3 This doc and a part of the charger implementation (especially voltage curves,
4 remaining time estimation, trickle charge) is written by Uwe Freese. If you
5 miss some information here, write to mail@uwe-freese.de.
11 This doc describes how the charging works for the recorder. The algorithm can
12 be found in firmware/powermgmt.[c|h]. Debug output is done in
14 Charging for the player and the FM/V2 recorder is done by the hardware and
15 therefore isn't implemented in rockbox. Only the functions that calculate the
16 battery level are also used for these models.
18 All following information is related to the recorder.
21 [TECHNICAL POSSIBILITIES AJB]
23 - The AJB can read the voltage of the battery (all four cells in series,
24 resulting in about 5V).
25 - We can switch the charging current (about 350mA, constant) on and off.
30 See http://www.uwe-freese.de/hardware-projekte/rockbox/ladeverfahren.html
31 for some voltage curves taken while charging and decharging an AJB.
33 These voltage curves are implemented as arrays in rockbox. We can then
34 calculate how full the batteries are (in percent) after taking the actual
35 voltage. Both voltage curves (charging and decharging) are used here.
40 - If voltage drops under a certain value (with "deep discharge" option on the
41 value is lower), charging is started.
42 - If end of charge is detected, go to top off charge.
43 - Make the batteries completely full. 90 minutes of top off charge (voltage
44 regulation at a high value).
45 - After that, do trickle charge (max. 12 hours with voltage regulation at a
47 - When trickle charge is done and you did not disconnect or shut off your AJB
48 by now, the AJB decharges normally since it reaches a low voltage and
49 everything starts from the beginning.
54 When charging is started, the charger is turned on. The batteries are charged
55 with a constant current of about 350mA. The charging is stopped for three
58 - the voltage goes down in a 5 min interval (delta peak, see below)
59 - the voltage goes up only a little bit in an 30 min interval (is mainly
61 - the charging duration exceeds a maximum duration
64 [DYNAMIC MAX DURATION CALCULATION]
66 The max duration is calculated dynamically. The time depends on how full the
67 battery is when charging is started. For a nearly full battery, the max
68 duration is low, for an empty one, it is a high value. The exact formula can
69 be found in the source code. The battery capacity is also considered here.
72 [LIION BATTERY IN FM RECORDER]
75 http://www.seattlerobotics.org/encoder/200210/LiIon2.pdf
78 [DELTA PEAK - WHY DOES IT WORK?]
80 Delta peak means to detect that the battery voltage goes down when the
83 Two facts on batteries are the reason why this works:
85 - If the batteries are full, the charging current cannot charge the battery
87 So the energy is absorbed by heating up the battery.
88 - Each battery has a negative temperature coefficient, that means the voltage
89 goes down when the temperature goes up.
91 NiMH batteries have a smaller delta peak than NiCd, but is is enough for
92 Rockbox to detect that the batteries are full.
94 Related documents on the web:
96 http://www.nimhbattery.com/nimhbattery-faq.htm questions 3 & 4
97 http://www.powerpacks-uk.com/Charging%20NiMh%20Batteries.htm
98 http://www.angelfire.com/electronic/hayles/charge1.html (soft start idea)
99 http://www.powerstream.com/NiMH.htm (discouraging)
100 http://www.panasonic.com/industrial/battery/oem/images/pdf/nimhchar.pdf
101 http://www.duracell.com/oem/Pdf/others/nimh_5.pdf (discharging)
102 http://www.duracell.com/oem/Pdf/others/nimh_6.pdf (charging)
103 Philips TEA1102/1103/1104 PDFs available at www.philips.com.
106 [TOP OFF CHARGE AND TRICKLE CHARGE]
108 After a normal charge is completed, trickle charging is started. That means
109 charging to keep the batteries full. While trickle charge in other (stand
110 alone) chargers means charging the amount that the battery loses because of
111 self decharging, here it's charging the amount the AJB consumes when it's on.
