Lux V on 8xAA NiMH or on 4x18650 Li ion?

Hey guys. I came across an old 2D industrial flashlight that I'm planning to mod with a single Luxeon V W__S or W__T and a Downboy 1000 mA converter. Which battery solution would be best: eight NiMH AAs or four Li ion 18650s? I'm not at all sure of the run time I'd get with each setup. I want to keep the light mainly as an emergency and car light, so it might sit for a while without being used.

There's a lot of room in the barrel here. It's just over 130 mm deep (with a lot of extra room in the tail), and about 36 mm wide at the tail end. It opens up to about 38 mm after the contact ring. 8xAA fits very easily, but I don't have 18650s to test with. Maybe there would be a problem fitting the Li ions side-by-side with only 36 mm to work with.

So what do you think?

Also, is there another board I should consider besides the Downboy? I don't know much about this stuff yet.

Nobody...? Is my question too weird?

Is the light plastic or metal? How do you plan on sinking the lux to the flashlight body?

Ikonomi,

Sounds like an interesting project you have for yourself. I would definitely go for the 18650 LiIon cell option as a power source as they have a small fraction of the self-discharge of NiMH and lighter weight (greater energy density). A good cell to try is the LG chem 2400mAh from Battery Space. Since you plan on leaving the light loaded with cells and unused for significant time, lithium rechargeable makes perfect sense. NiMH is a very good power solution for high current drain setups (greater than a single lux V, especially incan bulbs) as long as you are able to keep them charged regularly.

As to the converter issue, from what I have learned the typical Lux V setups commonly use "buck" converters, those that reduce to voltage to match the forward voltage of the emitter itself. The downboy is common and very recommended. 1000mA of drive is fairly hefty but the huge capacity of the 18650 cells paralleled should give you plenty of runtime. Sounds like wire them up two in series two in parallel. With 38mm ID there's just barely enough room for 2 18650s side by side. Four 18650s with a load like that should give you over three hours of burn time, which is really something significant. The NiMH cant hope to match the runtime of LiIon. I think you may be extremely lucky if your ID measurement of 38mm is accurate and you can fit the cells. 2 18650 side by side is a KILLER power pack. 4 is twice as nice.

There's a CPF member called modamag who makes excellent custom battery holders that might be able to offer you a kit or complete assembly if you are not up to it. Should be a nice bright utility light great for near field and midrange use. Be careful of properly heat sinking the emitter, because at that high drive level the heat will be an issue hurting longevity if you use it for long continuous runs. Some people drive them at 1500ma, but Sir Don once recommended a sweet spot of 750mA with a Lux V. Beyond that you get diminishing returns in brightness, paying larger costs is lost life hours and waste heat.

Sorry someone didn't jump on this sooner and offer advice. Sounds like a novel platform. I've invented new curse words trying to cram LiIon cells into modded Mags and sooooo many times wished for a few extra mm of clearance to run more fat 18mm cells. Your industrial light with the generous battery space may be the ticket to making a bright light with long runtime.

I just thought of something else. As per NIMH, consider larger 4/5 A cells instead of smaller capacity AAs. They might be a viable alternative to LiIon, BUT if sitting dormant for long periods of time and having FULL power available after that is a priority then LiIon is the clear choice.

I hope some of this info is useful to you. I'm looking at some ideas with the Lux V and am a beginning modder myself, so I'm just passing on what I learned here. There is a virtual WEALTH of exerience and knowledge in these forums, part of the fun of learning is the research by reading so much entertaining material!

Enjoy your time here and definitely follow through and build that light! I really hope to see pics posted someday! I love the feeling of accomplishment acquired by taking something and improving it using your own ingenuity as the tool to make it happen. You've got the platform there -- use it!




Steve

Hey legtu -- The light is plastic, but it has a hefty metal reflector and a lot of empty space between the reflector and the Vin+ contact spring. I was thinking of making a heatsink to fit in there as an additional thermal path.

Lunarmodule -- Wow, thanks for the great post. Lots and lots and lots of interesting information. I really appreciate all the good advice. The 1A current may be too much/too inefficient, eh? I'll go for 750 mA, then. And the Li ion batteries. Wiring them in series/parallel sounds great, as you recommend.

This project is sounding more interesting. This flashlight, I have to say, has absolutely the most pathetic beam I've ever seen: Orange and ringy/splotchy/patchy. I have three or four of them, and they're all the same -- nice construction, lots of O-rings and stuff, but horrible beam. One of those $2 Eveready flashlights is about three times brighter. You better believe I'll be posting some before and after beamshots when I get it finished.

Well, I'm excited about these 18650s. Time to hop on over to custom/mod BST.

Perhaps I might offer some additional comments.

1) The light is going to be sitting around a lot, but when it is needed, it needs very long run time.

2) The light is an industrial 2 D Plastic light, and the goal is lots of cells for long run time.

In my mind, the main reason for going to 8 x AAs are 2
a) To gain the (normally) much higher current flow capacity of AAs vs D cells
b) Easy access to AA recharge types vs D NiMH
c) Increase the voltage over 2 D cells in series
d) Ability to access a locally avaiable, common cell.

