Electronic – arduino – Solenoid Operation for Hours


My boiler is connected to a sun-water-heating system. After the sun goes down this system start to draw heat from my boiler.
Today I'm manually closing the valve connecting my boiler to the system.

I'll like to build system based in Arduino that will operate a solenoid that will open and close the valve.

The solenoid will probable by normally-closed and I'll open it only when sun is up which is a few hours every day.

I remember reading somewhere that solenoid should be operate for short time, is that true?
Can I leave the current on for say 6 hours to keep the solenoid open?
Is there a better way?

Best Answer

There are a couple of solutions to this. The first is to use a specially designed latching solenoid. These typically have a permanent magnet in them so that they can hold in position without power. It's probably the simplest way.

However, you may still be able to use a regular solenoid depending on its design. The force the solenoid exerts is basically proportional to the 1/displacement (though this relationship can be adjusted by shaping the magnetic pole pieces). This means that when the solenoid is disengaged it requires a lot more current to provide the same force to the plunger than when it is fully engaged. Depending on your load and the force-displacement characteristic of the solenoid, you may not need the maximum holding force to keep the solenoid engaged. This means you can reduce the current and hence the amount of heat dissipated in the solenoid coil. If this amount of heat is within a range that can be continuously dissipated by the solenoid then there will be no issue doing this for a long time.

It is quite common in solenoid circuits to have this sort of force/current reduction mechanism, and if you have a well defined load, you can simply reduce the current after a fixed timeout.