I have a large supply of NiMh rechargeable batteries that I use for all my gadgets. I have several small very bright LED flashlights that use these. My question is how can I construct, from parts, a strong bike headlamp that uses such batteries? Based on review of many product recommendations offered, I have not found a 300+ lumen light, so I'm looking for a way to construct such a light. It would need to be easily detachable so I could remove it when locking the bike in public.

I am interested in solving the problem of getting such a light, either buying or constructing such a bike light, by someone who has done this and tested it successfully, not a "which brand is best" product recommendation. I would think that pointing me to a general approach and/or a general place (links, marketplaces, etc.) where I could find such items would also answer the question without violating the norms, as long as they are fact based (e.g. successfully used by someone to solve this specific problem) and avoid naming specific brands or models. I don't know or care about electronics because it's beyond me how to put together circuits or LED's, I just want to understand how to get components that can be combined to attach and mount something very effectively and waterproof to a bike. I'm not looking for instructional material or training on bicycle repair or how to upgrade a specific kind of bike. Just how to solve a problem.

I'm just kind of a clueless dude here trying to ask how to go about this, looking for different approaches, some involving DIY and some involving using framework approaches, and letting people vote on which approaches worked best for them. (See https://stackoverflow.com/questions/9329446/for-each-over-an-array-in-javascript/9329476#9329476 for an example of this kind of a question/answer dynamic on a different StackExchange type site.) If that's not the intent of this site I guess I get it, keep the question closed. I put up a question in meta about whether this question is appropriate and so hopefully, as this is closed, the discussion on the appropriateness of this kind of question can be contained there.

One other thing is I'm looking for inexpensive way to go about this; $200 is out of my range.

I want to just point out that I am approaching this as an engineering problem with a bunch of requirements and looking for empirical evidence to support a solution. I am hoping the fact that some components involve electronics or that there are cost constraints does not take this out of the realm of ordinary bike problems.

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    What do you mean by "get"? If you mean "buy", then shopping questions are off-topic. If you mean "make" then you're asking about electronics, not cycling. – David Richerby May 16 '19 at 16:05
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    Why not just use the LED flashlights you have? In which case you could ask the question " How do i attach these to my bike " or " Can these be mounted to my bike " – Dan K May 16 '19 at 16:13
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    @Michael your comment exhibits one reason why product-rec is off topic. One cannot claim something is legal without saying where it is legal, which is very likely a different place to OP. And such an item may not even be available to OP's location. – Criggie May 17 '19 at 7:59
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    There's a good reason most manufacturers have moved over to Lithium batteries. They have better energy density, and better tolerance to high current applications than NiMH. Most users are demanding 500+lm now, and the current drain to produce that would exhaust a 4xAA pack in a very short time. You might be able to get some help at candlepowerforums which is full of LED light enthusiasts – Andy P May 23 '19 at 15:31
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    Hi All, to avoid crowding this comment thread I've created a post in meta to talk about the appropriateness of such questions as this, which is seriously something I am also interested in! – user42036 May 23 '19 at 15:43

As suggested by Dan K, you might use the LED flashlights that use NiMh batteries you already have. Assuming that those are bright enough for your needs, you could get bike mounts for flashlights (a quick search on amazon.com for flashlight bike mount reveals plenty of options).

These mount on your handlebars, and are small enough that you could fit more than one and point them at different angles, to get more side visibility as needed and a bit downward to avoid blinding other people heading your way, as a way to compensate for the improper beam shape your lights may have, which is a great point Chris H raises.

  • This is a pretty promising provided the beam shape is okay and I can build a quick-release mount. I'll give it a try. – user42036 May 23 '19 at 15:16
  • A helmet mount is more tolerant of a non-cycling beam shape than a handlebar one, as at least if you can zoom it in narrow then you can aim it at the patch of ground that matters, and position your head to keep it out of others eyes. – Chris Stratton May 28 '19 at 21:29

Until recently there were a few high quality lights running off such cells on the market, but they've been discontinued, and anyway were expensive. This means you'd have to make something. If you're not happy with the DIY aspect (soldering and waterproofing) of this, the project probably isn't for you.

Many front lights, including some with good beam shapes, are designed to run off lithium rechargeable packs. These put out roughly 7.4-8.4V. You may get away with 6NiMHs in series but you're more likely to need 7. You'd have to make up a pack, and a holder for 7 cells is uncommon.

There are other lights designed to run off the 5V of a USB battery pack. These are likely to run off 4 NiMHs in series (for 4.8V nominal) but good ones tend to be expensive. Again you'd need to build your own pack around a 4-cell holder. They should, in theory, run off an AA emergency phone charger (such things exist and by coincidence ice for one on order) but I haven't tested that. You could avoid any construction by putting the phone charger in a toptube bag.

Beyond that, lights that charge off USB tend to use a single lithium cell. This is a good match to 3NiMHs in series.

A good beam shape is important at this power, which is capable of dazzling other road users while simultaneously falling to illuminate your path.

  • I do have a such a phone charger. Any tips on how to affix items to bike with quick release capabilities? – user42036 May 23 '19 at 15:12
  • @JohnMeyer I use a cheap toptube bag (with snacks on top of the charger). I leave the bag on the bike and take the charger out when I don't need it. The bag protects the charger from rain, though mine is supposed to be splah-proof. Some of these bags have a headphone cable exit port at the back (big enough for micro-USB), but I've cut another cross at the front to use a shorter cable. – Chris H May 23 '19 at 15:15
  • Do you use a bike light designed for use with a separate power pack or do you hack into a light that uses a propietary power pack? – user42036 May 23 '19 at 15:20
  • @JohnMeyer currently I mainly use dynamo lights, and my main backup has a built-in battery. I also have one with a proprietary battery pack for my other bikes (that's waterproof and can be strapped directly to the frame but I find it more convenient to put it in the bag). Some of the people I ride with use the USB-pack solution, usually in a bag of some sort. – Chris H May 23 '19 at 15:41