[Gta04-owner] charging gta04 on my bicycle

Alexander Lehner lehner at edv-buero-lehner.de
Sat Jul 12 00:05:00 CEST 2014

On Fri, 11 Jul 2014, Andreas Kemnade wrote:

> The GTA02 charger has no problems with hub dynamo. You will get 500mA without problems,
> I grounded the ID pin so current is set automatically to automatically to 1000mA (but the gta02 does not whine when it does not get that 1000mA)
> You will not get 1000mA without tricks. (page 12 on the slides, which 
> compare the U/I curve of a switching regulator input with a gta0X 
> attached to it with the U/I curve of a hub dynamo). If you have 
> following wind a lot or cycling a lot downwards these tricks can help if you can cycle 30km/h or so.

Same experience here.

> The hub dynamo can be best regarded as a 500mA current source which can 
> achieve these current even at higher speeds also at higher voltages. That 
> is also the reason why bicycle lamps do not break that easily when you 
> are cycling faster. They would consume more than the 500mA at higher 
> voltages which the hub dynamo cannot deliver.
> With a switching regulator this picture changes a bit: An ideal 
> switching regulator would give 5V/1A as output with 10V/0.5A as an 
> input.
> The general idea is to keep the operating point on the right side of 
> the "hill" by intelligently regulating the charge current if you want to 
> have more than 500mA on usb.

I guess this is what max power point trackers (MPPT) do, used for solar 
charger systems.

Another gadget for charching which I will try out is the following item:


It uses a stove with a peltier element.
I guess, the efficiency will be as poor as solar cells.

Finally, the dynamo is the best solution.
Compared to a wall (230V) charger, which delivers 1000mA: a smartphone 
needs 2-3 hours to charge.
Cut it down to 500mA dynamo, takes 4-6 hours.

Solar energy, peltier elements or fuel cells are even worse, need external 
resources and take aproximately a whole day to charge.

It's really a mess, not to have a portable nuclear plant ;)


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