112 That's because it is not possible to switch off the AJB when charging is done.
113 It goes on again and then the archos firmware charger code would charge again.
114 So we have trickle charge in rockbox.
116 In simple words, rockbox charges about 15 seconds per minute in trickle mode.
117 An AJB consumes 100 mA when it's on and the charging current is about 300mA.
118 So charging 15 s and decharge 45 s will keep the batteries full.
120 But the number of seconds the charger is on in trickle charge mode is also
121 adjusted dynamically (between 1 and 24 sec). Rockbox tries to hold the battery
122 level at 5,65 V (top off charge, that means "make the batteries completely
123 full") for 90 minutes, then a level of 5,45 V. If the voltage drops below the
124 wanted value, rockbox will charge one second more the next minute. If is is
125 greater than this value, is will charge one second less.
127 Trickle charging runs 12 hours after finishing the normal charging. That
128 should be enough for charging the AJB over night and then unplug the charger
129 sometime in this 12 hour trickle charge time. It is not recommended to trickle
130 charge over days, that's because it is stopped after 12 hours.
132 Many chargers do top off and trickle charge by feeding a constant (low)
133 current to the batteries. Rockbox, as described, makes a voltage regulation.
134 That's because the power consumption of the AJB changes when backlight is
135 on/disk is spinning etc. and doing a voltage regulation is the simplest way
136 to charge exactly the needed amount.
138 There are two charge ICs I want to mention here: The Philips TEA1102 and
139 TEA1103 do voltage regulation for NiCd and NiMH at 1,325 V per cell. That
140 would be 5,3 V for four cells, but I think 5,45 V is best for Rockbox with the
141 maximum time of 12 hours.
142 Note that the voltage values are taken in the part of a minute where
143 the charger is off, so the values are a little bit smaller than the actual
144 average of the whole 60 seconds.
145 The Philips TEA1102 top-off charge time (with 0,15 C) is one hour.
147 My test results with trickle charge (battery capacities measured with an
150 - after normal charge and top off time: 1798, 1834, 1819, 1815 mAh
151 - after normal + top off + trickle charge (12h): 1784, 1748, 1738, 1752 mAh
152 - charged with external charger: 1786, 1819, 1802, 1802 mAh
154 Result: Trickle charge works. :)
157 [REMAINING TIME ESTIMATION]
159 In simple words, it is
161 remaining time = remaining battery energy / power consumption of AJB
163 With using the battery curves described above and the battery capacity you
164 selected in the settings menu, the remaining capacity is calculated. For the
165 power consumption, a usual constant value is used. If the LED backlight is set
166 to always on, it is also considered. Having a modified Jukebox with 8 MB of
167 RAM leads to about 22 percent longer estimated running time.
170 [BATTERY DISPLAY HOW THE USER EXPECTS IT]
172 To not confuse the user with the shown battery level, some tricks are used in
173 the battery level calculation (this does not affect the charging algorithm,
174 because it uses the raw voltages):
176 - if charging is completed, top-off charge or trickle charge is running,
177 always set the battery level to 100%
178 - the battery level is only allowed to change 1% per minute (exception: when
179 usb is connected, it is allowed to go 3% down/min)
180 - if charging just started (or stopped), ignore the battery voltage for the
182 - after turning on the device, add another 5% to the battery level, because
183 the drive is used heavily when booting and the voltage usually gets a
184 little higher after that
187 [WHICH CHARGING MODE TO USE]
189 If you use your AJB connected to the power supply the whole time, select "deep
190 discharge on" and "trickle charge off".
192 If you want to charge your AJB over night and take it with you the next day,
193 select "deep discharge off" (that it starts charging immediately) and "trickle
194 charge on" (that the batteries remain full).
196 A special case: If you fill up the batteries that are still nearly full every
197 night, it is recommended that you make a complete charge cycle from time to
198 time. Select "deep discharge on" and "trickle charge on" and wait till the
199 whole cycle is over (you can speed up the discharging a little bit by turning
200 on the LED backlight). Even if the battery sellers say NiMH cells don't show a
201 memory effect, I recommend making this procedure from time to time (every 10th
202 charging cycle). BUT: Don't recharge the batteries completely every time if