# Contactless dynamo powering bike safety lights

7 Steps
Hello everyone!! On this instructable you will see how to build a simple contactless dynamo for powering a bike safety light from a relay coil and some hard drive magnets.

As you will see, the electric circuit is really simple and contains only 3 bright red leds and a 4700uF capacitor. The capacitor is used just to keep one of the leds steady while you are driving. The other two leds will be blinking as the magnets pass by the coil. To have all three leds blinking you can remove the capacitor if you want. If you decide to place some more capacitors in parallel, the steady led should keep on even when you're stopped.

On part two we have more 2 coils installed for powering 5 white bright leds for the front light. The circuit is completely independent from part one's.

For more information about how to improve this kind of system, just look around the site, there are several instructables on the subject. You will find different kinds of generators and other circuit ideas.
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## Step 1: The coil

To avoid spending time building your own coil, just look around for an old relay. I got this board from an old telephone central station.

The second picture shows the coil disassembled from the relay. On the bottom part you may notice that the magnetic circuit is open. In fact that's where the relay's moving parts were attached. I didn't noticed much difference closing the magnetic circuit with a peace of metal, so I just left it as it is. But theorically it should improve efficiency.

For a simple system like this, you should try to keep the coil's resistance between 100 and 200 ohms. This one has 200 ohms. With more than that you will generate more energy but efficiency drops because you also have more losses in the coil.
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mkretman says: Apr 25, 2013. 10:02 AM
Anyone trying this to power revolights?
ranelson93 says: Feb 1, 2013. 12:11 PM
So do you actually need a relay to make this work or Could i just make my own coil by wrapping some copper around a pvc pipe?
pedrogg95 says: Jan 20, 2013. 10:17 PM
how can i build the coils, or where can i find it, or by it??
rchanter says: Jan 19, 2013. 9:46 AM
Hi I'm using the theory from this to make a version for myself just trying to sort a few bits out, when mounted like this the magnets rotate for mine I am rotating the coil past a magnet, will I get a better output if I pass the coil between two magnets? assuming the poles are aligned to increase the magnetic field.

Cheers.
adhawan says: Nov 4, 2012. 11:34 AM
I am having trouble finding the coils? Any help on where I can either buy them or get them would be appreciated.
I got them in a junk yard, pulled the relays from an old car harness... I did not carry my multimeter with me so I went looking for the heavier ones, they end it up measuring 80-90 ohms, but give up to 15V positive spikes and ~6V negative spikes as measured in the oscilloscope... The magnets I got are not as large as the ones pictured here, so I placed 4 of them in the rear wheel, I got these from my factory, they sell the damaged HD's to a recycling company, so I just got permission to remove the magnets before they go to recycling bin :-)
gtoal says: May 23, 2012. 2:49 PM
Has anyone done this in reverse? Put the magnets on the bike and the generator on the wheel, to power spoke lights or a POV (persistence of vision) display?
kent1956 says: Mar 26, 2012. 3:36 AM
Metal Drilling 101.

-Buy more expensive carbon drill bits.
-Use a cutting oil, and be liberal with it. It will help to cool the bit and keep it from melting and help to clean out the metal bits from the hole.
Cutting oil can be bought in small 8 oz. bottles
-Use a low speed, high speed causes the bit to make small metal bits and can lubricate the drill bit, causing it to ride above the metal you are trying to cut through.
-Drill bits are actually cutting tools, look at one, they normally have two cutting flukes (surfaces). You will know you are using the correct speed when you get a nice ribbon of metal, rather than a lot of small chunks.
-Keep good hard force on the drill, if you don't it will again make small chunks and just float on them above your metal surface.
-For very hard metal, It becomes necessary to start with a smaller pilot hole, and enlarging it drill size by size to your desired hole size.
I don't think these magnets have a very hard metal strap, they are not made for really hard abuse as other metal parts are, so this should not be necessary.

vbnicolau,

I have used the FreeLights and am not impressed with them. They are way too dim. But the idea is good. The paper from the NM students is good information. I like the way you have made use of salvage parts.

I would consider ways to make this all waterproof, as I commute come rain or shine. PVC tubes with caps could be used to house the relays, with a small hole on the bottom side for the wires to come out, sealed with some silicone.

Thanks for sharing this, over all a great idea, and a great presentation here.
The.zafootz says: Jan 8, 2012. 8:09 AM
This device is awsome I am learning to make one myself and hope to learn everything there is to know about contactless dynamos =D
SinAmos says: Jul 26, 2011. 10:49 PM
Simple, yet awesome. I can't wait to try.
jules15 says: May 14, 2010. 2:18 PM
i did this and i was only getting .01 volts around there. I used a 5 volt relay. i don't know what to do :p
scraptopower in reply to jules15Jul 13, 2011. 12:39 PM
You're not using the DC setting on your meter are you ?
loccci says: Jul 5, 2010. 4:55 PM
hi, i dont understand where to put the capacitor if i want one led or more to stay on constant. do you have to charge the capacitor intitially. why is the only place you could put it parallel with led3? why does it not get negative voltage? why arent all of the leds in parallel? led2 and led4 seem to be in series, why is this? sorry i just dont get it. thanks
scraptopower in reply to loccciJul 13, 2011. 12:38 PM
I don't think it is possible to add capacitor smoothing to this circuit without adding a bridge rectifier (use schottky diodes for efficiency).

He has wired the circuit in that way because the waveform is not mirrored, so there's less load when the coil - wire is more positive. At least, that's what I think,,,
yonutzky says: Jan 13, 2011. 8:58 AM
I have only one screw hole in my magnets. I tried to drill another hole in the panel the magnet sits on, with an ordinary drill, but it only dented the metal. It won't go through. Any suggestions?

