docs/CHARGING_ALGORITHM - rockbox - Gitiles

 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.


 [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 is done by the hardware and therefore isn't implemented
 in rockbox. Only the functions that calculate the battery level are also used
 for the player.

 All following information is related to the recorder.


 [TECHNICAL POSSIBILITIES AJB]

 - The AJB can read the voltage of the battery (all four cells in series,
   resulting in about 5V).
 - We can switch the charging current (about 350mA, constant) on and off.


 [VOLTAGE COURVES]

 See http://www.uwe-freese.de/rockbox for some voltage courves taken while
 charging and decharging an AJB.

 These voltage courves 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.


 [CHARGE OVERVIEW]

 - If voltage drops under a certain value (with "deep discharge" option on the
   value is lower), charging is started.
 - If end of charge is detected, go to top off charge.
 - Make the batteries completely full. 90 minutes of top off charge (voltage
   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.


 [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:

 - 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 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.


 [DELTA PEAK - WHY DOES IT WORK?]

 Delta peak means to detect that the battery voltage goes down when the
 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.
   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.

 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:

   http://www.nimhbattery.com/nimhbattery-faq.htm questions 3 & 4
   http://www.powerpacks-uk.com/Charging%20NiMh%20Batteries.htm
   http://www.angelfire.com/electronic/hayles/charge1.html (soft start idea)
   http://www.powerstream.com/NiMH.htm (discouraging)
   http://www.panasonic.com/industrial/battery/oem/images/pdf/nimhchar.pdf
   http://www.duracell.com/oem/Pdf/others/nimh_5.pdf (discharging)
   http://www.duracell.com/oem/Pdf/others/nimh_6.pdf (charging)
   Philips TEA1102/1103/1104 PDFs available at www.philips.com.


 [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.

 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
 level at 5,65 V (top off charge, that means "make the batteries completely
 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.

 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
 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.

 My test results with trickle charge (battery capacities measured with an
 external charger):

 - after normal charge and top off time: 1798, 1834, 1819, 1815 mAh
 - after normal + top off + trickle charge (12h): 1784, 1748, 1738, 1752 mAh
 - charged with external charger: 1786, 1819, 1802, 1802 mAh

 Result: Trickle charge works. :)


 [REMAINING TIME ESTIMATION]

 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
 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.


 [BATTERY DISPLAY HOW THE USER EXPECTS IT]

 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 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


 [WHICH CHARGING MODE TO USE]

 If you use your AJB connected to the power supply the whole time, select "deep
 discharge on" and "trickle charge off".

 If you want to charge your AJB over night and take it with you the next day,
 select "deep discharge off" (that it starts charging immediately) and "trickle
 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.
	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.



	[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 is done by the hardware and therefore isn't implemented
	in rockbox. Only the functions that calculate the battery level are also used
	for the player.

	All following information is related to the recorder.


	[TECHNICAL POSSIBILITIES AJB]

	- The AJB can read the voltage of the battery (all four cells in series,
	resulting in about 5V).
	- We can switch the charging current (about 350mA, constant) on and off.


	[VOLTAGE COURVES]

	See http://www.uwe-freese.de/rockbox for some voltage courves taken while
	charging and decharging an AJB.

	These voltage courves 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.


	[CHARGE OVERVIEW]

	- If voltage drops under a certain value (with "deep discharge" option on the
	value is lower), charging is started.
	- If end of charge is detected, go to top off charge.
	- Make the batteries completely full. 90 minutes of top off charge (voltage
	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.


	[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:

	- 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 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.


	[DELTA PEAK - WHY DOES IT WORK?]

	Delta peak means to detect that the battery voltage goes down when the
	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.
	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.

	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:

	http://www.nimhbattery.com/nimhbattery-faq.htm questions 3 & 4
	http://www.powerpacks-uk.com/Charging%20NiMh%20Batteries.htm
	http://www.angelfire.com/electronic/hayles/charge1.html (soft start idea)
	http://www.powerstream.com/NiMH.htm (discouraging)
	http://www.panasonic.com/industrial/battery/oem/images/pdf/nimhchar.pdf
	http://www.duracell.com/oem/Pdf/others/nimh_5.pdf (discharging)
	http://www.duracell.com/oem/Pdf/others/nimh_6.pdf (charging)
	Philips TEA1102/1103/1104 PDFs available at www.philips.com.


	[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.

	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
	level at 5,65 V (top off charge, that means "make the batteries completely
	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.

	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
	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.

	My test results with trickle charge (battery capacities measured with an
	external charger):

	- after normal charge and top off time: 1798, 1834, 1819, 1815 mAh
	- after normal + top off + trickle charge (12h): 1784, 1748, 1738, 1752 mAh
	- charged with external charger: 1786, 1819, 1802, 1802 mAh

	Result: Trickle charge works. :)


	[REMAINING TIME ESTIMATION]

	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
	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.


	[BATTERY DISPLAY HOW THE USER EXPECTS IT]

	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 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


	[WHICH CHARGING MODE TO USE]

	If you use your AJB connected to the power supply the whole time, select "deep
	discharge on" and "trickle charge off".

	If you want to charge your AJB over night and take it with you the next day,
	select "deep discharge off" (that it starts charging immediately) and "trickle
	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.