12Vdc Solenoid Driver Circuit requ'd.

[PT]

Could someone suggest/draw a simple driver circuit that would energise a
12Vdc, 500mA solenoid slowly, if that is possible. The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

My understanding would be some form of current control. I have tried crudely
PWM but it is a bit stuttery.

Thanks for any help,
Pete.

 

[petrus bitbyter]

Could someone suggest/draw a simple driver circuit that would energise a
12Vdc, 500mA solenoid slowly, if that is possible. The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

My understanding would be some form of current control. I have tried
crudely
PWM but it is a bit stuttery.

Thanks for any help,
Pete.

The solenoids I know are not meant to make controlled moves other then "on"
anf "off". For controlled moves, components like stepper motors, servos or
even voice coils are used.

petrus bitbyter

 

[Frithiof Andreas Jensen]

The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

That's really hard to do without all sorts of complexity - the
force/displacement characteristics is very nonlinear and position control
would be hard.
You would be better off using f.ex. a door actuator for the central locking
in cars which will do what you want out of the box. If the slow movement is
to maintain silence, "muscle-wires" are cool too. Maybe a pneumatic actuator
supplied with air compressed by the solenoid?

 

[Spehro Pefhany]

Could someone suggest/draw a simple driver circuit that would energise a
12Vdc, 500mA solenoid slowly, if that is possible. The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

My understanding would be some form of current control. I have tried crudely
PWM but it is a bit stuttery.

Thanks for any help,
Pete.

Solenoids are very difficult to control "slowly" because the force
varies strongly with the position of the plunger. If you feed back
either the position of the plunger or some other parameter you may be
able to control things. A mechanical damper (dashpot or similar
device/mechanism) may be a better solution.



Best regards,
Spehro Pefhany

 

[Terry Pinnell]

Could someone suggest/draw a simple driver circuit that would energise a
12Vdc, 500mA solenoid slowly, if that is possible. The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

My understanding would be some form of current control. I have tried crudely
PWM but it is a bit stuttery.

I'm curious about your reasons for wanting to do it? For slow motion,
how about a geared motor, either mechanically attached via a lever or
cam, or winching via a pulled wire/cord, or turning a 'nut' on a
thread?

Actually I had same question a year or so ago. I had a pair of new
shoes that were pinching my toes. I improvised a contraption powered
by a very large 24V soloenoid, whose pull was converted into a
'scissor' action, stretching the appropriate part. With a full 30V it
was on the violent side. I proposed to leave it on overnight, so
played for a while with trying to calm it. Essentially in vain, for al
the reasons given by others here.

One other idea would be to use the full-speed solenoid to close a
bellows or pump of some sort, and connect an exit of that to a piston.

 

[Joerg]

Hi Frithiof, Hi Pete,

That's really hard to do without all sorts of complexity - the
force/displacement characteristics is very nonlinear and position control
would be hard.

That's right, it is hard. There are ways to do that though. For example,
you could send an increasing current through it and measure how much
current you need for each millimeter. Or tenths of millimeters if you
need to be more precise. Then look at the curve to see if it can be
mimicked with analog circuitry. If it can't, you could then store the
response digitally in a ROM or flash chip. When the button is pressed a
counter would clock out that memory into a DAC which sets the current
corresponding to each memory position. Plus a powerful current driver,
of course.

If the ROM method costs too much in hardware there is the analog way:
Set up a diodes-resistors ladder which approximates the desired slope.
It can be temp compensated in case that is an issue.

It would not be very accurate but maybe it is enough for your appliccation.

Regards, Joerg

 

[CBarn24050]

Subject: Re: 12Vdc Solenoid Driver Circuit requ'd.

From: Terry Pinnell [email protected]
Date: 06/10/2004 16:33 GMT Standard Time
Message-id: <[email protected]>

No simple way I'm afraid. The problem is that the position of the core is load
dependent and the thrust is position dependent. You can measure the di/dt of
the pwm, which will give you the position of the core, you can use that to
control the current. Not easy but it will keep you off the streets for a while.

 

[Jamie]

ah.
that is a problem.
we did that once but its hard to
control the position/load.
PWM signal generating a DC pulse
works well.
it can be done because it has been done
but not with reliable pull speeds verses
load changes unless you have a movement
feed back pot of something like that.
i think a servo motor would do you much
better, one with an actuator on it.

 

[Ken Smith]

Could someone suggest/draw a simple driver circuit that would energise a
12Vdc, 500mA solenoid slowly, if that is possible. The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

Just sort of thinking out loud here:

As the plunger of the solenoid moves in, the inductance increases greatly.
If a PWM chip applies a voltage to it for some short fixed amount of time,
the current will ramp up to a higher current with the plunger out than
with it in.

With only a little trickiness, a circuit can be made such that the voltage
on the solenoid reverses and puts its stored energy back onto the
input power line.

If the supply voltage is above twice the normal DC voltage for the
solenoid, the PWM chip will never need to run over 50% duty cycle and thus
we can be sure that the current stops between pulses.

For this idea to work, I think we need a PWM chip that has a fixed on time
and a variable frequency. One of the Linear "Burst mode" chips may do.

We need some sort of peak current detector. If the peak is too low, the
plunger is too far in and we need to delay the next pulse from the PWM by
some amount. Over time, we slowly lower the peak current we demand
allowing the PWM to move towards 50% duty.


