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'[EE] High current solenoids and how to switch them'
2005\07\12@201641 by Gerhard Fiedler

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Hello all,

I'm looking into moving a lever with a solenoid. It's around 5 Nm torque
and I need to move it 30 degree from a center position in both directions.
It comes back to the center position through its own spring force. My
thought was to use two solenoids and a lever of around 3 cm. That would
give a throw of 17 mm in each direction and a force of 150 N. It seems
that's something a solenoid can do. Needs to be for 12 V.

However, I didn't yet find a manufacturer of such solenoids in the USA.
Does anybody know some places I can start asking? The only one I found so
far is Kendrion http://www.kendrionmt.com/ , but they are in Europe.

I'm also looking into using starter solenoid coils. They probably only need
a steel rod added to them that they can pull. That may work.

The other question is how to switch such solenoids. From the Kendrion site
and the solenoid data sheets I found there, I imagine that it may take up
to 60 A to get the force I need. This doesn't seem impossible to switch
with MOSFETs or IGBTs, but I wonder how you get that current to and from
the transistor. A 10 A trace is already large. We don't really need a high
duty cycle, so maybe that works out, temperature-rise-wise. I was just
wondering... are there any special tricks to it? Even connecting the thick
wire to a circuit board seems tricky.

Thanks for any pointers,
Gerhard

2005\07\12@212847 by PicDude

flavicon
face
I'm can't easily imagine how stong 5Nm is, but since you mention 12V, perhaps
an automotive door-opening solenoid might work for you?  These are popular on
hotrods to pop doors and trunks open with a switch.  The best source of this
would be to look thru an issue of "Street Rodder" magazine since it has tons
of ads for stuff like this.  Some sites I can remember are autoloc.com, and
autodax.com.  A google search for "door open solenoid" should bring up a
bunch.

Cheers,
-Neil.


On Tuesday 12 July 2005 07:16 pm, Gerhard Fiedler scribbled:
{Quote hidden}

2005\07\12@220022 by R. I. Nelson

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Gerhard Fiedler wrote:

{Quote hidden}

You might want to look into the solenoids for electric door locks on cars.




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2005\07\12@225355 by Dwayne Reid

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face
At 06:16 PM 7/12/2005, Gerhard Fiedler wrote:
>Hello all,
>
>I'm looking into moving a lever with a solenoid. It's around 5 Nm torque
>and I need to move it 30 degree from a center position in both directions.
>It comes back to the center position through its own spring force. My
>thought was to use two solenoids and a lever of around 3 cm. That would
>give a throw of 17 mm in each direction and a force of 150 N. It seems
>that's something a solenoid can do. Needs to be for 12 V.

I'm sure this has been suggested before, but why not consider a
servo?  There are some pretty hefty units rated for industrial duty
available.  May even be less expensive than the solenoids.

{Quote hidden}

High voltage DC stored on a large capacitor.  Decays to Vbatt for holding
current.

I used to fire large solenoids that operated folding seats (Carnival Dunk
Tank systems).  I charged around 350,000 uF to around 70 Vdc and dumped
that into huge solenoids rated for 12V continuous operation.  No problems
and no failures.

FWIW - the solenoid chosen would not work the mechanism reliably below
around 36 or so Vdc.  I could have used less than 70V but that's what I got
out of the transformers I had handy at the time.  Used a honking big triac
as the switch with a separate bipolar device to disconnect the bridge
rectifier from the caps during the firing cycle.  All run from a single
CD4093 quad schmitt NAND package and a handful of passives.

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam@spam@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2005\07\13@212443 by Peter

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On Tue, 12 Jul 2005, Gerhard Fiedler wrote:

> I'm also looking into using starter solenoid coils. They probably only need
> a steel rod added to them that they can pull. That may work.

Lucas makes some actuators for automotive and a/c use use but not 150Nm.
They are rotary action (90 degrees).

> The other question is how to switch such solenoids. From the Kendrion site
> and the solenoid data sheets I found there, I imagine that it may take up
> to 60 A to get the force I need. This doesn't seem impossible to switch
> with MOSFETs or IGBTs, but I wonder how you get that current to and from
> the transistor. A 10 A trace is already large. We don't really need a high
> duty cycle, so maybe that works out, temperature-rise-wise. I was just
> wondering... are there any special tricks to it? Even connecting the thick
> wire to a circuit board seems tricky.

Use thick wire and thickened traces (copper rail soldered on the traces)
and don't worry too much about it *except* for the kickback which will
be terrific. Does it really have to be a solenoid ? A wiper motor will
do what you need at 10A or less.

