I am building a Mearm robot using an Arduino to control it. The kit came with 4 servos which are rated at 5v. The Arduino doesn't output enough power to power all 4 servos so it suggests buying an external power supply.

I did this, my power supply outputs 5v and when I measure on my ohmmeter it says it's outputting 3.3 amps. The problem is I connect the live and ground servo wires to the positive and negative pins on the power supply and the control wire to the Arduino and nothing happens apart from a very small sound from the servo. I think I also blew one up trying this as now it doesn't even work from the Arduino.

They all worked perfectly when powered from the Arduino which output5 5v also, but only 0.3 amps when I measured it. I thought the current didn't matter if the voltage was correct? Am I blowing them up because of too much current?


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    \$\begingroup\$ Did you connect both grounds together? You have to so that the servo has a reference for the Arduinos signal. \$\endgroup\$ – Wesley Lee Feb 6 '17 at 14:16
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    \$\begingroup\$ Thank you! I just connected both grounds and it began working, although the servos moving much faster and aggressively than before, even though I dint change the delay in the Arduino program. I guess underpowered before? Don't understand about the ground reference, been many years since I studied electronics so going to look it up! \$\endgroup\$ – Si-N Feb 6 '17 at 14:41
  • \$\begingroup\$ Yeah. Most likely with one servo being attached to your Arduino it was dragging the voltage output down to a level closer to 4.5V or even 4V or so. The Arduino may have been able to function at that voltage but the servo would be starved for power to operate at full rated performance. \$\endgroup\$ – Michael Karas Feb 6 '17 at 15:45
  • \$\begingroup\$ @Si-N the servo was only being powered through the Arduino port pin if the ground was not connected. \$\endgroup\$ – Spehro Pefhany Feb 6 '17 at 16:02
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    \$\begingroup\$ I hope you weren't measuring the current output by just putting your meter across the power supply while set to current measurement! If you do you are shorting the output of the power supply and you can damage the supply, the meter or cause a fire. You only put the current meter in series with a load to measure the current being consumed - it is not possible to simply measure the current capability of a supply. Look at the label on the supply or a data sheet. \$\endgroup\$ – Kevin White Feb 6 '17 at 16:28

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