Suggestions for making an auxiliary battery pack for an MacBook Air

I'm interesting in making an auxiliary battery pack for a MacBook air.

I'm guessing the best way to go is use 4x18650 batteries and then use a buck regulator to take things down to 12V? It would be nice if there was pre-made PCB that would take 14.8-17V and regulate things down to 12 volts, but most of the PCB's I've found are specialized for flashlights and are current limited instead of voltage limited. Funny, that....

A charging circuit would be nice but not necessary since I'd like use removable 18650 cells and I don't mind charging them in an external charger.

Any suggestions on how how I might go about this project?

Thanks!!

Here is what I used in a similar project:

http://www.castlecreations.com/products/ccbec.html. (the bec pro). It regulates a 4s lipo down to 12v for a halogen video light I use or for charging 12v accessories. The battery I use is a killer deal at hobby king, just look for the 4s 5000mah hard case lipo, it's less then 25$.

My problem is the bec pro heats up in the project box I have it in and will steadily climb past 135f which can't be good and it might keep climbing, I don't know, I didn't let it go long enough to find out.

If you have any ideas that will do the same thing but generate less heat or some ideas to remove the excess heat (maybe a little 12v fan?) I'd love to hear them. I also have a protection circuit on then way and will need to find a switch that is ok with 16v because I want the power switch for the box between the bec and the battery (the hv side, not the 12v side).

Here is a photo of the unfinished box:

Bp

What kind of battery life do you get? I think computers are the Work of Satan but my wife wants to get one of these Bad Apples anyway.

xul said:

What kind of battery life do you get? I think computers are the Work of Satan but my wife wants to get one of these Bad Apples anyway.

Click to expand...

My Lenovo x220t gives me 6-12 hours depending on how I use it and my "box" will recharge it 1.2 times per 5ah battery (I have 3). So on a backpacking trip you could have 36+ hours of laptop (more without wifi) for about 3-4 pounds.

Since weight is a consideration I'd choose the battery technology based on the Energy and Power Density

Ragone chart in this link.
http://www.mpoweruk.com/performance.htm
For some reason the graphs can take a while to show up.

You also need to know your average discharge current because apparent battery capacity strongly depends on the current.

xul said:

Since weight is a consideration I'd choose the battery technology based on the Energy and Power Density

Ragone chart in this link.
http://www.mpoweruk.com/performance.htm
For some reason the graphs can take a while to show up.

You also need to know your average discharge current because apparent battery capacity strongly depends on the current.

Click to expand...

The lipos I used in my setup are 20C so should easily provide the rated 5ah at the drain rates a laptop would put on it.

Hey,

I am looking at getting a 11.6" Macbook Air and have plenty of the 4x18650 and 2x18650 boxes off ebay which work great charging my smartphones. I have a lot of 18650 batteries and familiar with their operation. This unit here: http://au.suntekstore.com/goods-140...er+18650+Box+for+Mobile+Phone+and+Laptop.html can it satisfy the Air's power requirements? Or if someone can make me a box that will?

Thanks!

Alex