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Old 06-29-2014, 08:52 AM
Berenicus Berenicus is offline
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Join Date: Jun 2014
Posts: 2
Default Calibrating battery capacity and charging in Rockbox

I'm going to change my Battery in my Clip+ and was looking for a way to change the Battery time remaining setting in Rockbox. Unfortunately I didn't find any instructions . But I did find the solution.

For someone who is interested in having an accurate battery Time remaining display here is a how to.

Run a battery bench before to know the Voltages on % Levels

You have to edit Rockbox source files and compile Rockbox for it to work.

Voltage % Levels
Edit the Numbers according to what your battery bench results were.

/* voltages (millivolt) of 0%, 10%, ... 100% when charging disabled */
const unsigned short percent_to_volt_discharge[BATTERY_TYPES_COUNT][11] =
{ 3300, 3653, 3701, 3735, 3768, 3790, 3833, 3900, 3966, 4056, 4140 }

Battery time remaining aka Battery Capacity
The standard Clip+ battery capacity is 290 mAh
If you only wish to set a permanent capacity set the lines CAPACITY_DEFAULT/MIN/MAX to same Value and CAPACITY_INC to 0

If you however wish to play around from within Rockbox menu set the Values as you see fit. My new battery will be 2200 mAh so this are my example settings

#define BATTERY_CAPACITY_DEFAULT 290 /* default battery capacity */
#define BATTERY_CAPACITY_MIN 290 /* min. capacity selectable */
#define BATTERY_CAPACITY_MAX 2200 /* max. capacity selectable */
#define BATTERY_CAPACITY_INC 50 /* capacity increment */

Battery charging speed and duration

If you have Replaced for a High Capacity Battery you may notice that it takes very long time to recharge and that the charging process terminates after some hours. To speed up the charging and prolong the charging duration you can edit the following file. The as3525 supports up to 400mA for charging according to datasheet.


#elif defined(SANSA_CLIPPLUS)

/* Check if topped-off and monitor voltage while plugged. */
#define BATT_FULL_VOLTAGE 4160
#define BATT_CHG_V CHG_V_4_20V
#define BATT_CHG_I CHG_I_350MA
#define CHARGER_TOTAL_TIMER (6*3600*2) /* about 1.5 * capacity / current */

and the line in rockbox\firmware\export\config\sansaclipplus.h

/* maximum charging current */
#define CURRENT_MAX_CHG 350

Last edited by Berenicus; 07-01-2014 at 05:53 AM.
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