This safety light system blinks as far the wheel spins: faster it spins, faster rate the leds blink. I'ts contactless so here is quite no friction. It uses magnetic induction so it’s battery and maintenance free, waterproof and really clean in design. Perfect for all purposes!
Here in Italy Reelight’s are quite famous, but i preferred to reply the system by myself: is cheaper, custom and more exciting! There are a lot of DIY versions of this kind of safety lights, and some of those were very inspiring for me. I want to share my design for you because it’s even simpler, cleaner and more reliable thanks to the heat shrinking tubes coating.

- MAINTEINANCE FREE, waterproof assembly gives high reliability
- CONTACTLESS, which means quite no friction (check out the video)
- CHEAP, you can take all materials from "scrap"
- SAFE, it lights up as the wheel spins

Will follow only some tips and hints, due the design is really simple and you can get it just from the images. For any doubt leave a comment!

Step 1: Materials, Tips, Hints


- neodymium magnets (i took two couples from a pair of old 6Gb HDDs)

- coil (i took one from a 12DC, 10A 250V Relay)

- mastic adhesive

- heat shrink tubes, in different diameters

- 5mm red leds, ~3V 20mA

- wire (coaxial stereo wire worked perfect for me)

- wooden icecream sticks

- cable ties


- everything you need to solder

- heat gun (or lighter)


- the center of the design is to use heat shrink tubes to wrap all components, and then fix it to frame with cable ties. Before heating the tubes, i filled those a bit with mastic glue, this way i obtained a watertight sealing (and these rainy days confirm this!)

- note that there is a convenient combination between magnets and coil orientation, try changing the led connection polarity.

- i found out it’s better to put less in parallel. Less leds, less the rotation speed to light them up.


- the coil produces alternate current. If you want to have a smoother blinking use a diode bridge to rectify the current and feed a capacitor placed in parallel with the leds.


- Reelight’s: http://shop.reelight.com/bicycle-lights/17-sl600-...

- best inspiring DIY project for me: https://www.youtube.com/watch?v=KsA369MMkCk


i’m using this since a week ago, 150km some under the rain, and is working good. During night i prefer to use another blinking tail light powered by batteries and a yellow reflective jacket, so i don’t think at this light as my only tail light, but in some situations it could be. Tail light blink from 4kph, this means it works also pushing the bike walking!

Hope you enjoy this project, and do even better!

Cheers from Italy!


