aa battery pack

[_wb_]

Hmyeah, but suspend to disk (SD card) is a bit problematic. With a UHS SDXC card you can get maybe 100 MB/s read speed and 50 MB/s write speed, so with 512MB of RAM that means 5 seconds to get out of suspend (and 10 to get in, but that doesn't matter much). However, the Pandora 2 will probably have more RAM: maybe 2-4 GB. So that means 20-40 seconds to get out of suspend, and twice as much to get suspended. This could very well be longer than the time needed to boot and is almost certainly longer than the time needed to shut down. Also note that those two minutes of heavy SD card transfers will probably consume quite a bit of power, so the question will be: how long do I have to keep it suspended to make it worth the trouble? (e.g. if it's just for half an hour, you're probably better off closing the lid)

 

[Exophase]

Hmyeah, but suspend to disk (SD card) is a bit problematic. With a UHS SDXC card you can get maybe 100 MB/s read speed and 50 MB/s write speed, so with 512MB of RAM that means 5 seconds to get out of suspend (and 10 to get in, but that doesn't matter much). However, the Pandora 2 will probably have more RAM: maybe 2-4 GB. So that means 20-40 seconds to get out of suspend, and twice as much to get suspended. This could very well be longer than the time needed to boot and is almost certainly longer than the time needed to shut down. Also note that those two minutes of heavy SD card transfers will probably consume quite a bit of power, so the question will be: how long do I have to keep it suspended to make it worth the trouble? (e.g. if it's just for half an hour, you're probably better off closing the lid)

You wouldn't normally need to write out the entire RAM. A lot of it is going to be marked as read only or something the kernel is free to drop like disk cache, mmapped files, and other things that can be recreated from storage. Signals can be sent out to alert running programs to try to get them to reduce their memory footprints. And the memory doesn't have to be loaded instantly, but only as it's accessed, meaning that you can have stuff running in the background that's still backed by storage and committed pages that were not being touched don't get loaded at all. So the actual time before you can start using the device again is much lower than you're making it sound. In this case the write cycle actually is worse since it does need to save anything that can't be recreated regardless of if or when it's touched again, and it matters if you're ready to jump back in with another battery.


If I have a bunch of stuff running and want to swap batteries I'd probably prefer to just do the suspend because it's easier, even if it took longer than manually shutting down/saving everything and rebooting and reloading.

 

[monstercameron]

aa battery dimension is ~1.5cm diameter and ~5cm height, so a pack of 9 would be 5cm high, 15cm wide, 1.5cm depth and ~25grams.

• Now if we take the sanyo eneloop pro, 2000mAh*1.2V x3 (cells in series) -> 2000mAh*3.6V x3 (batteries in parallel) -> 6000mAh*3.6V = 21600mWh -> 21.6Wh (for ~1500 cycles)
  
• 25grams*9(cells) = 225grams (same weight as 2 iphones)
  
• Energy Density 96mWh/gram
  
• price ~$40 USD (6pack w/ charger & 4pack)
  

current pandora battery dimensions ?h, ?w, ?d and ? weight

• 4000mAh*3.7V = 14800mWh -> 14.8Wh
  
• weight (same as what?)(pandora Weight: 335g with battery)
  
• energy density ?mWh/gram
  

 

[Grench]

No I'm not on the AA battery pack idea, that idea sucks

Good to have that settled.

Of course you can do this with custom battery circuitry (or some additional chip) if the PMIC doesn't already support it. That isn't the point. The point is that that's a really big design effort for something like Pandora, and not really worth it for a feature most won't want to use, especially if it eats up precious board space. To facilitate hot swapping one of two batteries you would also have to design it so the battery you aren't removing stays securely in place while you swap the other one out.

I really don't understand the point of hot swapping batteries to begin with, when the OS should be capable of suspend, including automatic suspend + shutdown when the battery gets low. Then you can do a complete swap instead of only swapping out the batteries in 50% capacity increments, and just have to spend several seconds to get in and out of suspend.


_wb_ says he wants to be able to use smaller batteries because it lowers the weight of the device. Having used the Pandora w/o a battery I really don't like this kind of weight reduction because it makes it partially hollow and uneven.

Oh, don't get me wrong. I think that the development costs of such a system make it cost prohibitive. However, I can envision how it could work and be pretty cool.


I never said anything about truly 'hot swapping' batteries - at least not in the term of like hot swap HDDs. My description is more along the lines of fail-over without the end user physically removing/adding them hot. Removing the battery that is 'in use' would likely be a no-no. The battery module itself should probably have an LED on the end of it - have it go solid for charging and flash for discharging? Or two colors - red/green?


Yes, this is all a hypothetical, 'that'd be cool' discussion and a complete hijack of the silly AA idea. Although it -would- be possible in this hypothetical modular system to have a double-wide module with enough AA batteries in it - call it 16 or so in four parallel banks of four in series ~ 6VDC. Tack it on and let it charge the 'primary' LiPO?


The modular idea could be cool. Very cool.


It'll never happen.


it would be cool though.

 

[3_bit]

Well, if you want the cost lowered you could buy it without a LiPo pack. i don't see why we couldn't make AA's optional, but the only problem is we'd need regulators and they'd need to be replaced and stuff.

 

[TrashyMG]

Well, if you want the cost lowered you could buy it without a LiPo pack. i don't see why we couldn't make AA's optional, but the only problem is we'd need regulators and they'd need to be replaced and stuff.

Outside that it would take an absurd amount of AA batteries to power a device like the Pandora.


Like Exophase said the idea sucks.