Using NiMH to charge a laptop

I'm sure this has been done before (maybe), but here I ask..

My idea is to use 12 or more NiMH batteries (5000mAH) to charge a laptop, using a detachable plug, soldering on a kensington plug onto one, and a charge plug onto another.

Can I charge a laptop off of this battery pack? or do I need an inverter?

I'm by no means an EE I just had this idea pop in my head and it wouldn't be too hard to do.

 

haha not a bad project netherwind.
unfortunately my electronics knowledge is rather at a basic level, however
as long as the current supplied is higher than the draw, it should work right?

i'm pretty sure an inverter will not be necessary since the power brick converted from AC -> DC prior to actually reaching the laptop.

there is one question i have however, in some laptops, the bios detects the default AC adapter's wattage rating... what would it do if batteries were connected instead?
how would it handle the eventual decay?
will you be using the laptop during charging?

also, the original power adapter, what is the power rating? what is your voltage?

bleh, i think i just brought more questions onto the table rather than answers... sorry

 

My worry would be the voltage variation coming out of the NiMH cells. A freshly charged cell is 1.35V or more which drops towards 1V as the cell discharges. The computer's DC socket expects a fairly steady voltage (usually +/- 0.5V from the rated voltage is OK). You may be able to use a voltage stabilisation circuit to overcome this potential problem.

John

 

As to the batteries: I don't know that one actually, 12 NiMH's is 14.4v, i'd imagine? that's enough, I don't know, can always add more if it's not.

As for decay: Then they just stop providing the 5000mAH, and slowly die, the batteries aren't prohibitively expensive, and I believe there may be ways to counter the decay.

As for using while charging: I don't see why not, it would basically be providing me with a AC power source, almost like a 5000mAH UPS.

Currently my laptop is 5 years old, and my beloved m1210 has died, so I'm stuck with a crappy Inspirion 6400 (my sisters old laptop) until my job starts in October.

 

basically i think to ensure success, you need the correct voltage or thereabouts. the current should also be as high as the default charger or as close as you can get.

my laptop is 19.5V @ 7.7A
so 19.5 * 7.7 = 150w

cells in series will add the voltage while cells in parallel will increase the amperage. find the right combo and i think it will be good, otherwise it may have issues... not too sure.

*edit*
just checked http://www.laptopbatteryinc.com.au/dell-inspiron-6400-ac-adapter.html
so to be on the safe side, i'd say try to match those specs and if you have extra room to spare, add on the amperage with more cells in parallel.

 

One of my friends mentioned this to me, but putting it inside a cooler, would be an interesting concept, so instead of lugging around the big pack, you could kill two birds with one stone, good cooler + extra battery

Edit: I won't be able to complete this project until late October, and if it is successful the way I'm hoping I may just make a little guide or something incase anyone else wants to do it

 

This is certainly a do-able project. There is no way without having schematics for your laptop internal charge circuits to know how much overvoltage they could tolerate, so that’s why I would highly recommend battery regulation to the same voltage as your power supply. It would probably be okay if your voltage was up to 1 volt higher, but no more.

As for the battery packs, your best bet would be looking into packs that are used for RC cars. They will be the most cost effective. You can get packs of various voltages at Digi-key. Here is a link to the base battery, if you look under associated products you will see what I am talking about. You can select different packs to get and put them in series to get your high voltage needs. The problem is it’s very expensive to go that route.

Digi-Key - SY148-ND (Manufacturer - HR-DUX(10.0AH))

Unfortunately coming across an easy solution for a dc-dc regulator at high voltages and currents will be your biggest obstacle. I think your best solution would be some kind of pre-fabbed power module that allows you to program the output voltage with a programming resistor.

I don’t have time to look into that right now, but give me a few days and I may be able to come up with something that could work.

Once a module and battery packs have been identified, it will actually be pretty easy to hook it all up.