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Subject: Bug: Battery Charging with low voltage

Bug: Battery Charging with low voltage

From: Matthias Klumpp <>
Date: 2005-01-31

Hi all,

I'm observing by own experience and due to the fact that this topic is
posted very often, that the battery charging of Rockbox is unfortunately one
of the weak features.

I was once mentioning a problem (unfortunately uncommented until now :-?),
that the batteries were discharged with USB connection:

Since some time, I'm facing another problem, were my JBRV1 is running out of
battery power.

Here's a short description about what is happening:
- JBR V1 with Rockbox 2.3 flashed
- 2000mAh NiMH batteries
- deep discharge: on (see also tests below)
- trickle charge: off
- battery capacity: 2000
- car adapter mode: on

I'm operating the JB only in the car, with a car adapter connected always.
That adapter supplies with 9V max. 1A (original Archos adapter supplies with
After more or less 3-4h of continuos playing, the JB is shutting down with a
ATA Error because of low power.
The problem is always (and reproducable) occuring in that condition.
If the JB is switched on/off after e.g, 1h of driving, the problem is not
Before using the JBR, I was owning a JB Studio with Rockbox 2.2 and that
worked perfectly with the same adapter.

I know, that the voltage might be too low, but I'm not able to increase the
voltage, because then I receive some strange kind of distortion produced by
the car. Well, I probably could find a way to increase the voltage, but this
Also it is not a indivudual problem of my JB/batteries, because I know 3
more people, who have exactly the same problem.

Some guys told me, that the problem might be, that the HDD spin-up could
consume more energy, than the charger is able to provide back during the
time the HDD is not active. The mesurements below will proove, that there
should be a way to solve this in the SW.

In the following, I'll describe what kind of tests and measurements I did,
hoping that somebody is willing to submit a modification.
I'm not very familiar with the Rockbox code :-( , but I would be glad to
help in extended testing and measurement, if necessary :-))

Best regards


Here now the test results:
Rockbox V2.3 flashed
4x NiMH 2000mAh batteries
battery capacity: 2000
deep discharge: on
trickle charge: off

Start with NOT FULL charged batteries !

run time remaining bat. time displayed
00:00 6h 44m
00:27 6h 44m
00:34 6h 12m
00:49 6h 16m
01:06 0h 48m
01:23 4h 48m
01:47 3h 46m
02:04 3h 25m
02:26 2h 10m 1)
03:15 6h 44m
04:07 6h 16m
04:26 6h 16m
04:59 0h 41m
05:07 0h 41m 2)

1) JB was hanging up (no reaction on key presses):
- charger disconnected, OFF
- charger re-connected
- measurement was going on, as described above

2) JB shows ATA Error -1:
- charger disconnected, OFF
- charger re-connected, JB boots Rockbox, ATA Error -1
- charger disconnected, OFF
- F1+ON+charger re-connected, JB boots Archos firmware
- batteries are charged
- wait until batteries are charegd fully
- going-on with test b)

same as a), but:
deep discharge: off

Start with FULL batteries !

run time remaining bat. time displayed
00:00 6h 44m
00:49 6h 44m
01:31 1h 08m
01:44 1h 08m
01:52 9h 56m
02:24 1h 44m
03:13 3h 20m
03:20 3h 48m
03:57 5h 42m
03:59 4h 34m
04:51 4h 32m
05:02 5h 04m
05:17 6h 04m
05:38 6h 16m
06:01 6h 16m
06:53 0h 41m 1)

1) JB was hanging up (no reaction on key presses):
- no ATA Error
- charger disconnected, JB shuts down on its own
- charger re-connected, JB boots Rockbox and hangs up (no reaction at all)
- charger disconnected, JB shuts down again on its own
- F1+ON+charger re-connected, JB boots Archos firmware
- batteries are charged
- wait until batteries are charegd fully
- going-on with test c)
Archos Firmware V1.26 dated 19.03.2002 flashed

Start with FULL batteries !

JB run more than 10h w/o problems.
Some current measurements I did:

Same supply voltage as during tests above.
Batteries were first charged fully with original Archos charger.
I measured the total current at the power plug and between 2 batteries on
one side (I guess the all 4 are connected in serial).
HDD was not running during the current measurements.

With Rockbox V2.3:
Total current: 79mA (battery symbol bar running, means no '?')
Current between batteries: 4-15mA
I tested several times (switch on, measure, wait several times, switch off)
and had very different results between 4mA and 15mA.

With Archos Firmware:
Total current: 90mA (battery symbol bar running)
Current between batteries: 30mA
I did the same test as with Rockbox, but always measuring the same current
of 30mA (+/- 2mA).

Charge current of Rockbox is too low in that condition and it seems that the
charging algorithm is not clearly knowing the current battery charge state
(differences between currents 4mA = nothing and 15mA = low charge current).

Received on Mon Jan 31 18:35:55 2005

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