Solenoid Tutorial

Posted on Feb 5, 2014

Not drive a solenoid directly from your Arduino. It requires more current than you can provide and produces destructive voltages when it is switched off. There is a simple solution. The solenoid I was testing with is a 12 volt solenoid the size of my thumb. It passes 1 amp of current when turned on and becomes uncomfortably warm to hold if

Solenoid Tutorial
Click here to download the full size of the above Circuit.

left on. Your Arduino can only pass about 40mA from a pin. You probably will need to measure your solenoid before you can choose components. Use your ammeter to measure the solenoid`s current draw when you power it directly from the power supply. A solenoid is a coil of wire with a magnetic core. This is virtually identical to a large inductor, so it should not be surprising that they have inductance. i. e. Once a current is moving in the solenoid it will attempt to continue moving that current. This can be fatal to your digital device when it switches off the solenoid and the solenoid creates a voltage across its leads large enough to either move the current, arc through the air, or burn through a semiconductor. The solution is to provide an easy and safe path for the current to flow until it dissipates the energy stored in the magnetic fields of the solenoid. Most of the schematic is test point labels and my extra protection circuitry for testing the bad configurations. You really only need D1, L1, Q1, and a resistor to be named later. The schematic shows a bypass diode, D1. When the solenoid is on or idle this diode will not conduct. Its top terminal will be at a higher or equal voltage. When the solenoid is turned off and tries to continue forcing current downward, this current can flow back up through D1 until the energy is dissipated. This will clamp TP2 to no more than 13v or so. This diode must be able to pass...

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