I am making a trailer to pull behind my 26" bike. I am wanting to run a bottle dynamo off of each of the trailer tires and charge 1-2 car batteries off of them which will power my light setup as well as phone charger, speakers and various other electronics that I may desire. The trailer, besides being my on the go power source, is all intended to be a mobile power station.

I play a location based game similar to Pokemon go and we have gatherings where we get together and play in a localized area and would like to be able to drop the trailer, with the batteries charged, and have everyone be able to plug in and charge their devices/battery packs then show up later and hook back up to ride off and recharge.

What I need to know is what I need to put between the dynamos and the battery and also what I need between the battery and the usb hub that will distribute the power to all the electronics.

Have also been considering adding a motor to power the wheel so that I can relax some over my longer distance rides(generally ride a minimum of 10-20 miles one way). Had considered finding a gas powered motor designed for a bike but have since come to consider an electric motor, which from my understanding should be able to be wired directly from the battery though if someone has a reason that won't work please feel free to say so.

  • \$\begingroup\$ Welcome to EE.SE. Have you done any calculations at all? (1) What is your sustainable cycling power in watts? Mine is about 150 W. (2) What is the power you hope to get out of the system? (3) What do you reckon the efficiency of the dynamos will be? (It will be much less than 100%.) (4) With just those few numbers do some calculations to figure out how much of your pedalling power will be going into your charger instead of trying to move your bike + trailer. \$\endgroup\$ – Transistor Oct 19 '17 at 21:30
  • \$\begingroup\$ "Have also been considering adding a motor to power the wheel so that I can relax some ...". You do realise that you will have to supply all the stored energy and the losses in storage and supply of that energy unless you charge from the mains. My bike has a decent low-friction hub alternator rated at 3 W. Assuming it's about 70% efficient that means it costs me about 5 W of effort or about 3% of my pedaling. \$\endgroup\$ – Transistor Oct 19 '17 at 21:43
  • \$\begingroup\$ I'm voting to close this question as off-topic because this has nothing to do with electronic design, EM-theory, ect \$\endgroup\$ – Voltage Spike Oct 19 '17 at 21:46
  • \$\begingroup\$ It does - he's asking about a charging circuit. He needs to show some work though. \$\endgroup\$ – Transistor Oct 19 '17 at 22:09
  • \$\begingroup\$ Why not invest in a solar panel or two - only losses are weight and air resistance so better for cycling - also will still work when stationary : unless you are inside.... or do you only cycle at night... \$\endgroup\$ – Solar Mike Oct 20 '17 at 4:16

I'm not sure if this really counts as an answer, but I don't mind doing some maths for you: On a 10 mile journey, assume that you're cycling at 150W output, at about 10mph, and half of that power goes into your power system (the other half is fighting against friction etc, but not sure about the percentage for that). Assume you have a 70% efficient alternator, you'll get 0.7*75=52.5W. Your journey is 10 miles, so that rounds out nicely to 52.5WH. Phone batteries are at ~3.7V, so 52.5WH=14Ah, which is equivalent to about 7 iphone 8 batteries. That will probably be ok for your phone charging needs.

Your relaxation needs are a bit more tricky. This website says a typical motor will be around 10WH/mile at minimum, which means if you pedal 10 miles to the place, and charge 3 phones, you're only getting about 3 miles back before you have to pedal again. Of course, you could pedal at the start and use the motor later.

This isn't too bad, but none of this takes into account the fact that you're dragging a big trailer with heavy lead acid batteries behind you. I'm imagining that these calculations are sort of a best case scenario.

Also, the connections and stuff are a bit complicated. To do it properly requires control systems and power conversion. If you just want to wing it and hack it all together, you probably could, but your efficiency would probably suffer a large amount.

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  • \$\begingroup\$ Thank you. While not being the answer I had hoped for it actually has pointed me in the right direction and while another issue may arise along the path I will work with current info to return with either a finished product or a question as to why it isn't working. \$\endgroup\$ – Josh Pearson AllanonDreavor Oct 20 '17 at 14:58

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