Re: Hotlips w Magic Resistor constant current circ
Attention my fellow hotlippers! /ubbthreads/images/graemlins/smile.gif After painstaking R&D in my state-of-the-art labs (okay, more like grabbing a 2D flashlight from the kitchen cabinet and trying to cram a bunch of CR123A's into it /ubbthreads/images/graemlins/wink.gif ), I think I've identified the most cost-effective throwaway power source for the MR Hotlips TK. The plan is to slide TWO columns of three CR123A's into the battery tube... in other words, 2x3xCR123A. This should provide an estimated runtime of 1 hour 44 minutes at a cost of $2.60 per hour when CR123A unit cost is $0.75 each (Countycomm is selling Tekcells for this price in lots of 100).
Six months ago I probably would have been all over those Energizer L91 lithium AA cells -- they've been personal favorites for a long time, and for those lucky enough to get a MR Hotlips TK directly from Hotbeam, he'll reportedly be loading them with these cells for an estimated 1 hour 56 minutes runtime right out of the box! Very sweet. /ubbthreads/images/graemlins/grin.gif In recent months, though, the CR123A prices have been dropping like crazy, to the point that these little guys are now the lowest-priced power source available, short of rechargeables. In the 2x3 arrangement, they approach the runtime of the L91 cells, too, all the more so because the parallel arrangement should meet the high current flow demands of MR Hotlips TK better than a single stack o' batteries would, making the whole arrangement more efficient. For reference, Energizer L91 cells cost about $2 each at BatteryStation.
On the rechargeable front, as stated before, 2x2xPila 150s would probably be the best option in terms of runtime, with this arrangement providing an estimated 1 hour 20 minutes of juice. Actually, NiMH cells theoretically should do just about as well, with 2100mAh capacity NiMH cells offering an estimated 1 hour 24 minutes. However, Hotbeam's graph (several posts prior to this one) shows NiMH providing significantly shorter runtime than calculated here. There could be two reasons for this. First, Hotbeam's NiMH cells might have been lower capacity than 2100mAh. Second, the fact that it's a single stack of batteries means they were expected to provide 1.5A of current, which might have stressed the cells and made them less efficient than they theoretically should be. (High current draw does that to batteries.) The Pila Li-Ion cells probably won't have this problem because just as in the CR123A example above, these also will be running in two parallel stacks, reducing current demands on the cells.
Finally, for those who'll need light for a long time, the SAFT LSH-20 lithium D cells would provide runtime of an estimated 8 hours 40 minutes. Holy electrons, Batman! There is a price to be paid for this, though, literally: $5.54 per hour of runtime, which is a bit cheaper than the per-hour cost of the Energizer L91 cells but more than double the cost of CR123As.
So there it is! Now one of my little projects will involve fashioning some sort of quickie battery tube adapter for 2x3xCR123A use in the MR Hotlips TK. Stay tuned! /ubbthreads/images/graemlins/grinser2.gif
