Question regarding inductors and air coils

Thread Starter

ECM

Joined Jan 3, 2009
7
Hello,

Having a heated discussion on a different forum about irrigation valve solenoids and air coils.

We are discussing what the importance, if any would be to coiling the leads of wire in a irrigation valve box before hooking it to the solenoid.

My theory and others is that you make an air coil to stop a charge from lightning and static electricity from destroying the solenoid. Others say that the inductance of the air coil is so small that there would be no benefit in this application.

There are usually three coils or more in each box. The hot wire that is comes from the controller has one. The common wire has two or more coils in series, one where it comes in the box from the controller, the other where it leaves the box on its way to the next box. The same is happening in the next valve box and the next and so on. So it is possible to have many coils in series on one line increase the total inductance to do any good?

If so do you have any theory behind it.

Thanks in advance.

 

Thread Starter

ECM

Joined Jan 3, 2009
7
A paving slab placed over the box would give you better protection.
I'm not talking about a direct hit of lightning on the valve box. If that is what your thinking the paving slab would be for.

I'm talking about transient voltage carried down the wire from a strike near by.
 

studiot

Joined Nov 9, 2007
5,003
Sorry if I misunderstood.

I can't see your coils of wire have more than token inductance. Certainly not sufficient to slug a lightning induced surge. The surge would probably jump the coils anyway.

In any event inductors are energy storage devices, they eventually give back this energy. Surge arrestors divert it to earth, hopefully safely. Inductive ones are based on a Pi filter to provide this path to earth. Power and telephone lines are protected by arrestors with kilovolt breakover ratings that short to earth on overvoltage. These are like fuses and must be replaced after thay have fired.
 
Last edited:

duffy

Joined Dec 29, 2008
44
Need to know more about the coils - how big are they, and how are they positioned in relation to each other?

Also - does the solenoid have a diode connected across the terminals?
 

Thread Starter

ECM

Joined Jan 3, 2009
7
Need to know more about the coils - how big are they, and how are they positioned in relation to each other?

Also - does the solenoid have a diode connected across the terminals?
No diode just the coils. They are usually just made by wraping the wire around a piece of 1" PVC pipe 8-10 times or so, and are lying loosly in the box.

Here is a picture. Click on it to make it larger so you can see more detail.
MVC-007S.JPG
 

Bernard

Joined Aug 7, 2008
5,229
Looks like the coils are just there to use up some wire. A MOV ,20 J @ 160V across each coil should do.A bigger one,or two, across 120-240 V mains also good idea. MOV, metal oxide varistor.
 
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