Peter

2005\07\14@073600 by Peter

picon face


On Tue, 12 Jul 2005, PicDude wrote:

> I'm can't easily imagine how stong 5Nm is, but since you mention 12V, perhaps

5 Nm is pretty high. It's about 3.6 lbf*ft.

Peter

2005\07\14@160056 by Gerhard Fiedler

picon face
Peter wrote:

> On Tue, 12 Jul 2005, Gerhard Fiedler wrote:
>
>> I'm also looking into using starter solenoid coils. They probably only need
>> a steel rod added to them that they can pull. That may work.
>
> Lucas makes some actuators for automotive and a/c use use but not 150Nm.
> They are rotary action (90 degrees).

It's 150 N in the configuration I thought about, but it's "only" 5 Nm.

>> The other question is how to switch such solenoids. [...]

> Use thick wire and thickened traces (copper rail soldered on the traces)
> and don't worry too much about it *except* for the kickback which will
> be terrific. Does it really have to be a solenoid ? A wiper motor will
> do what you need at 10A or less.

Hm... maybe. It may be too slow, and not have enough torque, but it's worth
a try. I need to do the 30° in 100 ms. That's about 1 rev/s, which could be
in the range.
In the meantime I've pretty much abandoned the solenoid idea; mechanically
it just doesn't get there. They're either too weak or too short, or really
heavy. Currently the thought is more around linear actuators, but the wiper
motor idea is a good one to check out.

Thanks for helping me bounce ideas around,
Gerhard

2005\07\14@161319 by R. I. Nelson

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do You have any other energy sources available to use? compressed air
for example.

{Quote hidden}


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2005\07\14@161840 by Richard Prosser

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Do You need this amount of speed (30 degrees 100ms) in both directions?
You could use a motor or rachet drive to pull against a spring to cock
the system and a small solenoid to release it.

On 15/07/05, Gerhard Fiedler <.....listsKILLspamspam.....connectionbrazil.com> wrote:
{Quote hidden}

>

2005\07\14@175712 by Gerhard Fiedler

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R. I. Nelson wrote:

> do You have any other energy sources available to use? compressed air for
> example.

Not really available. I've thought about hydraulics or pneumatics, but I'd
need to generate the pressure. May be viable; I don't know how much this
would add to the overall cost and system complexity. Has anybody any good
pointers to pumps (and cylinders, and ...) for such an application? I tend
more towards hydraulics; seems smaller, quieter and easier to deal with.


Richard Prosser wrote:

> Do You need this amount of speed (30 degrees 100ms) in both directions?

Yes, from a center position in both directions.

> You could use a motor or rachet drive to pull against a spring to cock
> the system and a small solenoid to release it.

Something like that could work. It would buy me approx. a ratio of 1:4 (it
needs to be ready to fire again after 500 ms). I'd like to avoid that
though and be able to fire as quickly as somebody can push a button. And
I'm shying a bit away from the mechanical complexity ... :)

What's a "rachet drive"?

Thanks,
Gerhard

2005\07\14@202202 by Richard Prosser

picon face
A Rachet drive uses a reciprocating action to accumulate movement.
Uses a sawtooth like profile to wind up a spring or rotate a drum.
Easier to picture than decribe!

Similar to an hand winch or fence wire strainer where you use a rachet
to hold the winch in position while you move the handle for the next
pull.

Also used in large circuit breakers to wind up a spring so that the
disconnect can be remotely operated by a low power device, or in
sequencing relays to save the cost of a motor.

Richard P

On 15/07/05, Gerhard Fiedler <EraseMElistsspam_OUTspamTakeThisOuTconnectionbrazil.com> wrote:
{Quote hidden}

> -

2005\07\14@204949 by Jinx

face picon face
> disconnect can be remotely operated by a low power device, or in
> sequencing relays to save the cost of a motor.

I have a very old serial printer that uses a ratchet / solenoid for LF

2005\07\15@100133 by Alan B. Pearce

face picon face
>> do You have any other energy sources available to use? compressed air for
>> example.
>
>Not really available. I've thought about hydraulics or pneumatics, but I'd
>need to generate the pressure. May be viable; I don't know how much this
>would add to the overall cost and system complexity. Has anybody any good
>pointers to pumps (and cylinders, and ...) for such an application? I tend
>more towards hydraulics; seems smaller, quieter and easier to deal with.

My Volkswagen Golf uses a pneumatic drive for the central locking on the
passenger doors. It takes a moment or two for the pump motor to start, and
then the locks go. Gives them a nice slow actuation compared to solenoid
actuated ones.

2005\07\15@104832 by Gerhard Fiedler

picon face
Alan B. Pearce wrote:

> My Volkswagen Golf uses a pneumatic drive for the central locking on the
> passenger doors.

Can you tell me please what model/year that is? This could be a pump that
works for me.

