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 .

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

Let It Glow!

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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 9 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


    10 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 10 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


    10 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 10 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


    10 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 10 years ago on Introduction

    A moderately-cheap price dynamo has circuity to prevent this situation.


    Reply 10 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 10 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 .