Beginning the Ben

Werner Almesberger werner at openmoko.org
Fri Oct 15 07:48:16 EDT 2010


Jane Andreas wrote:
> I so far have charged my Ben with a Solar panel that outputs 5.5v at
> 800mah, is that harmful to the unit?

The maximum VBUS voltage specified for USB is 5.25 V, so 5.5 V are a
little high. But that should still be within the acceptable range for
the components exposed to this voltage. Here are the ones I found:

Ref     Part            Max     Abs Max
U5      SE9016 [1]       6 V     7 V
U2/U3   EUP3406 [1]      5.5 V   6 V
U4      BL8555 [2]       8 V    10 V
U7      BL8506 [3]      10 V    12 V
U10     GPY0030B [1]     6 V     7 V

All but U5 are connected to +VBAT0, which is fed from +VBUS via D2,
a MSCD104 [1] with Vf around 0.1 V at a current of ~0.5 mA, and Vf
~0.24 V at 10 mA.

So it should be perfectly safe up to 5.5 V and probably still okay
at 5.6-5.7 V. If going higher, the device may malfunction, but
without suffering permanent damage. I would start to worry about
the Ben's well-being around 6.2 V.

Now, does your solar panel really output 5.5 V ? If the 5.5 V are
the panel's open-circuit voltage, then it will provide a lower
voltage under load. This can be only around 70% (~3.9 V) at maximum
power, or should be about 80% (~4.4 V) when the Ben draws as much
as it dares to. The charger circuit wants a USB volatage of at least
4.25 V.

If the 5.5 V are the voltage at which the cell achieves maximum
power efficiency, then its open-circuit voltage would be about 30%
higher, around 7.2 V, and may be dangerous. So you may want to check
the panel's data sheet and/or measure.

[1] Link at http://en.qi-hardware.com/wiki/Inventory
[2] http://www.belling.com.cn/2010p/BL8555_en.pdf
[3] http://www.belling.com.cn/2010p/BL8506_en.pdf

- Werner




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