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Subject: Bug: Battery Charging with low voltage

Bug: Battery Charging with low voltage

From: Matthias Klumpp <>
Date: Mon, 31 Jan 2005 18:36:29 +0100

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 2005-01-31

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