Noob Q, Old laptop battery to usb charger...

[Drew S]

I have an old laptop battery that I took apart and would like to turn it into a USB charger for on the go, It is 6 cells, total 11.1V 4400mAh, I want to be able to use it to charge my USB devices, and also charge it via a seperate USB so I can through a car, Outlet, solar. Ext. There's a pic below.

keep in mind I dont have any real experience with this stuff.

[UAirLtd]

those cells are called 18650 cells: 18mm diameter, 650mm long, and are standard for many laptop batteries.

You've got two options for these:
1. make your own, this is one of mine from a couple years ago: http://hackaday.com/2010/05/02/a-more-p ... t-charger/
2. a far easier AND better option is just get yourself one or more of these: http://www.ebay.com/sch/i.html?_trksid= ... &_from=R40

These are little boxes that hold 18650 cells (most commonly 4 or 2 of them), and act as a USB 5V supply to charge your devices. The boxes themselves can be charged via 5V, which can be obtained from a computer via USB, a suitable wall wart, or a car lighter socket (via a lighter sockt to 5V USB). They also have proper cell discharge protection.

Tip: look closely at the picture, get the ones with a USB-mini ports, USB-mini is a far more convenient plug than barrel jacks, because you'll probably already have the right cable, or even a wall-wart with the right plug. Also pay attention, some of them have nice battery level status LEDs that light up when you push a button to check battery level, I recommend this one: http://www.ebay.com/itm/5V-2A-Mobile-Po ... 27cbf35645

While you're at it, if you're looking for other things to do with those batteries, they make great flashlight batteries for 18650 LED flashlights, very compact and powerful, I've ditched all my regular AA/C powered flashlights, and I used one of these flashlights mounted to the front of my bike when I used to cycle to work.

[Drew S]

Well i want to build it myself. Let it be a learning project for me to understand whats going on.

[UAirLtd]

Ok...well in that case you have three options depending on which level of detail you want to go into. In increasing order of complexity:


1. The hobbyist way: wire together some pre-build modules readily available from hobby electronics companies like Adafruit: http://www.adafruit.com/products/390 and http://www.adafruit.com/products/14

This is the method engineers would use to quickly prototype circuits to test certain aspects of an early-stage product, or to produce a quick proof-of-concept. This is also great for hobbyists who want to quickly built up a project without necessarily having to learn all the ins-and-outs of the circuits they're using, or the principles behind them. This is the approach I would recommend to you if you're just interested in getting started building some simple projects.

2. The electrical systems design way: source a 5V output DC/DC boost IC, and a single cell lithium-ion charge IC, and simply build up the recommended circuits, hit up your preferred chip supplier and search for DC/DC boost chips, and li-ion charger chips; things like the LT1303 (actually don't use the LT1303 this was just an example, I used this before several years ago, there are better, cheaper, chips out there now) etc.

This is the method engineers would use to design functional circuits for use in consumer, commercial, and industrial goods and applications; where the aim is to produce a low-cost integrated system a part of a larger product. This method requires knowing or learning some of the principles behind circuit design (particularly with high-frequency DC/DC boost circuits which require at least some consideration of the circuit layout to avoid instability or ringing). And is what I would recommend to you if you're looking for a project that'll teach you how to build circuits.

3. The low-level electronics engineering way: build your own DC/DC boost and regulation circuit for 5V output, and your own DC/DC buck circuit with CC/CV control for the charger. Stuff like implementing DC boot circuits, and dealing with charge profiles.

This is the method engineers would use to build highly custom circuits that are needed when pre-fabricated ICs are not sufficient. This is also excellent for learning about the field of power electronics, and DC/DC boost circuits and battery charging. This is the approach I would recommend to you if you're looking to learn more about power circuits, and control loops.

[Drew S]

Well I would have to go with option 2. I want to learn about the hardware and that seems the best way to go. I have a good knowledge of Software and programming no problem, but, really know nothing about the hardware. I barely know how to put my PC together.

[UAirLtd]

Alright, so I suggest that you take this in two steps: get the 5V DC/DC section working first before tackling the li-ion charger section.

I suggest you replicate the circuit of the MintyBoost, which uses an LT1302 to do the boosting. In fact, if you were familiar with SMT circuit design, I would have recommended instead, smaller, cheaper, SOT-23-5 package fixed 5V output chip. But as it is, you'll find far more support from hobbyists for the LT1302 due to the popularity of the MintyBoost project: http://www.ladyada.net/make/mintyboost/parts.html

(If you're interested, I would have given chips such as Taiwan Semiconductor TS1935 or On Semiconductor NCP1450A as examples, which cost a fraction of the LT1302, and because these are fixed output, you need fewer components to build the circuit. However these chips are surface-mount SOT-23-5, and for these you would preferably design a PCB rather than use prototyping board as you would for the LT1302. It's worth mentioning that since it's a switching converter, you should really be designing a PCB for the LT1302 as well rather than using prototyping board, which WILL work probably most of the time...)

Then for your next step, I suggest looking up a lithium ion charger IC that is used already in some hobby boards, since you'll be able to get more support. The one I know of off the top of my head is the MAX1555 (which is also surface-mount SOT-23-5 package).

Alternatively if you're looking for something awesome and a challenge, you could try your hands at using an all-in-one combo IC designed for use in cell phones and tablets, like TI's new BQ24195L, which packs the charge circuit and 5V (actually 5.1V) boost circuit into the same chip. It also includes USB functionality (it will actually negotiate as much current as possibly via USB for computer-connected charging), and also has an I2C interface (I don't know if this is required for operation or not). All of this in a low-cost 4mmx4mm QFN-24 package (which means only attempt this if you're familiar with SMT circuit design and assembly).

[Drew S]

I may have been a little confusing here. I do not know much if anything about electronics or circuits, I would like to learn and thought this would be a good way to start. The most I do know about electronics is Basicly, Cells, Wire, Batterys, Resistors, Leds, Switches. That USBs can only take 5v. I know the physics of electricity enough so I do not need to know that, its the practical use of all the components to do something. Perhaps I should learn by some kits with step by step instructions or a good book to start at. Does the minty boost have step by step instructions? If so I think I will start there.

[UAirLtd]

humm humm...ok ok...I think I understand the picture better. Those kits that you can buy from Adafruit or Sparkfun, they let you create projects easily, and it's suitable for beginners, but you won't learn as much about practical use of components or circuits from it. It's a bit like color by numbers: "here's all the components you need, here's where you put them", and not really explaining what function of the circuit is, or why you should use that particular component value.

So by all means, try out these kits, they're great for building experience with handling electronics, but you'll want to put in a lot of extra effort in to understanding what the circuit is doing.