Picture of Dynamo powered LED bike lights
Unfortunately dynamos seem to be forgotten by many modern cyclists. I'm not going deeper into reasons of this situation - instead I'm going to show You bicycle LED light that works better than many of commercially available battery (an dynamo) powered ligts.

The advantages of dynamo powered bicycle LED light:
- lots of light!
- always available - You can not forget to take it with You
- unlimited burn time
- no cells, batteries, chargers (think of costs and environment)
- unattractive to thieves.

I use this light for daily bike commuting since one year. The instructable misses some photos, because I didn't took many when I was building the light :) The circuit idea comes from the page http://pilom.com/BicycleElectronics/DynamoCircuits.htm (highly recommended!!)

Step 1: Electrical schema

Picture of Electrical schema
The bicycle dynamo works as a current source - it always "tries" to deliver its typical 500mA of current. This is an ideal source for light emitting diodes, which are current driven. The 500mA is way too much for single diodes, but it is just good for modern power LED (such as Luxeon, SSC, Cree etc). Power LEDs are delicate when it comes to reverse voltages, so we will rectify the dynamo current to power them.

The circuit is super simple - the graetz bridge rectifer, some smoothing capacitors and power LED diode.

Red LED diodes for the tail light are put as one branch of the rectifier. 13 diodes are connected in parallel - that multiplication gives more light and splits the current on more diodes (as You know, one diode can take only 20 ~ 25 mA current).

Please note, that the bicycle frame is usually used as the ground in AC dynamo circuit. The rectifier on the AC side is connected with the dynamo and with bike frame. The DC circuit needs 2 wire cable for its connections - there mustn't be any electrical contact with the frame.


How are you attaching the Dynamo to the bike? And what part of the bike rotates it? (the wheel or the sprocket?)

mkvinoth1235 months ago


mkvinoth1235 months ago


shareghe10 months ago


how much all together that cost you? the materials you bought and the time you spent to make that. thank you.

rob82b1 year ago

So where is a good place online to get these electronic components? I found the 1w LED but the site says its 350mA. I wonder if it will take 500? I am working on a project to teach kids about the differences between LED and Incandescent bulbs.

astral_mage rob82b11 months ago

try radioshack.com or dxsoul.com

kptBurek (author)  rob82b1 year ago

Maybe try to find the datasheet for this diode - usually you can find the maximum ratings there...

baggins1 year ago

What is your reasoning for using the tail light as part of the bridge rectifier instead of powering it in parallel with the front?

kptBurek (author)  baggins1 year ago

Red and white leds have different voltages and I'm not sure what happens when You connect them in parallel :-)

You can power it serial with front, but then it would get all the current the front gets (and You would need more leds or red power led).

When it's in rectifier branch it gets only half of main led current.

HI guys,

very good and easy tutorial. I have just few question. Your heighpower diode should be 1W and withstand 500mA. I am not a professional, but in this tutorial, the author uses 3,8W 1000mA. What is the difference?

Btw, I am asking, because in my country it is hard to find 1W diode which can withstand at least 500mA.

Thanks very much!

(i will use dynamo 6V 3W)

kptBurek (author)  knihovna1231 year ago

There's no difference - the 3,8W diode will just not reach its maximum current rating and probably will not be as bright as it would be with 1A supply (but you would have to check the current/lumen characteristics to confirm that)

You should not use diode which cannot withstand current lower than 0,5A.

sconner11 year ago
If you live in a metro area with those rental bike kiosks (like Boston), You may notice the leds on the rental bikes flash while in motion. I believe they work just exactly the way this author describes only more simply. Just a 12V dynamo and sets of 4 LED's in series front and back that flash as the dynamo's AC is rectified through them.
Maybe figure a way to use a couple capacitors in their or add a small charging circuit for a set of rechargeable batteries so you have light at stops.

I am aware of the issues some battery chemistry's have so doing the rechargable dynamo powered led light might be up in the air.
Amen, Brother!
Or just some high capacity caps that take a minute or so to discharge while at a stop and forget the batteries altogether.
Sworthed4 years ago
the heat conducting layer, must have to isolate or can be conductive? Thanks.

kptBurek (author)  Sworthed4 years ago
This depends on Your diode and light construction. Some diodes have neutral conductive area, some not. You have to decide, whether the contact with the "radiator" is "dangerous" for the circuit (for example possible contact with frame or sth...)
I want to thank you for this guide, I've just finished to soldering and assembling everything. It works really fine! Just an idea for the radiator: I used an old radiator from an old PC, just resized with a little saw, add a conductive paste and to keep all together I used 2 paper clip. I put all in to an old stile dynamo's light, a really cool effects!! I'm going to try it tomorrow, and I'll let you know.
Thanks and greetings from Italy,
sacanagem5 years ago
Hi to all, I'm new here and I wonder if you can help me building a same circuit but including a rechargeable battery of 6V or 12v, that can be charged through the dynamo, so it can light both head and back light not with leds but normal bulbs. WHY??  because whenever you need to stop and cross a road at night you'll have LIGHTS ON, cuestion of safety.
I really appreciate all suggestions.
UPwoodsguy5 years ago
Okay, I build the rectifier, and hooked it up to test it. I used a tantalum capacitor for the 4v 2200uf cap, not a aluminum. When I hooked up the rectifier to my bike dynamo, the test lights I hooked up didn't come on, and the tantalum capacitor did what it likes to do best, explode and burn.

