Building my own portable battery pack...

Amp34 said:
ALthough the idea in the OP may work I'd suggest looking at a single decent rechargable 12v battery (or regulated 5v battery and do away with the transformer). I can't see the battery being that expensive, normally the cost ramps up when you start getting circuitry with them.
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Any suggestions for 12V batteries? Not sure what I'd search as all I get is car batteries :p

Amp34 said:
Also I'd look into creating a fake "battery" for the phone itself so I could run the phone directly from the home made battery. Constant trickle charging may damage your phones battery (and would also reduce the voltage needed for the battery). If you got a reasonable regulated battery/system then it should be fine and it could last for days!
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Technically it's not trickle charging, actually float charging controlled by the phone circuitry, so not too bad hopefully. I also want to maintain the ability to unplug the phone quickly (if it rains for instance) and have it stay running.

Amp34 said:
Also may be worth looking at the candlepower forums, yes they are mainly torch fanatics but the regulation and general circuitry will be the same.

Just depends how interested/much of a whiz you are in electronics and how much you want to spend. :D

(I love doing this sort of thing myself)
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I could build a regulator, I'd just rather I didn't have to :p The car charger accepts a 10-30V input and outputs 5V USB, so seems perfect for an easy bodge. I just need to get the battery/capacity choice right for the input.

arknor said:
GOOGLE "bike dynamo phone charger"
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See above.
 
tim80bwi said:
Read the OP again.
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Well the reason I suggested that software is that my wife gets a good 9-10 hours on a full charge just using mytracks on her desire while walking and it does everything you want.

However, for power, you could go battery powered as you've suggested but again this can run out. I'd go with a bike light dynamo to constantly give it a trickle charge as suggested, or trickle the batteries.

And do they do a bigger battery for the desire?
 
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tim80bwi said:
Any suggestions for 12V batteries? Not sure what I'd search as all I get is car batteries :p



Technically it's not trickle charging, actually float charging controlled by the phone circuitry, so not too bad hopefully. I also want to maintain the ability to unplug the phone quickly (if it rains for instance) and have it stay running.



I could build a regulator, I'd just rather I didn't have to :p The car charger accepts a 10-30V input and outputs 5V USB, so seems perfect for an easy bodge. I just need to get the battery/capacity choice right for the input.



See above.
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Try searching with a battery type (like Li-ion, Li-po etc) and voltage. I had a quick search and you can get large capacity batteries in an assortment of sizes, for example this http://www.spycameracctv.com/spycam...-lithium-6800mah-battery-for-security-cameras (first link when searching for "li-on 12v").
 
Energize said:
D batteries have much greater capacity than AA's but still work at the same voltage, so I would use them instead of AA's.
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Surprisingly, this isn't the case. The high performance line doesn't seem to be available in C and D sizes for some reason, so I'd be looking at the cheaper versions with lesser capacities, and in the end it comes to AA @ 2450mAh vs C/D @ 2200mAh.
 
I'd be less worried about the power and more worried about the extra weight you'd be carrying during a long cycle.

You're trying to get a square peg in a round hole. Use a cycle computer - that's what they're designed for.
 
LordSplodge said:
I'd be less worried about the power and more worried about the extra weight you'd be carrying during a long cycle.

You're trying to get a square peg in a round hole. Use a cycle computer - that's what they're designed for.
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I think people are underestimating the idea because of it's simplicity. 10 AA cells in series gives me 2450mAh at 12V, or 29.4Wh. My phone's battery capacity is 5.18Wh. Even allowing for losses and lower than expected battery capacities, that's still a hell of a lot of charging potential! (At this point someone points out a mathematical error :p).

How so? It's simple and there's no reason why it shouldn't work. GPS cycle computers are £200+...
 
Energize said:
That's just the shop category it's listed in.

Any high capacity battery is going to be heavier and more expensive. All that energy has to be stored somewhere.

Even these ones are twice AA capacity though.

http://www.battery-force.co.uk/detail_AMDNIM002A-Ansmann-D-NiMH-5000mAh-Pack-of-2.html

And that's just one website, there are a million retailers of batteries.
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I guess it becomes a capacity vs weight argument then really. With AA I could get 29.4Wh out of 240g. With those D size batteries you posted I'd get 60Wh out of 1kg. For price and Wh per gram, I'd probably stick with the AAs. Not to mention I don't need 60Wh.
 
Bought one of these for £10 and it's actually really good :D

Charges my HTC HD 2 (WP7 + Various Android ROMS) 1.5-1.75 complete charge cycles :-)

Not bad for a tenner, should be enough to give you 75-100% full charge which in turn will double your ON time.

1330701ascan.jpg
 
one of these

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PM me if you want the link

or popular auction site
"5V Mobile Power Supply USB Battery Charger 18650 Box"
£9.57


basically your circuit as described, but cheaper than you can build it.
 
Interesting design there bitslice. Have you got one of these?

18650 cells as with all Lithium-ion cells need to be treated with respect. They are not like an eneloop or standard Ni-Mh rechargable, definitely not as forgiving.

Lithium-ion cells can be dangerous if mistreated. Especially so when wired in series during charging and discharging. I would not recommend anyone buy that unit unless they have extensively read up about lithium-ion cells.

I also wouldn't put much faith in that circuits ability to cut off the charge at 4.2v per cell. As the unit is wired in series you would need to ensure the cells are the same voltage before even placing them inside that unit. From the looks of it the two banks are wired in series giving the circuit 8.4v? It is an interesting design none the less!

But the more I think about it, the more that product worries me. If used by someone that is doesn't fully understand the dangers of lithium-ion cells it could end badly.
 
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Energize said:
Lithium batteries of that type aren't rechargeable are they? So that would end up costing much more over time.
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Your thinking of the throw away non rechargeable lithium batteries which are 1.2v

18650 cells are rechargeable lithium ion cells which have a cell voltage of 4.2v each and are found in laptop battery packs and are used in high output torches.
 
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