Since the light will be sitting around a lot, but needs long run time when it is needed, then you should not use rechargeable cells of any type. The R cells WILL discharge even if not used, although certainly the Li cells will take longer.

As far as 18650s go, they are fantastic cells, but unless you are using protection circuitry of some kind, you can hurt yourself and burn down your house. The correct choice for all but the experts is a well protected cell such as the Pila brand cells. The protection means that the cells are larger in dia. or will have less capacity. They are a well proven performer.

By the time you buy 4 cells, a charger, etc, you will have a lot of $s invested in cells, and don't necessarily plan to get the value proposition of R cells, which is "regular heavy use". I don't consider a pack of cells once / month to be heavy enough use to justify the cost and risks, nor is this setup going to help you if your cells are dead and you are needing some fresh cells.

The AA option is a good one, but for your application, I would save myself the trouble of boring it out for 8 cells and just use 6 x AA energizer Li cells. The capacity of 6 AA Li cells is very close to 8 X AA NiMH under that load and allows you to skip the boring step. The AA setup also allows use of more common, locally available cells in a pinch.

My personal favority for 2 x D's is the SAFT primary cells. You can buy them at hdssystems.com (look under products). They are protected, primary cells with plenty of power and 3 volt nominal output.

If you are going down the rechargeables path and plan to charge them up regularly, I would suggest 2 x D NiMH. There are some very high capacity cells out there, and life is much simpler than boring that body out.

As far as a Lux V in the light, That is a nice LED. Heat management in a 2 D light is all about getting the heat transferred from the back of the LED to your hand - in the end, nothing else really matters. The metal reflector is one small part of getting heat to your hand, and you really have no heat transfer path though the plastic walls. The bottom line is that if you use a large slug of metal under the LED and only turn the light on for 1 - 2 minutes at a time, it is ok (the metal slug will heat up, and eventually cool down), but a 15 minute run will likely not work out, esp at 1000ma. It might work at 250ma.

If you really like that host light, then perhaps a simpler and more effective mod is the 2 X D cell SAFT cells, and a 6 V incan bulb. The metal reflector will work out for that application.

A Lux V really needs a metal bodied light, the more, the better. I hope that helps.

HarryN, you bring up some good points. I wasn't aware the Lux V would produce so much heat. I am planning to drive it at 750 mA. If this turns out to be unusable, I'll have to find another home for the converter. This might benefit from a two-stage switch. The stock switch is three position: off, momentary (with a separate button), on. I suppose it's possible to add a resistor to one of those modes, but would that work with the Downboy, or would it just keep on regulating? Well, there's a solution somewhere.

Since I have quite a few of these lights around, I was planning a few different mods. I certainly considered a bulb upgrade. Do you have any recommendations on 6V bulbs, or know where I can find information about them? This Lux V came to mind first, but I'd like to make a quick incan upgrade, as well as a Lux III light out of these.

For me, this is as much an exercise in modding as it will be a finished, usable light. I've never done anything like this before, and I'd like to push the boundaries of what I can do. If the Lux V setup turns out really not to work... I can cannibalize the parts for other projects. :naughty:

Ikonomi said:

Hey guys. I came across an old 2D industrial flashlight that I'm planning to mod with a single Luxeon V W__S or W__T and a Downboy 1000 mA converter. Which battery solution would be best: eight NiMH AAs or four Li ion 18650s? I'm not at all sure of the run time I'd get with each setup. I want to keep the light mainly as an emergency and car light, so it might sit for a while without being used.

There's a lot of room in the barrel here. It's just over 130 mm deep (with a lot of extra room in the tail), and about 36 mm wide at the tail end. It opens up to about 38 mm after the contact ring. 8xAA fits very easily, but I don't have 18650s to test with. Maybe there would be a problem fitting the Li ions side-by-side with only 36 mm to work with.

So what do you think?

Also, is there another board I should consider besides the Downboy? I don't know much about this stuff yet.

Click to expand...

I am not the expert, you probably need to ask Wayne, but 4 x 18650's would exceed the input voltage limits on the downboy when the 18650's are fresh off the charger. The spec's I have seen say 16 volts max (but suggest not exceeding 12V), so 8 AA NiMh's are safe, but 4 x 18650's are going to start at close to 17 volts, and the upper limit on input is 16V. The 4 Li ions will give you about 32 watt hours, the 8 NiMh will give you about 25 watt hours, but will always be within spec on the downboy.

I'd suggest if you want to go the 18650 route, only use 3....YOu will have about the same power as the 8 NiMh, better storage characteristics, and not push the limits on the downboy.

If you really want capacity, you could go with 6 18650 as two sets of three. That would give runtime on the order of 8 hours.


I'd also be concerned about heat dissipation with the downboy running a 1000ma and such high input voltage, you are looking at probably dissipating about 7 watts in the Luxeon, and another watt or so in the Downboy. That is going to require a hefty heat sink. Perhaps you can use some of the excess battery capacity to provide forced air cooling!