120v solenoid coil resistance will vary depending on the model of the solenoid. Therefore, it is best to test an identical coil’s resistance. You could test a new solenoid or one that is working. You will become familiar with the resistances of coils in your facility over time.
Should a Coil Have Continuity?
Coils require continuity to work properly. When a coil doesn’t have continuity current cannot flow. Because of this, a magnetic field cannot be created. Your multimeter’s continuity tone may or may not sound depending on coil resistance.
How Can You Tell If Your Solenoid Is Bad?
You can tell if a solenoid is bad by completing a few tests.
Manually actuate the valve. If the valve doesn’t work manually, check system pressure. A valve with proper pressure that doesn’t work should be replaced. If the valve passes this test, move on to the next check.
Now check the coil resistance. Shorted coils have very low resistance. For example, one to five ohms. Coils with higher than normal resistance may not function properly. Higher resistance means less current to move the spool. If resistance checks out move on to voltage tests.
Next, use an electrical tester to check the voltage. The voltage should be within the nominal operating range. For instance, 120v AC ASCO valves operate between 102 and 120 volts.
An incorrectly wired coil may pass these tests. Additionally, a problem may exist somewhere else in the system.
What is the Resistance of a Solenoid Coil?
The resistance of a solenoid coil is created by the turns of wire in the coil. Engineers design coils with different resistances to accomplish the required tasks. For instance, a 120v Schrader Bellows valve solenoid that I work with is around 120 ohms. Additionally, our 24v cartridge-style proportional valves are 26 ohms.
You can compare the resistances of different coils to become more familiar with them. Of course, this isn’t always possible but over time you will learn what is normal.
Is that Solenoid Good?
You’ll hear this often in manufacturing facilities. So knowing how to effectively troubleshoot solenoids is critical. I’ve head many millwrights say, “the valve works manually so it must be electrical!” Then I start troubleshooting and discover the valve’s internal solenoid is bad.