battery packs - parallel or serial?

[pduncan]

my current robot project has 4 servos for the drive wheels, a handful of other sensors, etc.  If my information and calculation is correct, the power drain is around .5A.

I want it to be able to run for extended amounts of time so I went heavy (kinda) on the battery.  I picked up two 7.2V 1400 mA batteries from Radio Shack.  They are normally used in remote control cars.

Currently I am only using one of the batteries.  It is connected to a Dimension Engineering 5V switching regulator because I was concerned about heat/battery waste.

I would like to use the second battery and now am wondering about what the best configuration would be.  I have been told that since I am using a switching regulator, connecting the batteries in series would be optimal.  This would also be helpful for recharging purposes.  From what I learned in college (forever ago) I was planning on connecting them in parallel, but then again, back then all we covered were linear, not switching.

Also - aside from leaky batteries from overcharging, what are your feelings about "in chassis" battery charging.  I was planning to incorporate I plug into the power board that I could use to connect the charger.  I thought a toggle switch could be used to change modes from "run" to "charge". 

Any suggestions or tips on how best to connect the batteries (series or parallel) to the switching regulator would be greatly appreciated.

Thanks,

pduncan
Memphis, TN

[ed1380]

connecting them is series will double the voltage. the regulator might not be designed for 14v.
paralllel will double the battery life.

i've never heard of switching regs being better w/ series vs parallel, but then again im still a noob

[Admin]

You don't want/need to regulate voltage to motors, only your electronics. The lower the voltage going into a regulator, the higher the efficiency.

The dimension engineering switching regulator has some useful datasheets on voltage worth checking.

aside from leaky batteries from overcharging, what are your feelings about "in chassis" battery charging.  I was planning to incorporate I plug into the power board that I could use to connect the charger.  I thought a toggle switch could be used to change modes from "run" to "charge".

Sounds fine to me, unless your charger is really heavy or takes up a lot of space.

This should help you out a bit:
http://www.societyofrobots.com/batteries.shtml

Be sure to try out the calculators.

[pduncan]

I was going to do that but since I am using servos and not DC motors, their max voltage input is 6V.  My batteries are rated at 7.2

[omar1991]

hi
I would suggest you to go to towerhobbies.com and buy an NiMH 4200mah battery pack or just build your own pack from Duracell  2650 NiMH
AA batteries.





have good luck

[bukowski]

you wont have any problem running your servo's at 7.2V