Battery Choices For Small Robot

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BobCochran
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Battery Choices For Small Robot

Post by BobCochran »



Can anyone suggest a reputable internet merchant who sells lithium ion or lithium polymer batteries? They will be used to power a robot -- namely the "balancing bot" featured in the December 2006 issue of Nuts and Volts.

I'm very interested in the low weight of the lithium polymer batteries, but I can't seem to find one in the 8.4 to 11.1 volt range in a compact shape which can be hidden in a foam half-ball four inches (4") in diameter. I'd like the batteries to have enough oomph that I can reuse them in different projects, and a circuit protection PCB to help prevent over-discharging and over-charging is very important to me.

Is there a vendor out there who sells reliable, trustworthy batteries?

Thanks

Bob
Krbjmpr
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Post by Krbjmpr »

What you might consider are batteries for cell phones. Most are Lion chemistries, and you can buy external chargers as well. Would save you having to build an external charger. For a higher capacity, though at a larger size, look at the batteries used in small camcorders and digital cameras - there are some Lion chemistries there as well, and the external chargers are a dime a dozen now. Sony is one potential choice, but I think that there is some kind of "enabler" in the pack that has to be turned on before the battery will be allowed to discharge.


Krbjmpr
BobCochran
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Source of Cell Phone or Camcorder Batteries

Post by BobCochran »

Thank you for suggesting cell phone or camcorder batteries. I hadn't thought of this. What is a good source for such batteries?

Thanks

Bob
Krbjmpr
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Lithium Batteries

Post by Krbjmpr »

There are many sources, but there are a couple things that you might want to consider first.
1) do you have a charger already?
2) if not, can you build / buy a charger?
3) what devices do you have now that run on lithium batteries?
4) What are going to be your power requirements?

The batteries themselves are going to be easy to get a hold of. Just goto any mall. Radioshack will sell a selection, as will the cell phone kiosks. Walmart has quite a few, but the best place for selection would have to be Frys Electronics. If they don't have it, then it hasn't been made in last 5 years.

Lets start with #3. If you already have a camcorder / digital camera that use Lithium batteries, you might consider getting the same model of battery. You will already have a charger, and you will have extra spares ready to go when the novelty of the project wears off. You will also be able to see if the battery that you have will work for your project.

#4. These batteries are going to be mediocre in capacity, at least in the class that you are shopping in. Around 1000mAh will be the norm, but don't expect to be able to draw that much current - there probably is protection circuitry built in to the battery assembly itself. Usually, this protection is only temporary, self resettable.

#2 & #1. If you are going to use additional batteries for a device that you have already, then you already have a means of charging the battery. This is a big plus. On the same note, you can buy rapid / fast chargers for 99% of consumer devices on the market. Expect for Sharp Camcorder batteries. BTL-225L is a battery that there is not an external charger for. When I bought the camcorder, Walmart had replacement batteries for a great price. $2.50 each, on clearance. (Regulary $29.99, sort of makes you wonder what their markup is.) I bought about 3 dozen of these things, but there is not an external charger to charge them. The camcorder itself is not able to charge them because it is a different battery chemistry. The OEM cells are 7.2 volts, but the aftermarket cells are 7.4volt. My camera is not able to charge them properly. But, I am able to charge them using a regulated power supply at work, I just set charging current for 100mA, and the voltage is set for 7.5 volts. I doubt that they are getting a full charge, but I am getting excellent performance out of them on my handheld 2Meter radio. I have a way of charging mine, but the point that I am making is that make sure that you have a way of reasonable charging the batteries that you use. 2 batteries x 8 hour charge time =16 hours of downtime between play periods.

I just thought of another choice, but is pricey. Look for replacement batteries for Ipaq, Axim, and other PDAs. At least for the Axims, the deskstand has a slot for charging a second battery. I will see if I can convince the wife to let me open hers up to see if the charging circuitry is present. If it is not, then all that you have to add to the battery is voltage, the circuitry will already be in the battery.
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slamer
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You can try these guys

Post by slamer »

These online stores are reliable for many of your robotic parts needs including batteries

http://www.robotcombat.com/marketplace_batteries.html

http://www.battlepack.com/index.asp
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