I think this whole thing could be done with a PIC and a few power
components. It would be fun to try.

 

[PT]

Could someone suggest/draw a simple driver circuit that would energise a
12Vdc, 500mA solenoid slowly, if that is possible. The solenoid ideally
would move about 10mm over a period of about 1 second. Initiation would be
by pressing a button.

My understanding would be some form of current control. I have tried crudely
PWM but it is a bit stuttery.

Thanks for any help,
Pete.

All replies sofar have provided me with lateral thought and I thank each and
everyone for that. My current thinking now is to continue with PWM and/or
some form of damping such as springs and a cap. Spehro mentioned "dashpot"
which sounds interesting.

What say?

As well, I have a maximum space consideration of 30mm in height, which is
why I have chosen this path. However I am still open to any suggestions.
The load is approx. 500g.

Cheers,
Pete.

 

[John Fields]

All replies sofar have provided me with lateral thought and I thank each and
everyone for that. My current thinking now is to continue with PWM and/or
some form of damping such as springs and a cap. Spehro mentioned "dashpot"
which sounds interesting.

What say?

As well, I have a maximum space consideration of 30mm in height, which is
why I have chosen this path. However I am still open to any suggestions.
The load is approx. 500g.

 

[PT]

---
Could you say something about the physical orientation of the solenoid
and the load? That is, are they coaxial and vertical with gravity
supplying the restoring force for the load, or are they arranged in
some other way?

It forms part of a product development. Solenoid orientation is
horizontal. Load is sprung which restores the plunger after a "on"
period of about 4 seconds. The need for slow motion is to add
sophistication.

 

[Tom Seim]

All replies sofar have provided me with lateral thought and I thank each and
everyone for that. My current thinking now is to continue with PWM and/or
some form of damping such as springs and a cap. Spehro mentioned "dashpot"
which sounds interesting.

What say?

As well, I have a maximum space consideration of 30mm in height, which is
why I have chosen this path. However I am still open to any suggestions.
The load is approx. 500g.

Cheers,
Pete.

I dont think your pwm method will work. Solenoids are highly
nonlinear; trying to measure this and store it in a rom is doomed to
failure because current doesnt control position of the plunger-it
controls acceleration. To have any hope you will need a solenoid with
a linear force/distance curve. I have seen designs in books, but not
as products you can buy.

Tom

 

[John Fields]

It forms part of a product development. Solenoid orientation is
horizontal. Load is sprung which restores the plunger after a "on"
period of about 4 seconds. The need for slow motion is to add
sophistication.

---
Assuming no friction between the plunger and the bore of the solenoid,
the force the spring exerts on the solenoid plunger will be linear,
but the force the current will cause the magnetic field to exert on
the plunger will follow an inverse square law and will depend on the
location of the plunger within the solenoid and the force it must
overcome which is exerted by the spring. The game, then, will be to
determine how the current must change in order to get the plunger to
move from point a to point b in the time alloted, against the force
exerted by the spring.

 

[Ken Smith]

I dont think your pwm method will work. Solenoids are highly
nonlinear; trying to measure this and store it in a rom is doomed to
failure because current doesnt control position of the plunger-it
controls acceleration.

Plunger position varies the inductance so there is some chance of a closed
loop solution. If you servo the inductance to follow a ramp, the punger
would have to move slowly. The tricky bit is measuring the inductance,
applying the power and closing the loop all at the same time.

 

[Fred Bloggs]

I dont think your pwm method will work. Solenoids are highly
nonlinear; trying to measure this and store it in a rom is doomed to
failure because current doesnt control position of the plunger-it
controls acceleration. To have any hope you will need a solenoid with
a linear force/distance curve. I have seen designs in books, but not
as products you can buy.

Tom

Well- that post is just pseudo-OnT #10,000 indicating you don't know
your butt from a hole in the ground about anything electronic. Give it
up, non-technical maggot swivel chair operator senior scientist IV. Your
only skill set is making a power point presentation about your
half-assed organization that serves no purpose other than preserving itself.

 

[Rich Grise]

It forms part of a product development. Solenoid orientation is
horizontal. Load is sprung which restores the plunger after a "on"
period of about 4 seconds. The need for slow motion is to add
sophistication.

Then just mount a dashpot to slow down the plunger. No changes
to the electronics at all!

Good Luck!
Rich

 

[John Fields]

Then just mount a dashpot to slow down the plunger. No changes
to the electronics at all!

 

[Ken Smith]

Then just mount a dashpot to slow down the plunger. No changes
to the electronics at all!

[/QUOTE]

I suggest a spring and dashpot. The solenoid can snap in and pull on the
spring. It is easier to get springs that repeat well.

I think 4 seconds is too long of a time.

Hardly "sophisticated"...

If you make the air leak on the hash pot just right, you might be able to
get the Startrek door opening "pshhhht" sound out of it.

 

[John Fields]

I suggest a spring and dashpot. The solenoid can snap in and pull on the
spring. It is easier to get springs that repeat well.

I think 4 seconds is too long of a time.

Hardly "sophisticated"...

If you make the air leak on the hash pot just right, you might be able to
get the Startrek door opening "pshhhht" sound out of it.[/QUOTE]