[REQ]Build a battery based battery charger (for Laptops)

[LukePC1]

Hi I'm trying now for some time to build a thing, which can power other electoncial devices, such as Notebooks, Mobiles MP3 players or whatever you might want to recharge.

The Idea was to have an extra battery, which can be powered by many different energy sources. It should be highly energy efficient and shouldn't damage the connected devices.

It should be like this Multi-Charger, but maybe a little less complicated

I liked the Idea, to power things with a dynamo hub, since it doesn't use that much extra power to use it, and it's always available, no matter where you are.

I just ordered 12x AA 1,2V Ni-MH Betteries at ebay, which could be used for testing purposes. They are like These!

Tests with smaller batteries (AAA) had as a result, that the current was not high enough, to power a Laptop (ca. 2A and more). If that doesn't work, it should be usefull to extend the time the battery lasts.

For a high energy efficiency I'd like to use as little resistors as possible.

What do you think? Are there some heavy errors I didn't put in account? Do you think it's a usefull thing to have? One more original batterie is very expencive, so at least the price could be worth it.

[sharky]

hi..

please rname your topic adding [REQ] before the title.. this will help to understan that help is needed..

personally i didnt study electronics but i think that a laptop will kill the batteries in some mins.. i would go for 2/3 12V lead batteries. maybe lead/gel to avoid acid problems. theyre quite heavy but also powerfull. with 3 1.2AH batteries you could do much more than with the 12 small batteries and theyre probably cheaper too.

[LukePC1]

Well 'little' 1,2Vx12 = 14,4V @ 2,4Ah if I'm right. So if the Laptop draws a current of 2,4A, which I don't hope, this battery will last about an hour - if the Voltage is ok.
I checked some Laptops and one battery has 10.8V, so I think I can get to that. The power supply has 15V or 18,5V depending on laptop.
So if I simulated the power supply with this pack, I could be sucessfull with 14,4V - if the voltage doesn't drop too much on load

I thought into lead batteries, but the problem with these is, that they might have the wrong voltage - I'm not shure of that...

I'll have to see, what these accumulators can do - how much output they have...
If it's not enough it will at least take some burden from the normal laptop battery

Or it will power a mobile or a MP3 player, which do need just little energy...

[sharky]

can you post the link of the batteries on ebay please? i wasn't able to find them with the same specs.




ps: you still have to rename your topic title..

[wuhlei]

http://cgi.ebay.com/New-Universal-Exter ... dZViewItem

I was thinking about using a drill gun battery the voltage was close but the shape was all wrong

[LukePC1]

Well I'm not shure about the design or how to fit them jet, but I bought these:
http://cgi.ebay.de/12-Energizer-Testsie ... dZViewItem
I also inserted the link in the first post.

I measured the current with smaller ones - and no resistor, because I had no time to look for one and had currents of 3A with the AAA cells, which are even smaller. When I put 3 in a row I had 9A current, but I doubt that it'll be good for the cells. However this prooves, the concept could and should work.

One of my tested cells had not 3A but 0.2A, so it's either empty or defect

edit:
Basically it's like the link from Wuhlei, but not from China, not as powerfull, maybe lighter(?) and hopefully cheaper.
On top of that, I'd like to power or charge it with my own input - A dynamo of a bicicle or a solar panel or both.

Appart from that, the linked item is quite nice. 20Ah seem to be a little exagerated, though. Maybe that is measured at the lowest voltage?

74WH/20Ah = 3,7V
It seams like that, if the 74WH are not exagerated, too...
74WH/19V = 3,9Ah
So the battery is approximatly as strong as a common 4Ah battery of a notebook, or about 2 or 3 times as strong as the battery we/I are going to build.
On top of that, we can't be shure, that the commercial product doesn't fire up all the stored energy into heat in the resistiors...

[sharky]

wow almost 24 euro for 12 batteries???????? thats mcuh! well you can try it but i think that at the end the cost could be higer than buying a prof one...

let me know..

good luck

[LukePC1]

I didn't want to choose the cheapest, and they are more expencive, if you add the shipping --> 28,5€ in total if I'm right.

I bought them, because I had a paypall voucher for 20€ , so the total cost was very inexpencive realy. I just didn't find anything for a reasonable price, I could use more...

[sharky]

www.alkapower.it has good prices, very good materials and ships in whole europe

[sharky]

www.alcapower.it

[LukePC1]

I just saw a comercial from Aldi. They'll have them, too.

But mine arived already and are charging now...

[wuhlei]

have you checked out the drill batteries? you can crack one open its like long AA's.

[LukePC1]

I found the time to check the 'externel' battery out. I don't have a good case or a correctly fitting plug jet, but I was able to get the energy to it with some other peaces cable.

My notebook should get 15V at 3A, but I could only provide 14V, which dropped to 13V under load. The current flowing into the laptop was about 0.5A at that voltage. The test was done with only 11cells!

That is only about 6-7W, but the power supply was detected, like usual. The screen got brighter, because it was not in power saving mode anymore. The controll for charging the internel battery was on, but the battery-status didn't change.

I think I'll try again when the batteries are fully charged - and with all 12 or maybe one more from sowhere else.

____________________
I also disassembled an old internal LI-IO battery, which didn't work and is not needed necessary. Unfortunatly this one needs a different voltage. 18,5V from the outside and something about the 14-15V from the inside.

The battery itself contains some possible complicated or defect electronics and 2x4 cells. There seem to be allways 2 cells plugged parallel.
One pair has still 3.6V left, the others are at about 2V. These values reduce fast on when you put load on them, but that migh be due to the fact, that it was empty

____________________________

Does someone have experiance with a car battery based mobile charger? I think about getting a cheap one from ebay, to disassemble it and maybe conect it to this external battery, so I could charge the mobile from it.

Possible problems:
1) The voltaga might be wrong
2) It wasts too much energy by becoming hot

1) this shouldn't be the problem, since the producer claims, that it can use power from 12 to 24V
2) this worries me. If half the energy running through it is wasted, this is no option. If it is 'only' 1/4 it is acceptable, but more efficience wouldn't hurt

[PalmerTech]

Do you still need help with this? I have a lot of experience with Li-Po battery systems, I have a 6600mah 7.4v system I built that goes into 3.3 and 5v switching regulators with about 96% efficiency from TI, it would be very easy to make a multi-voltage one for laptops.

Let me know, I can show you what to buy and how to put it together!