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schematic

simulate this circuit – Schematic created using CircuitLab

I had a very simple circuit that used a mosfet with an arduino to power a motor. The whole thing is run off of a 12v supply (5v reg. added to supply power to the arduino). The circuit was working fine before (a few months ago), but when I tried turning it on today, the motor wouldn't start. Here are my findings:

Multimeter says the motor wires (w/o motor connected) are in fact getting the needed 12v, but it drops to under a volt when I reconnect the motor.

I tried connecting my motor directly to the 12v supply, but it just made a big spark (I am not sure if the motor actually started, but it should not have sparked the way it did).

Nothing 'smells' like it is burned out, and nothing got abnormally hot. Does anyone have any idea as to what could have happened (I used the same PSU as before).

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  • \$\begingroup\$ If the motor is not working when powered directly (I assume it is DC motor, isn't it?)- it is dead. What is the question here? \$\endgroup\$ – Eugene Sh. Jun 24 '15 at 20:08
  • \$\begingroup\$ I tested it with two motors (same model bought at the same time). Neither of them work, so I doubt it is that. \$\endgroup\$ – electricviolin Jun 24 '15 at 20:11
  • \$\begingroup\$ How could it be anything else? The motor doesn't do anything when connected to power! \$\endgroup\$ – Nick Johnson Jun 24 '15 at 20:12
  • \$\begingroup\$ What are these motors? Are they DC? Brushed? \$\endgroup\$ – Eugene Sh. Jun 24 '15 at 20:13
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    \$\begingroup\$ You should have a flyback diode. It may be that your mosfet has been fried and is acting as a largish resistor. Try measuring the resistance between the source and drain of the mosfet when it is turned on. It should probably be < 1 ohm.. \$\endgroup\$ – avl_sweden Jun 24 '15 at 20:35
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There is nothing in your circuit that should age while in storage.

In fact, those components would typically have a very long life even under load.

Some components, such as batteries and capacitors, can age while being stored, especially if stored in a hot location.

The lubricant in the motors would age slightly, the metal might corrode in an aggressive environemnt, and dirt could aggregate in the moving parts, but unless they've been stored in an extremely aggressive environment, the answer to your question is simply no, a circuit doesn't stop working just because it hasn't been used for a long time, not even the motors.

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