I am extremely puzzled on how to power my robot correctly. I would like to use 6 rechargeable aa batteries, 1.2v and 1300mAh each, to form 7.2v to power it (since it is what I have purchased and have a battery holder for). Here is the schematic: enter image description here

The l298 motor driver wants anything from 7v to 24v. Can I hook the battery supply (7.2v) straight to the arduino and l298 without overheating or any other issues? If i cant (hopefully I can) can someone point out what I have to do instead? thanks.

  • \$\begingroup\$ What is the motor DCR? It better be a lot more than 1 Ohm the approx ESR of the L298. If the DCR is less than 1 Ohm, then thermal issues are possible at max load. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 24 '16 at 22:10
  • \$\begingroup\$ Yes. Next question? \$\endgroup\$ – Majenko Aug 24 '16 at 22:13
  • \$\begingroup\$ If the Motor DCR is say 1 ohm and the bridge has two ~ 1 Ohm , there will be torque loss from 7.2V with a drop to 5V or less. Then AA batteries also have an ESR which is much higher than LiPo 3.6 V 16850 cells. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 24 '16 at 22:19
  • \$\begingroup\$ No, that won't work very well. You asked this already, it was migrated to arduino.stackexchange.com/questions/28678/… and answered. So this is really a duplicate. \$\endgroup\$ – gbulmer Aug 24 '16 at 22:46
  • \$\begingroup\$ What are the specifications of the motors? \$\endgroup\$ – gbulmer Aug 24 '16 at 23:01

The main issue is the voltage drop for the vin regulator for most Arduino's is 2V or more.

A 6xNiMh battery supply is a nominal 7.2V, but quickly drops below 7V, before it is even half exhausted. The 1300mAh rating might assume the voltage of each cell drops to under 1V, maybe as little at 0.9V, which is under 6V for 6 cells.

So those batteries will quickly drop to a point where the Arduino's voltage regulator doesn't have enough voltage headroom to operate reliably.

Worse, because they are low capacity, they are likely to have quite a high internal resistance, so when the motors are pulling current, the battery pack voltage will drop even sooner.

I think your best approach is the one commonly used by people making simple robots, use two battery supplies:

  • Use a 9V supply (or 8.4V NiMh) PP3 for the Arduino barrel-jack or vin
  • Use whatever makes sense for the motors, directly without a regulator
  • 5xNiMh might be okay for servo's, or 4xNiMh may be better, depending on the servo, again directly without a regulator.
  • Join the ground (battery -) together, and connect to Arduino GND

You haven't told us what the specification of the motors are so this might be even simpler, and the motors might operate at the same voltage as the servo.

One approach for jetting multiple voltages for the servo and motors is to make your own battery pack. Make a connection at 6 cells, for the motors, and another connection at 4 or 5 cells (depending on the servo). This should avoid needing a regulator for the servo or motors, which take larger current.

Post Edit:
If you can afford it, get something better than the L298D. It drops (wastes) a minimum of 1.8V at 1A, and a typical (more likely) drop of 2.55V at 1A. Worse 2A could be as bad as 5V, leaving only 2.2V to drive the motors! With something better, with a lower voltage drop, or low resistance, you could use one or two fewer NiMh cells, and still have the same voltage to drive the motors.

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