Hi
First timer here, please be gentle
Im looking for help with a circuit Im working on, well it has so few parts in can hardly be counted as a circuit but its got me beat!
I want to use my Shimano hub dynamo on my bike to charge my iphone. So far, Ive connected four diodes and a capacitor to make a fairly standard (well very standard) bridge rectifier and smoother. I feed that into a 5v regulator and then connect that to the iphone.
A few thing that may help you answer my question! The Shimano dynamo is rated at 6v but in open circuit it can produce much more than that (just spinning the wheel shows that it can go up to 24v AC on my multimeter, but when Im whizzing down a hill at 30mph, I would guess it may be higher)
Ive also used the four resistor trick to make the iphone think its connected to a compatible charger (Connect 1 100k between pins 1 and 2, two 100k in parallel between pins 2 and 3 and another 100k between pins 3 and 4 - all pins referring to the USB socket)
The circuit produces a very stable 5v once I get to about 8mph - thats probably when the dynamo starts to get to around 7v, ie the necessary 2v above the 5v regulated voltage.
The problem is that the iphone actually starts to discharge even faster when I connect it! The charging icon does come on but the battery then starts to rapidly discharge, something like 5% battery life in ten minutes.
Can I connect 4x2500mah AA nimh batteries to the output and see if that helps?
Would I need to add a diode or two to stop the iphone trying to power the charger? (grasping at straws here!)
Many thanks for any light you can shed on this issue. Im basically competent with a soldering iron, working on a very limited budget but my main issue is Im dyslexic and have to study simple problems for hours before I develop a deep understanding!
Phil Waud
PS - great forum, already had a good look around to see if this question had been answered and going to have another good trawl now for other ideas!