Powering Arduino and a Motor Shield using 2 separate DC power supplies

Hi all,

I am struggling with my project and have a few questions.

I have two “Venom 6v 3000mAh 5-Cell Large Scale Receiver NiMH” batteries. I am planning on using one to power an Ardunio Uno, and the other to power the motors for an RC tank I will be making (two 6V motors).

I have included a list of parts I am using at the bottom of the post and their links just in case

My question is, would this be possible using the two batteries I have?

I am very confused with the connections of the pins from the power supplies to the arduino and to the motor shield.

If I understand correctly, one power supply goes into the Vin and ground of the arduino and the other power supply connects the the “EXT_PWR” + and - terminals on the motor shield.

The shield basically uses up all the pins that the arduino provides. Does the motor shield use power from the “5V” pin in addition to the external power that I will provide to run the motors?

Thank you in advance.

-----supplies list-----

SainSmart L293D Motor Drive Shield

Two Venom 6v 3000mAh 5-Cell Large Scale Receiver NiMH Batteries

Two Brushed DC Motor: 130-Size, 6V, 11.5kRPM, 800mA Stall

motorshieldconnectionprediction.png

With a 6 Volt battery connected to Vin of the Uno you are operating at the lowest edge for input power to the regulator. Perhaps you missed this paragraph under Products overview for Uno:

“The board can operate on an external supply from 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may become unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.”

Thank you, any suggestions?

One possible suggestion would be to put both batteries in series for 12 Volts, get a buck switcher DC - DC converter set for 7 Volt output and supply 7 Volts to Vin on the Uno and 7 Volts to the motor shield. The 293D output stages are bipolar transistors and will probably lose half a volt or better driving the motors. Put a Large Electrolytic cap on the 7 Volt rail to prevent Voltage sags when the motors start up.

Another suggestion would be to use one Venom pack for the motors and make up a 7-8 Volt battery pack from AA NiMh batteries for the electronics. Use the second Venom pack as a quick replacement when the bot starts running slow.

An L293D is old technology.
That chip "looses" ~2.5volt in the H-bridge with 600mA motor current (see datasheet).
You will get 3.5volt on the motors if you use a 6volt battery.
Leo..

I second the idea of stacking the batteries, to obtain 12V for the motor driver board.

Then connect the batteries to the motor driver board, and from there to the Uno Gnd. The positive battery pin can be routed through a small (10 Ohm) resistor and fat cap to the Uno Vin, to reduce the power waste in the on-board regulator. More efficient were a step-down regulator from 12V to 7V. The resistor value can be optimized for the current consumed by the Uno and attached 5V devices. It must be powerful enough for the voltage difference (5V) and total Vin current.

DrDiettrich:
I second the idea of stacking the batteries, to obtain 12V for the motor driver board.

Then connect the batteries to the motor driver board, and from there to the Uno Gnd. The positive battery pin can be routed through a small (10 Ohm) resistor and fat cap to the Uno Vin, to reduce the power waste in the on-board regulator. More efficient were a step-down regulator from 12V to 7V. The resistor value can be optimized for the current consumed by the Uno and attached 5V devices. It must be powerful enough for the voltage difference (5V) and total Vin current.

Thank you for your input. If I were to use this method, do you think the current that the motors draw would affect the Arduino Uno in any way? Also, is a fat cap another way of saying a large capacitor? What value capacitance do you think?

Thanks again

Due_unto:
One possible suggestion would be to put both batteries in series for 12 Volts, get a buck switcher DC - DC converter set for 7 Volt output and supply 7 Volts to Vin on the Uno and 7 Volts to the motor shield. The 293D output stages are bipolar transistors and will probably lose half a volt or better driving the motors. Put a Large Electrolytic cap on the 7 Volt rail to prevent Voltage sags when the motors start up.

Another suggestion would be to use one Venom pack for the motors and make up a 7-8 Volt battery pack from AA NiMh batteries for the electronics. Use the second Venom pack as a quick replacement when the bot starts running slow.

Thanks for the reply, would you recommend possibly making a buck switcher DC - DC converter myself? Also, would you by chance know if I have to remove the 5V jumper on the motor shield in order to power the motor shield "separately" (By "separate" I mean from the 7V rail).

Thank you

belae1ka:
If I were to use this method, do you think the current that the motors draw would affect the Arduino Uno in any way?

As long as the motor currents runs over separate lines, they won't affect the Arduino. They may affect the battery voltage, though. that's why:

Also, is a fat cap another way of saying a large capacitor? What value capacitance do you think?

Yes, a capacitor of at least 100µF.

belae1ka:
Thanks for the reply, would you recommend possibly making a buck switcher DC - DC converter myself? Also, would you by chance know if I have to remove the 5V jumper on the motor shield in order to power the motor shield "separately" (By "separate" I mean from the 7V rail).

Thank you

As best as I can tell from the Adafruit schematic for the same board, the Berg jumper just above the power connector will direct the input power to the Vin pin of the Arduino to supply the Arduino onboard regulator with power from that source. The Arduino +5 pin provides logic power back to the shield. If you remove this jumper you will have to provide a power source to the barrel jack or Vin for the Arduino. With the jumper in or out you still have to provide power to the shield through the power connector.
As for making your own DC-DC converter, they are much too cheap on eBay or Amazon to bother.

Due_unto:
As best as I can tell from the Adafruit schematic for the same board, the Berg jumper just above the power connector will direct the input power to the Vin pin of the Arduino to supply the Arduino onboard regulator with power from that source. The Arduino +5 pin provides logic power back to the shield. If you remove this jumper you will have to provide a power source to the barrel jack or Vin for the Arduino. With the jumper in or out you still have to provide power to the shield through the power connector.
As for making your own DC-DC converter, they are much too cheap on eBay or Amazon to bother.

Thank you so much, you have been great help!

DrDiettrich:
As long as the motor currents runs over separate lines, they won't affect the Arduino. They may affect the battery voltage, though. that's why:Yes, a capacitor of at least 100µF.

Thanks man! really appreciate the help!