High power torch cuffed ?

My daughter handed me one of those big torches the other day saying it had stopped working - she'd put it on charge but it now doesn't work!

I found a 6v lead acid battery in it - warm after my attempts to charge it but reading only 4+ volts. Clearly a cell down. I take it that this is due to leaving it on charge for too long - the charger is just a walwart transformer type.

Rob

Lead acid are quite tolerant of charging regimes - although this is likely a SLA type which is less so than a wet one. The charger should be a constant voltage type. For a 6 volt battery it should be 6.9v.

If the torch has been run totally flat a few times - especially left on when flat - the battery will be knackered. Lead acid don't like this. And of course many think you must run a battery flat before recharging to avoid the memory effect. That bit of nonsense is responsible for lots of early battery failures.

Lead acids on a proper constant voltage charger (2.25v per cell) will regulate their own current and tolerate continuous float charging. A faster charge at 2.35v per cell needs to be taken off charge after charge is complete. If the charger is a voltage source with a resistor, then you can possibly kill the batteries mainly be heating/drying out and cells venting. Normally sealed lead acid die from not being charged often enough and the cells go high impedance. Some life can be regained by charging from a high voltage (say 5-10v per cell) with a filament lamp rated at that voltage in series. The supply should be rated at the lamp current or more. When the lamp starts to glow, some current is flowing and charging should begin. Then switch to a 2.25v/cell constant voltage.

Bob

If you can get at the battery to measure the voltage, it's probaby a standard type, available by searching for the type number printed on it. Otherwise, if you measure it, then Maplin have a reasonably large range of SLA batteries, or your local model shop may be able to get one that will fit.

It'll probably be cheaper to buy a replacement rechargeable torch, though.

I've had two of these torches and neither lasted a year. Maplin were selli ng near-identical - vs. Rolson - replacement batteries a few weeks ago for £5. Just a smidgen bigger due to a different bend on the terminals.

Cree LED torches are a much better bet these days and last ages.

rusty

Yep. I have a couple of fairly expensive yard torches and bought a new battery last year for ?17 for one of them. I'm now fed up with the high death rate of teh filament bulbs and have decided to treat them to an LED upgrade, with a XML-T6 in each, and associated driver. This is partly stimulated by the money already laid out on that battery and I've no desire to simply bin it. Apart from that, both have large reflectors and I think those will make good use of a nice bright LED. Even so, to buy the equivalent torches now, already fitted with a modern battery, LED, etc from the same makers wouldn't leave me much change out of a 100quid, so I'm quids in, whatever way I go. When the SLA batteries finally turn their toes up, I'll fit them with some 18650s in bundles.

It seemed to be true for early NiCads, About 30 years ago we had bleepers at work. Instructions included return to gatehouse every night for recharging. I slid out the battery compartment at night and took the bleeper for recharging once a week. After 12 - 18 months, all other bleepers /needed/ recharging every night - mine was still doing a week.

Probably down to a poor charger. Many early one were, and cooked the batteries. If they used an overnight 1/10th rather than fast charge, the cells lasted a great deal longer.

The LED upgrades I have seen (e.g. for Maglites) effectively don't benefit from the reflector at all, because all the light from the LED is directed forwards and never hits it.

Richard.

I have an LED replacement in my Maglite 2D and certainly there is focussing of the beam when I twist the front. I happened to try it last night.

Depends on the positioning of the LED, and the shape of the reflector. This is basic optics, man.

And, rather importantly, the polar diagram of the LED.

In which I specialised when I did my Oxford physics degree!

Richard.

All the LEDs I've seen have a lens on the front. I suppose you could have an LED which throws back into a reflector, but is there any point?

There is if you want to be able to focus the beam using external optics (not that you need to throw it backwards if the reflector is designed correctly).

Hmm... handy. I'll be happy enough to get a useable beam and some side spill. Even the klutziest conversion on one of these lamps should yield something useful. Roughly, I envisage slicing off the rear 7~9mm of the reflector(s) and thermal glueing a T6/heatsink on the back with the LED pretty close to the plane the filament was in. Sure, it's not a point source, but should be adequate and more importantly, gives the handlamps a new lease of life. Having paid some serious enough wonga for the pair of them, admittedly a few years ago, and also having shelled out for a new battery for one not so long back, I'm not chucking them out.

That would be easier with a second lens in front of the LED.

A tungsten lamp emits near 360 degrees fairly uniformly. I've not seen an LED which does the same. So a reflector designed for tungsten is not going to be ideal for an LED.

It was never true except in very specific situation which do not occur in a domestic environment. Everything else is down to cooking the cells in cheap chargers.

MBQ