1. ## BATTERIES BATTERRIES BATTERIES!!!!!!!!

Providing power to my robot is really getting on my nerves , I have been searching far and wide for the battery i need but so far all i have found are batteries which are way below my requirement...

My robot has the following power draw

2 dc motors rated at 12v 550 ma
1 servo rated at 1A
the controller board

so i need a battery pack which should have the following ratings

12v, 1700 mah battery pack min

so any of you having any idea where i can find this battery pack and its equivalent charger then please do post in this forum ...

****please do not post abt international shipments as it will be way above my budget, please give a more indian base solution :wink:

2. You dont necessarily need a battery pack with 1700mAh+
There is a difference between the Ah rating of a battery and the maximum discharge current (usually rated something in terms of C i.e. 5C, 10C) of a battery.

The mAh rating of a battery decides the run-time of the battery whereas the discharge current capacity is the crucial factor which decides how much maximum current will the battery be able to supply without dropping much voltage (or getting loaded). This depends on a lot of factors including the chemistry of your cells and the internal resistance.

In your case, you say your total current consumption is 2200mAh. Now, a battery with a lesser mAh but a higher discharge current, say 700mAh and 5C (700 x 5 = 3500mAh) will serve your purpose while another battery, say 1700mAh and 1C will not.
In general, lead acid batteries provide a much higher discharge current than others. Ni-Mh, though mostly preferred, do not usually have a higher discharge current. So you might see them getting loaded easily. Li-ion/Li-poly are in general difficult to handle, but most of them are rated for a higher discharge current capacity.

Another important point, the mAh are hugely misunderstood. We generally assume a battery rating of say 1700mAh means a continuous discharge of 1700mAh for one hour. THIS IS NOT SO! The complete battery rating is 1700mAh over 20 hours. This basically means, that the battery will be able to provide 1700/20 = 85mAh continuously for 20 hours. If you try to discharge them at 1700mAh, you ll find that they ll get discharged in a much lesser time.

Sorry I couldn't help you regarding the actual batteries to buy. But I hope I have given you enough pointers to make a better choice.

3. @ ppppking04
We generally assume a battery rating of say 1700mAh means a continuous discharge of 1700mAh for one hour. THIS IS NOT SO! The complete battery rating is 1700mAh over 20 hours.
can you explain why it is 20 hour. is it empirical, or dependent on batteries.

@superchiku
you can use Ni-Mh cells use for digi cams and club to make it a battery

or try with these http://triindia.co.in/shop/product_i...products_id=60

4. lead acid batteries will be quite bulky for my application so i cant go with them

do u have any other alternatives.. please specify

suppose i use nicd batteries at 700 mah that are available in the market, will they be able to provide sufficient power??

5. Nicd - put them in parallel. but then you need 12 V - which means you will need 10 of them, and 20 of them if you put it in parallel.

or, use Li ion.. its available with robokits. etc, , but then you might need to get a charger. (You can charge at home, but yo should be able to monitor the current., and you should know what you are doing...
)but the good thing, is, you need only 3 of them to get your 12V - good in terms of weight, & performance.

I have been using them, and will be using them, till i get my Lipo s.

6. the problem remains with the charger , i need the charger do u have any products where i can get both the battery and the charger

7. so anybody know where to get the equivalent battery charger for the new 12.6 v 2000 mah li-ion battery available in robokits.org ???

without the charger there is no use buying the battery...

8. http://www.linear.com/pc/productDeta...78,C1089,P1495

use this charger from linear technology. It can charge any number of cells up to 30v.

Unlike TI's BQ2057 it's even available in 8 PIN DIP. So you can easily use it in ur PCBt.

9. cool.. but still there are problems

10. the problem is that its quite difficult to get a 25v wall adapter nad the inductor coils from coltronics also when it says 30 v it meant fot NimH or NIcd not for lithium ion coz you can see in the graph that the charging voltage graph for a 2 cell 8.4 volt lithium-ion battery is given , so thats the problem...

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