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this question is about the many small and light usb-rechargeable COB "wide strip" type lights which have a day-flash mode, for all-round DRL type visibility in bright sunlight. I've previously settled on using Moon Nebulas, but would be happy to use something else of a similar style.

on my e-road bike I'd really like to power these from the ebike battery, so I no longer worry about having to charge my "be-seen" lights separately. I have several where the battery no longer holds charge properly but the LED's work just fine, so I could do something with those, if there was a way. They don't run from USB power though, they only charge from USB (or don't, as the case may be).

I've walked my way around what is pretty much the entire "hard wired ebike lights" market and there seems to be nothing that comes in this form factor, particularly for the front, everything is "spotlight to the front" in one form or other . which isn't what I want for this use case. And proper day-flash modes are rare for hard wired lights as well. There are a couple of high end lights (supernova and lupine) which have low beam, high-beam, and separate DRL, but that is way overkill for purely a DRL requirement, and are too high power draw for e-road bike motor anyway in the other modes. on the other hand there many many COB small form factor lights on the market that fit the requirement in terms of all round visibility, day-flash etc - but they are all rechargeable.

does anyone know of COB small form factor lights that are able to be externally powered, or any that are easy to convert to external power, 12V or 5V?

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You're right - can't just connect 5V to the USB connector because very few if any of these lights will illuminate while charging.

Almost all of those lights will have a tiny Lithium battery with a nominal voltage of 3.7V.

If you were to open the light, remove the battery, and wire it to a 5V external line then it might be fine, or it might fry. Only experience will tell.

Your best option might be to take the 5V supply and run that into a buck converter, to drop voltage to ~3.7 V and then waterproof and secure the wires, that may be your best option.

Note, it might be a bad idea to use the frame as one leg of the circuit like on old-school dynamos. I would suggest running a twin-core cable if possible.

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