Thanks
bricabracwizard in reply to yonutzkyJul 12, 2011. 9:55 PM
Use a proper drill for metal, they are a bit more expensive but they cut through metal like its cheese. Another thing is keep the drill cool while drilling they will stay sharper longer.
The Insignificant User in reply to yonutzkyFeb 15, 2011. 9:34 AM
Something I've found that helps is to drill the hole and then use a hammer and a sturdy roofing nail to drive the rest of the way through. However, this works best with smaller diameter holes, so if you intend to use a larger bolt to hold it in place, that might not be the best method.
Best of luck.
snowluck2345 says: May 18, 2011. 8:57 AM
Could you give an example of some other windings you could use? For example would a toroid work? or a transformer?
SuperKuper says: Apr 13, 2011. 8:53 AM
Where could I get my hands on some of these coils? Also are they sealed/waterproofed at all, and if not can the bike be open to the elements? (looks like there's a plastic coating on it)
golddigger1559 says: Apr 6, 2011. 12:11 PM
how long do you think it would take to charge a 200v 10000UF capaciter?
ploomus says: Mar 25, 2011. 11:49 AM
Really nice project, i'm thinking about making my own but maybe i also want to use it for charging my Ipod. Well i'm not sure will it be powerful enough but i could find it out. I don't want usual dynamo because it feels boring and i love building myself =P
rpvanpatt says: Feb 11, 2010. 10:10 PM
..i'm new to all this so dont mind the question... could it be possible to put a capacitor in front of all the leds?  and maybe with a switch, so that you could turn them all on and off with out any blinking?  thanks
The Insignificant User in reply to rpvanpattFeb 15, 2011. 9:38 AM
http://www.instructables.com/id/Contactless-dynamo-bike-wheel-lights/
It's by the same author as this instructable. The circuit diagram is similar enough to what is happening here for you to get some idea as to what's going on. If you need a place to get capacitors/LED's, try Jameco.com. It's a pretty good site if you want low prices and fast delivery.
iceng says: Feb 4, 2011. 4:36 PM
It is a nice generator but those magnets are powerful enough to grab street metallic scraps and possibly jam the wheel.
f22archrer says: Nov 29, 2010. 8:16 AM
can i use the part of motors on which the wiring is done ??? as i fail to find myself a relay coil
joel26 says: Oct 22, 2009. 9:50 AM
Doesn't the magnetic field slow the bike down?
kikiclint in reply to joel26Aug 18, 2010. 3:13 PM
it will slightly, but generally only the amount by which it is giving you power. Unless you have wierd stuff happening with eddy currents or ferromagnetic materials pulling on it.
xsmurf in reply to kikiclintAug 22, 2010. 6:27 AM
"only the amount by which it is giving you power" To put that in perspective, 3 leds at roughly 3V and 25mA so 3x0.025x3= 0.225W (no loss I'm aware) of power consumed. Considering a cyclist might put out 300W of power (total ball park, I'm aware), that would be a reduction of power of 0.075% way way under anything noticeable to the rider.
james.mcglashan says: Jun 9, 2009. 12:57 AM
how mant volts does this make: 1 relay, 1 magnet, i want to do the relays and magnets so i can hopefuly get enough power to power my little list i want to first put power in 10 very good capastor then through regulators to do theese things, and power 8 usb divices (usb battery charger, mp3/4, mobile, camra and other divices), and power my lights, will this work with how many relays and how many magnets to get the wanted power
kikiclint in reply to james.mcglashanAug 18, 2010. 3:14 PM
that will depend on the relay and the proximity and speed of the magnet passing. I was able to get 5 volts ac off of one of my coils.
midnightsky says: Mar 4, 2010. 11:18 PM
coils aka relays you can find anywhere like auto zone to walmart lol homedepot  most gate openers whill have relays in them find an gate or a door company they will have tons of old gate sys boards andold relays that i am sure they will give up for free or a cheap price hehehe
mid
rpvanpatt in reply to midnightskyMar 23, 2010. 10:55 AM
how bout in any other typical household electronics, can you find one in anything else?
kikiclint in reply to rpvanpattAug 15, 2010. 9:14 PM
All electronics that have power switching are going to have relays. If you look for dead microwaves, they will have some in them. Other places I have found them are in large power filters for computers. 12 volt relays work good if you get the magnets to pass close to them.
jules15 in reply to rpvanpattMay 14, 2010. 2:19 PM
if your computer is old, it might have a modem in it still.  Theres a 5 volt surface mounted relay. But BE CAREFUL taking it off.
midnightsky in reply to rpvanpattMar 23, 2010. 4:24 PM
http://www.gatehousesupplies.com/SearchResults.asp?Search=relays
go here and you can find them once you got the name of the relay you can find for cheaper
rpvanpatt in reply to midnightskyMar 23, 2010. 8:13 PM
thanks...but i have no idea, which one would I use for this?
cdcobre says: May 15, 2010. 9:26 PM

# this guy really helps in youtube search for how to wind copper coils tightly for wind turbine stators part 1

thanks mignightsky and rpvapatt you help me not to spend a lot in just test for my project.
rpvanpatt says: Feb 11, 2010. 7:50 PM
how much voltage is put out by the coil/magnets?
rpvanpatt says: Feb 10, 2010. 10:13 PM
could you charge a battery with this as well?  I would love to use this idea instead of a motor to generate power to charge batterys, which then will power other things
mheffner says: Dec 21, 2009. 7:18 PM
There is a plus to using the hard drive magnets in this situation. They have both a north and south on each side, thus each time the magnet passes you're giving it the polarity change needed.
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