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?
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
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'em Mike Keesling sent you, not that it'll get you a discount...
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
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There are several other home-made chargers here. Just do a search here for diy. (do it yourself)
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-- Jay
-------------------------------------------------------------------- "I'm pullin' for you; we're all in this together", Red Green
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
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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?
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)
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-- Jay
-------------------------------------------------------------------- "I'm pullin' for you; we're all in this together", Red Green
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