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docs/CHARGING_ALGORITHM
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@ -1,16 +1,17 @@
CHARGING ALGORITHM
This doc and a part of the charger implementation (especially voltage courves,
remaining time estimation, trickle charge) is written by Uwe Freese. If you miss
some information here, write to mail@uwe-freese.de.
This doc and a part of the charger implementation (especially voltage curves,
remaining time estimation, trickle charge) is written by Uwe Freese. If you
miss some information here, write to mail@uwe-freese.de.
[INTRODUCTION]
This doc describes how the charging works for the recorder. The algorithm can be
found in firmware/powermgmt.[c|h]. Debug output is done in apps/debug_menu.c.
Charging for the player and the FM recorder is done by the hardware and
This doc describes how the charging works for the recorder. The algorithm can
be found in firmware/powermgmt.[c|h]. Debug output is done in
apps/debug_menu.c.
Charging for the player and the FM/V2 recorder is done by the hardware and
therefore isn't implemented in rockbox. Only the functions that calculate the
battery level are also used for these models.
@ -24,14 +25,14 @@ All following information is related to the recorder.
- We can switch the charging current (about 350mA, constant) on and off.
[VOLTAGE COURVES]
[VOLTAGE CURVES]
See http://www.uwe-freese.de/rockbox for some voltage courves taken while
charging and decharging an AJB.
See http://www.uwe-freese.de/hardware-projekte/rockbox/ladeverfahren.html
for some voltage curves taken while charging and decharging an AJB.
These voltage courves are implemented as arrays in rockbox. We can then
These voltage curves are implemented as arrays in rockbox. We can then
calculate how full the batteries are (in percent) after taking the actual
voltage. Both voltage courves (charging and decharging) are used here.
voltage. Both voltage curves (charging and decharging) are used here.
[CHARGE OVERVIEW]
@ -43,27 +44,29 @@ voltage. Both voltage courves (charging and decharging) are used here.
regulation at a high value).
- After that, do trickle charge (max. 12 hours with voltage regulation at a
lower value).
- When trickle charge is done and you did not disconnect or shut off your AJB by
now, the AJB decharges normally since it reaches a low voltage and everything
starts from the beginning.
- When trickle charge is done and you did not disconnect or shut off your AJB
by now, the AJB decharges normally since it reaches a low voltage and
everything starts from the beginning.
[NORMAL CHARGE]
When charging is started, the charger is turned on. The batteries are charged
with a constant current of about 350mA. The charging is stopped for three reasons:
with a constant current of about 350mA. The charging is stopped for three
reasons:
- the voltage goes down in a 5 min interval (delta peak, see below)
- the voltage goes up only a little bit in an 30 min interval (is mainly constant)
- the voltage goes up only a little bit in an 30 min interval (is mainly
constant)
- the charging duration exceeds a maximum duration
[DYNAMIC MAX DURATION CALCULATION]
The max duration is calculated dynamically. The time depends on how full the
battery is when charging is started. For a nearly full battery, the max duration
is low, for an empty one, it is a high value. The exact formula can be found in
the source code. The battery capacity is also considered here.
battery is when charging is started. For a nearly full battery, the max
duration is low, for an empty one, it is a high value. The exact formula can
be found in the source code. The battery capacity is also considered here.
[LIION BATTERY IN FM RECORDER]
@ -79,13 +82,14 @@ batteries are full.
Two facts on batteries are the reason why this works:
- If the batteries are full, the charging current cannot charge the battery anymore.
- If the batteries are full, the charging current cannot charge the battery
anymore.
So the energy is absorbed by heating up the battery.
- Each battery has a negative temperature coefficient, that means the voltage goes
down when the temperature goes up.
- Each battery has a negative temperature coefficient, that means the voltage
goes down when the temperature goes up.
NiMH batteries have a smaller delta peak than NiCd, but is is enough for Rockbox
to detect that the batteries are full.
NiMH batteries have a smaller delta peak than NiCd, but is is enough for
Rockbox to detect that the batteries are full.
Related documents on the web:
@ -102,16 +106,16 @@ Related documents on the web:
[TOP OFF CHARGE AND TRICKLE CHARGE]
After a normal charge is completed, trickle charging is started. That means
charging to keep the batteries full. While trickle charge in other (stand alone)
chargers means charging the amount that the battery loses because of self
decharging, here it's charging the amount the AJB consumes when it's on. That's
because it is not possible to switch off the AJB when charging is done. It goes
on again and then the archos firmware charger code would charge again. So we
have trickle charge in rockbox.
charging to keep the batteries full. While trickle charge in other (stand
alone) chargers means charging the amount that the battery loses because of
self decharging, here it's charging the amount the AJB consumes when it's on.
That's because it is not possible to switch off the AJB when charging is done.
It goes on again and then the archos firmware charger code would charge again.
So we have trickle charge in rockbox.
In simple words, rockbox charges about 15 seconds per minute in trickle mode. An
AJB consumes 100 mA when it's on and the charging current is about 300mA. So
charging 15 s and decharge 45 s will keep the batteries full.
