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What FT means in an SMD fuse?

Y

Yuki

Jan 1, 1970
0
I have to replace one with FT engraved on it, size is 1206.
Thanks
 
N

N Cook

Jan 1, 1970
0
Yuki said:
Thanks,

I'd found a spec sheet from Littelfuse that uses TF (instead of FT) for a 500mA
slow fuse but not sure if the markings mean the same in all manufacturers.

I rarely come across surface mount fuses, but for a more general query.
Has anyone tried cracking open a SM fuse to see if the size of any remnant
film can give an indication of amperage. ?

Where you cannot be sure, I would wire off of the pads to a conventional ,
but lower amperage fuse, than the 0.5A that it maybe in this case. Then see
how it blows if it blows.
Then replace with a smt device when confident.
 
N

N Cook

Jan 1, 1970
0
N Cook said:
Yuki said:
a manufacturers.

I rarely come across surface mount fuses, but for a more general query.
Has anyone tried cracking open a SM fuse to see if the size of any remnant
film can give an indication of amperage. ?

Where you cannot be sure, I would wire off of the pads to a conventional ,
but lower amperage fuse, than the 0.5A that it maybe in this case. Then see
how it blows if it blows.
Then replace with a smt device when confident.

By "see" i mean if you wire in a glass cased 100mA fuse and you see it glow
orange before fusing then 500mA rating is probably about right.
If it blows very quickly and intensly white or green then still an
underlying fault or a fuse rating higher than 500mA
 
Y

Yuki

Jan 1, 1970
0
N Cook said:
By "see" i mean if you wire in a glass cased 100mA fuse and you see it glow
orange before fusing then 500mA rating is probably about right.
If it blows very quickly and intensly white or green then still an
underlying fault or a fuse rating higher than 500mA

This particular one is encapsulated in transparent resin and looks like having a
blob of tin in the center, no glow here for this reason and because it's located
in the phone line input of and ADSL router for protection.
 
R

Ross Herbert

Jan 1, 1970
0
This particular one is encapsulated in transparent resin and looks like having a
blob of tin in the center, no glow here for this reason and because it's located
in the phone line input of and ADSL router for protection.


Since this fuse is in series with the telephone line the telco line
current maximum will be in the order of 100mA. My opinion is that any
SMD delay type fuse of 200mA - 500mA will be adequate. I would first
be wondering what caused it to blow. Usually, the line interface is
current limited so I doubt the current which blew the original would
come from the exchange, but I could be wrong there.
 
Y

Yuki

Jan 1, 1970
0
Since this fuse is in series with the telephone line the telco line
current maximum will be in the order of 100mA. My opinion is that any
SMD delay type fuse of 200mA - 500mA will be adequate. I would first
be wondering what caused it to blow. Usually, the line interface is
current limited so I doubt the current which blew the original would
come from the exchange, but I could be wrong there.

The cause is known, it was a nasty electrical storm with several direct hits in
phone and power poles. A lot of phone line connected equipment was killed that
day.

I have fixed this problem before but with proper labeled fuses in the board.

Now my problem is sourcing it for a reasonable cost as I'm far from decent
component stores. I somebody can suggest a supplier I'm located in southern
Spain.
 
M

Michael Kennedy

Jan 1, 1970
0
Yuki said:
The cause is known, it was a nasty electrical storm with several direct
hits in
phone and power poles. A lot of phone line connected equipment was killed
that
day.

I have fixed this problem before but with proper labeled fuses in the
board.

Now my problem is sourcing it for a reasonable cost as I'm far from decent
component stores. I somebody can suggest a supplier I'm located in
southern
Spain.

You could solder leads on a glass tube fuse and use that to replace it. That
should be much easier to find than a SMD fuse. DSL Modems usually have
extra room inside so space shouldn't be a problem.

Mike
 
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