Wt burns a bulb or fuse, over current or volt??

[mamun2a]

We saw electric bulb or electronic circuit is burning sometimes for supply, what is the actual cause over volt or current?

 

[SHAHRAM_MOJTABAIE]

you need to study phisic books.

 

[mamun2a]

if so, why this forum????

 

[qsiguy]

Assuming your load doesn't change and you increase voltage you are increasing amperage at the same time. Say your load is 10 ohms and you supply 12 volts. You have 1.2 amps through your load. If you increase voltage to 24 volts with the same 10 ohm load you now have 2.4 amps through your load. So if you increase one you are increasing the other. That said I believe it is the amperage that causes the failure. If you limit the current through a given load you can supply it with a higher voltage (within certain limits) and still be ok but you can't run a lower voltage and increase the amperage.

 

[Aily Sajjad]

This is Power - the heat dissipation across the bulb filament. Increasing the voltage will increase the current (as qsiguy described). If the filament has a resistance R, V is the appplied voltage and I is the current passing, then the power across the filament will be (I)squared x R. Alternately it will be (V) sqaured / R. Increasing either I or V will increase the power or in other words the heat dissipation of the filament. This heat dissipation causes the filament temperature to rise, eventually causing it to melt and burn out.

Same is the reason with other electronic circuits, they have components which when applied with voltage higher than rated value dissipate more power and get heat up untill they burn out.

Aily
-------
MOM!!!!!!! I just wanted to experience how wires feel when current passes through them.

 

[RODALCO]

Correct!
But over voltage is the critical factor in here, which causes the lamp to burn out.
The power dissipation goes up very rapidly as per V²/R. hence heat and meltdown of the filament.
The resistance doesn't change (within reason), The amperage only changes because of the increase in voltage.

A lamp at 85% voltage, brightness 53%, Life 1000%
A lamp at 90% voltage, brightness 67%, Life 440%
A lamp at 95% voltage, brightness 83%, Life 210%
A lamp at 100% voltage, brightness 100%, Life 100%
A lamp at 105% voltage, brightness 120%, Life 50%
A lamp at 110% voltage, brightness 145%, Life 28%
A lamp at 120% voltage, brightness 200%, Life 6%

As from Bosch datasheet for normal filament lamps ( not halogens )

Source: Electricity and Electronics book, B. Kierdorf ISBN 90 201 1554 5

Hope this gives you a bit of an idea re overvoltage on lamps.

For a 12 Volts automotive lamp 13.5 volts is the design voltage for the filament. The 14 volts from the car alternator minus 0.5 volts for wiring drop.

 

[RODALCO]

For fuses.

Current causes a fuse to blow or burn out.
Other factors which may lead to an early demise are poor connections near the fuse carrier which could transfer heat into the fuse element and stress it out more and fail.
All fuses ran at maximum design current will dissipate some heat and rely on good connections to transfer the heat away from the fuse itself.

Voltage has to do with the insulating level of the wires and equipment.

12 volt wires may need insulation of 0.3 mm while 230 volts wires need insulation of 2mm thick.

For practical reasons the 12 V and 230 V wires look almost the same , insulation wise. The wires need to be able to handle some external abuse, otherwise if insulation was to thin they would fail very quickly especially in automotive conditions.

at 230 Volt a minimum gap has to be 6 mm while at 11000 volts it needs to be around 15 cm. for example for bare wires.

 

[Gayan Soyza]

Nice Discussion ...........It really gave a nice Idea......

Thanks Every body...............

 

[Hero999]

I remember reading an artical about the efficiency of incandessant lamps vs life. Normal domestic light bulbs last for 1000h, because a longer life would mean a cooler filament making the bulb less efficient and the cost of electricity will outweigh the cost of changing the bulb.

 

[Marks256]

{Sorry, i can't resist!!!}

you need to study phisic books.

And you need to learn how to spell.....

 

[audioguru]

And you need to learn how to spell.....

Try spelling the name of his country or try finding his country on a sattelite pic on Google Earth.
(Sorry, I couldn't resist and I don't know how to spell sattelite)

 

[Marks256]

Don't worry, i don't know how to spell it either... man, i love spell check...

 

[audioguru]

What is wrong with English spelling??
Sat e light. Satt ehh lite. It sounds right.
Sate ee light. It doesn't sound right but is spelled like this: satellite.

 

[Marks256]

Remember, opium was legal when our freaky forefathers created our plagiarized language.