Solenoid design help 2

[TMcRally]

I'm well out of my comfort zone sorry . I would like to develop our own design and understanding. I have had quite a good look and only seem to find very basic or very advanced topics, I was hoping for some middle ground for dummies

Requirement...

• latching solenoids
• I hope to get the maximum possible pull force at 12mm stroke. =/>12N...more is better.
• 24Vdc @ 3Amps, I will use these on existing sites that already have run cables and power supplies. Not ideal, but it is possible to increase the Amps a little if necessary
• The available size within the housing restricts the coil bobbin to 49mm long (clear space on the bobbin, not including the bobbin itself or latching magnets) and an OD of 25mm.
• These will have very low duty cycles.

I think I understand....

• more coils the greater the force
• more current the greater the force

I'm having troubles finding or understanding...

• more coils = longer wire = greater resistance = less current. The 2 variables, (number of coils and current) seem to be in opposition to each other for increasing pull force.
• suitable armature diameter
• Is there a "best" armature material
• Is there an optimum armature "energized" retracted position, with reference to the end of the coil.
• Wire diameter calculation
• I have been working with U shape open frames, not sure if this is optimal.

Thank you
Dave

 

[waross]

more coils the greater the force

For DC, no. Double the coils, effectively double the resistance.
Double the resistance, halve the current.
Half of the current times twice as many turns = the same Amp-turns and the same force.
But.
More turns often means longer turns and more than twice the resistance.
Net result, less Amp-turns. Less force.

DC solenoids of any size typically have two windings.
A low current "Holding winding"
and
A high current "Pull in winding".
The magnetic force is inversely proportional to the air gap.
The force to hold a solenoid in is a small fraction of the force needed to pull it in from fully open.
A good example is a starter solenoid on an automobile.
A very heavy current is used in a very low resistance coil to pull in the solenoid.
A much finer coil is used to hold the solenoid sealed in.
A switch disconnects the heavy coil just before the armature seats in the fully pulled in position.
In the event that the switch fails to close, the solenoid fails to pull in.
In the event that the switch fails to open, the heavy current will melt down the solenoid very quickly.

Consider charging a large capacitor and using that to energize a low resistance pull in winding.
Amp turns depend primarily on wire size or resistance per turn.
Current draw depends on the number of turns.
It all changes on AC due in part to the effect of more turns on inductive reactance.

 

[TMcRally]

For DC, no. Double the coils, effectively double the resistance.
Double the resistance, halve the current.
Half of the current times twice as many turns = the same Amp-turns and the same force.
But.
More turns often means longer turns and more than twice the resistance.
Net result, less Amp-turns. Less force.

DC solenoids of any size typically have two windings.
A low current "Holding winding"
and
A high current "Pull in winding".
The magnetic force is inversely proportional to the air gap.
The force to hold a solenoid in is a small fraction of the force needed to pull it in from fully open.
A good example is a starter solenoid on an automobile.
A very heavy current is used in a very low resistance coil to pull in the solenoid.
A much finer coil is used to hold the solenoid sealed in.
A switch disconnects the heavy coil just before the armature seats in the fully pulled in position.
In the event that the switch fails to close, the solenoid fails to pull in.
In the event that the switch fails to open, the heavy current will melt down the solenoid very quickly.

Consider charging a large capacitor and using that to energize a low resistance pull in winding.
Amp turns depend primarily on wire size or resistance per turn.
Current draw depends on the number of turns.
It all changes on AC due in part to the effect of more turns on inductive reactance.

Thank you very much for your answer, it's much appreciated.

I will struggle with the packaging of a capacitor, I'd like to explore the single coil, pull type with non-energized magnetically latching if that's possible.

From your answer, my new understanding is...

• If I am limited to 24Vdc @ 3Amps
  
  • I should choose a wire diameter that will fit on the bobbin that gives me the most number of coils for my 3Amp limited draw.
  • Using an online calculator for annealed copper wire of 0.315mm over 90m gives a resistance of close to 8 Ohms @ 24V and 3Amps.
  • My first thought is there a better conducting wire that could give me more coils for the same resistance so I could reduce the wire diameter and have more coils for the same resistance/current draw.
• A longer length coil with lower profile coil winding is more powerful because of the reduced air gap to the centre line of the armature for the same number of windings.

 

[waross]

A longer length coil with lower profile coil winding is more powerful because of the reduced air gap to the centre line of the armature for the same number of windings.

Are these clapper type solenoids or is the armature drawn into the core?
Can you give us a sketch of the proposed solenoid?

 

[TMcRally]

Are these clapper type solenoids or is the armature drawn into the core?
Can you give us a sketch of the proposed solenoid?

It is a straight linear armature pull type with magnetically latching.

It pulls a mechanism that when latched back it reverses the spring action from push, to pull, when the solenoid is released and extended the action reverts back to push type again, beyond this mechanism is a 90° crank to push/pull a bolt perpendicular to the direction of the solenoid.

The stronger the solenoid the stronger the springs I can use, the stronger the springs, the more user friendly it will be.

I'll send through an image of the solenoid I've drawn up. It's not set in concrete but it is limited buy the confines of its hhousing.

 

[TMcRally]

Sorry, I should have said 0.5mm diameter wire above.

90m X 0.5mm wire with 7.8Ohms resistance.