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The ledlyt PS 1B power supply

The manufacturers specify a maximum continuous current, through the white LED that is used in the ledlyt, of 30 milliamps. If there is no heatsinking provided, and the LED gets hot, that figure is reduced to 20 milliamps. The ledlyt heatsinks to the ground brass tube that holds it, so we can use the higher current value.

Compared to most microscope illumination systems, this represents a staggering drop in current consumption. A 6 Volt lantern battery will supply 30 milliamps for about 100 hours, and these batteries are very cheap. It makes no sense really to drive a ledlyt from a Mains-driven power supply, and once you move to a 6 Volt battery-driven unit, your microscope becomes portable anywhere. A great number of safety concerns, about having your fingers in continuous contact with a metal object directly connected to a Mains-driven supply, simply disappear.

Optical microscopes are still honest products, and the makers have yet to work out how to add options to them to reduce their working life from fifty years to ten. We have to consider, both with the ledlyt and its power supply, that they are likely to be in use for many years. The PS 1B power supply is over-engineered, with an Alps potentiometer for brightness variation and a C and K on/off switch. The circuitry intentionally contains no electrolytic capacitors, which have a shorter life than the other components. Mains transformers, rectifiers and storage capacitors are always under voltage stress, and more likely to fail. A battery supply needs none of these, and we cannot see a 6 Volt lantern battery becoming obsolete shortly. The power supply body has two brass rails, with aluminium end pieces and a polycarbonate front panel. All fixing screws used are stainless steel, and there are no click-together plastic mouldings.

There is no cosmetic outer cover to be removed to replace the battery. The battery is pushed in against its contact springs, and lifted clear of the back end piece so it can be taken out and replaced by a new one. If the power supply falls from the bench to the floor, the battery may jump out, and the body may distort (it won't break). Loosen the four setscrews locating the brass rails, and hold the power supply down flat on a surface while you re-tighten the setscrews. Replace the battery and off you go again. There are three soft feet on the power supply, not four, so it will stand steady on irregular surfaces.