Gerhard

2005\07\15@121751 by Alan B. Pearce

face picon face
>Alan B. Pearce wrote:
>
>> My Volkswagen Golf uses a pneumatic drive for the central locking on the
>> passenger doors.
>
>Can you tell me please what model/year that is? This could be a pump that
>works for me.

Ahh - Umm - lets see. It is a mid-90s IIRC. I don't know if the pump would
be enough power to do what you want, I just pointed at it as an example of
how air can be used in place of a solenoid, seeing someone mentioned the
possibility. It does give the lock/unlock quite a soft action compared to a
solenoid lock with its "clunk" as the solenoid works, so I suspect the air
pressure is not a lot, but rather works on the volume of air.

2005\07\15@171952 by Gerhard Fiedler

picon face
Dwayne Reid wrote:

> I'm sure this has been suggested before, but why not consider a
> servo?  There are some pretty hefty units rated for industrial duty
> available.  May even be less expensive than the solenoids.

It is probably. Less expensive and smaller. I just didn't find anything
that "out of the box" fits my requirements. I'll probably do it with a
motor and some gears to it; mainly a matter of finding the right stuff.

Gerhard

2005\07\16@161345 by Peter

picon face

Just in case this is a fruit sorter or something like that, maybe you
can think about using the chute or the energy of the object to drive the
'flap'. F.ex. rolling melons or such over trapdoors held by small
solenoids and opening the solenoid for the right size would require less
energy than a flap in a through (never mind the solution can then be
entirely mechanical with adjustable hysteresis trapdoor locks).

Peter

2005\07\16@170522 by Peter

picon face


On Fri, 15 Jul 2005, Gerhard Fiedler wrote:

> Dwayne Reid wrote:
>
>> I'm sure this has been suggested before, but why not consider a
>> servo?  There are some pretty hefty units rated for industrial duty
>> available.  May even be less expensive than the solenoids.
>
> It is probably. Less expensive and smaller. I just didn't find anything
> that "out of the box" fits my requirements. I'll probably do it with a
> motor and some gears to it; mainly a matter of finding the right stuff.

You could use a malta cross mechanism to do the movement. This allows
the motor to pick up speed for 1/4 malta cross drive wheel revolution
before the pin hits a slot and some leeway in starting/stopping the
motor. Thus no load on the motor when starting and you could use a
smaller motor.

Peter

2005\07\17@014932 by Gerhard Fiedler

picon face
Peter wrote:

> You could use a malta cross mechanism to do the movement. This allows the
> motor to pick up speed for 1/4 malta cross drive wheel revolution before
> the pin hits a slot and some leeway in starting/stopping the motor. Thus
> no load on the motor when starting and you could use a smaller motor.

I don't understand this. Doesn't an electric motor have its highest torque
at 0 rpm (when stalled)? If that's the case, what good would it do to get
the motor going first?

Gerhard

2005\07\17@133937 by Peter

picon face

On Sat, 16 Jul 2005, Gerhard Fiedler wrote:

> Peter wrote:
>
>> You could use a malta cross mechanism to do the movement. This allows the
>> motor to pick up speed for 1/4 malta cross drive wheel revolution before
>> the pin hits a slot and some leeway in starting/stopping the motor. Thus
>> no load on the motor when starting and you could use a smaller motor.
>
> I don't understand this. Doesn't an electric motor have its highest torque
> at 0 rpm (when stalled)? If that's the case, what good would it do to get
> the motor going first?

It has the highest torque at stall but *zero* mechanical power. If you
want to use something as energy reservoir (e.g. the flywheel formed by
the spinning parts of the mechanism) then you have to let it pick up
speed before applying load. E.g. with 1:100 gearing the motor would spin
essentialy accelerating freely 12.5 turns before the 1/8 turn to the
nearest malta cross slot (assuming it starts at the middle between two
slots), when its load would be applied.

Another option would be a continuously rotating wheel and a solenoid
that would engage a mechanical clutch on it when you need to 'flap'. The
power for rotation can be provided by a small dc motor. Of course you
have to calculate this.

Peter

2005\07\17@183757 by Gerhard Fiedler

picon face
Peter wrote:

>> Doesn't an electric motor have its highest torque at 0 rpm (when
>> stalled)? If that's the case, what good would it do to get the motor
>> going first?
>
> It has the highest torque at stall but *zero* mechanical power.  
I can see that now... you get the motor quicker in a more efficient rpm
range and accumulate more kinetic energy -- which then hopefully will be
transferred to the system as a whole without too much loss.
> E.g. with 1:100 gearing the motor would spin essentialy accelerating
> freely 12.5 turns before the 1/8 turn to the nearest malta cross slot
> (assuming it starts at the middle between two slots), when its load
> would be applied.
Since I only need 30° movement, I'm not sure this would help me a lot.
Possibly the motor would have turned the whole system by 30° by the time it
has turned the flywheel part only by 45°.

Gerhard

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