LIGHT BULB QUESTION

[BT1324]

i recently blew out a light bulb because of over voltage. What i want to know is how your suppose to tell how many volts a light bulb is capable of if theres no indicactions?
And if it says something like 2.5 volts...how many volts of eletric can i put in it without blowing it out in a few minutes? Thx, if i can get an answer id really appreciate it.

 

[stephenanderson2]

I usually go 1.3 times the rated voltage, but i'm no expert!
I haven't noticed a shorter runtime on that principal yet, and have been doing that for years. Also it is much brighter /ubbthreads/images/graemlins/cool.gif Tried 1.6 once, and it blew in about a half an hour.

 

[PlayboyJoeShmoe]

Even though Alkalines are nominally at 1.5v they are rated as if 1.2v, hence a 4cell bulb is 4.8v, 3 cell 3.6v etc.

In my experience, a 2.4v .75a bulb doesn't live very long on 3 cells. a 3.6v on 4 cells has a better life, and any higher number like 5cell on 6 or 6cell on 7 seem to live just fine.

Right now I have a 5 cell M*g bulb being driven by 10.5 volts nominal. It is QUITE BRIGHT.. and has lived at least 20 minutes so far...

 

[BT1324]

is there a way to tell how many volts a light bulb can take if theres no indications?

 

[Doug Owen]

The Unknown Bulb problem......

Yes, I suggest there is (although it's not that simple to do) and more interesting, at least to me, is I think you can do it without having to see (or measure the light from) the bulb itself.

We can easily measure the resistance cold. We can also drive it with a known current and measure the voltage drop and thus calculate the resistance at that time. We know that tungsten has a known positive temperature coefficient (that is it's resistance goes up with temperature, and how much it does per degree) and we know how hot we want to run it........

I also suspect that you could do it by driving the lamp say to the edge of the orange/yellow change, then up the total power a given percentage. Exactly what that is I don't have a clue, but I suspect you could fairly easily come pretty close. Make some measurements on similar bulbs with known specs.......

Fun idea.

Doug Owen

 

[BT1324]

Re: The Unknown Bulb problem......

yea...thats a lil too complicated for me now...i want to find out because i have a rechargeable flashlight with 7.2 volts, and i have another flashlight that runs on 6V, and i want to use that flashlight's bulb on the rechargeable, but i do not want to blow the bulb out.

 

[PaulW]

Re: The Unknown Bulb problem......

Unfortunately, when you're going for bright, you have to expect some losses.

 

[RussH]

Re: The Unknown Bulb problem......

I use 4.8v krypton bulbs in both 6v lanterns with 6v gell cells (6.6v fully charged) and my 6 cell Maglite (7.2v, nicad or NiMH cells) with acceptable life. I'm sure it is shorter life than the standard bulbs but I've never checked. I'm happy that either setup lasts thru several battery charges. HRH, Russ