# Neat windings vs sloppy windings for Solenoid Actuator?

Hello,

I am a hobby machinist and also an EE PhD student. Recently I have been trying to make powerful solenoid actuators. I have succeeded, but they aren't perfect. I really want to make a professional, powerful solenoid. To give a sense of how deep I am going, here is what I have found so far by trial and error. (My question is at the end)

1. The solenoid must be in a housing of high permeability (in my case, I chose cast iron) so that the magnetic flux has a small reluctance and therefore increases the inductance of the solenoid and therefore the force. The plunger must also be high permeability.
2. The tolerance between the plunger and the housing must be as small as possible, as the smaller the gap the smaller the reluctance and greater the force.

What I DON'T know, is how does the neatness of the windings come into play? Do they? What I mean by that is, if I were to wind the coil very neatly, laying one wire right next to the other perfectly, does that make a difference? How? What I have been doing is making my spool on the lathe, and then just winding the wire around the spool (semi) randomly while the lathe is on.
My other question is, what is a good source to read about solenoid actuator engineering? I found some design equations online, but I would rather have a rigorous mathematical analysis.

## Answers and Replies

Nidum
Science Advisor
Gold Member
The solenoid actuator is an extensively researched and very well understood mechanism . There is extensive design information available in books and on the internet . There are also FEA programs which can be used to model proposed designs .

Anyway :

(a) Cast iron is not the best material to make solenoid parts from .

(b) The neater the windings the more windings you can get in a given space .

(c) Random windings and especially windings with gaps and isolated single turns will be prone to hot spots and premature failure .

(d) Random windings tend to be unstable and to move around when energised . This can cause abrasion and premature failure .

(e) The design of the magnetic path is critical for successful design .

(f) Many solenoid actuator manufacturers now use multi coil sections rather than one long coil . The coils being packet switched so as to optimise pull .

(g) One step further on is the linear motor based 'solenoid' actuator .

Why does someone with your educational background need any help with this ?

Thanks for your reply!

The solenoid actuator is an extensively researched and very well understood mechanism . There is extensive design information available in books and on the internet . There are also FEA programs which can be used to model proposed designs .

Yes, I figured as much. However I am having a hard time finding a good book to use. Perhaps I am not searching for the right key words. That is why I am asking for other who have learned about this formally for advice on where they learned it from. What I am looking for is to start from scratch and derive design equations.

(a) Cast iron is not the best material to make solenoid parts from .
Yes I know, but it is the easiest for me to get. Soft iron and other kind of materials are difficult to find. At least for me. I can't seem to find a distributor that sells these kinds of materials in the dimensions I require.

(b) The neater the windings the more windings you can get in a given space .

(c) Random windings and especially windings with gaps and isolated single turns will be prone to hot spots and premature failure .

(d) Random windings tend to be unstable and to move around when energised . This can cause abrasion and premature failure .

(e) The design of the magnetic path is critical for successful design .
Great! I haven't thought about these kinds of points before. Thanks!

(f) Many solenoid actuator manufacturers now use multi coil sections rather than one long coil . The coils being packet switched so as to optimise pull .
Do you know where I can read about this kind of design?

Why does someone with your educational background need any help with this ?
My field of study is actually more of theoretical physics and Radar (it is a weird kind of situation for my research) so when it comes to the engineering of electrical components I am not knowledgeable of the manufacturing details. (Isn't that funny? My degree will be in "Electrical Engineering" yet when it comes to engineering electrical/magnetic components, I need help. Shows you how much names can be labels.)

Averagesupernova
The only benefit to sloppy windings is that it reduces stray capacitance (in audio transformers or guitar pick ups, for example).

The neatness of the winding is most important related to the available space it will occupy, and other reasons mentioned.
Winding "crossovers" are inevitable even in one's attempt to create a neat winding.
Of course it's always easier winding a neat round coil as opposed to something square, or rectangular as shown here:

http://www.pbase.com/visual_first/image/130613676

There are numerous books written on the subject of winding magnet wire coils.
One of the most insightful I remember learning from was written by Terrell Croft.
And thanks to this big ole Internet, you can explore it here:

https://babel.hathitrust.org/cgi/pt?id=wu.89089681241;view=1up;seq=207

John