Building the Ultimate Endurance-Road Bike Light

I am looking to build a bike light for on-road usage that is reliable, long lasting, and with swappable battery packs. My thought was to use an existing e-bike light like the IQ-X E , and make my own remote battery pack that can be tucked away. I realize that B&M are going to make a "speed" version of the IQ-X -- but I don't like that it only gets 5 hours at 150lux or settle for 25 hours at only 30 lux.

I found a German velomobile website where people drive them off their onboard batteries successfully: http://www.velomobilforum.de/forum/index.php?threads/bumm-cyo-premium-vs-iq-x-in-dc.46666/page-5
It contains this tidbit on current:
Published spec from mfg: 520 mA@12 V (6.2 Watt), 260 mA@24 V (5.7 Watt), 175 mA @36 V, 130 mA@48 V
Measured by user: 548mA @ 12,15V (6.6 Watt), 416mA @ 16V (6.6 Watt) , 350mA @ 19V (6.6 Watt)

So using the 6.6 Watt observed consumption, using 18650 3400 mAh batteries give about 11.5 Watt Hours from what I understand, so running them in 4 in series should power the light at 150 lux for ~6 hours, ~12 hours for an 8 pack and so on...

The German forum goes on to run it through a voltage regulator below the prescribed 6v minimum to get a dim/lower consumption mode. Would there be a smart way to do this on a regular bicycle that would be small/waterproof?

Is my math sound? Any recommendations on how to get this setup with a remote on/off or even remote level switch in a rugged, waterproof way?

Thanks!

Sounds interesting.

I'd search for battery cases on websites that cater to the raspberry pi crowd. A lot of their portable power solutions rely on 18650 batteries, and you can probably find a water proof battery case with an on/off switch for pretty cheap, I imagine under $5.

Even if you don't find a 4x18650, you can probably rig 2 double cell cases together. And since the cases are cheap you can buy extras and swap the whole thing out instead of carrying a bunch of loose batteries in your bag. There are dozens of reputable websites where you might find something, but I'd check adafruit first.

I wish you luck with achieving multiple modes, and I hope you manage to get an efficiently running light. It seems like the only mods that get attention these days are the ones trying to achieve blindingly bright turbo modes. Its refreshing to see someone interested in sustainable brightness over a long run time.

What do you have in mind for the light itself?

What you need for dimming control is probably something like this:
http://www.dx.com/p/mini-dc-to-dc-synchronous-step-down-power-module-green-316402#.WMVlCfkrK70

You could mount it in a small plastic box with a switch to select direct battery or stepped down for low power.

There are many flavors of these around, with various bells and whistles. Go to your favorite gadget supply place (eBay, mtnelectronics, DX, KaiDomain, Alibabba, etc) and search on 'Step Down' or 'Buck'.