Who Has Used Resistors as Fuses

[D from BC]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

I was blowing 2amp fast blow pico fuses.
D from BC

 

[ian field]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

I was blowing 2amp fast blow pico fuses.
D from BC

Most consumer electronics manufacturers use a variety of fusible resistors
which are specially designed not to burst into flames, seek out component
catalogues aimed at the service trade.

 

[John Popelish]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

I was blowing 2amp fast blow pico fuses.
D from BC

I suggest you use thermistors that switch from a low
resistance to a very high resistance at a critical
temperature. They reset back to low resistance when they
cool off.

For instance:
http://www.epcos.com/inf/55/db/ptc_03/00740083.pdf

 

[Eeyore]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

Fusible resistors
http://uk.farnell.com/jsp/search/br...1&Ntt=fusible+resistor&Ntx=&_requestid=194422

Graham

 

[Jan Panteltje]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

Just do not use metal film, I did, and it burned a hole in the peeseebee.
Carbon is OK.
But the energy dissipated in it when a sort circuit or overload
happens must be high enough to evaporate the carbon.
And the size must be enough so the electrons do not take a shortcut and flash over.
Old tube TVs used wirewound reistors in ceramic tubes that heated a soldering
joint holding a spring breaking the contact.

There are also microfuses that are re-usable for a variety of volatges and currents.

I have also split apart the strands of flatcable and soldered that over the fuseholder
clips... when no fuse at hand.

 

[Meat Plow]

Most consumer electronics manufacturers use a variety of fusible resistors
which are specially designed not to burst into flames, seek out component
catalogues aimed at the service trade.

But, more expensive than a fuse no?

 

[D from BC]

I suggest you use thermistors that switch from a low
resistance to a very high resistance at a critical
temperature. They reset back to low resistance when they
cool off.

For instance:
http://www.epcos.com/inf/55/db/ptc_03/00740083.pdf

Digikey only has stock of a 100mA 230V version of the above link.

An LVR200S with 2A 240V looked good...but no Digi stock.

Digikey doesn't always list the voltage rating for PTC thermistors.

I'd like >170Vpk. So when the PTC trips it doesn't internally arc,
burn or decompose or whyever it's got a voltage rating.
I"ve notice on Digi that prices are about $1.00 each.. Maybe shoe-in
resistors are much cheaper and easier to get and therefore easily
expendable..
D from BC

 

[D from BC]

But, more expensive than a fuse no?

http://www.phoenixpassives.com/resistors/fusible_resistor_nfr25_nfr25h.pdf
I quickly found this as an example..
I also did a quick average at about 20centsCAD each from Digikey..

I'll stare at the data sheets for awhile. I'm not familiar with these
devices..
I don't know how it compares to a cheapo resistor..
D from BC

 

[Eeyore]

I don't know how it compares to a cheapo resistor..

They don't catch fire. Instead of a flamamble lacquer coating, it's typically
cement.

Graham

 

[D from BC]

Just do not use metal film, I did, and it burned a hole in the peeseebee.
Carbon is OK.
But the energy dissipated in it when a sort circuit or overload
happens must be high enough to evaporate the carbon.
And the size must be enough so the electrons do not take a shortcut and flash over.
Old tube TVs used wirewound reistors in ceramic tubes that heated a soldering
joint holding a spring breaking the contact.

There are also microfuses that are re-usable for a variety of volatges and currents.

I have also split apart the strands of flatcable and soldered that over the fuseholder
clips... when no fuse at hand.

I've seen the wire used in glass fuses.. I've been tempted to source
that wire to make custom fuses or temporary fuses.
It might be just a matter of selecting a wire length or winding for
different fuse currents.
D from BC

 

[ian field]

I've seen the wire used in glass fuses.. I've been tempted to source
that wire to make custom fuses or temporary fuses.
It might be just a matter of selecting a wire length or winding for
different fuse currents.
D from BC

For prototyping only - just solder a length of fuse wire to the end caps
outside the glass tube, just remember to replace with proper fuses when its
finished.

 

[Eeyore]

I've seen the wire used in glass fuses.. I've been tempted to source
that wire to make custom fuses or temporary fuses.
It might be just a matter of selecting a wire length or winding for
different fuse currents.

The wire in fuses may be lead or have a high lead content. You can't buy it any old where.

Graham

 

[Robert Adsett]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

I was blowing 2amp fast blow pico fuses.

Polyswitches (PTC resistors) work in that range as long as your voltages
aren't too high. You might even consider them in place of the pico
fuses.

Robert

 

[Robert Adsett]

Digikey only has stock of a 100mA 230V version of the above link.

An LVR200S with 2A 240V looked good...but no Digi stock.

