The failure of an original equipment solenoid can usually be traced to some condition of the installation itself. These conditions are not overly difficult to spot. With a little practice, you can do your own solenoid troubleshooting.
Standard DECCO coils are rated class 105oC, which means that they can safely reach and sustain temperatures up to 105oC or (221oF) -temperatures hotter than boiling water! Therefore, a solenoid too hot to touch may not be overheated.
Remember, when a solenoid is energized, the coil receives a pulse of high inrush current which decreases as the plunger closes.
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If, for any reason, the plunger does not close, the high inrush pulse continues, and the coil overheats and burns out. This type of coil burnout is the most common cause off solenoid failure. It's easy to spot. Here's how...
When a coil burns out, the bobbin melts and nylon runs into the space under the plunger. If you find melted bobbin material, check to see if the plunger was mechanically blocked open. On a double solenoid valve, see if both solenoids were energized at the same time.
A drop in supply line voltage can prevent a solenoid from closing by reducing its force until it can't overcome the load. Check out the line voltage with a GOOD meter or have the local power company check your line voltage with a recorder over a 24 hour period.
Another thing to check is the ambient temperature. If the ambient is too high, the coil will lose its ability to dissipate heat. Resistance increases, current flow and force are reduced, and the solenoid will not close. Result- coil burnout.
And finally- check the cycling rate. If cycled too fast, heat will build up faster than it can be dissipated.
The solenoid soon becomes too weak to close, receives a continuous inrush current, and burns out.
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In rare cases, a solenoid coil will burn out due to OVERVOLTAGE. The plunger WILL close, because the solenoid has extra force. (You'll find no melted bobbin.) The high voltage causes excessive holding current which will overheat the coil and burn it out.
Another possible cause of coil burnout is SHORTING. Water base coolants often carry fine metallic particles from a grinder or other machine tool. Splashing or soaking can cause shorts between the coil's lead wire junctions.
This "C" stack and plunger were subjected to excessive force for a long period of time. Note the worn copper shading coils and the deep grooves in the "C" stack and plunger laminations. This causes the air gap at the base of the plunger to disappear.
When you put everything together, you get a chart that looks like this.
A solenoid can literally hammer itself to pieces. Excessive force can be caused either by overvoltage or by a reduced load on the solenoid, and must be absorbed when the plunger hits the "C" stack or field. Be sure the solenoid's force closely matches the load.
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