Any electricians?

[guest18]

Yup the electrical pixies are taking the mickey out of me again :/
Swmbo asked me to fix a new torch of hers which isn't working...

So I checked the batteries, all 1.5v or thereabouts.
Then checked them in situ, 6.2v so close enough.
Then I checked the switch operation, all good.
Then I checked all together, yup 6.2v at the bulb terminals.
So...
I checked the bulb (and the spare) good continuity, hmmmm
So I checked the bulb contacts, also good :?
So...
I checked the voltage across the bulb contacts without a bulb again, 6.2v and with a bulb... 0.05v and not a glimmer from either bulb.
Huh?!?!?
Now I'm confused! (well more confused than usual anyway!)

Anyone got an answer?
Cheers,
Smudge
(bulb is 4.8v 0.5a if it makes any difference)

[Steve H]

Unlikely but is the bulb shorted out ?. Measure its resistance.

[guest18]

Ok, there's where I begin to show my ignorance as I normally just check continuity to see whether they have blown or not...
What sort of resistance should I expect? (he says going off to check it anyway!)

[guest18]

Ok checked resistance and with the dial set to 200 on the Ohm scale (heavy meditation man, like, 200 Ommmms man) I got a reading of 1.2
Tried thinking about V=IR or whatever and confused myself (been a long day) so I stuck it in a different torch... and the bulb worked!?!
Now I'm even more confused (sigh)

addendum(?) Just thought more... can I measure the resistance in a bulb with no current through it? Does it make a difference?

[SteveL]

basically, the batteries have some charge left, but only a teeny weeny (technical term for nearly bu55er all) bit, enough to swing the meter (which has a very high internal resistance) but stick something across them that represents nearly a dead short and there's nowt there, probably about 23 electrons passing through the bulb (try counting them) :-)

[guest27]

Could always claim that the torch is fine and that it is her eyesight that is getting a bit iffy through age?

If you do can you warn us so we can all listen out for the thump - we could have a comp for the furthest distance it was heard at...?

R

[jacklebentz]

oh dear!,after the third post i wanted to be kicked in the face,if its a new torch as you say take it back,its faulty!!!!!!!! DER!!!!

[guest18]

No need, turned out to be two sets of batteries knackered despite being in date and straight out of the packet...
Ah well, all sorted now!

[guest27]

Dont you just love Poundland batteries...