Question about charging

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Question about charging

Helge Hafting
I plan on making a generator for my bicycle. It will power some LEDS,
but if I can make enough current, I could charge the phone as well.

According to documentation, the freerunner wants 100mA, 500mA or 1000mA,
and no more than 5V. Limiting to 5V should be easy enough. I just wonder
if the charging can handle unstable voltage, for example if it
alternates between useable 5V and "too low" 10 times a second.

Will the phone be able to draw some current at moments where there is
enough voltage, or does it need a more stable supply of power?

Helge Hafting

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Re: Question about charging

andy green-3
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Somebody in the thread at some point said:
| I plan on making a generator for my bicycle. It will power some LEDS,
| but if I can make enough current, I could charge the phone as well.
|
| According to documentation, the freerunner wants 100mA, 500mA or 1000mA,
| and no more than 5V. Limiting to 5V should be easy enough. I just wonder
| if the charging can handle unstable voltage, for example if it
| alternates between useable 5V and "too low" 10 times a second.
|
| Will the phone be able to draw some current at moments where there is
| enough voltage, or does it need a more stable supply of power?

The charging state machine probably can't cope with that in a reasonable
way.

But, it should use whatever's present to feed VB_SYS dynamically,
favouring it instead of the battery.  If you have an A6 or A7 GTA02, it
might even not crash your CPU while it's doing that :-)

If you are pedalling steadily, the charger can get started too, so it
sounds worth a try.

- -Andy
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Re: Question about charging

Werner Almesberger
In reply to this post by Helge Hafting
Helge Hafting wrote:
> According to documentation, the freerunner wants 100mA, 500mA or 1000mA,
> and no more than 5V. Limiting to 5V should be easy enough. I just wonder
> if the charging can handle unstable voltage, for example if it
> alternates between useable 5V and "too low" 10 times a second.

The PMU may be able to keep up with this, but I'm not sure the
battery will like it. If you google for "short charge cycles", you
find claims that this kills Li-Ion batteries.

In particular, if you look at page 84 of
http://people.openmoko.org/tony_tu/GTA02/datasheet/PMU/PCF50633UM_6.pdf
you see that dropping below the USB detection threshold (~4V) will
reset the charger state machine and thus defeat the mechanism that
avoids trickle-charging the battery when it's full.

Harald posted a while ago that such trickle-charging changes the
battery's chemistry and damages it.

- Werner

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Re: Question about charging

andy green-3
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Somebody in the thread at some point said:

| The PMU may be able to keep up with this, but I'm not sure the
| battery will like it. If you google for "short charge cycles", you
| find claims that this kills Li-Ion batteries.

Actually that's another use for Cedric's request for independent control
of charging current.

- -Andy
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Re: Question about charging

Helge Hafting
In reply to this post by Werner Almesberger
Werner Almesberger wrote:

> The PMU may be able to keep up with this, but I'm not sure the
> battery will like it. If you google for "short charge cycles", you
> find claims that this kills Li-Ion batteries.
>
> In particular, if you look at page 84 of
> http://people.openmoko.org/tony_tu/GTA02/datasheet/PMU/PCF50633UM_6.pdf
> you see that dropping below the USB detection threshold (~4V) will
> reset the charger state machine and thus defeat the mechanism that
> avoids trickle-charging the battery when it's full.
>
> Harald posted a while ago that such trickle-charging changes the
> battery's chemistry and damages it.

I see. A homemade charger should stay between 4V and 5V then. Cutting
below 4V shouldn't be hard to do.

Helge Hafting

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Re: Question about charging

Flemming Richter Mikkelsen
Just use a voltage regulator that has
built in step up and step down.

You can find one that always output
5V. Just be careful you have enough
current i.e. cut the power when the
current drops below 500mA.

Maybe also use a huge cap.

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