Basic fuse question

[Dan]

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

 

[mike]

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.

 

[Arfa Daily]

"Dan" <bugaboo@yabahoo.com> wrote in message
news:52607920$0$61377$c3e8da3$5e5e430d@news.astraweb.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

 

[Dan]

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.

 

[Dan]

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" <bugaboo@yabahoo.com> wrote in message
news:52607920$0$61377$c3e8da3$5e5e430d@news.astraweb.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

 

[mike]

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?

 

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?

G˛

 

[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.

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

 

[Phil Allison]

"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

 

[Shaun]

"Phil Allison" wrote in message news:bcbhbdF2bkbU1@mid.individual.net...


"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!

 

[Dan]

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.

 

[JW]

On Fri, 18 Oct 2013 12:21:09 +1100 "Phil Allison" <phil_a@tpg.com.au>
wrote in Message id: <bcbgo8F28evU1@mid.individual.net>:

"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-Test-Equipment-/92074/i.html?_from=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.

 

[dave]

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

http://www.kendrick-amplifiers.com/mm5/merchant.mvc?Screen=PROD&Store_Code=KOS&Product_Code=KEN04-limiter&Category_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]

On 10/18/2013 02:51 AM, JW wrote:
> On Fri, 18 Oct 2013 12:21:09 +1100 "Phil Allison" <phil_a@tpg.com.au>

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-Test-Equipment-/92074/i.html?_from=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.

 

[Gareth Magennis]

"dave" <ricketzz@earthlink.net> wrote in message
news:VLKdnRM-fvS72fzPnZ2dnUVZ_radnZ2d@earthlink.com...

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)

 

[Phil Allison]

"dave"

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

http://www.kendrick-amplifiers.com/mm5/merchant.mvc?Screen=PROD&Store_Code=KOS&Product_Code=KEN04-limiter&Category_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

 

[Gareth Magennis]

"Phil Allison" wrote in message news:bcdp0jFgrg3U1@mid.individual.net...


"dave"

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

http://www.kendrick-amplifiers.com/mm5/merchant.mvc?Screen=PROD&Store_Code=KOS&Product_Code=KEN04-limiter&Category_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]

"Gareth Magennis"

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.

** A bulb that passes 0.5A rms when lit will pass 8A peak at switch on.

That is no soft start.

The amp will still run and make sound with the bulb in place.

** Then you have to remove it and all protection is lost.

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.

** A valve guitar amp of over 100 watts will not warm up and run with a 0.5A
bulb in the AC.

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.

** A"soft start" is always provided when using a Variac.

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.

** You can stick with what you like and are used to.



.... Phil

 

[dave]

On 10/18/2013 04:17 PM, Phil Allison wrote:

** A valve guitar amp of over 100 watts will not warm up and run with a 0.5A
bulb in the AC.

I routinely repair 100 Watt "valve" Marshalls, Fenders, Peaveys, Ampegs
(SLM), etc. and always use a 150 Watt bulb in series (and my 8 Ohm 100W
dummy load) until its time to check the bias. The one I use is clear (at
Home Depot fyi) and the orange glow on the filament is as sensitive an
indicator of current change as a panel meter. On very low idling only
part of the filament glows; play a power chord and the room lights up.

For a solid state amp up to about 75 Watts (no load) I use a clear 40
Watt oven bulb. Even on the bulb Marshall DSP works fine, the voltage
drop is low if the filament is cool.

Mine is a ceramic lamp socket, crudely spliced into a 15 Amp molded
extension cord, with a ground lift to accept 3 prongs, a switch, total
expenditure about $4.20. Oh yeah, the bulbs cost another tree fitty.

 

[Arfa Daily]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bcbgo8F28evU1@mid.individual.net...

"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