Adding up all of the servos plus the Arduino Mega we plan to use, it's going to be have to be around 4 A of current max, to be safe.
Here's the problem: batteries don't list maximum current output. They have mAh, but that's capacity.
So, I'm contemplating NiMH or NiCd batteries. Would four of these:
in series support 12 servos?
Also, I'm not sure what 2C or 0.2C means. Discharge?
I've also read that NiCds can output more current. Does anyone have numbers?
Sorry about the questions, but I've been worrying about this since we started, and I really don't want to find out after we order parts that the batteries can't run the servos.
Wow those batteries can output 5 AMPS of current, Anyways, they are at 1.2 volts, you would need quite a few, why don't you use a Lead Acid battery?
Say, like this one?
At 12 Amps, They should work Wonderfully, They should be able to power the arduino alone for a bit over a month.
And charging them is very easy, use any 12 power supply with at least 1 amp of current and no more than 3 amps.
Be careful with it though, reverse polarity, and your arduino is fried, along with anything else, these batteries are serious business.
The thing that determines the maximum current from a battery is its "internal impedance". Its like a built in series resistor that limits the current / voltage when an external load is applied. Try googling for this or see:-
Ah. I think I see. When more load is put on a battery, voltage drops. If you demand too much current, the voltage drops to a level you can't use. So if a 1.5v battery is rated at 5000 mAh, it could output 5A continuously for an hour, at 1.5v. But if you demand 10A (2C), it's voltage would drop, maybe to around 1.2v.
I'd love to use a lead acid battery, but it's almost 4kg :o. We'd like it to be really light. I've done some calculations for how much the servos will be able to support, and though I can't remember the exact numbers right now, I'm pretty sure this is too heavy.
Thanks so much for the help, but now I have another question. How would wiring an external power supply to the arduino mega work? Do I plug the + and ground into the headers, or do I have to buy a 2.1mm plug?
Edit:
Can NiMH batteries work at 1C? That's all I really need. Maybe I should use NiCd?
Do I plug the + and ground into the headers, or do I have to buy a 2.1mm plug?
External voltage (if greater then around +7.5vdc) and be either plugged into the external power 2.1mm jack on the board or the Vin pin and a ground pin on the header connector. The external plug into adds an advantage of having a polarity protection series diode.
If you demand too much current, the voltage drops to a level you can't use.
And/or the cell gets hot enough to destroy itself! Short out a high-capacity cell with low internal impedance, and it's like a stick of dynamite going off.
NiCads are my favorite choice for these applications. They're cheap, easily available, durable, not picky about charging, relatively compact, relatively high capacity, and can stand wickedly high currents (some can take 100A in short bursts, your 4A draw won't be a problem at all.)
Thanks for all the advice! I'll look into NiCads some more.
With some further research, I've found that Tenergy isn't exactly a good company to buy batteries from. So: anyone have any suggestions for a good NiCd company and place I can buy it?
Edit: I didn't see retrolefty's message. I broke my Illuminato because of reversing the + and - on a 9v. I think I'll just get a plug.
