail
immediately ... :-\

Arfa

"Arfa Daily"

So, bottom line, by all means try a replacement fuse first. You may be
lucky and get away with it. But be prepared for your new fuse to fail
immediately ... :-\

** Fuses cost money and I don't like to see them blow at switch on.

So my standard practice is to fit a new fuse and then connect the AC lead to
a Variac via a current meter ( true rms) and slowly wind up the voltage.
With a SMPS, the current reading should be small until it suddenly strikes
and runs at some voltage between 80V and 160V as shown on the Variac's dial.

If a current near to the fuse's rating appears at a low setting on the
Variac, then its game over.

In cases where the PCB has to be exposed to get at the fuse, visual
inspection for damage is the first step and then an old fashioned moving
coil multimeter on the low ohms range to check PSU diodes and the switching
transistor for shorts.

BTW:

Guitar amps regularly arrive with either no fuse or a glaringly wrong size
or type fuse - ie fast fuses in the AC.

However, the ones I really hate arrive with NO fuse cap in the holder.

Grrrrrr.........


..... Phil

On Fri, 18 Oct 2013 12:21:09 +1100 "Phil Allison"
wrote in Message id: :


"Arfa Daily"

So, bottom line, by all means try a replacement fuse first. You may be
lucky and get away with it. But be prepared for your new fuse to fail
immediately ... :-\

** Fuses cost money and I don't like to see them blow at switch on.

So my standard practice is to fit a new fuse and then connect the AC lead to
a Variac via a current meter ( true rms) and slowly wind up the voltage.
With a SMPS, the current reading should be small until it suddenly strikes
and runs at some voltage between 80V and 160V as shown on the Variac's dial.

If a current near to the fuse's rating appears at a low setting on the
Variac, then its game over.

In cases where the PCB has to be exposed to get at the fuse, visual
inspection for damage is the first step and then an old fashioned moving
coil multimeter on the low ohms range to check PSU diodes and the switching
transistor for shorts.

BTW:

Guitar amps regularly arrive with either no fuse or a glaringly wrong size
or type fuse - ie fast fuses in the AC.

However, the ones I really hate arrive with NO fuse cap in the holder.

Grrrrrr.........

Better yet if you can find one cheap, a Sencore PR570.
http://www.ebay.com/sch/Electrical-T...R40&_nkw=PR570
It has the capability to automatically trip and shut down it's AC output
if the current exceeds whatever setting you dial in. It doubles as an
isolation transformer and variable AC power supply as well. Got one of
these for $150 a year ago on Ebay, I can't count how many times I've used
it.

On 10/18/2013 02:51 AM, JW wrote:
On Fri, 18 Oct 2013 12:21:09 +1100 "Phil Allison"

http://pinyot.com/dimbulb/dim_bulb_tester.htm


Better yet if you can find one cheap, a Sencore PR570.
http://www.ebay.com/sch/Electrical-T...R40&_nkw=PR570
It has the capability to automatically trip and shut down it's AC output
if the current exceeds whatever setting you dial in. It doubles as an
isolation transformer and variable AC power supply as well. Got one of
these for $150 a year ago on Ebay, I can't count how many times I've used
it.

A Dim Bulb current limiter will protect better than a Variac. fyi.

http://www.kendrick-amplifiers.com/m...tegory_Code=04

On 10/17/2013 06:21 PM, Phil Allison wrote:
"Arfa Daily"

So, bottom line, by all means try a replacement fuse first. You may be
lucky and get away with it. But be prepared for your new fuse to fail
immediately ... :-\

** Fuses cost money and I don't like to see them blow at switch on.

So my standard practice is to fit a new fuse and then connect the AC lead to
a Variac via a current meter ( true rms) and slowly wind up the voltage.
With a SMPS, the current reading should be small until it suddenly strikes
and runs at some voltage between 80V and 160V as shown on the Variac's dial.

If a current near to the fuse's rating appears at a low setting on the
Variac, then its game over.

In cases where the PCB has to be exposed to get at the fuse, visual
inspection for damage is the first step and then an old fashioned moving
coil multimeter on the low ohms range to check PSU diodes and the switching
transistor for shorts.

BTW:

Guitar amps regularly arrive with either no fuse or a glaringly wrong size
or type fuse - ie fast fuses in the AC.

However, the ones I really hate arrive with NO fuse cap in the holder.

Grrrrrr.........


