BRIGHT IDEAS Archive IndexThese articles first appeared in Audax UK's hardcopy magazine, Arrivee, and have been only slightly adapted for the web.
1st use of an LVR2
A slightly adapted reprint of the article first published in Arrivee, August 1998
On a recent 400 I did just this - Sheila used the NiMH pack described above while I used a pack of 8 'C' cells, weighing 620g, both into similar Vistalite VL500s fitted with 5W bulbs. Both packs delivered the same bright light for the 4 hours 20 that we needed them. Sheila's pack has never been run down but we know it's good for at least 6 hours. The 8 'C' cells were run down later and continued to give the same bright light until they packed up at about 6 hours 10.
Now anyone who has tried running a high-wattage lamp off alkalines will be raising a mental eyebrow at this. Typically, the light swiftly turns from white to yellow and then to useless, giving a run time measurable in minutes rather than hours.
The secret ingredient that has really boosted our lighting performance is the Wille Hunt Pulse-Width Lighting Voltage Regulator, or LVR2 for short. This is a tiny but brilliant bundle of electronics, bought directly from Willie in the USA. Basically, it accepts any voltage (up to 15) and converts it down to precisely 6V (or any other voltage you care to specify) with 99.8% efficiency.
What is the point, when 6V batteries are so readily available? The LVR2 does two things superbly well. It enables us to use all sorts of odd-voltage but high-tech batteries, such as computer or camcorder stock, to drive our 6V bulbs. Sheila's NiMH pack is actually 8.4V.
And it's especially good for sucking batteries completely dry whilst maintaining a white light. That 6V 4 cell pack of alkalines reaches the useless stage when individual cell voltage drops from 1.6 (fresh) to about 1.2V. Now imagine using the LVR2 with a pack of 8 cells in series. Starting voltage is around 13 - no problem to the LVR2. As the night wears on the voltage in each cell will drop and drop but the light will still burn as bright as ever - in fact at a cell voltage of 1.2 the pack is still delivering over 9V - no problem. Below 6V the light goes out rather suddenly but by now the individual cell voltage will be way down at 0.75. Now that's what I call a dead battery. It would do the same to a rechargable, which would be rather sad - put a 12V lead-acid onto the LVR2 and, unless you take precautions, it will be destroyed.
Back to the 8x 'C' cell setup. As a side-effect, by doubling up from 4 to 8 the current drain on each cell is halved - now this is rather important with alkalines and high-wattage lights. As a rough guide, if you halve the current, you treble the run time. You don't need the LVR2 to achieve this - you could configure your 8 cells as two 4's in parallel and get treble the run time for double the weight. The magic of the LVR2 comes when the 8 cells are run in series. Or even 9 cells - if you can find somewhere that sells them in nines.
There are other tricks - in fact Willie supplies an add-on circuit to protect rechargables. The LVR2 also incorporates a really sexy soft-start, so when you switch your light on it fades up in about half a second - this saves the bulb from thermal shock which is a major cause of bulb failure. There is also a built-in 'flicker' mode which indicates when the battery has reached the set cut-off voltage. In fact with the alkalines this mode was engaged for over 3 hours - more than half the total run time. It was only very mildly irritating but Willie supplies instructions for changing a component to disable it altogether. Since he also tells you how to modify the output voltage, the best configuration would be to disable the flicker and instead fit a switch enabling 6V/5V operation. When the light finally gives out (suddenly) at 6V simply switch to 5V for another 20 minutes or so of slightly yellower running.
Willie Hunt built the LVR2 to help him in his own chosen sport, which is potholing. The circuit is public domain, Willie supplies it and the board layout free of charge for anyone to build. You would be mad to do this, as he also supplies the units ready-built and tested, customised to your precise lighting system and sealed in waterproof gunk. Tell him exactly what you want, and he will supply exactly what you need. The circuit is tiny and weighs nothing, the build quality excellent, the price around £25.
His address is: Willie Hunt, 1600 Maplecrest, Bloomington, IN 4708-1253, USA
Website: http://www.cs.indiana.edu/hyplan/willie/lvr.html
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