Heavy duty electric motors rely upon solenoid switches to operate. The Solenoid Switch (SS) is basically a large power switch operated by smaller switches.

Inside the SS are typically two magnets (yellow in the diagram) that will push a contactor (red in the diagram) upwards, overpowering a spring that pushes it down when the magnet is not activated.

One side operates the ‘up’ contactor and the other side the ‘down’ contactor.

The power being switched is typically 100A or more. This leads to arcing – a small spark being generated between the contactor plates when it is being operated. (See the red spark symbols in the diagram). Over time, this can cause problems leading to malfunctioning. Either the motor (anchor winch) does not operate in one (or both) directions or (even worse) it doesn’t stop operating.

Not operating

In this event, the successive arc sparks have created a coating on the contactor(s) that prevents electric connection. Due to the resistance created by the coating, the contactor can also have become so warm that the plastic around it has melted, creating a ridge that prevents the contact to close properly.

The solution is to disassemble the SS, clean the contactor surfaces (fine sandpaper is best) and/or cutting away the ridge so that the contactor can operate again.

Non-stop operating

In this event, the arc spark has welded the contactor shut permanently. Most likely, there was no time to do anything and the fuse (you have one installed, right?) tripped when the anchor winch tried to work against the chain in one direction or the other.

The solution is similar to the other case – disassemble the SS, pry the welded contactor plates open, clean/sandpaper the surfaces and re-assemble.

Replace the Solenoid Switch

This fix helps for a while but the contactor surfaces are worn. You should get a new Solenoid Switch as soon as possible but you’re up and running for a while again.