Dynamo Charger

[crashmeplease]

I quite fancy having the ability to charge my phone while out on my push bike. I've seen a nice little Hub mounted dynamo that outputs 6v @ 3W The phone requires 5v. It would charge on minimum 500mAh, so in theory all that's required is to step down the voltage.

However, I think I would like to make it a bit more complicated than that

To get the most out of the dynamo, for times when I don't have the phone connected, I think I want to charge a bundle of batteries. The batteries could then be used for a camera ect. When the phone is connected, I would like it to be charged from the batteries @ 1A to give a quicker charge if possible. It is kind of like the **broken link removed** Kit but powered by dynamo rather than Solar. Actually I could just get a basic Freeloader kit, and use the dynamo as a secondary usb charger.. No that would be silly!

Do you think this is a feasible project to consider building the advanced idea, or just stick with the basic 500mAh one?

 

[Nigel Goodwin]

I presume you are aware that driving the dynamo takes power, and makes your bike harder to pedal?.

Phones usually have the charger circuit inside the phone, so you could probably connect the dynamo directly, making sure it's actually DC though (many 'dynamos' are actually alternators).

 

[bychon]

A full wave bridge rectifier would make DC out of the AC and reduce the voltage from 6 to about 4.7. It costs less than a dollar.

 

[crashmeplease]

I presume you are aware that driving the dynamo takes power, and makes your bike harder to pedal?.

Some dynamo hubs have been quoted to require as little as 5 feet per mile extra effort, they're integrated into the wheel hub, fully enclosed, quite efficient, not an additional block that sits on the tyre or anything like that

Phones usually have the charger circuit inside the phone, so you could probably connect the dynamo directly, making sure it's actually DC though (many 'dynamos' are actually alternators).

Mine is a mini USB connector, it can be charged by pc, mains charger with mini USB, or anything that can power USB. I would have expected it to adhere to the USB standard and expect 5V input. I don't know if I would like to risk giving it 6V!

Ah forgot about the dynamo being AC not a problem though, that's easily sorted!

 

[crashmeplease]

A full wave bridge rectifier would make DC out of the AC and reduce the voltage from 6 to about 4.7. It costs less than a dollar.

Yep I was just thinking the same, thanks!

 

[Nigel Goodwin]

Check what's coming out of the mains charger, it may well be more than 5V.

 

[philwaud]

Also, you may find that the dynamo produces much more than 6v when under a low load. My Shimano hub dynamo can produce 24v - and Ive been told this can go up to 60v under some curcumstances. You will fry your phone if you dont add a regulator, something like a TS9040

Phil