I needed some cheap but effective bike flashlight solution. I bought “CREE XM-L T6 LED Bicycle Light Torch Headlamp” from ebay for $5.64.
It has 3 mode driver high-low-strobe. On high mode it draws 1.6A from 18650 battery which is OK for my needs. Dims below 3.0V and shuts down at about 2.7V. It is compact and easy to mount on the handlebar.
First I planned to put batteries in a handlebar bag like this one
But then I had this idea to put them in the steerer tube instead. The internal diameter of the tube is 22mm and there is plenty of space for two 18650 batteries. I used a 3d printer in a local hackspace for enclosures. To charge the pack I bought tiny “Micro USB 1A 18650 Lithium Battery Charging Board Charger Module” also from ebay for $0.71. I can use phone charger or USB port on my computer. For 2 batteries with 2500mAh capacity charging will take about 4.5 hours. Discharge around 3 hours on high mode.
Enclosure is thin enough to see charging indicator through it.
Note that battery pack has to be flexible in the middle, otherwise will be problematic to insert. When inserted, it sits tightly inside the tube and does not fall out, but just in case I added a plastic cable tie.
Overall I’m happy with the result. Check your steerer tube, maybe this will work for you too!
A friend of mine will not ride horses because there is no “emergency stop” button on them. LIon’s need that function too, some way to physically uncouple them from the circuit instantly should things go wrong, especially when they’re used in series. It’s very unlikely you’ll have a problem but something to consider in design. Otherwise I really like the idea as it uses otherwise wasted space, does not add to the aerodynamic wind resistance, plus offers some air-cooling of the housing in the windstream while riding. 3 out of 4 isn’t bad at all with the 4th being such an unlikely issue, so very well done with this!
eebowler, good point, my setup is not prepared to deal with water. But what can be done:
Use fenders (I guess most people who ride under rain already use them)
Fill bottom part near connectors with silicone sealant. Use waterproof DC connectors instead of Micro USB.
Micro USB is input, not output. Nothing happens if you short-circuit it. To make things really bad, a lot of water needs to go inside an fully cover DC connector. But even though 18650 will not explode I googled “18650 water”
If you can 3D print a cap to fit tightly into the bottom of the stearer tube that’ll help a LOT. It would mean that the charging port etc will be further inside of the sterer tube making a bit more inaccessible but should keep it dry.
.
My waterproofing solution was very different: A few years ago, I made a tail light out of an old 18650 cell, mini heatsink and 7135 based driver (and waterproof switch). Everything was epoxied together as one (to make it waterproof) and I used two small, chrome plated screws as charging inputs (+ve and -ve from the battery were soldered to the screws). The charger is what you used above and has magnets at the output. It has worked well over the years but now, the chrome plating of one screw is flaking off. I’ll just have to put in a new screw
I’ve considered this but never tried it. Nice work! Maybe a right angle barrel plug and use the zip tie to hold a plastic lid over the whole shebang. Anyone with quick release axles wouldn’t need the articulated cells. The current is higher with 1sXp so it’s good to keep the wires as short as possible and this fits the bill. My cells ride in tubes that clip to a carrier under the bottle cage which lengthens the wire but keeps the weight lower. 2s per tube and the nice cells we have now give me more than 50 Whrs to play with.
great implementation! I've seen a number of these over the years, don't think I've seen one with the charging board before. I'd second the idea of a cap - you can get waterproof USB plugs and obviously waterproof DC jacks. I've ridden for years with fenders and trust me, that area still gets hit with plenty of water. Then you can ditch the zip tie and it'll truly be stealth.
btw, can't believe you can get one of those light heads for that little now. Crazy.
Your output connection is wrong. I made the same mistake. The battery connections are the two in the middle (positive is the same so you can leave that) while the two on the outside are a 2A protected output. I assume it has low voltage protection too but haven’t verified that as yet.
I have probably 15 of those modules - all really cheap about 40c each from ebay/ali, all clone IC, but none really overcharge. At CV stage they go ranging 4.13V to 4.17V.
Two out of five of your module overcharging is not good statistically. Just out of curiosity, you sure your DMM is good? They always overshoot voltage when low on battery.
How could you prevent the micro usb port from getting wet?
. Out of five modules, two didn't work like I wanted so I discarded them (overcharging), that is a fact.