Retrofitting LEDs in a Dynamo Bulb




About: Engineering Enthusiast

Hello , again ,

As you know there are several instructables on building Bike Lighting systems ,but , hey i wanted to post my own .

After a couple of hours searching instructables ,I haven't saw a proper Bulb-Led conversion , i've just saw some spam or ones with incomplete instructions .

Now i will show you how to retrofit an LED array into a Regular Light bulb , which i think is brighter cleaner , and lotsa times cooler .

As a Bonus i used this LED array in my Bike's Dynamo, Voila, Much more output and half the Power .

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Step 1: Materials 'N' Tools

For my Array I used 3 LEDs but you can use up to 5 (well you can really use more , but there is not enough space...)

The List:

3-5 White Ultra-Bright LEDs (mine were 4900mcd)
1 Used, Burnt or Spare Screw-type Bulb
5-10 CMs(2-5inches)of Small Gauge Wire (mine came from an IDE cable,which is 26AWG)
1 Small Piece of Scrap circuit board (mine had a Dotted design,which is pretty Common)

-The Usual Soldering Equipment ( Soldering iron , Solder , Helping Hands, Sponge ,Etc)
-Needle or fine tipped Pliers (mine are rusty, That's Why i used my Multi-tool)
-Small Cutters
-A round file
-Hobby knife (i used A hobbico body and a X-acto blade)
-Hot glue and hot glue gun
(Not shown but handy to have )
-A fine tipped Permanent marker
-6 Volt supply and alligator clips
-A Small alligator clip

Step 2: Some Notes About LEDs

(thanks for the suggestions , PKM , Killerjackalope,and AndyGadget)

Our LED array should be Arranged in Parallel , it means LEDs should share positive and Negative Rails .

LEDs are diodes by themselves , so the need for A bridge rectifier is almost unnecesary , yet you
can put one if desired .

The Specs of my LEDs are
Forward Voltage 3.2 - 3.8 Volts
Average Current 25mA
And mcd is 4900

Step 3: Crack That Sucker !

This step can be a little messy and/or Dangerous ,
You've heard right DANGEROUS , i'm not liable if a small shard of glass poke one of your eyes

Remember to remove the solder from the nipple(if it's called like that...)and from the side .

The Safe Method to Remove the old bulb , consist of wrapping the Bulb in A piece of paper and cracking it with the Pliers.

My bulb was loose so it came out by just pulling it gently .

Step 4: Clean That Sucker !

Using the round file , and the X-acto Knife , The result will be a clean inside bulb-less base , (and a small pile of a cement Residue , it is not toxic , but you shouldn't eat or lick it , is nasty!)

Step 5: Plan Your Array

Figure out how to form a Triangle-like figure (or square or pentagon...) using the LEDs

Then, draw the outline of the base using the Marker ,

And at Last but not at least cut the board trying to adopt the shape of the base as much as you can ,
When done , Dry fit the board and the LEDs

It is pretty Straight-forward , you may also use the pictures as reference

Step 6: Soldering Those LEDs !

I think this is self explanatory , be careful not to burn yourself

Solder all the leads to the board

(in case you Ask , i decided to solder each LED one by one)

Step 7: Anode With Anode

This step is also Fast

You need to join electrically the three positive leads , just bridge them with solder .

When done, dry fit the array in the bulb base

Step 8: Common Anode to Wire

This is when that little wire comes in , cut a small 2.5 cm (1Inch)piece of wire , strip it and tin it with solder , do this same process in the other side.

Now is time to cut off the Leads of the Common Anode .

When Done , solder one of the sides of this little wire to the common Anode(positive) of the Array.

Both Pictures have Photonotes , that can be used as reference

Step 9: Wiring the Ground

This is also an easy step

Clip the cathode leads , Then apply a little bit more of solder

Now , Strip about 1 and a half (1.5)inch of wire , twist it gently , and tin it ,

Proceed to wire all the ground together , making a kind of loop , when done ,
cut the excess wire .

Now is when the PSU comes in , Give the array a try , you know you want to !

Step 10: Wirin' It All

This step consists of soldering the Positive wire to the nipple of the base

Then clipping off the excess of wire.

The picture make this step pretty straight-forward

Step 11: Gluin' It Down

Using hot glue (and gun) fill the base with glue , than quickly putting down the
array taking care that the Ground loop touches the body of the base .

let it harden for 15 minutes , and give a final test , Congratulations

You have finished your new LED bulb

Step 12: Final Thoughts , a Note About Resistors and Things That Just Didn't Fit Into Another Step

As you can see this array is reliable , shockproof and it will not burn in a loooooong time ,

I just have a single test Picture since where i live is raining , but believe is as bright (or more!)
than the Original bulb .

Yes , i know that there are several more powerful LEDs in the market , but I was too lazy
to wait 2 weeks of shipping, so i went to my local surplus store and bought them , you may also
salvage the LEDs from a toy or a Chinese flashlight , or better , order them online .

About Resistors :

As most of you know LEDs must have a Current limiting resistor to prevent burning

MATH time , yay!:

5.9 volts of the dynamo minus 3.3 of the LEDs is 2.6
2.6V divided by 0.075A = about 35 ohms (thanks PKM!),the neares safe value is 33

So I just soldered a 1/2 watt 33 ohm resistor in series to the array , I haven't suffered any
disgrace so i think is pretty much OK ,

Resistor color code is orange orange black gold

Anything you need : if you have questions , suggestions , mods feel free to put a comment
or PM me

Thanks , Lots of thanks , for watching ,analising ,doing ,modifying commenting and whatever-ing you
do with this Instructable . Perhaps destroying it ?

