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  Reply # 793202 4-Apr-2013 13:56
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I guess you have to weight up how much you value a kitchen, a toilet, a shower, and some power. $15 sounds super cheap to me. Plus you're not meant to pitch a tent just anywhere.




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  Reply # 793207 4-Apr-2013 13:58
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If you're anywhere near Wellington I'm happy to lend/sell you a nice meaty 12V to 5V DC-DC converter (5 amps!) which will do a decent job of turning 12V from a solar panel or SLA battery into 5V for your USB-charged devices.  It looks like one of these. (Assuming I have a spare but I'm pretty sure the one from my old CarPC is still sitting there)


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  Reply # 793841 5-Apr-2013 13:43
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  Reply # 794386 6-Apr-2013 19:32
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If you want a light weight high energy battery which can be charged identical to an SLA (so use normal solar regulator) then you want to go LiFePO4. 12V 12Ah (4 cells) is about 1.2kg. If you balance the cells once, they will usually stay balanced for a long time. And they have none of the fire safety issues of LiPo (please tell Boeing that). I've designed products with LiFePO4 for over 3 years, they are great. A good source of large prismatic cells is a company called Servovision and they sell through eBay.

It is a good idea to add a balancer, but not nearly as critical as with LiPo. It is just a load resistor which is switched across a cell if it gets to the range 3.7V - 3.9V.

A number of products do not charge off a USB charging port even if it indicates it is charging. My phone actually goes flat when plugged into a non-PC USB port. So check first to make sure.

I can get my hands on 3.2V 3Ah cells with built-in protection circuit (over/under charge and over current), 26mm diameter and 65mm long, about 70g to 100g. Price is about $14 each, but I have to confirm and cannot take lots as it is stock we use for our factory. Can get you 4 if you are interested. A 10Ah prismatic cell is about US$20-25 off eBay, but without any protection circuit.




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  Reply # 794410 6-Apr-2013 21:28
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Cheers Niel I'll look into those, seems like good price as well. My LiPo balance charger may be able to charge them as well, will look up the spec sheets.





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  Reply # 794411 6-Apr-2013 21:45
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Niel: 
A number of products do not charge off a USB charging port even if it indicates it is charging. My phone actually goes flat when plugged into a non-PC USB port. So check first to make sure.


Sorry for the thread drift, but there's a fix for this problem. If you can get to the back of the output socket on the charger connect the middle two pins of the USB connector together and your device will charge.




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  Reply # 794649 7-Apr-2013 16:28
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Alkaline batteries (not carbon zinc "heavy duty" rubbish) has a surprisingly high capacity (as someone suggested). A D-cell is about 18Ah. Four in series is 6V, just a tad over the maximum for USB. Put a Schottky diode in series to drop it to 5.7V, then you can charge directly off that but it will work only until you get to about 1.2V per cell. A better solution is find a switch mode regulator. There are some options on Deal Extreme and eBay. That will be much cheaper and more reliable than solar power behind a bicycle.

Personally I still prefer LiFePO4, but that is because I'm a geek.

On the side, Alkaline batteries are also dangerous. They produce (I think) oxygen while they are used. Ni-based rechargeable batteries produce hydrogen only when they are charging and nearly full (catalytic recombiners inside the cells convert it to water, which is why they get hot).




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  Reply # 794805 8-Apr-2013 07:20
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Correction: Alkaline batteries produce hydrogen when in use (not oxygen).




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