Making a mobile device charger to work with your hub dynamo, part 2

[Andre Jute]

It gets easier and cheaper all the time. Here's an A$2.61 USB socketed buck board.

5V USB Output Converter DC 7V-24V To 5V 3A Step-Down Buck KIS3R33S Module

http://www.ebay.com.au/itm/New-5V-USB-Output-Converter-DC-7V-24V-To-5V-3A-Step-Down-Buck-KIS3R33S-Module-/350675929815

I don't know if they ship to the UK, but you can probably find the same thing from a vendor who does.

In the top illustration the input from the rectifier (see below) is at the left to the two screws and the output is to the right at the USB socket.

According to James Stewart of the famous Melbourne cycling family to whom I am indebted for discovering this module, the output to the USB is steady at 5V at any input from 1V above, i.e. 6V and up. That should be a doddle with the output of any of our hub dynamos after rectification.

You'd need to convert the AC from the hub dynamo into DC at the input of the module above, and for that you could buy another inexpensive little board or cobble up a Schottky bridge and a cap across the input screws to the left of the buck in the top illustration.

TIP: Normally I prototype such things in a small electrician's junction strip, attaching the leads with the strip's captive screws. Such junction strips are available from any hardware store and easily cut into sections with your wife's bread knife. The strip also has holes through for attachment inside a little mint tin or whatever you use for mounting this small assembly to your bike. (I know, Dan and the real engineers are curling up in shame and claiming they never knew me, but not all cyclists own temperature-controlled soldering stations and plenty of breadboard lying around.) For myself, I'd build this thing in a piece of square tube ali, with a glued-in furniture plug across the top for weather sealing and the USB socket pointing downwards for weather protection, and the two modules on opposite sides -- inside! -- for thermal separation.

[Danneaux]

(I know, Dan and the real engineers are curling up in shame and claiming they never knew me, but not all cyclists own temperature-controlled soldering stations and plenty of breadboard lying around.)

I'm proud to say I *do* know Andre Jute. 

Nice little piece, Andre, and very useful for many.

All the best,

Dan.

[bugmenot]

I just ordered one from ebay.  I'm interested to see visually how you mounted your diode bridge.    Thanks for sharing.  Seems like just the thing.

[Andre Jute]

I just ordered one from ebay.  I'm interested to see visually how you mounted your diode bridge.    Thanks for sharing.  Seems like just the thing.

I haven't built this one, Bug. I just passed on a reliable source. And added a few tips. You can be the forum's lead mechanic on DIY USB charging. Don't forget plenty of photos.

[bugmenot]

Couple images attached.  Hub power comes into my switch, where I can toggle back and forth between

• AC headlight/taillight
• OFF
• Regulated USB

I went quick and dirty and after shielding the leads, just jammed the Bridge Rectifier and Capacitor into the input leads of the prefab China Buck regulator module.  Seems to work from prelim testing.  Voltmeter says i get 5.08V = Perfect.   I intend to get a few images that give a sense of output current after some more testing.


http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0.H0&_nkw=KIS3R33S&_sacat=0&_from=R40  Regulator module seems easy to come by for under $3 USD.  The only required items remaining were 1x bridge rectifier, 1x capacitor.

[Andre Jute]

This looks like the business, Bug! A genuine homemade proto. It seems to me unlikely that on the far side of the onboard cap and line impedance the recipient device plugged into the USB will even notice the rough and ready linking of the rectifying diodes and cap. 5V08 is spot on, too. Congratulations. Thanks for the photos, which save a thousand words. Keep us updated.

[Danneaux]

Very nice, bug. Unless I miss my guess, that is a Rema Tip Top flat-repair box as cabinet?

Love the photos!

Best,

Dan.

[bugmenot]

You got it.  Size Medium.  Could do it in the small box, but would have taken a bit more fussing...

I may redo the housing soon - since it turned out so janky, but most discussion on the web seems to indicate that the actual USB port is likely to be a main failure points in waterproofing.  I would argue that no matter how tight your case/wiring is, a female port USB charge device just plain isn't waterproof, so keep it in your Hbar bag and call it a day. 

(if you do integrated charge cable, that's a different story, but I specifically wanted the USB-A (female) port for charging multiple devices.  I'm about to tour with devices that charge via: Mini-USB, Micro-USB, and a proprietary camera charge cable that uses the USB standard.)

Still, I can do better, so I might beef it up in an ever-useful mint tin before i leave on tour...

[Andre Jute]

I would argue that no matter how tight your case/wiring is, a female port USB charge device just plain isn't waterproof, so keep it in your Hbar bag and call it a day. 

Smart thinking that. Whoever decided the USB can be an outdoor port didn't put his gear in mind that day.

[macspud]

I may redo the housing soon - since it turned out so janky, but most discussion on the web seems to indicate that the actual USB port is likely to be a main failure points in waterproofing.  I would argue that no matter how tight your case/wiring is, a female port USB charge device just plain isn't waterproof, so keep it in your Hbar bag and call it a day.  

Maybe you could add something like this http://www.selectronix.co.uk/series.asp?did=190&sid=311 to waterproof the box better in the future?

[bugmenot]

That would certainly be the ticket.  Definitely changes the project from "what can I do to make a charge box out of a $3 readily available subcomponent" back to "Lets build a purpose designed adventure charge system."  Might do that before I go out global trekking, but no need for right now.

-Adam

[Danneaux]

no need for right now.

<nods> And, too, field-testing the present model will show where is is brilliant and where it is lacking. Model 2 (if required) will be just the ticket for meeting all your needs, Bug!

All encouragement your way.

Best,

Dan. (...who is a great believer in field-testing)

[bugmenot]

Pre-trip tested OK.  

Here's the Mint tin, a bit Higher-Fi than the Rema Patch box, and should keep the innards well insulated/anti-shocked.

Also a (blurry) shot of the phone indicating charge.  A tool I found useful was this Android App that gives real time charging status, including fairly precise read on your charging current in mA.   Only use this after your multimeter tests indicate that you're actually putting out a clean 5V power stream, but it saves the hassle of trying to get your ampmeter in the middle of the circuit to measure current.

[Andre Jute]

Very nice work, Adam. Small and light enough to remain permanently wired in, carried in a bag. You've inspired me to go looking for an ammeter that works on my phone, though I actually have (somewhere!) a USB cord gimmicked to measure current.

[il padrone]

most discussion on the web seems to indicate that the actual USB port is likely to be a main failure points in waterproofing.  I would argue that no matter how tight your case/wiring is, a female port USB charge device just plain isn't waterproof, so keep it in your Hbar bag and call it a day. 

Sinewave Revolution do it with a solid PU-encasement of the wiring and circuitry, together with gold-plated USB plug. They claim the charger is waterproof.