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]

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.

 

[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

 

[mike]

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?

 

[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

"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.

 

[[email protected]]

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

 

[JW]

"Arfa Daily"

** 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.

 

[Phil Allison]

"dave"

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

http://www.kendrick-amplifiers.com/...S&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

 

[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

 

[Bob F]

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'.


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.

 

[mike]

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

Chill.
My bad, I forced the issue.
Blame me for my inciteful response.

 

[Phil Allison]

"Arfa Daily"

"Phil Allison"

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

 

[[email protected]]

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]

Phil Allison


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.

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