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Rockbox . Main . BatteryFAQ

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Frequently Asked Battery Questions

Pour la version française de ce document : FaqBatteries

Note! This FAQ applies to the models with NiMH batteries, such as the Archos Studio and Archos recorder V1. If you have a device with LiIon batteries, such as the Archos FM recorder or Archos V2 Recorder, see LiIonBatteryFAQ.

Q1: Are my batteries charged all the time when connected to my Player/Recorder?

A1: Player: the charging is all done by hardware and the exact functionality is hard to determine. It is however not recommended to keep the charger connected for more than 10-15 hours if you're not using the unit.

Recorder: no. The charging algorithm is carefully crafted to fully recharge the batteries and then go to a "maintenance" trickle charge that won't stress the batteries.

Q2: Will keeping my charger connected a long time damage my batteries? Can I leave it over night?

A2: Charging for a long time will not damange the batteries. Charging over night is definitiely not a problem. The batteries should last longer plugged in than cycled charge/discharge.

There basically are two methods to wear out batteries: batteries can take only a finite number of discharge/charge cycles (typically several hundred). That is the "good" way: use them. The bad way to wear out batteries is to charge them too hard for too long: this causes them to heat up and deteriorate. The software charging algorithm detects the end of the charge cycle and switches to a low level charge rate that will not cause the batteries to deteriorate.

Trickle charge is needed to keep the batteries full. That's necessary because the device will stay powered on and continue to consume some power from the batteries (the hardware does not allow running from the charger without charging batteries, or powering off with the charger connected).

As the Battery FAQ at http://www.greenbatteries.com/ puts it:

"A NiMH battery can be charged and discharged hundreds of times, but whether that means 200 times or 800 times has a lot to do with how (you use it)".

Q3: Does Rockbox charge the batteries more/less/worse/better than the Archos firmware?

A3: Player: Rockbox doesn't affect the charging on Players, it is all done by hardware logic out of software control.

Recorder: The whole algorithm is made to carefully charge the batteries full and keep them full after that with a trickle charge option. Many documents about charge ICs were considered. If you want to know details, then look into docs/CHARGING_ALGORITHM. If you have comments, write to the Rockbox mailinglist.

Q4: What kind of batteries are there in my factory default Player/Recorder?

A4: Both ship with 1500 mAh NiMH (Nickel Metal Hydride) batteries.

Q5: Is it hard to change the batteries? Does it void my warranty?

A5: It is not very hard - the Archos manual and the FAQ on their web site describe how to do it. Their technical support confirmed that replacing the batteries with NiMH cells (of different capacities) will not void the warranty. Just don't remove the screws.

Some units have been shipped with two sets of batteries, my Recorder 20 only had one set. Someone actually had Archos send him new batteries free of charge after they had weared out, under the warranty.

Q6: How much do replacement batteries cost? Where can I buy them?

A6: http://www.greenbatteries.com sells 1800 mAh NiMH cells at $3.25USD each, and I bought 4 of the same GP batteries for 20 euros in an home electronics & household appliance store in Finland. NiMH batteries are sold in almost all shops that sell consumer electronics, and in many online shops. Browse around. There's a pretty good comparison between different battery makes and models at the digital imaging resource site: http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM In Germany, www.reichelt.de sells GP 2000 batteries for 2,75 EUR (12/2002).

Q7: What kind of run-time can I expect on a set of fully-charged batteries when running Rockbox?

A7: For the stock 1500 mAh cells, from 6 hours to 8 hours, depending on which charger was used (see Q3) and the bitrate you use (higher bitrate means more harddisk runtime). It depends a lot on the condition of the batteries. With 2000 mAh batteries, you should reach about 10 hours or more. If you have a modified AJB with 8 MB, you can reach playing times of up to 16 hours with 2100 mAh batteries.

Q8: Can I use different batteries in my Archos? How much playtime would I gain by using 1800 mAh batteries instead of the 1500 mAh ones?