.... Phil

"dave" wrote in message
...
A Dim Bulb current limiter will protect better than a Variac. fyi.



$99?! I made one of them out of a piece of wood, a wall mount switch, a
wall mount switched 13A outlet, and a bulb holder, for thruppence ha'penny.

I use it a lot. In fact I used it today after a combo came in with a blown
fuse.


Gareth. (cheapskate)

"dave"

A Dim Bulb current limiter will protect better than a Variac. fyi.

http://www.kendrick-amplifiers.com/m...tegory_Code=04


** A Variac alone provides no protection.

But the method I outlined is vastly superior to the old light bulb trick.

Variac + true rms current meter + fuse (which can be a fast blow type).

There are far too many anomalies when a series lamp is fitted to the AC
supply.


.... Phil

"Phil Allison" wrote in message ...


"dave"

A Dim Bulb current limiter will protect better than a Variac. fyi.

http://www.kendrick-amplifiers.com/m...tegory_Code=04


** A Variac alone provides no protection.

But the method I outlined is vastly superior to the old light bulb trick.

Variac + true rms current meter + fuse (which can be a fast blow type).

There are far too many anomalies when a series lamp is fitted to the AC
supply.





I find the old lightbulb trick quick and easy, providing it is used in
appropriate circumstances.

Case in point being the bog standard small combo with the blown mains fuse I
used it on today, where it is a binary Yes there is a problem, or Not - the
fuse just blew.
And no harm done in the process, being as maximum mains current draw is 500
mA or so.
The amp will still run and make sound with the bulb in place.


I understand you can't use this techinique reliably on high power things
like Power Amps, cos they don't like undervoltage and will trip and
misbehave and do all sorts of weird stuff.
Here, I do use the variac in series with the bulb, just to see visually what
current is being drawn and how, and when.
And it is also sometimes useful to use the bulb as a soft start, then bypass
it, once you are happy the amp isn't going to explode.

Likewise I use the variac and bulb on SMPS's, again to visually and audibly
get an idea of whats happening and when.
You can hear when it kicks in, or shuts down, and that auditory information
is backed up by the behaviour of the bulb.



Horses for courses.


Gareth.

"Phil Allison" wrote in message
...

"dave"

A Dim Bulb current limiter will protect better than a Variac. fyi.

http://www.kendrick-amplifiers.com/m...tegory_Code=04


** A Variac alone provides no protection.

But the method I outlined is vastly superior to the old light bulb trick.

Variac + true rms current meter + fuse (which can be a fast blow type).

There are far too many anomalies when a series lamp is fitted to the AC
supply.


... Phil


Agreed. The dim bulb limiter is a bit of a catch-all largely designed for
production testing by people no necessarily skilled in electronics. A variac
used in the way you suggested, and the way that I too use mine, is just as
effective at avoiding burnups in a fuse-blower, whilst actually providing a
greater level of information about where to be looking for the problem. The
trick is that like an ESR meter, a degree of skill is required to use the
variac correctly (for this type of fault finding) and to interpret the
results obtained ...

Arfa

"Phil Allison" wrote in message
...

"Arfa Daily"

So, bottom line, by all means try a replacement fuse first. You may be
lucky and get away with it. But be prepared for your new fuse to fail
immediately ... :-\

** Fuses cost money and I don't like to see them blow at switch on.

So my standard practice is to fit a new fuse and then connect the AC lead
to a Variac via a current meter ( true rms) and slowly wind up the
voltage. With a SMPS, the current reading should be small until it
suddenly strikes and runs at some voltage between 80V and 160V as shown on
the Variac's dial.

If a current near to the fuse's rating appears at a low setting on the
Variac, then its game over.

In cases where the PCB has to be exposed to get at the fuse, visual
inspection for damage is the first step and then an old fashioned moving
coil multimeter on the low ohms range to check PSU diodes and the
switching transistor for shorts.

BTW:

Guitar amps regularly arrive with either no fuse or a glaringly wrong size
or type fuse - ie fast fuses in the AC.

However, the ones I really hate arrive with NO fuse cap in the holder.

Grrrrrr.........


.... Phil



All agreed. I too always bring a fuse-blower up on the variac, looking for
the same tell-tales as you. I didn't bother mentioning it, because I'm sure
the OP will not be familiar or equipped with such a workshop specific item.

