I have a power supply from a laptop computer and I need to use the laptop's liion battery on my arduino rc car project. I would also like the car to be able to charge itself in some type of dock. Is there anyway I can use the laptop's power supply to charge this battery? My coworker who is knowledgeable on batteries told me I need to charge it with constant current first at around 3.5amps since I have a 4000mah battery.
This power supply says it can go up to 3.42 amps, but I want it to be able to sustain at that rather than cutting off power after that. Would it do so?
At first glance, it seems the power supply is perfect for my project, but I dont want to kill it if the battery draws too much current.
Your laptop has an on-board charging circuit for the LiIon battery.
You would need to either "extract" or replicate (build from scratch) that circuit in the car's dock.
Or buy a commercial Li-Po battery and charger, I bought 2 5000 mAh 18650 3V7 Li-Po batteries 2 holders and a charger for about $13.00 from Ebay and a couple of 3V7 2800 mAh batteries for ~$3.00 Ea the charger was another $5 or $6.00 from Electrodragon, Tayda is another source as well.
BE VERY CAREFUL, VERY CAREFUL with Li-Po or any lithium batteries, they ARE DANGEROUS if mis-handled in any way. I would AVOID their use until you learn how to care for them. They Are Not Recommended unless you are very aware of the dangers involved, like fires involving the Lithium metal internal to the batteries and they WILL explode it not handled carefully. NOT FOR BEGINNERS AT ALL. IMNSHO
Hmm...I see your point, but is there anyway then that I can run a couple of dc motors for an rc car off a cordless phone NiMh battery then? I have the charger all set...
yes certainly I might recommend an RC battery pack. They are typically 7.2 V which is no trouble to use with the Servo's and chargers are commercially available to recharge the Pack... there are also available Li-Po packs and chargers. There are 2 main considerations with using a battery pack. 1. is depleting the pack's charge completely and 2. recharging the battery. Use only recommended chargers and especially in the case of the Lithium batteries the load must be disconnected from the battery at a specific discharge point (cell voltage) or damage will occur. Ni-Cd's and Ni-Mh batteries will under long term discharge conditions will form Ni whiskers that will 'grow' through the insulator/electrolyte separator and short the cell, once shorted in this manner the packs are pretty much worthless as even though the 'shorts' can be literally Blown away with a high current short pulse the whisker will form a great deal easier on the original site. The Moral I guess is that the care and feeding of any battery is a subject unto itself and Must be learned If you would like to use them well. One last point. Either battery can deliver GREAT amounts of Short Circuit Current... Fuse them carefully and knowingly.
can run a couple of dc motors for an rc car off a cordless phone NiMh battery
Sure, as long as your motors require 2-5V, like these ones:
Another power source you may consider is the batteries of power tools (drills, saws etc). Those batteries tend to be high-capacity (also high voltage, at least 9V) and they too come with chargers.
Used drill batteries are just that, Used Drill Batteries and frequently tired too. New they are in the 50 - 80 dollar range / charger and once soldered to usually don't fit back in the chargers very well. Rc packs have similar current capacity and a simple connector, usually female 2 pin molex and fit either a Pigtail connector for your circuitry or the 2 pin charger, More Ideal I think and capable of some real work... not at all like the 100mAh batteries found in cordless phones. 100 mA total to run a 200 mA motor for how many minutes?? Yes you can use the cordless phone batteries for a few minutes evaluation and then recharge them for 3 or 4 hours. There is one thing I didn't mention (Yes Just one) batteries and old cordless phones are just that old tired and likely retired for a reason... But you could go to Radio Shack and buy a NEW 2 or 3 cell AAA equivalent replacement... for 6 to 10 dollars more for a few minutes more operation...
Laptop batteries are usually lithium ion and not lithium-polymer (LiPo). Chargers for the two should not be mixed up as the cell parameters are different.