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Subject: Re: More aggressive Rockbox battery charging

Re: More aggressive Rockbox battery charging

From: Jens Arnold <arnold-j_at_t-online.de>
Date: 2005-02-07

Hi,

>> Matthias is using a 9+v charger which, according to the FAQ,
>> gives him about
>> 140mA current into the Archos. The problem is, this is only
>> slightly more than is necessary just to run the AJR (and less
>> than needed when the disk spins up). With a limit of 40% duty
>> cycle (24/60), his charger is falling behind.

> The Recorder hardware can measure both the cell voltage and
> the DC input voltage, and could derive the charging current
> from that. Perhaps the duty cycle should be a function of
> this?

That should definitely be done instead of simply taking out the
max. duty cycle safety measure (by allowing almost full time as
maximum).

The problem is that (1) Voltage is *not* a reliable indicator
for NiMH charging state, (2) Voltage measurement may differ
between individual units about 1..2%, (3) the trickle
algorithm tries to regulate the voltage and (4) doesn't check
the input voltage in order to estimate the charging current.

So it may happen that the batteries get overcharged, and that
should be avoided if possible. Continuous overcharging of NiMHs
with >0.05C (that's only 75 mA with stock batteries) *will*
damage the cells over time.

Regards, Jens

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Received on Mon Feb 7 19:24:59 2005


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