In simple words, rockbox charges about 15 seconds per minute in trickle mode.
An AJB consumes 100 mA when it's on and the charging current is about 300mA.
So charging 15 s and decharge 45 s will keep the batteries full.
But the number of seconds the charger is on in trickle charge mode is also
adjusted dynamically (between 1 and 24 sec). Rockbox tries to hold the battery
@ -120,21 +124,22 @@ full") for 90 minutes, then a level of 5,45 V. If the voltage drops below the
wanted value, rockbox will charge one second more the next minute. If is is
greater than this value, is will charge one second less.
Trickle charging runs 12 hours after finishing the normal charging. That should
be enough for charging the AJB over night and then unplug the charger sometime
in this 12 hour trickle charge time. It is not recommended to trickle charge
over days, that's because it is stopped after 12 hours.
Trickle charging runs 12 hours after finishing the normal charging. That
should be enough for charging the AJB over night and then unplug the charger
sometime in this 12 hour trickle charge time. It is not recommended to trickle
charge over days, that's because it is stopped after 12 hours.
Many chargers do top off and trickle charge by feeding a constant (low) current
to the batteries. Rockbox, as described, makes a voltage regulation. That's
because the power consumption of the AJB changes when backlight is on/disk is
spinning etc. and doing a voltage regulation is the simplest way to charge
exactly the needed amount.
Many chargers do top off and trickle charge by feeding a constant (low)
current to the batteries. Rockbox, as described, makes a voltage regulation.
That's because the power consumption of the AJB changes when backlight is
on/disk is spinning etc. and doing a voltage regulation is the simplest way
to charge exactly the needed amount.
There are two charge ICs I want to mention here: The Philips TEA1102 and TEA1103
do voltage regulation for NiCd and NiMH at 1,325 V per cell. That would be 5,3 V
for four cells, but I think 5,45 V is best for Rockbox with the maximum time of
12 hours. Note that the voltage values are taken in the part of a minute where
There are two charge ICs I want to mention here: The Philips TEA1102 and
TEA1103 do voltage regulation for NiCd and NiMH at 1,325 V per cell. That
would be 5,3 V for four cells, but I think 5,45 V is best for Rockbox with the
maximum time of 12 hours.
Note that the voltage values are taken in the part of a minute where
the charger is off, so the values are a little bit smaller than the actual
average of the whole 60 seconds.
The Philips TEA1102 top-off charge time (with 0,15 C) is one hour.
@ -155,11 +160,11 @@ In simple words, it is
remaining time = remaining battery energy / power consumption of AJB
With using the battery courves described above and the battery capacity you
With using the battery curves described above and the battery capacity you
selected in the settings menu, the remaining capacity is calculated. For the
power consumption, a usual constant value is used. If the LED backlight is set
to always on, it is also considered. Having a modified Jukebox with 8 MB of RAM
leads to about 22 percent longer estimated running time.
to always on, it is also considered. Having a modified Jukebox with 8 MB of
RAM leads to about 22 percent longer estimated running time.
[BATTERY DISPLAY HOW THE USER EXPECTS IT]
@ -168,15 +173,15 @@ To not confuse the user with the shown battery level, some tricks are used in
the battery level calculation (this does not affect the charging algorithm,
because it uses the raw voltages):
- if charging is completed, top-off charge or trickle charge is running, always
set the battery level to 100%
- the battery level is only allowed to change 1% per minute (exception: when usb
is connected, is is allowed to go 3% down/min)
- if charging is completed, top-off charge or trickle charge is running,
always set the battery level to 100%
- the battery level is only allowed to change 1% per minute (exception: when
usb is connected, it is allowed to go 3% down/min)
- if charging just started (or stopped), ignore the battery voltage for the
first 25 minutes
- after turning on the device, add another 5% to the battery level, because the
drive is used heavily when booting and the voltage usually gets a little higher
after that
- after turning on the device, add another 5% to the battery level, because
the drive is used heavily when booting and the voltage usually gets a
little higher after that
[WHICH CHARGING MODE TO USE]
@ -190,9 +195,9 @@ charge on" (that the batteries remain full).
A special case: If you fill up the batteries that are still nearly full every
night, it is recommended that you make a complete charge cycle from time to
time. Select "deep discharge on" and "trickle charge on" and wait till the whole
cycle is over (you can speed up the discharging a little bit by turning on the
LED backlight). Even if the battery sellers say NiMH cells don't show a memory
effect, I recommend making this procedure from time to time (every 10th charging
cycle). BUT: Don't recharge the batteries completely every time if you don't
have to.
time. Select "deep discharge on" and "trickle charge on" and wait till the
whole cycle is over (you can speed up the discharging a little bit by turning
on the LED backlight). Even if the battery sellers say NiMH cells don't show a
memory effect, I recommend making this procedure from time to time (every 10th
charging cycle). BUT: Don't recharge the batteries completely every time if
you don't have to.