[Gta04-owner] Battery charge profile

d0m1n1k at gmx.net d0m1n1k at gmx.net
Sat Feb 25 23:41:17 CET 2012


as far as i know the gta04 can run on usb, at least if there isn't too
much activity.
wouldn't that be the preferred way once the battery is charged?
are the components connected in a way that the software can switch
between power sources?

Am 25.02.2012 22:14, schrieb NeilBrown:
> Does anyone know much about battery charging?
>
> I've been looking at what the battery charger is actually doing.
> Attached are two graphs created by taking 5 minute samples of various numbers
> while the GTA04 was on with the screen lit, so it was drawing over 200mA
> (deliberately).
>
>
> The first, charge-current.png compares the current seen by the battery with
> the current seen by the USB port.
> It just gives a simple picture of what is happening.  The battery is charged
> for a while.  As it gets full the current flowing in to it slows and stops.
> Then the charger switches off for about 100 minutes, then turns on again
> and charges the battery back up.
>
> The second, charge-volts.png, compares the voltage at the battery with the
> charge in the battery (i.e. how much charge it holds).
>
> Here we see that when charging stops, the voltage and the charge steadily
> drop until the voltage reaches 3.95V, then charging starts again.  This
> agrees with the docs.
>
> When the voltage is 3.95V, the charge (on this battery at least) is
> approximately 75% of full.
>
> My inclination is that I would rather it didn't get quite that low.  90% is
> about the minimum I feel comfortable with, 95% is probably better.
>
> I can program that voltage cut-off level to anything from 3.75V to 4.1V
> (approximately) in 23.4mV steps.
> 4.1V corresponds to a charge of about 94%.
>
> So to my question:  What is a good profile for a battery to encourage long
> life, or to balance that sensibly with usefulness?
>
> How much would it hurt the batteries to make 4.1V the default so that when
> plugged in to charge, it never lets it get below 94%??  Or should I aim for
> 90% (4.05 V).
>
> Thanks,
> NeilBrown
>
>
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