Bike light powered by USB battery pack?

So, I have a battery pack mounted under my stem to charge my iPhone. Does a light exist that could be powered by this battery pack via micro USB (or similar). Some battery lights can be charged this way, but don't seem to operate when plugged in. Ideally, it would be a small dyno type light that I could mount at the crown of the fork and power by the battery pack mentioned above. I only see these with their own proprietary external battery packs, something I'd like to avoid since I already have a battery pack on the bike.

Any advice or pointers much appreciated as the days are getting shorter...

Plenty of the generic Magicshine clones in Cree XML formation have a USB variant. Like this: http://www.amazon.co.uk/dp/B00IWOX8NW/

I suspect the head unit on the linked light has a male USB plug.

But your phone charger power pack would probably need a 2 amp output to make the most of the light.

It's 5200 mAh and outputs 1A. Would this be a problem for the light?

The highest mode will probably not work as it should (it might just be no brighter than the next mode, or it might flicker/shut down).

I was just wondering the opposite.

Can I charge my USB devices (phone/GPS) from my 8.4V light battery?
Something like this, but perhaps more reputable:
http://mtigersports.en.alibaba.com/product/1620430839-220919362/2014_New_Mtigersports_Bike_light_8_4V_Battery_DC_Power_5Voutput_Phone_charge_Adaptor.html

I don't think this would be a very practical solution. USB would not be my preferred choice for anything other than data transfer or charging devices. Lights need a lot of power and cables that can be used for charging are not the same as power cables designed for operational current demands.

The connector is also not designed for the environment you are proposing. Bikes transmit a lot of shock to anything fixed to them, the USB connection is not designed for shock resistance not is it even slightly water resistant.

You might get a few recharges of your phone out of that battery pack, but run a light off it and you will be recharging it very frequently. You also have a single point of failure, your light goes out and your phone is out of power.

I would suggest a light with built in batteries, perhaps something like the new Fenix BC30 or other light that does not need a separate battery pack.

Battery packs that charge tablets are usually ~2.1 A at 5 V.

It's possible to run some light this way, but an actual bike light is so much better.

I guess it depends on the amount of light you want. Amperage is going to be the issue using USB. USB is gonna max out around 1amp. That's enough to slowly charge a battery that is running a light, but not enough to properly power a real bike light. But you could run some USB to micro adapter and plug in a simple USB light? But you aren't going to be able to make the Tour De France with that light.

znomit said:

I was just wondering the opposite.

Can I charge my USB devices (phone/GPS) from my 8.4V light battery?
Something like this, but perhaps more reputable:
http://mtigersports.en.alibaba.com/product/1620430839-220919362/2014_New_Mtigersports_Bike_light_8_4V_Battery_DC_Power_5Voutput_Phone_charge_Adaptor.html

Click to expand...

Yep. I bodged a test: http://forum.ctc.org.uk/viewtopic.php?f=5&t=86041&p=787125&hilit=mc34063#p787125

Worked fine. One 2s2p battery charged a 3000mAh phone battery from 40% to full, topped up another phone and also charged a single 18650 in a USB charger. It's not optimised for the voltage (the circuit I used was made from a car cigarette charger, so never expects to see less than 12V), so some capacity is wasted.

The official solution is: http://www.magicshine.com/ShowProduct.aspx?id=108

gkohn said:

Does a light exist that could be powered by this battery pack via micro USB (or similar). Some battery lights can be charged this way, but don't seem to operate when plugged in.

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The Busch & Müller IXON Core can be switched on during charging and has an microUSB-Port.
Busch & Müller: IXON Core