Portable USB Charger

Picture of Portable USB Charger
Does your iPod run out on you all the time?
Well, i have a soulution for you!
This USB charger utilises 2 standard cellphone batteries to charge your iPod, much more storage than a usual USB charger.

N.B.  To construct this project, you will need a mild understanding about electronics, how to read schematics, solder etc.
I am not liable for any damage that may occur to your iPod from using this project.
Li-ion batteries can be potentially dangerous. Handle them with care and NEVER short-circuit.
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Step 1: Parts & Tools

You will need:

2 Nokia (or equivalent) Cellphone batteries

1 DPDT slider switch

1 7805 regulator

1 Small heatsink

1 Female USB connecter

1 330 Ohm Resistor

1 Small red LED

A box to put it in (I used a small DickSmith one)

1 Small set of male/female connectors (I used old style nokia charger M/F connectors)

Lots of small wires

4 47k resistors (optional)




Hot glue

Soldering iron and solder


Step 2: Schematic

Picture of Schematic
Here is a Schematic on the circuit.

Step 3: How it works

When the switch is in the 'internal battery charge' position the 2 batteries are in parallel, so they can be charged together by the 5v power source.
When the switch is in the other position the 2 batteries are in series, with a total voltage output of about 7-8v. This then feeds the 5v regulator (the 7805) which puts the voltage down to 5v.
sanyo80882 years ago
cool portable charger
aekara3 years ago
hi threre i have a problem with the diagram

I cant understand the connections on the swich

Can you please send me a better schematic just to understand how to cannect the swich?

slipknot rules (author)  aekara3 years ago
What part cant you understand?
I´m also unsure of how the switch is supposed to be connected. As it has 6 connection points, what goes where?

Rookie question i know but hey, I am one...

Forget that it is double ganged (effectively two switches in parallel) for the moment. Lets look at any one of the 'two' switches.

On a switch one connector will be able to be switched to one or the other of the other two. Like this:

0----------- Sw pos 1
0---------- Sw pos 2

The switch contact is connected to the point I've referred to as common and moves between Position 1 and 2. OK so far?

In the diagram above we have a double ganged switch, so one physical switch to throw, but two sets of contacts associated with it.

Hopefully if you look at my crude diagram and think about the explanation then you should be OK. If you are still struggling then I would, respectfully and with serious concern for your safety, suggest that you seek advice from someone more knowledgeable who can assist you with this project. I mean no offence. As I commented before, lithium cells can be dangerous. If you are not 100% sure what you are doing - seek assistance - don't just 'have a go', this is a great little circuit but very simple and subsequently has little in the way of inherent safety. Again, not a criticism but an observation.
Thanks for the comments and you concern :-). I would have figured it out from your post but I actually already built this a while ago and everything is working perfectly. I´ll post pictures of my "Läkerol charger" when i get around to it.

Some hands on testing when the mail delivered my parts and this video helped me figure it out

Next project will be a "Solar charger with status LEDs" for the "Läkerol Charger"

P.S. You are totally right about being carefull with DIY charging batteries. I have great respect for them. I'm a diver and a dive buddy of mine had his battery pack catch fire while using a proper CE marked name brand charger. It was a 10,4 Ah 14,8V litium-ion pack so no toy. Luckily the only casualty was a nearby piece of clothing...
The switch diagram didn't work too well, so lets try this:
The goblin3 years ago
The switch:

It is a two ganged switch. Both sets of contacts move with a single throw of the switch (shown by the dotted line)

In the current position the power to the 7805 IC is from the two batteries. To visualise this look at the negative terminal (smaller plate) of the battery nearest the 7805. This can be followed to the -ve input of the 7805. Follow the +ve plate and this is connected, via the switch, to the negative plate of the second battery, effectively placing it in series. The positive plate of the second battery then passes through the switch to the +ve input of the 7805. Assuming both batteries are charged to 3.7V this places 7.4V across the 7805 which can then produce a 5v output.

With the switch in the other position the 7805 is disconnected from the batteries, but they are then connected to the +v input, but are in parallel and can therefore be charged simultaneously from the one charger.

OUTPUT components:

The LED and resistor are used to demonstrate that there is an output. the resistor limits the current to about 10mA-ish.

Suggested potential improvement: (If I may be so bold)

Capacitors across the input and output would stop start up and shut down spikes and increase the life of the 7805.

NOTE: THERE IS A SMALL SAFETY CONCERN HERE! Imbalanced cells can result in imbalanced charging and a potential fire hazard exists. Lithium batteries are not nice when they go wrong (Google it!), so be careful when charging cells in parallel without a balancing system in place.

Not a criticism, just an observation. Clever use if the switch though!
slipknot rules (author)  The goblin3 years ago
Thankyou for such a great comment! :) yes I know capacitors on the input and output would be an inprovement but i didnt really have the space for them! And yes lithium cells can be very dangerous if used incorrectly, could you reccomend a suitable balancing system? :)

I'm no expert unfortunately, but I'd guess if you were looking for a balancing system it would increase the complexity and cost considerably. Personally I'd play it safe, ensure I used identical cells and charge them on the charger that was intended for them. My guess is you are using old laptop or even mobile batteries here (I appreciate that you can buy commercial off the shelf Lithium cells for projects). You'd have to be quite careful. Even the commercial chargers get called into question when it comes to balanced charging. If you want more info I'd look at a discussion on one of the many RC Chat Forums ref one of the many Chinese chargers available from HK via EBay. The IMax B5 always seems to generate some informative banter and differing opinions!
vtsnaab4 years ago
Older Nokia phones have very nice 3.7V packs with NiMH batteries in them - the 5xxx series, for example. (I have been wanting to re-use my good, but orphaned battery packs for a while now...and almost bought a battery-to-USB charger - but not now !) Those which have the lithium batteries always are marked as such, clearly, from what I have seen. I needed an idea of how to use 2 packs together - so I appreciate your work very much !
slipknot rules (author)  vtsnaab4 years ago
Your welcome! Much appreciated comment :)
MoritzB4 years ago
Hey great idea, I had also this idea but not the circuit to charge the battery. thanks.
Data6434 years ago
Serioulsy, you really need to learn how to do a better job on putting your components in the box.
slipknot rules (author)  Data6434 years ago
Well my drill was broken.... used an old soldering iron to make the holes :/
TSC4 years ago
slipknot rules (author)  TSC4 years ago
Thanks, I came up with the circuit design a few months ago, built it but never got around to making it into an 'Ible
Hm you're welcome!
Darn you took my idea. But mine uses a switching power supply. Good job though.
slipknot rules (author)  rocketman2214 years ago
Thank you, I think that a switching power supply would be a little bit big to fit in my little box ;)
GregorN4 years ago
Nice work, but on some cell phone will not work, because the new phones are "to" smart and they know different between 5V and 7,3V (on head I think for Nokia is 7,3V).
slipknot rules (author)  GregorN4 years ago
Yeah it can be rather annoying that all the new tech that is coming out is 'smart' about charging. The best soulution is probably to research what it takes to charge the device, then replicating it in your own charger. Cheers
ikeike404 years ago

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