A8: Only use NiMH-type rechargeable batteries. It is considered to be safe to use NiMH batteries of different capacities though, a lot of people have purchaced 1700 or 1800 mAh batteries to replace the stock 1500 mAh cells and have the device run a bit longer. 2000 mAh batteries are just appearing in shops are equally good to use.

In theory, running time = capacity of batteries / current drawn by device, so running time should increase linearly by the capacity, and 2000 mAh over 1500 mAh should give 33% longer running time. In practice, the mAh ratings are more or less tuned up by the marketing department (think of watts on the back of "hi-fi" speakers and amplifiers) and what you actually get out of the cells is something else than what is printed on them. Check the excellent imaging-resource link above for details!

Q9: Can I use non-chargeable batteries in my Archos?

A9: This is not recommended. The unit has been designed to operate with four 1.2V batteries producing about 4.8V at most, and using 1.5V alkaline/zinc carbon batteries will produce around 6.0V, which will heat up the unit a lot more and might even damage it. The Archos manual explicitly tells you not to do so. Also, if you connect the charger, it may even destroy both the batteries and the unit.

Q10: Can I use a different charger?

A10: The short answer is: Using a different charger will void your warranty and can be dangerous to your unit, so we can not recommend it.

On the other hand, people have successfully used different chargers with similar specifications as the stock charger. The charger must have the same kind of connector with same polarity (center positive/+). The charger should supply at least 7-8 volts, and if it provides more than 10V, it probably should be regulated to 10V (do not directly plug it in your 12V car battery or it's charger!). The universal travel charger sold by Archos is specified at 12V, 1.2A so that's probably the maximum rating you should use. A good circuit for powering from a car battery or other source with a higher voltage would be a 600 mA fuse and a 10V regulator like a 7810 of your favourite manufacturer in series.

Inside the Jukebox there is a regulator which limits the charging current applied to the batteries. The higher the input voltage, the hotter this IC gets. Don't use an input voltage above 12V. Using lower charging voltage < 10V will slow down the charging. But the rockbox charging algorithm should work then, too.

These are the output voltages of an original archos power supply:

connected to AJB Recorder, not charging: 13,7 Volt
connected to AJB Recorder, charging: going down to 10,4 Volt

Here is how changing the input voltage changes the charging current:

      voltage   charging current (limited only by the AJB)
      7,0V          10 mA
      7,5V          30 mA
      8,0V          50 mA
      8,5V          70 mA
      9,0V         140 mA
      9,5V         250 mA
      10,0V        330 mA
      10,5V        350 mA
      11,0V        350 mA
      11,5V        350 mA
      12,0V        350 mA

To summarize:

do not use an input voltage > 12V (it will only heat up the regulator)
car voltage is > 12v and has damaging voltage spikes
optimal input voltage is 10V (regulated)
use a fuse of ~600mA
using a different charger voids your warranty
wrong center positive/ground connections WILL FRY the charge circuit in the Archos

Many people are happy using an external quick charger which is specified to work with NiMH batteries. This is completely safe and will not void your warranty.

See this for a home made, simple and safe car power supply: CarPowerSupply (only Archos Players and RecordersV1)

Q11: Can I buy a replacement charger exactly as the one Archos shipped?

A11: The FAQ on the Archos web site and the top of the charger both read:

      Output: 9VDC 600mA
      Center positive (+) polarity

The universal travel charger sold separately on the Archos web site is specified for 12VDC, 1200mA output.

Chargers with similar (or user-adjustable) properties are available at shops selling consumer electronics.

Q12: I often need to stop my player for about 15 minutes or so, and when I do it runs off it's batteries. I was wondering, which is best: shutting the player down completely and rebooting it when I want to listen again, or leaving the unit on? Which way does it draw more power?

A12: In our testing we found the following results: HDD off, backlight off, idle 94 mA HDD off, backlight off, play 97 mA HDD off, backlight on, idle 129 mA HDD off, backlight on, play 131 mA HDD on, backlight on, play 230 mA HD on, reading, backlight off ~ 600 mA HD spin up before read max 800 mA

Using the power draw measurements shown above, lets look at the numbers: Power-down and restart vs. paused for 15 minutes.:

Pause for 15 minutes will draw: 94 mA / 60 minutes * 15 minutes = 23.5 mAh.

