Building my own portable battery pack...

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For a while I've been looking at means by which I can power my phone while out on my bike. I use my phone (HTC Desire) for GPS tracking and telemetry logging when I do long bike rides. In this role, it does well ... I can get around 6-8 hours out of it with the GPS on and 'Airplane Mode' enabled, which gets me 100km+ on the road. However, I'd like to try and go a step further and actually use the phone as a cycle computer in tandem with the above functionality, displaying either speed and altitude information or mapping. But this creates a problem ... power.

I've sampled the market a little for ways to up the power capacity of the phone, but have so far been unimpressed with what is on offer. I've looked at both a bigger internal battery (in both capacity and size) as well as external options. Both of which have so far proved to be unsatisfactory in terms to quality, reliability and actual capacity.

So I've moved on to another line of thinking - can I build my own? There are numerous posts on the net where others have done so, but this is mainly to power lighting, which isn't quite so delicate electronically! I'm worried I wouldn't get the power regulation right, and end up frying the thing. But then there's an alternative ...

Why don't I leave the power/voltage regulation to a stock travel charger, and simply worry about providing it with the correct voltage?

In other words, one of these, connected to one of these, padded and placed into one of these, then connected to this.

Any reason why it wouldn't work?

A before anyone asks, I've posted in GD because this question is of a general nature! Not necessarily phone or bike specific

 

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I don't know if it would provide enough power, but why not looking at putting a dynamo onto your bike and power your phone through that.

Well the plan would be to rig it with 10 1.2V Duracell rechargeable batteries. The current generation AA ones are rated at 2450mAh each, so 24500mAh for the whole lot (on paper at least). To put this into perspective, the phone has a 1400mAh battery as standard.

I would go with a more extravagant battery option, but with standard sizes you know you're dealing with something that works, is maintainable, and can be charged by almost anything.

A dynamo would add a whole new level of complexity to the situation, as the power output wouldn't be constant, not to mention fitting the thing. I was really just trying to judge whether I could do what I wanted to do while keeping things simple and stupid. If not, I'll move onto other things.

EDIT: Capacity calculations obv wrong

 

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If the batteries are in series then they will only have 2450mAh of capacity overall.

Good point. I couldn't work out why the numbers were so big

In that case I would probably try two packs of 10 in parallel, although to be honest, 2450mAh would probably give me hours of trickle charging as it is.

 

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Just get this:

http://www.amazon.co.uk/New-Trent-i...?ie=UTF8&qid=1311968312&sr=8-1&tag=acleint-20

My mate has the 5000mAh version, and it's worked fine for him.

I've used the 5000mAh version. It's satisfactory at best. Gives me two full charges normally, but dies in a couple of hours if I try to trickle charge, then messes up my phone's battery stats making it think it's got 25% left when it's actually dead. Cue the unexpected shutdowns Cheap chinese trash tbh. Not to mention the majority of their reviews on that site are paid for

 

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10 1.2V cells gives you 12V @ 2450mAh.

2x10 1.2V cells gives you 12V @ 4900mAh.

My iPhone uses a 5V source and I would assume that your phone also uses USB 5V to charge too?

So 3x4 1.2V cells gives 4.8V @ 7370mAh.

Assuming 30g/cell = 360g for the cells alone.

So basically you need four cells in series for the required voltage then keep adding sets of four in series for capacity.

Well the idea was to run it through a standard car phone charger, so I don't have to worry about getting the voltage spot on, and 12V is easily attainable.

Doesn't Mytracks do all of that?

Read the OP again.

Look at li-po battery cells. They also come in thin rectangles.

These sort of shape. Although you would need to source the correct voltage/ah

Will have a look, thanks. Although I'm a little worried these will be more expensive in terms of replacing/recharging.

 

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Why has nobody said the obvious? Buy a cycle computer?

I was really just trying to judge whether I could do what I wanted to do while keeping things simple and stupid. If not, I'll move onto other things.

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I still think the best thing would be to add a dynamo, you seem against it, but it seems like the best idea

kd

Dynamo output voltage would depend on cadence though right? Hence the increased complexity.

EDIT: Not to mention it would throw out AC...

 

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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.

Any suggestions for 12V batteries? Not sure what I'd search as all I get is car batteries

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!

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.

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.

(I love doing this sort of thing myself)

I could build a regulator, I'd just rather I didn't have to 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.

GOOGLE "bike dynamo phone charger"

See above.

 

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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.

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.

 

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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.

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 ).

How so? It's simple and there's no reason why it shouldn't work. GPS cycle computers are £200+...

 

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You can buy around 10,000mAh D batteries, I don't know where you're looking.

http://www.battery-force.co.uk/detail_AMDNIM002C-Ansmann-MaxE-D-NiMH-8500mAh-Pack-of-2.html

Well yes, but look at the price (and the weight!).

'Capacity Range: 2300.0mAh - 10000.0mAh' ... what's that all about?

 

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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.

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.

 

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Pic links don't work

 

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Looks interesting! Is that battery pack just fed straight into the USB Hub's power port?

Where does that input USB plug come from? (or is that just another output?)

 

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So what kind of performance did you get out of 4xAA?