[Gta04-owner] charging gta04 on my bicycle

[Andreas Kemnade]

On Fri, 11 Jul 2014 18:26:19 +0200 (CEST)
Alexander Lehner <lehner at edv-buero-lehner.de> wrote:

> 
> 
> On Fri, 11 Jul 2014, Dr. H. Nikolaus Schaller wrote:
> 
> > Hi,
> > the charger is a little critical about the VBUS voltage. It reports an issue if >5.2 V and drops charging if <4.4 V.
> >
> > But charging is only (re)started if VBUS goes below ca. 1.5V.
> >
> > So there is a situation for VBUS voltages where it does not charge even if you have 5.0V.
> 
> Is this related to the GTA04 only or does the charger of the GTA02 behave 
> the same?
> 
> I used my GTA02 with a self-soldered step-down converter and was at least 
> able to keep the battery charge at live for a whole day cycling.
> 
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.

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. 

Greetings
Andreas Kemnade
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