I'm working on a servo project. I connected 12 servos to a single Adafruit servo shield and plugged in a 5V 10 amp (http://www.adafruit.com/product/658) switching power supply to the shield. Instantly, the motors became very hot and one of the motor became unresponsive.

What could be the reason for this? The only rational reason would be that a large amount of current went through the motors but physically how could this happen? I thought V = IR, since voltage at 5 V, then current should have been divided evenly across the motors so it would have been very small?

  • \$\begingroup\$ How were the motors connected? In parallel? In series? \$\endgroup\$
    – Xcodo
    Sep 15, 2014 at 16:06
  • \$\begingroup\$ Looking at the picture on the servo shield (vetco.net/catalog/images/VUPN5788-1.jpg), the protruding pins in the middle was where the motors were connected, one column is a single motor so I guess all were connected in parallel \$\endgroup\$
    – Fraïssé
    Sep 15, 2014 at 16:08
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    \$\begingroup\$ Posting a schematic / drawing / photo of what you wired up plus specifying which motors you used would go a long way towards helping you get answers. \$\endgroup\$ Sep 15, 2014 at 16:10
  • \$\begingroup\$ Also, specifying which power supply you used will help with that part of the question. \$\endgroup\$ Sep 15, 2014 at 16:12
  • \$\begingroup\$ A trivial answer is the servos are wired up incorrectly, a more sophisticated answer is some Arduino pins driving the servos weren't generating PPM pulse, and the servos "didn't like it". So please post your code as well as something showing the way the servos are connected to the shield. (and a part number or link to the switched power supply, in case that contributed something) \$\endgroup\$
    – gbulmer
    Sep 15, 2014 at 16:39

1 Answer 1


(EDIT: This answered OP's original title question, which was "What happens if you use a load that exceeds the maximum regulated current output from your power supply?")

As for the power supply overload question, it depends on the power supply. Some behaviours include:

  • latching the output off
  • reducing the output voltage while keeping the output current constant
  • hiccupping (switching the output off and on)
  • going into thermal shutdown with autorecovery
  • blowing a fuse
  • blowing up

It will all depend on the power supply itself and the nature of the overload.

  • \$\begingroup\$ What "power supply overload question"??? Quite clearly, it is not that the supply has been overloaded, but rather that the servos have consumed more power than they are designed to. \$\endgroup\$ Sep 15, 2014 at 21:40
  • \$\begingroup\$ The one that was originally there before OP edited the question. Maybe you don't have the reputation to see the history of the question. The original title was "What happens if you use a load that exceeds the maximum regulated current output from your power supply?" \$\endgroup\$ Sep 16, 2014 at 1:17
  • \$\begingroup\$ Ah, I only focused on there having been no substantial edits to the question body. \$\endgroup\$ Sep 16, 2014 at 15:04

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