**EDIT (8th dec) ~400km, some under rain and some under 0°C, and still working :) Average speed ~27kph, Max <60kph

<p>Hi, </p><p>can you please tell me the characteristics of the relay coil?</p><p>I would like to know the resistance, volts, diameter of the wire etc.</p><p>When I tried to lit up a led like this, it did not work, I could hardly get 15ohms from an 880ohm relay.</p>
<p>Do you think connecting a 1watt power led would lit up ?</p>
Hi!<br>As i remember it lights up, but i finally preferred to use some common 5mm leds to have a bigger surface.<br><br>For best rusults i suggest you to use a pre-winded coil, there are many more turns and it is more precise.<br>In this other project i experemented myself how hard is to wind up a coil :)<br>https://www.instructables.com/id/DIY-contactless-magnetic-bike-rim-dynamo/
<p>hi, i made a coil using a perf board, so that it can stay flat and close<br> to the magnet(i removed the copper contacts of the perf board beneath <br>the windings). and just to test it, i connected 2 LED's(like a <br>rectifier, so when current flows in either direction any one of the LED <br>stays ON). BUt this did not work,.. Am i making any silly/blender <br>mistake... can you plz help.</p>
<p>It isn't just to have the coil. It needs a core allso.. the core is to be of iron. The magnet will magnetisize =&gt; the core, which will induct a altering AC electric field to the coil.</p>
<p>thanks for the information. I will try it with a meta piece that can magnetize and let you know my result.. </p>
<p>Hi this is the best DIY sor far.. but I cant figure out what is the purpose of the coil can i use solid state relay?</p>
<p>Go check: www.teksel.net and You'll find a nice solution to control Your dynamo</p>
<p>Go check: www.teksel.net and You'll find a nice solution to control Your dynamo</p>
<p>Thank you from Italy!<br>GRAZIE!<br>Simone</p>
<p>The main problem with this design is, If you aren't moving the lights aren't flashing. and so if you stop in the middle of the road at night,.. Cars will not see you until its too late. It probably wouldn't be too hard to put little magnets all around the rim and a coil near the rim with a few capacitors and a rectifier and that could go for both wheels,<br>and wire them both to one 18650 battery charger(with over discharge protection) and from the battery charger wire out to LED's for flashing red lights or even a front headlight. </p>
Hi Bullfrog!<br>I'm sure this design has pros and cons. For me the essential was to have a safety light ongoing. Usually i have a second battery powered tail light.<br>Anyway as i tested i suppose the electricity generated would not be enough, but if you will have good results please inform me :)<br>Thanks for the comment!
<p>maybe you could be interested in this other project i'm working on...</p><p>https://www.instructables.com/id/DIY-contactless-magnetic-bike-rim-dynamo/</p>
<p>~3400kms... Still Working!</p>
<p>After 2714 kilometers... still working!</p>
<p>It's easy to reduce the parts count because the LEDs are diodes. You may consider removing the rectifier bridge, which would eliminate that voltage drop (about 1.2 volts), making the LEDs brighter. It might be wise to insert a ~120 Ohm resister in series with the LEDs as a current limiter.</p>
<p>Hi!<br>Thanks for hints. The rectifier bridge serves to allow the insertion of the capacitor.<br>actually in my project there is no capacitor, as you suggest I preferred to directly connect the LEDs to get the most of the light at each flash.<br>In this other project I'm testing the use of capacitor and I thought one thing that soon I share, so if there was any flaw in the circuit we could talk about it!<br><br><a href="https://www.instructables.com/id/DIY-contactless-magnetic-bike-rim-dynamo/" rel="nofollow">https://www.instructables.com/id/DIY-contactless-ma...</a></p>
<p>here it is the link to the circuit i'm testing, is for another project but it could be used for this one also:</p><p><a href="https://www.instructables.com/id/DIY-contactless-magnetic-bike-rim-dynamo/step6/" rel="nofollow">https://www.instructables.com/id/DIY-contactless-ma...</a></p>
<p>Excellent idea. Presumably more magnets mean more flashes.</p>
<p>It's true!<br>From my point of view two magnets are the best compromise in lightness, balance and flashrate, but it's my taste!</p>
<p>If you added a few capacitors and more magnets, do you think you could keep the light fairly steady? If you were going for an always-on indicator? As long as you kept the wheel spinning, that is...</p>
<p>I copy-paste from another reply :)<br>&quot;...as i'm testing, you'll need first an ultracapacitor (1Farad or <br>more), and then a voltage bootster (dc-dc boost or joul thief). For make <br> a capacitor work you also need to rectify the current, and make some <br>connections in order to have blinking led while capacitor charges...<br>I'm trying these two ways for this project: <br></p><p><a href="https://www.instructables.com/id/DIY-contactless-magnetic-bike-rim-dynamo/" rel="nofollow">https://www.instructables.com/id/DIY-contactless-ma...</a></p><p>just waiting for the components.&quot;</p>
<p>nice!</p><p>Wouldn't it be possible to add a capacitor (to store some energy) and a resistor (to slow down the capacitor release) in the circuit in order to keep the light on while the magnet is away from the coil?<br><br>im not very good at electronics but it might help to at least reduce the off time no?</p>
<p>i'm also an electronic newbie :) ...as i'm testing, you'll need first an ultracapacitor (1Farad or more), and then a voltage bootster (dc-dc boost or joul thief). For make a capacitor work you also need to rectify the current, and make some connections in order to have blinking led while capacitor charges...<br>I'm trying these two ways for this project:</p><p><a href="https://www.instructables.com/id/DIY-contactless-magnetic-bike-rim-dynamo/" rel="nofollow">https://www.instructables.com/id/DIY-contactless-ma...</a></p><p>just waiting for the components.</p>
<p>Nice to see such experiment.</p><p>I am thinking to make one and I have started also.</p><p>But the problem I am facing is about the coil. Can anyone give me link or tell me how to make or get such coil. The main problem is I am non science student but interested in physics.</p><p>Thanks</p>
<p>Hi!<br>You can take one from a relay. Mine was like this one:</p><p><a href="http://www.ebay.it/itm/Finder-40-31-9-012-Relais-12V-DC-1xUM-10A-250V-AC-Relay-Steck-Print-854247-/311169605881?pt=Elektromechanische_Bauelemente&hash=item48732760f9" rel="nofollow">http://www.ebay.it/itm/Finder-40-31-9-012-Relais-1...</a></p><p>Actually you can also wind up a lot of turn of copper soil around a ferromagnetic core, but i think it's not the best deal :)<br>Cheers!</p>
