Laptop batteries for a robot

Hi, does anyone have any experience with using a modern laptop battery as power for a robot? I just looked at a Lithium-Ion one from Dell
that provides 14.8 volts - 3800 mAh, and has a charging current of about 3.5A. I was thinking of using it do drive a Mini-ITX system, or a Nano-ITX system when they arrive.
I weighted this and its around 400 grams which is a pretty low weight. Anyone else have experience with lower weight and high mAh?
And finally, do you know if its easy get the necessay electronics to charge one of these?
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Be careful with Li Ion. Discharge at no more than 2C, C being capacity. i.e. 7.6 Amps.
Li Polymer will discharge at a rate of at least 5C, and weighs less, because the cells are in plastic pouches instead of metal cans.
Discharge no Lithium battery to below 3V per cell ( i.e. unit of 3.6 V ) or you can damage them. Charge with a Lithium specific charger. Charge with a temperature probe if you can.
I get mine from http://www.lightflightrc.com Tell 'em Mike Keesling sent you, not that it'll get you a discount...
Mike
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A 14.8 volt battery would be 4 'cells' in series (Each 'cell' might be several lower current cells in parallel).
Don't discharge it below 12 volts or you risk damaging the battery. Li-Ion cells can explode from too much current, (charging or discharging) Li-Poly just burn-up. Do not charge at more than 1C, 3.8 amps. and lower is better and safer.

You can build a simple charger with 2 adjustable regulators. The first regulator limits the current and the second regulator limits the voltage. Here's a thread (over 200 posts) in RC-Groups.Com that uses 2 LM317 to build a charger . The LM317 will only output 1.25 amps but the thread lists other regulators that can handle more current
http://www.rcgroups.com/forums/showthread.php?s=&threadid 0567&highlight=di y
There are several other home-made chargers here. Just do a search here for diy. (do it yourself)
http://www.rcgroups.com/forums/forumdisplay.php?s=&forumid 9
-- Jay -------------------------------------------------------------------- "I'm pullin' for you; we're all in this together", Red Green --------------------------------------------------------------------
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As you can see from the previous posts, Li Ion is very difficult to use for a hobby roboticists. Do yourself a favor and use NiMH batteries.
BRW
On 16 Jan 2004 03:54:04 -0800, snipped-for-privacy@online.no (Jeceel) wrote:

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Yeah I see that it can be a bit harder to maintain Lithium-Ion and Lithium-Polymer. But if I am able to get hold of the necessary electronics to make sure that the battery is not misused it should be pretty safe and it seems I get more mAh/weight than any other solution.
I feel that weight is a big issue here, and if the robot is supposed to run for some hours without a recharge I guess some technology like Lithium-Ion and Polymer is needed.
Lithium-Polymer sounded a bit better as it is a bit safer and weighs less than Ion cells. I saw that link (http://www.lightflightrc.com ) and it seems only to have max 11.1volt packs. Does anyone know if you can get these in 14.8 volts as I need to power a Mini-ITX (or Nano-ITX) system?
Best

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LiPoly cells are charged up to 4.2 volts and can be discharged to 3 volts. The nominal voltage is usually quoted at 3.6 or 3.7 volts. An 11.1-volt pack contain 3 cells in series.
Battery packs are described based on their configuration 3S-2P would be 3 in Series and 2 in Parallel. You could buy 4 single cells and plug them in series yourself. The RC-Group website has several threads discussing the advantages of individually charging the cells in a series wired pack.
Charging the cells is relatively safe if you follow the rules. Don't charge over 4.2 volts. Don't charge at over 1C. Don't discharge below 3 volts. Charge in a safe location, just in case.
Lithium-Poly cells use Lithium-Ion chemistry, just in a soft case. Sometimes Li-Poly cells are referred to Li-Ion because of the chemistry.
There are new Lithium cells being released that are safer, Lithium-Phosphate. (New chemistry) http://www.rcgroups.com/forums/showthread.php?s=&threadid 6612&highlight=ne w+lithium
-- Jay -------------------------------------------------------------------- "I'm pullin' for you; we're all in this together", Red Green --------------------------------------------------------------------
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