On Saturday, 20 April 2019 23:31:22 UTC+1, Roger Mills wrote:

I have a Livarno Lux (Lidl) cordless spotlight - the sort with a large
diameter lens at the front, behind which is a powerful halolgen (55w)
bulb and a ring of LEDs, and with a white LED and flashing red LED at
the back.

It normally travels in the boot of my car in case of emergency, but
tends to roll around a bit - which may be related to the problem.

I recently found that it was completely dead - none of its 4 lights
would work. [You're supposed to charge it regularly since the battery
can apparently be damaged if it becomes deeply discharged. It was
working when I tested it 3 or 4 weeks ago, so it's possible that it got
turned on while rolling around (don't we all!) and flattened its battery.]

I recharged it for over 24 hours, and the battery's open circuit voltage
is well above its rated 6v. Three of the 4 lights now work, but the 55w
halogen doesn't. I've tested the bulb on a bench power supply, and it
lights up ok - but in the lantern, nothing. It's drawing several amps
but not lighting - or even getting warm, so I don't know where the
energy is going.

55w at 6v equates to over 9amps, so the filament resistance is only
about 2/3 of an ohm when hot - even lower when cold. Any additional
resistance in the circuit will have a dramatic effect on the current,
and probably stop it lighting.

Question to those who are knowledgeable about rechargeable batteries . . .
What sort of "damage" is likely to result from being discharged too
deeply? Is it possible that this could increase its internal resistance?
If so, is there any remedy - or is it scrap?

Likely the battery doesn't have enough oomph to drive the halogen. A multimeter will soon tell you whether that's where the fault is.

If the battery's not well you can try pulse charging it.
'Well above 6v' is too vague btw.


NT