Power-down and restart will draw about (800mA / 3600 seconds * 3 seconds = 0.6666 mAh) + (600 mA / 3600 seconds * 6 seconds = 1.0 mAh) + (230 mA / 3600 seconds * 8 seconds = 0.5111 mAh) = 2.18 mAh total used.

Thus, leaving it paused for 15 minutes draws more power (23.5 mAh) than turning off and then on again (2.18 mAh).

So where is the break-even point?

Each second of pause will draw about 94 mAh / 3600 seconds = 26 µAh.

2.18 mAh / 26 µAh = 2180 µAh / 26 µAh = 83.5 seconds

Thus a shutdown and restart uses as much power as 83.5 seconds of pause.

Q13: When I plug in the charger when the Recorder is turned off, it turns itself on and starts charging in the Archos software? What's up?

A13: There is a mechanism in the jukebox which turns on the jukebox when it senses DC power.

If the charger is providing power, the Archos firmware located on the FLASH ROM does not load a new firmware version (like Rockbox) from the disk, but goes into charging mode instead. You can use this feature to get to the Archos charger if you want to.

However, if you put Rockbox in flash, it will always charge with the Rockbox charging algorithm.

Q14: When I plug the charger in my Recorder, it doesn't immediately start charging the batteries!

A14: Upgrade your Rockbox! The power management code runs once a minute, but it runs immediately when the charger is plugged in (it use to not start immediately). Note that charge status is only an approximation and will be very approximate right after plugging in the charger or right after unplugging the charger because the voltages have changed abruptly and it takes some time for things to settle and average out.

Q15: What about the memory effect? Should I be worried about it or not?

A15: That depends on who you ask. ;-) NiMH sellers say NiMHs are better and do not have a memory effect, but the usual opinion seems to be that they do, although it is very small.

Q16: When I start my Jukebox, (dis)connect the charger and browse through the directories, the battery level changes a little bit. Sometimes it's even going up without the charger is connected! What's wrong?

A16: Nothing's wrong. The battery level is calculated out of the voltage. Because disk spinning, LED backlight, charger all influence the actual battery voltage, it is usual that the battery level is going a little bit up and down sometimes. This cannot be avoided although we tried to make the battery level display as consistant as we could.

Q17: My batteries are at 92%, the charger is connected to my recorder, deep discharge is off. But charging doesn't start. What's wrong?

A17: Upgrade your Rockbox! With the new charging algorithm, the charge level depends on the starting voltage:

< 85%: full charge cycle
>= 85% &lt 95%: top-off (moderate charge)
>= 95%: trickle charge This charges the batteries expeditiously without stressing them unduely.

Q18: Why does rockbox show a question mark for the battery level?

A18: Because you need to upgrade your Rockbox!

Q19: When I plug in the charger the LCD fades away and the the unit keep restarting, I guess my batteries are too weak to even hold until charging starts. What can I do?

A19: Hold F1 when you plug in the charger. This will make your unit boot into Archos firmware and start charging right away.

Q20: What happened to deep discharge?

A:20: It was removed. The object of deep discharging is to prevent the infamous "memory effect." The problems with this, however, are several:

NiMH batteries do not suffer from "memory effect" like NiCd batteries
The "deep discharge" was continually charging and discharging the batteries, causing wear cycles the whole time the unit was plugged in. In the humble opinions of the primary author of the charge algorithm rewrite and the developer(s) who accepted the patch, this caused more stress on the batteries than an intelligent recharge algorithm
The new recharge algorithm (and, indeed, the old algorithm) is designed to be gentle on the batteries.
With the "deep discharge" active, the user would generally not get a full measure of runtime because the batteries were almost never full: they were either charging or discharging and Murphy's Law says they would be low when you wanted them most.

CategoryFAQ: Frequently asked questions about batteries and charging.

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