I blew out the fire quickly, but the fire was very close to the shottky diodes and 63V 470uf caps. Hopefully these parts were not damaged.
I tested the circuit without the 2200uf 4v capacitor, and everything works fine. I'm pretty sure it just prevents flickering. It seems that it would be safer to use a 2200uf 6v capacitor. A 4v tantalum capacitor might have been too small, especially considering tantalums fail quickly when their max voltage is surpassed by only a small fraction.
UPwoodsguy5 years ago

Which wire on the AC side of the circuit connects to the dynamo, and what wire connects to the bike? I assume the dynamo connects to the section with the 470uf 63V capacitor, but tell me if I'm wrong.

kptBurek (author)  UPwoodsguy5 years ago
It doesn't matter ;-) this is alternating current....
UPwoodsguy5 years ago
I'm currently building this project, and I was wondering what is the output voltage of the section of the graetz bridge that connects to the tail light?

I bought 14 super small red Osram LEDs for the tail light. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=475-1133-2-ND

They have a max working voltage of two volts and can only take 20mA. Will I need any resistors to lower the voltage to the LEDs? I plan on wiring them in series, but I don't want to fry them.
kptBurek (author)  UPwoodsguy5 years ago
Please note that tail light acts as a branch of graetz bridge. These diodes get about 1/2 of headlight current. Your 15 diodes in parallel can take 300mA - so this should be no problem, since the dynamo gives 500-600 mA. This is a current source, so You don't need to care about voltage - when the red led gets 20mA it will have 2V (leds are current driven).

I have 13 noname clear diodes - they work 2 years without problems - I keep the light always on (hub dynamo without switch ;-)).

see: http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm#TailLight


Doing a little bit of math, the 14 leds wired in parellel will just be enough to keep the current to each led around 20mA. It might have been better to have 15, but 14 will work.
Ooops, I meant I will wire the LEDs in parellel.
chadeau5 years ago
kmossman means wheatstone needs balanc as a parralel battery sys does,or output will overload/overheat 1 branch of bridge ? I say mebbe use production rectifier...
Dr.Bill6 years ago
you already have a wheetstone bridge why not make it fully buffered with resistors and caps in parallel with the diodes?
kptBurek (author)  Dr.Bill6 years ago
I don't understand - what do You mean with wheatstone bridge? What would it bring here?
welder20006 years ago
I recently bought 2 mr16 - 2pin leds from eliteled.com for a pair of bike lights. I bought some simple housings from JC Whitney for $26.00. I also bought a red strobing 4 led light for a tail light. This is all powered by a 12volt rechargable screw gun battery. It will run all lights for about 2 1/2 hrs. before noticing a drop in light. All said and done, the light system cost me about $140.00 and works as well, or better than, any I have seen at my local bike shop at any price. With a little for thought and some good ole American ingenuity you can save some serious money and have fun doing it. Now I have to ask myself, "Should I get rid of the battery and try the dynamo?"
kptBurek (author)  welder20006 years ago
It depends how often do You need to ride at night. I use lights every day on my return from work, so the dynamo is perfect for me - I don't have to remember to charge it, take it with me etc. Batteries are ok, when You don't need to charge too often and wan to share the system between more bikes. My costs were 30$ max for parts, I think. Lately I bought a front wheel with hub-dynamo for next 40$.
amaze16 years ago
Great work. I like dynamo powered lights, get rid of all those batteries !
TopCatTC6 years ago
Yep thats the one. We here in the UK call them Dymano's. Elsewhere (US) call them Generators or such. I was toying with this kinda idea for a while. I raked out an old aluminium torch and stuck MR16 bulb in it and hooked it all up to a 12V Cordless drill battery ..... WHOOSH I went blind for a few minutes :-) This failed when I dropped the light and the bulb wouldn't work? In the end I found that the light had melted some washer inside and seald everything together? Back to the drawingboard. I am now looking at a lovely pair of Salt N Pepper pots in Asda £3. but I would need to use one of those smaller bulbs. These S&P pots look nice and neat for a light project. Will upload a picture later.
Aerospaced6 years ago
When you say dynamo, are you referring to the old style friction generator? the kind that rides along the tire and is held in place by a spring loaded bracket?
kptBurek (author)  Aerospaced6 years ago
Yes, I use the bottle-type dynamo, which runs on the side of the tire. You can also use the hub-generator (which is unfortunately much more expensive version).
TopCatTC6 years ago
Neat. I recently bought a dynamo for my bike and cant seem to get it work right? I may try out you Instructable, If I can find all the parts.