<p>Hi,</p><p>I chkd ur link but I think its hard for me to get such thing as I dont know that relay is for what purpose. I tried to make it by own. I took a nail which is attracted by magnet and wraped it with copper wire around 700-800 rounds. But now I am confused in which way I have to pass the magnet to generate the electricity. When I am taking the magnet near the head of the nail and striking it the LED are glowing. Exactly what In which way I have to do I am not getting. </p><p>If u help me by providing some link or pic of how to make the coil part, then it would be nice.</p><p>Thanks</p>
The fastest way is to fix the magnets on the spoke, and then try different positions of the coil. For me worked well parallel to the rear fork since was easier to fix.<br>For relay coil the best is to place those as you can see in this other project:
<br><a href="https://www.instructables.com/id/Contactless-dynamo-powering-bike-safety-lights/" rel="nofollow">https://www.instructables.com/id/Contactless-dynamo...</a></p>
<p>how about the coils from automotive relays? will they work?</p>
<p>Hi!<br>I don't know are big are, can you post a photo?</p>
<p>Good Job Thanks :)</p>
<p>What if you incorporated a light sensor to bypass the LEDS during the day, and charged a rechargeable battery - which would power the LEDS at night with a failover direct from the magnet/coils (if the battery were dead)?</p>
<p>~400km, some under rain and some under 0&deg;C, and still working :) Average speed ~27kph, Max &lt;60kph</p>
<p>I think, it can be easily combined with small beeper, to produce short audio signals in the forward direction too. It might be useful in darkness...</p>
<p>There are pretty good magnets in CD-rom drives too, they are used for the fine positioning of the laser. I had a sketch of something like this a few years ago, with magnets on the spokes, and a disk (like a brake disc) but attached to the frame with a series array of coils. Idea was to use that to charge batteries/supercaps to run headlights and tail lights.</p>
Awesome job...you rock...
<p>thank you! :)</p>
<p>I would think with those heavy magnets that wheel balance could become an issue, espesially at higher speeds. Might take some fiddling with to get two or more mages positions so it's not a problem. Obviously, placing the magnest as close as possible to the center to the wheel will minimize the balance issue.</p>
<p>Those magnet are extremely thin and light weight, but if I was to run my bike at very high speed, a simple placement of a second magnet on the other side of the wheel should answer your concern. Cheers. </p>
<p>i agree, i think two magnets is the best deal in blinking rate and balance/lightness on wheel!</p>
<p>I guarantee i don't feel balance issues when going, just needed to fix magnets opposite relatively to the wheel hub. My average speed in usual ride it's 27kph, with peaks of 50-60kph. Position of magnets was preferred in order to obtain a small distance between them and the coil. Also Andrea is right, as far the magnets are from the wheel hub, more the coil is working good, especially at low speed.</p><p>Anyway i understand you, in my mind don't like so much to have magnets on spokes, thought for everyday use it's really negligible, i like to have rims as light as possible... so i'm working on this:</p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/8U2gpYRdKps" width="500"></iframe></p>
<p>relative speed between magnet and coil will affect flow of current, so a bigger radius create a more efficient system</p>
<p>In the &quot;good old days&quot; a large portion of bikes came with this system built in to the wheel hub or you could buy a dynamo which would just rub on the tyre to make it turn to generate electricity to power the lights but the problem came when you stopped at a junction and the lights went out, I remember being stopped by the local police for not showing lights whilst riding at night even though i had a dynamo system on after he gave me a telling off and told me to get some real lights that do not keep going off when i either slow down or stop.</p><p>it is good to see someone re inventing old ideas.</p>
<p>Hi!<br>Yes, it's true, this could be avoided putting an ultracapacitor to achieve steady light for some time also when stopping, i'm waiting to receive it for some tests.<br>Anyway i like that my tail light blinks, i think it's more visible, so in that case i will find a way to put a 555... step by step it's getting more complex, and sincerely i like the semplicity of this current version. As i wrote as conclusion: &quot;During night i prefer to use another blinking tail light powered by <br>batteries and a yellow reflective jacket, so i don&rsquo;t think at this light <br> as my only tail light, but in some situations it could be&quot;... it's simply and i don't to think about it.<br>Anyway, a natural evolution could be this :) </p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/8U2gpYRdKps" width="500"></iframe></p>
<p>nifty, add more magnets for more bursts and at higher speeds, you get a much nicer stream. Encapsulate the coil and the electronics (if you do the full wave bridge/cap) in clear epoxy just leave solder tabs, perhaps using staycon sets. They are clamp on wire spade connectors. If you have access to a few HD's you can make two sets (front and back wheel). </p><p>nice piece of work actually!</p>
<p><a href="http://reelight.com/" rel="nofollow">http://reelight.com/</a><br><br>Practically the same, but with high prices. I like this instructables and will build my own in time. :)<br><br>Thanks!</p>
<p>Here's a useful Instructable on how to reclaim thin magnets from old hard drives.</p><p><a href="https://www.instructables.com/id/How-to-separate-the-Magnets-from-an-old-harddisk/" rel="nofollow">https://www.instructables.com/id/How-to-separate-th...</a></p><p>And maybe a flat coil will work well too.</p><p><a href="https://www.instructables.com/id/Making-Electricity-in-your-hand/" rel="nofollow">https://www.instructables.com/id/Making-Electricity...</a></p><p>bhunter736 also mentions using this method in his diy wind generator..</p>
<p>You DO realize this ALREADY exists:</p><p><strong>Revolights Arc</strong> www.revolights.com </p>

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More by stonioni:Bicycle Rubberband Handbrake DIY Contactless magnetic induction bike dynamo Magnetic induction safety bike lights. Nearly invisible design, cheap, waterproof and battery free! 
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