Arfa

"Arfa Daily"
"Phil Allison"
"Arfa Daily"

So, bottom line, by all means try a replacement fuse first. You may be
lucky and get away with it. But be prepared for your new fuse to fail
immediately ... :-\

** Fuses cost money and I don't like to see them blow at switch on.

So my standard practice is to fit a new fuse and then connect the AC lead
to a Variac via a current meter ( true rms) and slowly wind up the
voltage. With a SMPS, the current reading should be small until it
suddenly strikes and runs at some voltage between 80V and 160V as shown
on the Variac's dial.

If a current near to the fuse's rating appears at a low setting on the
Variac, then its game over.


All agreed. I too always bring a fuse-blower up on the variac, looking for
the same tell-tales as you.


** OK, my test set up is used with ALL items for repair.

The AC current meter uses a Hall effect transducer ( totally isolates the
mains supply) feeding a true rms converter IC and then a 3.5 digit LED
display. There are two ranges, 2A and 20A with 1mA and 10mA resolution
respectively.

A standard 3 pin outlet is fitted to the front and all jobs get plugged in
there.

A BNC socket on the back of the unit provides a waveform for the scope that
is either 1V or 100mV per amp of AC current. Signal bandwidth is DC to 100
kHz and max output is +/- 10V, so current surges up to 100 amps peak can be
seen on the scope.

The current meter's electronics has its own AC lead so the Variac does not
affect it.

The set up easily caters for the smallest plug pak (wall wart) right up to
2.5kW/ch stage lighting dimmers and the largest power amps. Been in
continuous use now since 1996.



..... Phil

Phil Allison wrote:
Guitar amps regularly arrive with either no fuse or a glaringly wrong
size or type fuse - ie fast fuses in the AC.

I see Australian musicians have discovered the "universal replacement"
fuse, too - it's the fuse in a particular physical size with the biggest
number preceding the "A" printed on the box. It is guaranteed not to
blow - something else will usually pop before the fuse does.

I used to work on trucks where AGC 10 A fuses were routinely replaced
with 30 A fuses in an attempt to stop the fuse from blowing. Usually
the actual problem was that an added wire had been run through a hole
with no grommet, sleeving, etc and was grounding out.

For a while in the 70s, some US cars had "SFE" fuses that were all 0.25"
diameter but different lengths - lower ratings were physically shorter -
to help prevent overfusing. An SFE 4 was a little over 0.5", and an
SFE 20 was the same length (1.25") as an AGC fuse. I think it was a
good idea, but it went away with the changeover to the flat blade fuses.

However, the ones I really hate arrive with NO fuse cap in the holder.

At a previous employer, one of our products was in a 6U 19" rackmount
chassis with two holders for 5 x 20 mm fuses on the back. We shipped
this in its own cardboard box, and it always showed up with everything
intact. Our customer then bolted that chassis into their cabinet, along
with other equipment, and shipped the whole shebang on a flatbed truck
to the site. When it got to site, there was a pretty good chance that
the fuse holder caps would be missing. We told them a) don't ship it
that way and b) put a piece of tape over the caps before shipping. They
ignored a), did b), and asked us for a case lot of replacement caps,
which we gave them.

In the previous generation of that product, the fuses were in the power
inlet module - one where you have to remove the main power connector to
open the little flap that lets you change the fuses. I don't know
whether that inlet module was eliminated from the design for cost or
customer reasons. (It wasn't quite an IEC inlet module, because the
incoming power was DC with a unique connector, but it was the same
idea.)

Matt Roberds

Phil Allison

Guitar amps regularly arrive with either no fuse or a glaringly wrong
size or type fuse - ie fast fuses in the AC.

I see Australian musicians have discovered the "universal replacement"
fuse, too - it's the fuse in a particular physical size with the biggest
number preceding the "A" printed on the box. It is guaranteed not to
blow - something else will usually pop before the fuse does.

I used to work on trucks where AGC 10 A fuses were routinely replaced
with 30 A fuses in an attempt to stop the fuse from blowing.


** I have a box full of 20A, 25A 30A and 35A automotive 3AG fuses pulled
from guitar and power amps.

Not to mention all the blown ones wrapped in foil paper from a cigarette
pack.

However, the ones I really hate arrive with NO fuse cap in the holder.

