Bike Headlamp Upgrade - AC to DC

One of the many things in life that totally confounds me is electricity.  Whenever I dig into the guts of something and see wires and such, danger sounds start to go off in my brain.  I get the feeling that if I touch anything with wires one of two things will happen: 1) I will hurt myself 2) I will break whatever it is I do touch.  I even get this feeling when using a simple travel power adapter in other countries without 110 outlets.  My natural instinct is to cringe when plugging my computer or phone in to an adapter when I am in another country.  The only AC/DC I am not nervous about is the rock band. 

This is an exciting post for me on a couple of fronts, the first of which should be obvious - it is about electricity and I don't have to actually touch any wires so I am excited about that.  Second, occasionally I will receive rather snotty emails from people stating something like, "Your site is basically about stapling stuff to bikes.  Get a life will you."  The Internets can be so unkind.  Could not this be phrased as something like, "It would be super cool if your site featured more technical hacks.  Is there a reason for a dearth of technical content?"

If the question were phrased as such I would kindly reply, "Why yes there is a reason. I am not a very technical person, I am pretty much a hack but I love bikes."  Implied in this hypothetical response is that anyone with technical knowledge out there is welcome to send stuff along.  Technical hacks sent to me will likely boggle my mind, but I would assume they would have the power (get it, "power") to inspire others.   Have said all of this, does this inspire you?

Does this make the hair on your arms stand up?

If you are technically minded perhaps you immediately knew that such pictures are focused on helping a cyclist be safer on the road.  If you are like me, perhaps you reached for your Back in Black album/cd/mp3. 

Reader Karl sent us links to a fantastic technical hack of his.  He states: 

I upgraded my Pashley's hub-dynamo driven halogen front lamp to a CREE 1W LED bulb, and built in some simple electronics to keep it lit for a minute or so after I stop. Total cost of the parts was £16.

The concept is quite cool and he covers the process in two entries on his site, Do the Right Thing . . . & Dead Poets' Bikes.  Post 1 is here and 2 is here and the pictures above, and much more, can be found on Karl's site.  Thanks Karl!

Comments

[Patrick]

I would recommend to use a higher volt-rated zener diode and to couple it with a heat sink. When the hub dynamo puts out moren than 6.2 volt the zener diode shortens to prevent overvoltage → loss → heat

[Wadim Dz]

Nothing new...
http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm

[Clind]

Capacitor have a tendancie to loose voltage rapidly when discharging ... the effect here being the light intensity going down even though there's still some juice in the capacitor !
To prevent that and, thus enhance this hack, you can probably adapt this little cricuit :
http://hackaday.com/2007/10/10/joule-thief-led-driver/

@Wadim Dz : impressive link, bookmarked :)

[John h]

I don't understand all the fascination with dynamos. Bike technology has been about making the bikes lighter, faster, easier to ride fast. So lets put a miniature generator on it... it makes no sense to me. It makes it harder to roll. And the diode bridge just burns off the extra energy.

[garryw]

Thanks for a great hack. I have the same Pashley set-up, it will be fun to build this and install it as the original halogen bulb is not so good.

[Karl McCracken (twitter: @KarlOnSea)]

@Patrick - The capacitor is rated at 5.5V, which it should get once the schottky diodes have taken their 0.5V forward voltage drop in rectifying the 6V AC input.

The maximum voltage for the capacitor is 6.3V, and to overload this I'd need the dynamo to be generating 6.8V. But in reality, I don't know the exact maximum voltage supplied by the dynamo is. It says 6V, but who knows? Maybe it does go ~15% over this?

So the zener is there just as a bit of belt and braces backup to prevent me blowing up the capacitor. Assuming the dynamo doesn't generate more than 6.7V, it'll never be used.

@John h - A dynamo with lights fixed to the bike means never having to worry about batteries, and far less worry about them being stolen. The CREE bulb includes reverse polarity protection, but that doesn't mean it's too happy to be fed with AC. This is why you need the rectifier. It's built with schottky diodes to minimise the forward voltage drop and associated power loss. This isn't about making the light brighter though, it's to make it run better at lower speeds.

[Ben]

That's about the simplest way to do it. For those wanting more info, check out Pilom's page on the subject:

http://pilom.com/BicycleElectronics/DynamoCircuits.htm