Self contained battery system.

[lapoltba]

I'm prone to compulsively modifying, hacking, and cobbling together electronics just because I can.

For a long time now I have wanted to create a Lithium chemistry based battery solution for integration into "custom" portable electronics. I want something with cell protection, balancing, charge control, and is bidirectional (buck/boost + regulation). Ie. it can be charged while powering your device.

I have looked at some of the evaluation kits that Maxim IC, Motorola, and TI have to offer, but none seem to do exactly what I am looking for.

I know the simple solution is to buy an external USB battery pack, but they don't offer much power, or storage capacity.

Is there anyone here familiar with lithium ion management and or charging circuitry that could help design a ~10Ah pack that could be integrated into a custom portable device?

[pygmy_giant]

I am successfully doing it.

I'm using this: http://www.ebay.co.uk/itm/DC-DC-3V-to-5 ... 43af414972

plus 8 x 3.7v lipos in parallel plus charger board from a wii fit battery pack plus this: http://www.ebay.co.uk/itm/160828270813? ... 1497.l2649

A bit heath robinson I admit but it works and I haven't burned my flat down yet.

If I was doing it again I would simply use something like this: http://www.ebay.co.uk/itm/Boost-and-Pro ... 33638162a9 If I could get it in the UK or Just one 7.4v lipo plus appropriate equivelant bits and bobs...

...ebay is your friend

[lapoltba]

Jeez, your google-fu is strong. I swear I searched Ebay for exactly this but didn't come up with much. My only issue with the DIY USB external power board in your last link is the current limit is still only 1.5A which doesn't leave much room for powering a screen.

I would love to be able to use a ~14V pack with something like this http://www.microchip.com/stellent/idcpl ... e=en520041 and still be able to get 12V without trying to step up from 3.6V to 12V.

*EDIT*
Forget that last comment, it doesn't make any sense. The whole point of the system I linked was that it handled both charging and discharging to and from a fixed 6V supply rail. I supposed you could boost to 12V from that, but it wouldn't be very efficient. Regulation to 5V to power the 3.14159 would be Pie.

[pygmy_giant]

My power requirements are less than yours as I am running headless without a screen....

You may have to cobble together different boards. The important stages are:

Lipo(s) -> over/undercharge protection board -> step up/down switching regulator to 5v -> Pi

and for charging:

balance charger -> lipo(s)

The addition of a screen complicates things and could require an additional switching regulator.

For switching down, these are proving popular: http://www.ebay.co.uk/itm/280942757086? ... 1497.l2649 (I've got two)

[lapoltba]

The problem with putting together separate boards is that it means you must remove the battery from the device in order to charge it. Charge circuits unless specifically designed for it, cannot handle powering the device while charging. They have no way to measure the load while also knowing how much current is going into charging the batteries. The beauty of the $70 dev. board I linked is that it works automatically off a 6-7V bus and is bidirectional.

Maybe i'm looking for a unicorn here, but it happens every day in our portable electronics so it must not be *THAT* complicated.

[pygmy_giant]

Good point - I guess these mini board manufacturers don't know what device you are eventually going to use them in so can't factor that into the design... You could maybe istall a dpdt switch so that the batteries are either set to charge or power the device so at least you can physically leave them in the housing...

[lapoltba]

Yeah, this is the type of thing that manufacturers have designed specifically for their application.

From reading the datasheet on that board I *THINK* it can buck the 14V battery pack to 6V up to 6A All the source code/firmware and Gerber files are published. I am toying with the idea of having one made custom. No idea how much it will cost, but it is a multilayer board. By the time all is said and done it may be more than the $70 they want anyway.

[xatinni]

What about Radio Control hobby stuff, there's an array of LiPo batteries, chargers and adapter's to suit different RC model power requirements

Would something like this adapter do the job see URL below - only 1Amp max output, but there's a whole range of 7.2v lipo batteries ranging from a couple of 100mah to 6000+ mah (and we could always parallel LiPo's up for more milliamps per hour

You can find cheap Lipo batteries, adapter, chargers etc at most RC model shops either locally or on the web

7.2v Lipo to 5v USB adapter (max 1Amp)
http://www.hobbyking.com/hobbyking/stor ... apter.html

[lapoltba]

I was looking for a more integrated solution i guess. I'm looking into having boards made and assembled. When you start getting into capacities of 3-6Ah, charging via USB becomes less of an option. Charge rates are limited to 500mA from a standard USB and maybe 1.5A from a wall adapter. Using a 1C or 0.5C charge rate, you need to be able to supply at least 2A to the charger, plus any overhead to actually run your devices. This makes an integrated solution attractive. This particular board is a bit on the large side ~15cm square, I would love to be able to compress things into a smaller package though.

If there is any interest I can have a batch made. Making 20 or more at a time reduces the cost significantly. As of now, I have been quoted $20 a piece for 10, plus taxes and shipping. That would likely go down to $15 doubling the quantity. Just have to confirm that is actually an assembled unit, not just the etched bare board. Language barrier is an issue dealing with fab houses in China.

[dROb]

I was looking for a more integrated solution i guess. I'm looking into having boards made and assembled. When you start getting into capacities of 3-6Ah, charging via USB becomes less of an option. Charge rates are limited to 500mA from a standard USB and maybe 1.5A from a wall adapter. Using a 1C or 0.5C charge rate, you need to be able to supply at least 2A to the charger, plus any overhead to actually run your devices. This makes an integrated solution attractive. This particular board is a bit on the large side ~15cm square, I would love to be able to compress things into a smaller package though.

If there is any interest I can have a batch made. Making 20 or more at a time reduces the cost significantly. As of now, I have been quoted $20 a piece for 10, plus taxes and shipping. That would likely go down to $15 doubling the quantity. Just have to confirm that is actually an assembled unit, not just the etched bare board. Language barrier is an issue dealing with fab houses in China.

Hi Lapoltba,

Many years passed since your last post, but I hope you still here Could you advise how did you solved your problem? My task is to use 3x LiPo batteries to power portable device, and I need to embed the charging circuit. In my case I am not concerned by the high currents. 1A will be fine for me. But I still havent found any good schematics/modules...