Quartz halogen light bulbs

[Edradour]

I have a 6 volt quartz halogen bulb from a torch, which won't light when 6 volts DC passes through it, but will light up with 2.5 volts AC.

Any ideas as to what the problem might be??

 

[sm1thson]

what is the wattage of the bulb?

what is your 6V power source? -maybe is isnt able to supply enough current!

 

[Edradour]

My bench power supply reads 100Ma when 6 volts is applied to the bulb. 100Ma is not top of the scale, but the voltage drops away to zero. Don't understand it.

 

[sm1thson]

it would help to know the wattage of the bulb, but if its from one of them 'big yellow torches' then it could be 10-50W

P=IV so I=P/V

at 10W I= 10W/6V =1.667A (2000mA)

its resistance when running will be

V=IR so R=V/I = 6V/1.667A =3.6ohm
and a bulb when cold has a much lower resistance, essentially your weak power supply may be seeing it as a short Circuit, look at the construction of the bulb -it is essentially a short circuit.

also if the bulb is a high power one be careful doing bench top experiments, if you get something wrong (too many volts) then the bulb may explode, also be sure not to get fingerprints on the quarts glass as they dont like that either.

 

[Edradour]

Strangely enough, it is from one of the big yellow torches. Stamped on the bulb holder is 6V 55 watts

 

[electronicsuk]

Then yes, your bench supply is unlikely to be able to power such a lamp. The current draw should be over 9 Amps when operating, and many times that during the time it takes for the filament to heat. You either need a beefier power supply, or use a 6v 4R25 lantern battery.

 

[Edradour]

Thanks sm1thson for the formula, I calculated the current to 9 amps and my power supply won't handle that.

electronicsuk, you're right, I need a beefier power supply, or a different battery.

I now know the reason for the bulb not illuminating, thanks to all for your help.

 

[bernardgreen]

also be sure not to get fingerprints on the quarts glass as they dont like that either.

almost any contamination will start a growth of crystals in the hot glass which seriously weakens the glass ( it changes to a crystalline form of quartz ) and ends up in premature lamp failure. Sometimes as a shower of molten glass and metal, most often as a black coating on the inside of the glass.

 

[plugwash]

My bench power supply reads 100Ma when 6 volts is applied to the bulb. 100Ma is not top of the scale, but the voltage drops away to zero. Don't understand it.

cr*ppy bench supply that folds back to almost zero when overloaded (rather than limiting the current at the set value and reducing the voltage as needed like better bench supplies do)

 

[bernardgreen]

cr*ppy bench supply that folds back to almost zero when overloaded (rather than limiting the current at the set value and reducing the voltage as needed like better bench supplies do)

Sometimes foldback is better, if the equipment being supplied will mal-function when supplied less than the rated voltage then a supply that foldbacks to zero prevents that malfunction.

A fuse is a fold back device. Imagine breakers that only reduced voltage so that the fault current was limited to the maximum for the circuit.