Digikey doesn't always list the voltage rating for PTC thermistors.

I'd like >170Vpk. So when the PTC trips it doesn't internally arc,
burn or decompose or whyever it's got a voltage rating.
I"ve notice on Digi that prices are about $1.00 each.. Maybe shoe-in
resistors are much cheaper and easier to get and therefore easily
expendable..

These look like new parts. You might be able to get samples from Tyco
or maybe just parallel up several smaller devices.

Tyco has a sample link on this page

http://circuitprotection.com/lvr/

Robert

 

[MooseFET]

Sometimes I burn too many regular fuses with prototypes.

Could I use a resistor as a temporary fuse substitute?
It's ok if the fuse bursts into flames..
Affer debugging, I'll used a proper fuse.

Has anybody sacrificed resistors like this?
If so, which resistor type makes for a good fuse?
Carbon? Thick film? Thin film? Wirewound?

I was blowing 2amp fast blow pico fuses.

I have used a resistor as a fuse in a PCB that went into production
equipment. Once the unit makes it through test and is installed, the
system fuse protects the fuse resistor. The fuse resistor is only the
protect against shorts during testing. It worked out quite well once
I explained for the 15th time "No, we don't need a higher wattage
resistor there".

Fuses have the advantage that they are clearly labeled as fuses.

Polyswitches are a good way to go but you may have to still have a
fuse to protect the PTC device. Don't trust the ratings you see on
the first page of the data sheet.

Later in the data sheet you will often find the real limit on voltage
is much less than the first page says. The first page's rating
assumes that you gently take the current up until it trips and then
apply a short pulse of the voltage. You can't take a 600V PTC and
hook it to a 600V supply and have it survive.

 

[D from BC]

I have used a resistor as a fuse in a PCB that went into production
equipment. Once the unit makes it through test and is installed, the
system fuse protects the fuse resistor. The fuse resistor is only the
protect against shorts during testing. It worked out quite well once
I explained for the 15th time "No, we don't need a higher wattage
resistor there".

Fuses have the advantage that they are clearly labeled as fuses.

Polyswitches are a good way to go but you may have to still have a
fuse to protect the PTC device. Don't trust the ratings you see on
the first page of the data sheet.

Later in the data sheet you will often find the real limit on voltage
is much less than the first page says. The first page's rating
assumes that you gently take the current up until it trips and then
apply a short pulse of the voltage. You can't take a 600V PTC and
hook it to a 600V supply and have it survive.

??? The system fuse protects the fuse resistor??
Does this mean the system fuse is more sensitive and the fuse resistor
can never blow..??

Was that fuse resistor in series with the true fuse?
But wouldn't a dummy fuse be needed during testing? The dummy fuse is
a short circuit. Assuming a removable fuse in clips.
The dummy fuse is replaced with a real fuse at the end..

I'll be looking carefully at those PTC voltage specs.. thanks..
D from BC

 

[John Popelish]

Digikey only has stock of a 100mA 230V version of the above link.

An LVR200S with 2A 240V looked good...but no Digi stock.

The voltage rating is an upper limit. They work at lower
voltages.

Digikey doesn't always list the voltage rating for PTC thermistors.

I'd like >170Vpk. So when the PTC trips it doesn't internally arc,
burn or decompose or whyever it's got a voltage rating.
I"ve notice on Digi that prices are about $1.00 each.. Maybe shoe-in
resistors are much cheaper and easier to get and therefore easily
expendable..

What current limit are you needing?

 

[colin]

The wire in fuses may be lead or have a high lead content. You can't buy
it any old where.

Graham

ive used fine copper wire before, I have an old book wich gives fusing
currents for copper and fuse wire etc.

I have an old multimeter wich has a repairable fuse, it has a tiny spool of
some wire wich you just pull and insert into the fuse space, then press the
catch down.

Colin =^.^=

 

[[email protected]]

Just do not use metal film, I did, and it burned a hole in the peeseebee.
Carbon is OK.
But the energy dissipated in it when a sort circuit or overload
happens must be high enough to evaporate the carbon.

Carbon is not okay. It has a negative temperature coefficient of
resistance and if things go wrong, you can find your 10k carbon film
resistor carrying about an ampere at a voltage drop of a few volts or
less - all the current is flowing down a narrow, red-hot channel
through the carbon film

Metal fim and metal oxide resistors do at least have a positive
temperature coefficient of resistance, They are designed to run hot
when dissipated their rated load - somewhere around 250C - so if yu do
want to use them as fuses, bend the leads so the resistor body sits a
couple of millimetres above the printed circuit board.

 

[D from BC]

The voltage rating is an upper limit. They work at lower
voltages.


What current limit are you needing?

Approx 2A... It's inline with the household line voltage.
D from BC