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I am trying to find the optimum electrical design for my project.

The project is a remote control vehicle that is moved by 2 DC motors, controlled by an arduino MC and powered by 2 X 12V 4Ah batteries.

Motor 1: 24V, 200watt, rated current- 14A. Motor 2: 24V, 10watt, 1A

To control the speed of each motor I bought a Dual DC driver module. http://www.ebay.com/itm/3V-36V-Dual-Motor-Driver-Board-Module-H-bridge-DC-MOSFET-IRF3205-15A-Peak-30A-/171205708868?hash=item27dca7cc44:g:JKEAAOSwR0JURgQC

For testing I have been running the motor driver and arduino off separate sources. But the vehicle needs to run everything off the 2x12V batteries.

I know I need to drop the Voltage down for the arduino, but I don't know the best way to do it. I don't want to be wasting power, as the vehicle needs to travel a specified distance therefore power efficiency is important.

Note: I thought maybe to tap off from one of the batteries so that I am only dropping from 12V, more research stated this will cause unequal battery power and is not a good option. Is this correct?

Any suggestions are greatly appreciated. I am unsure of noise and filtering so any insight here would be much appreciated too.

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  1. Powering the 'duino off of a single 12V battery, with other parts powered from the 2 batteries wired in series, would cause an imbalance of charge between the batteries. Whether or not this imbalance would be "enough to worry about" could be debatable in this instance (due to the difference in total consumption between the arduino & the motors).

  2. Luckily, if peak efficiency is the goal, #1 isn't something that needs considered.
    While a resistive voltage regulator would run more efficiently from a 12V supply, a dc-dc converter, or switched-mode power supply (SMPS) can run just as efficiently from the 24V "system power" for the motors.
    In this instance, I would recommend looking into a single-inductor [buck converter] topology.
    Here's one I found in a quick Google search, for under $2USD, that's rated for up to 3A output current, with an input voltage range up to 28V.

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  • \$\begingroup\$ very clear thanks, and in terms of wiring, it's fine to run the driver and buck converter in parallel, I'm quite new to visualizing the flow of current and get the impression that when the motors are put under load/stall and draw current, is there any chance of the buck converter and arduino getting surged? \$\endgroup\$ – KiwiOnTheShore Mar 10 '16 at 1:12
  • \$\begingroup\$ @KiwiOnTheShore If the motor drivers don't have any protection against inductive spikes backfeeding into the power supply when the motors start/stop, you should probably put a few zener/tvs protection diodes between the buck converter's power pins & the motor controller's power pins, to clamp any back-spikes that might try to hit you. Also, a couple good-sized (>=1mF) reserve caps across the buck converter's supply pins will help buffer the voltage drop when the motors first start up. \$\endgroup\$ – Robherc KV5ROB Mar 10 '16 at 1:55
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Sounds like you need a voltage regulator. They take an input voltage range (like up to 24 V) and output a fairly steady voltage (like 3.3 V). Digikey has over 50,000.

http://www.digikey.com/product-search/en/integrated-circuits-ics/pmic-voltage-regulators-linear/2556290?k=linear%20regulators

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    \$\begingroup\$ Linear regulators, while highly stable, are also highly inefficient, as they simply "burn off" all the input voltage above the desired output voltage. stepping 24V down to 3.3V through a linear regulator would give a max efficiency of 13.75%. Since the OP posted that efficiency was a primary concern (not to mention the added weight/space needed to dissipate all that waste heat), I don't think a linear regulator is a "good fit." \$\endgroup\$ – Robherc KV5ROB Mar 9 '16 at 5:09
  • \$\begingroup\$ Fair enough, but when dealing with a few milliwatts compared to driving 200 W, the simplicity might be worth it. Either way I would say a regulator is something you should use with a microcontroller anyway for protection. \$\endgroup\$ – Swarles Barkely Mar 9 '16 at 13:02
  • \$\begingroup\$ A well-built SMPS, with sufficient filtering is perfectly acceptable. You only really need the added stability of a resistive Vreg when you're needing to improve the accuracy of sensors or an ADC (or if you're using data frequencies close enough to the SMPS operating frequency for the noise to cause corruption, such as RF/IF/audio circuits). Even in many of these applications, however, high-pass/low-pass filtering on the SMPS output is often sufficient, and more cost &/or energy efficient. \$\endgroup\$ – Robherc KV5ROB Mar 9 '16 at 14:24

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