h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I have a head lamp that has a wee flashing light on the top of it that shows if the batteries are good or running low. It annoys me and is redundant for what I use the torch for anyway. I've just pulled the thing apart and see the wee light is part of a circuit board. Can I disconnect that (with pliers?) or do I run the risk of wrecking some of the other functions? (I can't solder it back on)

The other things it does are three LED settings (plus a flashing emergency setting, and the ability to switch between LED and incandescent.


My other question is how much will the wee flashing light affect battery life? I've been told not much, but it's a continuous thing so it must be drawing some power.

The flashing light will not noticeably affect your battery life.

The effect of removing it is unpredictable - it probably won't affect anything, but it is hard to be sure.

hmm, you'd think that the wee bulb blowing would be alright (it wouldn't be great design if a blown bulb took out all the other functions).

Stick a bit of Duck Tape over it.

Did that. It keeps coming off - the bit of plastic that the bulb shines through is a funny surface and shape. I could probably apply myself to solving that problem better than the circuit board one though. Maybe.

>>it wouldn't be great design if a blown bulb took out all the other functions

You're right. Except that LEDs aren't bulbs and they generally don't ever fail. So the designer might not have allowed for the failure of the LED.

In this case they did, for the main ones at least - there are two slots for spare bulbs. One slot is empty so I assume I've had to replace one of the bulbs at some point.

As I said, LEDs aren't bulbs. Are you saying that some of the other LEDs can be replaced?

Yeah, my bad. It's the other one that's replaceable (not sure what that is. It shines yellow)

Interesting terminology. Am trying to think what I would ask for if I went into a shop: can I please have a replacement LED? Can I please have a replacement LED bulb? (I wouldn't say Can I please have a replacement light emitting diode? ).

Green LEDs are quite easy to make and Red ones are very easy. In both cases, the colour comes from the quantum-mechanical process that takes place within the "bulb", rather than by any sort of colour filtering. Yellow LEDs are usually made by tying a green one and a red one together.

If you tie them back to back, then the LED will glow green when the current flows in one direction, red when it's flowing the other way, and yellow if it is alternating current.

I meant the replaceable bulb wasn't an LED, it's some other kind. I was going to say halogen, but it has a yellow glow.

Q1 : Is it a rechargable lamp kea ? If so does the little red LED tell you that it's charging ?

If so, it might be handy to keep it working.

If NOT rechargable, and it just flashes to tell you that it's working, and then flashes differently to tell you to change the batteries, then you CAN simply disable the LED, cut the legs close to the circuit board. It will not affect the function of the lamp.
If the lamp uses regular environmental destruction type batteries, then you will know to replace them when you start bumping into things in the dark.

Plan B might be easier : cover the flash with black nail-varnish or similar paint-like substance.

alec.

Thanks Alec. It's definitely a light to tell me when the batteries are getting low. I can tell myself though, because the light gets less bright.

Yes, environmental destruction type batteries (4 x AA). I should get some rechargeables, but I've found in the past that they didn't do very well in that torch. I wonder if that's to do with the flashing bulb - would that constant pull affect the ability of a battery to recharge?

I was also recharging those batteries using a solar recharger, and I wonder if that wasn't working properly. Does it matter if rechargeable batteries of that size get variable charge over the day or days, as opposed to a continuous charge from mains power?

Rechargeable batteries: I, too, have no satisfaction there, they don't last very long and seem to (no proof, but still) lose charge in the box waiting to be used.

Mind you, they're all more than just a couple of years old - are more recent ones better?

There two main types of AA rechargeable battery: NiCad and NiMH. These days, only the cheapest are NiCad. Most new batteries are NiMH.

NiCads can only store a limited amount of power, and they suffer from the memory effect - if you don't discharge them fully, they lose the ability to hold power. If you keep them topped up all the time, they eventually can only produce a tiny amount of power.

NiMH batteries are much better. You can top them up as often as you like. They only seem to last about 2 years, then their ability to hold power drops off and they lose their charge after a few weeks of non-use.

Thanks, Gnomon.
Now it's case for reassessment - economy calculations and date labels...
maybe not.

2 years... is that irrespective of use? ie if sitting for 2 years they would lose recharge capacity?

The 2-year thing is only from my personal experience. But yes, I'd say they lose their capacity for recharge whether you use them or not after about 2 years.

Indeed...unless you cycle the charge religously...
Thou shalt never recharge unless completely discharged.
Thou shalt never exceed the maximum charging rate in milliamperes.
Thou shalt never leave the battery laying around in the garage for months on end without using it and recharging.
...NiCads will soon lose interest in being useful.

The rechargables available in equivalent sizes, AA,AAA,D etc. have a maximum fully charged voltage of only 1.2 Volts, due to chemistry/size restrictions.
Compare this to a fresh environmentally destructive battery which leaps out of the pack with 1.58 Volts and makes your lamp really bright for a while.Then it settles down to 1.5 Volts.
With your 4 batteries in series :
1.2V + 1.2V + 1.2V + 1.2V = 4.8V rechargable.
1.5V + 1.5V + 1.5V + 1.5V = 6.0V non-rechargable.
Makes a big difference to an old-fashioned light-bulb.

alec.