At a previous employer, one of our products was in a 6U 19" rackmount
chassis with two holders for 5 x 20 mm fuses on the back. We shipped
this in its own cardboard box, and it always showed up with everything
intact. Our customer then bolted that chassis into their cabinet, along
with other equipment, and shipped the whole shebang on a flatbed truck
to the site. When it got to site, there was a pretty good chance that
the fuse holder caps would be missing. We told them a) don't ship it
that way and b) put a piece of tape over the caps before shipping. They
ignored a), did b), and asked us for a case lot of replacement caps,
which we gave them.


** In my example, the fuse caps were removed by the owners and thrown away
!!!

They all wrongly imagine techs can easily get spare ones to suit.

With many USA built guitar amps, it means drilling or punching a new hole in
the chassis to fit a new holder.


In the previous generation of that product, the fuses were in the power
inlet module - one where you have to remove the main power connector to
open the little flap that lets you change the fuses.


** That level sophistication of stops most of them in their tracks.



..... Phil

On Fri, 18 Oct 2013 12:21:09 +1100, "Phil Allison"
wrote:

** Fuses cost money and I don't like to see them blow at switch on.

I have a small collection of AC circuit breakers with clip leads
soldered onto the terminals. As I recall, 1A, 3A, 5A, and 10A. I
pick an appropriate value, clip onto the fuse terminals, and apply
power. If the circuit breaker doesn't pop, I install the real fuse. I
also use the variac trick, but only on my bench at home, as I don't
have one in the office.

Note: Some thermal circuit breakers will decrease in value if tripped
repeatedly. This is a safety feature as having the trip value
increase would eventually make the circuit breaker not trip at all.
Magnetic circuit breakers don't have this problem/feature.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thursday, February 5, 2015 at 11:35:42 AM UTC-5, Jeff Liebermann wrote:
Note: Some thermal circuit breakers will decrease in value if tripped
repeatedly. This is a safety feature as having the trip value
increase would eventually make the circuit breaker not trip at all.
Magnetic circuit breakers don't have this problem/feature.


I looked this up some time ago for the larger circuit breakers such as those in a main panel.

The manufacturers give specs for the number of cycles.

That number is very large for a circuit breaker being used as a switch to turn a circuit on and off. Many times lighting circuits, e.g., are operated with a breaker and don't have a switch. I don't remember offhand but I'm thinking in the range of 50,000 cycles.

Then you have the next case where the breaker "trips" on overcurrent. You have the toaster on when the refrigerator cycles, etc. You've exceed the 15 amp by enough to trip the breaker but it's not a dead short. The number of rated cycles goes down by a couple orders of magnitude but it's still high.

But now you have the dead short case, where you draw maximum fault current until the breaker trips. Breakers are only rated for 1 to 2 cycles of this kind of duty.

On Thu, 5 Feb 2015 09:08:16 -0800 (PST), Tim R
wrote:

On Thursday, February 5, 2015 at 11:35:42 AM UTC-5, Jeff Liebermann wrote:
Note: Some thermal circuit breakers will decrease in value if tripped
repeatedly. This is a safety feature as having the trip value
increase would eventually make the circuit breaker not trip at all.
Magnetic circuit breakers don't have this problem/feature.


I looked this up some time ago for the larger circuit breakers such as those in a main panel.

The manufacturers give specs for the number of cycles.

That number is very large for a circuit breaker being used as a switch to turn a circuit on and off. Many times lighting circuits, e.g., are operated with a breaker and don't have a switch. I don't remember offhand but I'm thinking in the range of 50,000 cycles.

Then you have the next case where the breaker "trips" on overcurrent. You have the toaster on when the refrigerator cycles, etc. You've exceed the 15 amp by enough to trip the breaker but it's not a dead short. The number of rated cycles goes down by a couple orders of magnitude but it's still high.

But now you have the dead short case, where you draw maximum fault current until the breaker trips. Breakers are only rated for 1 to 2 cycles of this kind of duty.

Sorta. There are many ways to use a circuit breaker, each with their
own unique way of causing problems. In my case, my collection of
assorted breakers came from a power supply that I designed, where I
made a big mistake. I used an AC rated breaker for the DC output. Bad
idea.

The contact material for AC and DC breakers are quite different. DC
breakers have a much larger spring to deal with the tendency for
arcing and welding the contacts when opening a high current DC circuit
under load. I did some crude testing and found that after tripping
about 10 times under 3x rated load, the contacts would weld. The same
breaker, with a 3x AC load seemed to work just fine. Moral: Don't
use AC only rated breakers with DC.

