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DIY laptop battery pack (textbook size) Answered

it took me a long time to find a suitable forum to ask this.

I have a thread at Cnet, a tech site.

I'd really like to have the power I need to last through the school day, and I'm sure other students feel similarly. 

I thought about solar, but it's too low of a yield. Nimh and Ni-cad have shorter lifespans than Li-ion.

What's necessary in this setup would be:
small enough to fit in a backpack
thin enough to leave room for my books if need be
must be able to fully recharge a laptop at least once while in use.
AC current preferred, DC if necessary, I can get an inverter.

I have a soldering gun in my electrical kit and would love to show off to my friends next school year.

edit: I forgot to include that this is to use with a laptop

update: I've decided that I can use a briefcase if I get a slightly larger backpack next year. I found some batteries, and I'm trying to figure out the voltage and amp-hours for the PCB and charger



So, the white boy with a big mouth side of me is going to say "prove your intelligence, and competence to your friends regarding a subject you have absolutely no idea about".

But then again we all started somewhere... Take an old laptop battery apart. Check it out, the type of battery, the general layout of it.. Take pictures if necessary.. Do a little research and find the equivalent readily available on the internet batteries you want to use, for every 1 battery in your current battery pack you'll need at least two. wire the pair of new batteries just like your 1 is now but paired.. So you'll have two batteries soldered together + + and - -. Attach the positive side to the next pair of batteries, and the - too. Just like your normal battery case was. The result with be the same voltage you've got in your normal battery, only twice the battery life. Repeat those steps as necessary, it'll end up being less than an inch thick, and whatever dimensions you want it to be..

If I want to be honest and say that part of me just wants to show off, why not?

Did you come up with a plan? how'd it work out? The suspense is killing me!

yes, I have, but it was postponed until thanksgiving break. I had summer reading, a college essay, and a little summer review work for two AP classes this year. I procrastinated it too long.

The plan is to go the li-ion route and wrap each cell in vented printer paper so I can direct the heat distribution. I'm increasing the budget by 50 to create a more controlled device.

To regulate the voltage and step down that 16.8v, I added a powerful voltage regulator to the build: http://www.ebay.com/itm/NEW-waterproof-DC-DC-Converter-Regulator-24V-Step-down-to-12V-120W-10A-/370872032505?pt=US_Power_Inverters_&hash=item5659b21cf9

To help dissipate heat, I'm considering modding the case to add a computer fan (80mm, "silent", probaby under 4.5w@12v), and if I do so, I'll need to add a small switch.

Will add to comment later, gtg

Looked up the 80mm consumption: http://www.overclock.net/t/607564/whats-the-power-consumption-of-80mm-fans

It's under 2w, so that should be nice. that means for a 4s4p battery pack rated 142w, with fan on at all times, it would go for about 70 hours not including power draw of other components.

if I'm going to use a switch for the fan, it should be automated and more efficient than the fan. here's a thermal controller, but it requires 12v and 5v: http://www.coolerguys.com/840556098690.html

I strongly recommend not trying to take it through an airport, or leaving it unattended in any public place. Taking it to school, where they know you, you'll just have to explain what it is. No wires showing, no crazy bomb like contraption unless you x ray it.. Just a clean thin plastic case you could even strap it under your current laptop if you're using it on a desk.

What laptop brand and model do you currently have? Many manufactures offer an extended life battery pack that will attach to the bottom or back of the laptop to double your battery life. Or you can find a battery upgrade that fits in the current battery slot.

Obviously your not able to plug your laptop in during class so you may need to just buy several batteries to keep in you bag and charges for them so you can charge them at night.

External battery pack, AC output using inverter

If your asking if it would be good to have a large battery powering an inverter so you can plug your laptop into it, its a very bad way of doing it. An inverter will drain even a car battery within a couple of hours. There is also a large amount of energy loss converting the DC to AC. You would be better off adapting the battery to supply the required voltage directly to the laptop's power connector. But that isn't a safe idea.

Just get extra batteries for your laptop and keep them in your pack and change them out as needed.

Buying an accessory would almost defeat the purpose of this project.
1. can't just replace a battery on an ultrabook. some can be changed, but not quickly. 
2. need a project to work on with my dad
3. need to avoid looking for a power outlet during class or causing a disturbance.
4. want to prove my intelligence and competence to my friends
5. want a new laptop to last a full day on a charge and not have to shut it down

I'm working on a DIY battery pack, do you know of any type of small case that would house this that would fit in a normal sized backpack with a few textbooks? 

I don't want to walk into school and have people think I'm carrying a bomb or something, my mom told me people might be suspicious of the case or the wires if I show it off at all. The dean of students especially doesn't like me. Are there any thinner cases that would be suitable for use in public? BTW, I'm already the weird, less social person in my grade.

I'm really not sure about a briefcase unless I put the battery in a second section. Any other type of case that would fit in my backpack would be perfect.

P.S. I can't carry around extra laptop batteries because the kind of laptop I'm shopping for doesn't often have an easily replaceable battery

I live in strange countries, the cheapest way to do this is with extra batteries. The problem with computer batteries is you only can charge them inside the computer. The only way I know is with one of these external chargers, you can buy on Amazon.com. Again, the name of the computer is important, I only buy HP because they are global, while the Apple people are too far away from the tree the USA to get parts.

With 2 extra batteries, you can keep the thing going between plug in times, which in the USA is easy. Note the solar stuff is just not going to keep you working 24/7. It is raining today here in Kara, Togo West Africa, do I stop working for a day? Solars is not mobile, unless you put a huge expensive thing on top of a van, or motorhome. I recommend you easy on into it, buy one battery backup. My guess is that is all you need, normally around 25-35 dollars on Amazon.