How to build a simple solenoid?

[lukyman]

Hi, All:
I am helping my kid with a school robotic project. One key element is
to use solenoid to release a latch. The project limits total power
voltage no more than 9 volts. This solenoid does not need to generate
strong force, just to pickup weight of an egg will be fine. Can anyone
please help me by showing one simple example? What gage of wire, how
many round coil around how big a plastic tube and size of the
plunger,...,etc. that use only 2 to 3 AA or AAA batteries. Thanks
Lukyman

 

[Larry Brasfield]

Hi, All: Hi, one.
I am helping my kid with a school robotic project. One key element is
to use solenoid to release a latch. The project limits total power
voltage no more than 9 volts. This solenoid does not need to generate
strong force, just to pickup weight of an egg will be fine. Can anyone
please help me by showing one simple example? What gage of wire, how
many round coil around how big a plastic tube and size of the
plunger,...,etc. that use only 2 to 3 AA or AAA batteries.

Methinks you need to specify the throw
distance for this solenoid. If it just has to
hold the egg, once thrown, it will consume
less power than if it must exert that force
over the whole throw range.

From your description, I would worry about
how long that solenoid could be energized
without depleting the battery. Perhaps that
should be added to your requirements. You
may want to devise something with a latch so
that continuous energizatization is not needed.

 

[lukyman]

Thanks Larry, you're right. I just forgot those things. The throw
distance is only 1/2 inch. It's not continuous holding. It just release
the latch that's all. I will use spring to hold the latch. What I need
is really like an electronic mouse trap, since I am not allowed to
touch the "trap" by hand, I can only use wire, you know what I mean.
The force to release the latch is really small. The project requires 2
AA or AAA batteries only. You think that would work?

 

[Larry Brasfield]

Thanks Larry, you're right. I just forgot those things. The throw
distance is only 1/2 inch. It's not continuous holding. It just release
the latch that's all. I will use spring to hold the latch. What I need
is really like an electronic mouse trap, since I am not allowed to
touch the "trap" by hand, I can only use wire, you know what I mean.
The force to release the latch is really small. The project requires 2
AA or AAA batteries only. You think that would work?

Sure. You may need an electrolytic cap to
supply the pulse current needed to move the
solenoid plunger. I would get a small permanent
magnet and experiment with a coil whose axis
is colinear with the magnet pole. You should
be able to repel or attract that magnet with a
short enough pulse to not warrant much worry
about battery consumption. I would start with
#32 magnet wire and 40 turns. For your ~3V
drive, there will be an optimum turns-count
somewhere if you are willing to find it. Since
this is a one-shot operation, I would not spend
much time trying to devise an efficient, closed
path magnetic circuit unless battery power is
really precious.

 

[lukyman]

Larry,
Can I overlap those 40 turns or make it 2-3 layers? Does it have to be
very neat? Thanks again!

 

[Larry Brasfield]

Larry,
Can I overlap those 40 turns or make it 2-3 layers?

Both. Get the winding into as small a volume
around the magnet to be moved as you can.
That could mean even more layers.

Does it have to be very neat?

Only if you want a gold star from teacher.

Thanks again!

Welcome again.