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  • Author Author: rctho
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Dynamo hub 5v usb charger

rctho

I have some pics from last winter i thought i'd share from my dynamo hub 5v charger project. I finally got it to work but unfortunately it doesn't work well. i think i would have to ride across Canada to fully charge my phone. The output of the hub is 6v 3w if i remember correctly. the first version did not include a diode on the output that resulted in actually draining my phones batter when i rode. I was a lil' discouraged and put it on the back burner for a bit. I finally got it to work successfully but my hub doesn't seem to produce enough juice to charge even a battery pack. I ride my bike often too. At least 30km a day. maybe that's not often but it is for me.

 

Here is the schematic

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and the breadboard prototype

 

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soldered it all together

 

image

 

then wired it up and jammed it into a dental floss container.

 

image

 

I calculated a 1 amp output on the hub. Not sure what i'm missing. Does anyone have any suggestions?

  • in reply to rctho

    Hi Craig,

    You can forget about the 7805 regulator. The little circuit can attach after the bridge which should be made of schottky diodes like the 1N5817, 5818, or 5819. I would put a relatively small electrolytic like a 100 uF on the output of the bridge just before the little circuit. If one of the better engineers on the forum are monitoring this thread and they have a better opinion on the capacitor hopefully they will jump in here. We do not have much information on the magneto generator inside the hub. I read that it has a feeling of detents as it is rotated so I am guessing that it is a multipole magneto and as such we should get a fairly decent frequency out of it when you are up to speed. Since the output of the little circuit is going to have a fairly constant load (recharging the battery of a cell phone) we should not need a lot of capacitance. If my description is clear enough let me know or I will take the time to whip up a schematic.

     

    John

  • in reply to jw0752

    Hi John,

     

    I'm going to resurrect this project and try out this lil' circuit. i didn't know such a thing existed but sounds like exactly what i need to make my bike charger work.

     

    I didn't use the diode bridge rectifier after i realized i could just buy a bridge rectifier. I forget what it's rated at but i'll let you know once i find it.

     

    At what point of the schematic should i add this circuit? right after the bridge rectifier or after the 5v regulator? Do i even need the regulator or will this circuit provide that function for me? I'm guessing I only need to rectify the ac to dc before the current reaches this circuit.

     

    Thanks again for your help. I still really like the idea of kinetic energy from my bike and i think this might actually work. fingers x'd.

     

    Craig

  • in reply to rctho

    Hi Craig,

     

    The problem as I see it at this point is that there isn't enough voltage being produced to make your circuit work. If we want 5 volts out of the regulator we must supply the regulator with about 7 volts on its input. Between the input of the regulator and the hub you have a bridge rectifier with 2 diodes always in the current flow. A diode will steal about 0.7 volts from the circuit so since we have 2 of them we loose 1.4 volts. If we add this 1.4 to the 7 we need at the input of the regulator we are at 8.4 volts minimum needed from the hub just to get the regulator to put out 5 volts. As soon as we plug a load (cell phone or other item to be charged) into the output of the regulator all the resistances in the components, wires and hub itself come into play and steal most of the energy that is available. Here are some suggestions that you could try that might help. Use a bridge made up of schottky diodes as these only drop the voltage by .4 volts. Now we connect a small boost converter like this to the 5 volts coming from the hub.

     

    https://www.ebay.com/itm/DC-DC-Boost-Step-up-Power-Supply-Volt-Converter-3V-3-3V-3-7V-to-5V-USB-Charger/322979623962?hash=item4b3315f41a:g:v2EAAOSw-KFXeioj

     

    This same type of boost circuit is used in many of the battery packs that are used to recharge phones. The battery packs actually have 3.7 volt batteries and they use a boost circuit to jump it up to the 5 volts needed to charge your phone. The other advantage of the boost converters is that a high percentage of the energy consumed by the converter is delivered to the 5 volt output. I can't guarantee that this will work for you but I can guarantee it will work better than the current circuit.

     

     

    John

  • in reply to jw0752

    Hi John. I have to refresh my memory. i was obsessed with this thing for a lil' bit. I remember the circuit outputting 1a. the hub is an alternating hub and is a very basic design since alternating dynamo hubs are not new technology. it is rated at 6v 3w but goes higher the faster the bike goes so determining exact measurements is difficult. i would require very little momentum for the circuit to activate though. if i bomb a hill i think it produces a lot of juice. I am no expert though. the idea of kinetic energy from my bike seemed like a good idea and i wanted to use it for more than just a light which is all it's intended for.

  • Hi Craig,

     

    How are you determining that the hub generates 1 amp and what is the voltage that is being produced at this current? Are you sure that the hub is producing AC current? 6 volts at 3 watts is only 0.5 Amps. The 7805 that you are using has a need for at least 7 volts to operate properly. You are loosing about 1.5 of the 6 volts in the bridge rectifiers of your circuit.

     

    John