If you liked it , please rate or better vote for me in the Let it Glow! contest

Thanks a lot

see you next time

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    43 Discussions


    10 years ago on Introduction

    <strong>Good project, but fails</strong>. I built this project and the end result basically looks just like <a rel="nofollow" href="">this $22 bulb</a>this $22 bulb. (I simplified it by soldering each negative to the base and running the anode down the middle. I installed it on my Brompton (which has a 6v dynamo) and it works great for the first hundred yards. Then it dims, dims, dims, fails. I removed the bulb after a few hours, checked it on some batteries and it worked fine. After re-installing it the same thing happens... I get about a mile and it's dead. What's going on?<br/>

    4 replies

    Reply 10 years ago on Introduction

    I'm not quite sure what is really happening with your light .
    What I can say from my perspective may not be the Real answer ,
    the problem , i'm not quite sure, it's thet the dinamo doesn't produce enough current to light every thing properly , what could be happening ( which i think impossible due to the air flowing around the dynamo ["air friction] )It's that the coils from within the dynamo produce some heat and it affects the energy production , OR the array doesn't properly convert the current to light .

    May I ask , is everything connected properly ?
    is the resistor in?
    how did you made the LED wiring?


    Reply 10 years ago on Introduction

    according to wikipedia, those dynamos produce AC. Leds are only capable of running on DC, so you might need a rectifier diode.


    Reply 10 years ago on Introduction

    Hi ACAZ93. Thanks for commenting. I simply built the unit as described (all three + to the tip of the base, all three - to the edge of the base). When I tried it initially (without the resistor) it lit up with batteries and the dynamo... no problem. So, knowing nothing about electricity or LEDs, I assumed (!) that the light would continue to work, even after several minutes of use. I will install a resistor and then put a few miles in on the bike to see if it solves the problem.


    Reply 10 years ago on Introduction

    If the resistor wasn't the cause of the issue , I recommend adding a smoothing buffer capacitor and a zener diode . Try with the resistor and tell me if it corrected the problem see ya !


    10 years ago on Step 11

    This is very interesting. Thanks a lot! But I have read, that LED need a resistor to survive longer. How long has your construction worked? best to you Steve

    3 replies

    Reply 10 years ago on Step 11

    over 3 months so far , yeah it needs a resistor to work the guarantee 10,000 hrs (that's described in the last step ), It's really robust ,someone dropped by bike and a bump appeared in the case but the LED bulb was intact. Thanks , Have a nice week!


    Reply 10 years ago on Step 11

    OH yes - now I have read the last page. All ist there. I am sorry for asking. Is it difficult to add a high Cap for making it light even without riding for a short time - but where and how? Allt the best Steve


    Reply 10 years ago on Step 11

    Yes! but you will need a Zener diode and really high cap (I mean like 0.55 F ) if you ive a day i'll make a schematic


    11 years ago on Introduction

    (For Fluorescente) Here's a simple circuit which should smooth the dynamo voltage, charge up a battery and get over the main failing of a dynamo - namely the lights go off when you stop moving. I haven't made this (no dynamo), but it should work, and fit in a small box between the dynamo and lights. Let me know if you try it.

    2 replies

    Reply 11 years ago on Introduction

    Oh wow that seems a step further, thank you! I'll study it but since I'm too novice I don't know if I... heh


    11 years ago on Introduction

    The new "green" idea uses Compact Fluorescent Light Bulbs, but don't those thing contain mercury? Wouldn't LED's be a much better idea? I'm very ignorant when it comes to circuitry. Any idea on how to do it to a regular 40, 60, or 100 watt light bulb? I'm sure it would be done approximately the same way, but with a bit more circuitry, but I wouldn't know where to begin.

    1 reply

    Reply 11 years ago on Introduction

    It will consume less than 2 watts , the problem is the step down regulation , using leds in series may not be the solution , something using a triac or transformer or better , use a rectifier ,a Transformer , regulator ,fuse , capacitor resistors and some more things


    11 years ago on Introduction

    Another issue that might come up with hooking LEDs directly to a generator - what if you're racing downhill and are suddenly generating far more that your nominal 6V / 75mA? You coudl over-design your LEDs and resistors such that you'll never exceed the max current even at yoru maximum speed. But then the LEDs will under-perform >90% of the time. One option might be to put a zener diode across the generator to clip the excess voltage. And in that case, you might as well rectify the generator voltage as well. Good luck fitting all that into a little bulb socket though..

    4 replies

    Reply 11 years ago on Introduction

    I case i've used a Zener diode , I would have used a 3.9 diode ,a 470microfarad capacitor and a 75 ohm resistor


    Reply 11 years ago on Introduction

    Using a PVC tube and my drill , I've tested the array with Succesful results , even at maximum speed , the LEDs are complete , I've registered voltage of 6.65 volts and 0.451 A (open circuit ) the LEDs perform almost as brigth as when running slower (tested 5.46 volts , 0.496 A (open circuit)) the voltage diference is about 1.2 volts , I'm sure those little buddies can withstand that .