I didn't have much trouble using such a breaker as an on/off switch on
the AC side of the power supply. By much, I had to install a PTC
thermistor inrush current limiter on the AC line because the rather
large inrush current was sometimes tripping the breaker immediately
after it was turned on.

The breakers in my pile are the "push to reset" flavor and are not
used as an on/off switch.

A 5 amp breaker will conduct 5 amps forever and not trip. The
time-current curves are far from linear or simple:
https://www.google.com/search?q=circuit+breaker+trip+curves&tbm=isch
For example, a "typical" breaker will require about 3 minutes to open
at 2x the rated current, and about 0.1 sec at 10x the rated current.

After my initial screwup, I spent some time looking at such
time-current curves trying to select a proper circuit breaker. It
would have been much easier if I were allowed to use a combination
thermal-magnetic breaker, but those were far too expensive.

One could also use a PTC inrush current limiter as a temporary fuse.
Too much current and it gets hot and goes "open". The problem is
selecting the right combination of on-resistance and trip current.
http://en.wikipedia.org/wiki/Resettable_fuse
I've had to go through the design process a few times trying to find a
suitable replacement for such a device, that had burned itself to a
cinder and no parts list was available. There's no problem at either
extreme of low current and over-current. However, the dissipation
reached a peak in between these two extremes. At some current,
usually just below the trip point, it gets VERY hot but does not open.
Be careful with these.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Em quinta-feira, 17 de outubro de 2013 20h55min39s UTC-3, Dan escreveu:
I need to replace a PSU fuse in an LCD monitor. The open fuse is

ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing

between the various markings. I understand the speed rating (T) and the

voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15

amps, or 15 amps? Did some searching, but all I can find are pages

trying to sell fuses, not any giving how to read the ratings.



TIA



Dan

Hi,

The Ceramic Fuse can be found in a specialized electronic store. But this fuse is a specific component. I have the same problem. The Fuse 3,15a/H250v. You need to replace the same component because there is a reason about the form and type in this device. Be carefull. I try another fuse and got a explosion. Yeah.

On Thursday, October 17, 2013 at 7:55:39 PM UTC-4, Dan wrote:
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan

Jeff
You mentioned that you have a number of different breakers fitted with clip leads for testing before you install an actual fuse. I hate to repeatedly blow fuses too, but doesn't that increase the time it takes for the circuit to open, thus subjecting the equipment to possible further harm? Lenny

On Sat, 7 Feb 2015 18:01:09 -0800 (PST),
wrote:

Jeff
You mentioned that you have a number of different breakers fitted
with clip leads for testing before you install an actual fuse.

Yep.

I hate to repeatedly blow fuses too, but doesn't that increase
the time it takes for the circuit to open, thus subjecting
the equipment to possible further harm? Lenny

Chuckle. That would be like comparing the old screw in electric panel
fuse with the more modern circuit breakers. Actually, the magentic
circuit breaker is faster than the thermal fuse up to about 2x rated
current.

However, it doesn't matter. If the power supply is shorted, blowing
the circuit breaker a bit late isn't going to make much difference as
the power supply is already fried. Whatever is blown or shorted will
probably protect the rest of the circuitry. However, if everything is
working correctly, the circuit breaker won't trip so it make no
difference how fast or slow it opens.

Where it might get a bit sticky is a fairly low resistance short
across the power supply output. That won't draw enough current for a
instanteous breaker trip and might cook a few devices or traces
between the power supply and the low resistance short. It's a
definite risk, which I'll gladly take, because I haven't seem much of
that. Most commonly, it has happened when I stupidly install
electrolytic caps in backwards, which hopefully will not become
chronic or epidemic.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thursday, October 17, 2013 at 7:55:39 PM UTC-4, Dan wrote:
I need to replace a PSU fuse in an LCD monitor. The open fuse is
ceramic, 5 x 20 mm, and marked "T3.15AH250V", with no obvious spacing
between the various markings. I understand the speed rating (T) and the
voltage (250V), but I'm unclear on the amperage. Is it 3.15 amps, .15
amps, or 15 amps? Did some searching, but all I can find are pages
trying to sell fuses, not any giving how to read the ratings.

TIA

Dan

I've probably had a few thousand TV's come in here over the years. (not any more). NAP sets seemed to use circuit breakers a lot. Some other brands I recall that had open B+ fuses smoked and then blew the fuse when a new one was installed for testing. Often wondered why it didn't smoke the first time before the first fuse opened. Lenny