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Re: (Mike's letter) Solenoids remaining on. Add a safety


snipped-for-privacy@yahoo.com says...
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Probably, if you can devise, with the help of a bit of geometry and some
balance a single solenoid "flip-flop" arrangement. So each time it activates
it flips from one state to the other :)

If you use the cap in series with the solenoid then you can drive it with
a higher voltage and it will be stronger. This is ok since the cap will
prevent it staying on.



--
Regards
Mike
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Re: Solenoids remaining on. Add a safety


On 17 Mar 2007 13:38:23 -0700, " snipped-for-privacy@yahoo.com"

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the


I think what you need is a solenoid driver circuit which applies
asharp "operate" pulse and then reduces the holding current to limit
power loss and overheating of the coil.

Here is an EDN idea which looks promising
http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID11%162

You can achieve something similar by the simple expedient of
connecting the solenoid in series with a suitable tungsten filament
lamp. When cold the lamp filament is low resistance and doesn't
dramatically affect the operating time but when heated the resistance
of the filament is higher thus reducing the coil holding current
without affecting its holding ability. This arrangment doesn't save
any power, it simply reduces the holding current and might be okay for
a jury rigged system.

Re: Solenoids remaining on.


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yes, unfortunately:  25% duty cycle - means it heats up 4 times faster than
it can cool down when operated at 12V


It should be safe to operate it at 6V cotinuously (because at half voltage
it uses 1/4 of the power) but

at 6V it'll only have half the pulling force,

would that work for you?

You can surge it at the start with the full voltage to get a stronger pull
at the start.

Bye.
   Jasen

Re: Solenoids remaining on.


Hi Jason

Thank you for your letter. It may not work at 6V as some power is
needed.

Is it easy enough to set up a solenoid so that there is a surge at the
start and the voltage is much lower later? How would it be done so
that it automatically happens every time a switch is activated?

Some of the other messages I received on this topic indicate that
would be fine to have the solenoid on continuously at 12 volts if
there is no force being pulled by it. What do you think?

Your help is appreciated,
Regards Richard.


Re: Solenoids remaining on.


On 21 Mar 2007 23:58:15 -0700, " snipped-for-privacy@yahoo.com"


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I posted a link to an EDN article under a thread started by Mike
showing how this could be done.

Here it is again
http://www.elecdesign.com/Articles/Print.cfm?ArticleID11%162

Re: Solenoids remaining on.


On Thu, 22 Mar 2007 09:21:49 GMT, Ross Herbert

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Nifty solution, Ross. Being a digital guy who doesn't work with opamps
very often, I always find it educational to look at peoples' analog
solutions for problems I tend to tackle in a digital manner.
(Give a guy a hammer, etc. ;^)

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
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Re: Solenoids remaining on.



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opamps


Hi Lionel,

A fixed duty cycle oscillator using a digital IC performs an
equivalent function with this EDN design.
http://www.electronicdesign.com/Articles/Print.cfm?AD=1&ArticleID12%124

TI datasheet here http://focus.ti.com/lit/ds/symlink/sn74lvc1g97.pdf

Re: Solenoids remaining on.


Hi

Thank you for your letters.

If a very strong solenoid with a low voltage cannot be easily found,
would it be easy enough to make one by coiling insulted copper wire
around a narrow pipe? Do you have any idea how much wire would be
needed? I have some very thin insulated copper wire. Probably a fair
bit of wire would be needed if the solenoid had to be left on all the
time. I read a home made solenoid can get hot and use a lot of power
in an example where not much wire used. So a longer length of wire
could solve the problem. What do you think?

A problem with the solenoids I bought is that they do not have a big
range. Perhaps one with a longer range could be made with a longer
pipe an coil. This would result in more potential energy as the force
would be over a longer difference and it would increase the chance of
a solenoid being able to open a vent or louver. What do you think?

Your help is appreciated,
Regards Richard.



Re: Solenoids remaining on.


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enamel coated wire is usually used, you'll need about the same weight of
wire as a solenoid made for a different voltage.

Probably a fair
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consider useing a central locking motor instead

they're cheap, operate off 12V, (and if switched off after they've done
moving) they don't heat up whilst holding their position.

the wiring's a bit more involved, but a dpdt relay and two normally closed
switches can make something that will respond to an on/off signal like a
solenoid does.


Bye.
   Jasen

Re: Solenoids remaining on.


Hi Jason, or whoever can help,

Thank you for your letter. Would I have to use enamel coated wire to
make a solenoid and if so why? I have a long strand of thin copper
wire that may have been used in a speaker. Could that work?

I have a central locking motor like at http://jaycar.com.au with a
CAT. NO. LR8814. However,  I did not think that they would have any
advantage over a high torque motor like at Jaycar CAT. NO. YG2732.
What do you think?

I remember you told me about a circuit to control motors at
http://groups.google.com/group/aus.electronics/browse_frm/thread/ae720342f1c3824c?hl=en
However, I know very little about circuit design. I would be happy to
pay you or anyone to do it. Could you possibly do it or know who
could?

Your help is appreciated,
Regards Richard.




Re: Solenoids remaining on.


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no, but some sort of insulated wire is needed, enamel coated wire has the
thinnest insulation, and that lets the maker get more copper into a smaller
space resulting in a more compact, stronger, more efficient, solenoid

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it's probably not long enough.

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That dpends upon the louvres,

If yoy have louvres that are operated by turning a crank the rotary output
motor (YG2732) would be the better suited, if it's by moving a lever then
LR8814 may do it or may not be strong enough.

If it's not a crank conversion on your louvres and YG2732 or one of it's
bigger brothers, driving the crank gearbox can probably do it.

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http://groups.google.com/group/aus.electronics/browse_frm/thread/ae720342f1c3824c?hl=en
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I could do it, but what if it doesn't work, or stops working, or is
installed incorrectly... I'm in NZ.
It also makes it hard for me to come and see the site.

maybe you should go and ask the louvre and window guys about it
it's possible they have access to a pre-built unit

Bye.
   Jasen

Re: Solenoids remaining on.


Hi Jasen or whoever can help,

Thank you for your letter. Actually I found out that the wire I have
is probably enamel coated. It is about 0.2mm thick and insulated and
has a copper like colour. I found a bolt the correct size after
cutting off the threaded part. It fit neatly into some aluminium pipe
so that it easily slid inside it. The bolt is about 8mm diameter. I
wrapped about 10 meters of copper wire around the pipe to see if there
was any pull. However, I did not notice any. I expected more wire
would be needed for a decent pull but I only tried a small amount for
a start to see how much pull there would be. How many meters do you
think I would need to get a reasonable pull?

Another way would be to possibly modify a washing machine solenoid so
that it works off a low voltage like 12 volts. Would that be possible?

How many hours of work do you think it would take to make up a circuit
to control a louver like I described?

Your help is appreciated,
Regards Richard.



Re: Solenoids remaining on.



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that aluminium tube will slow down the response rate of your solenoid

if you use two 5m pieces of wire the solenoid will be 4 times stronger :)
it'll also heat up 4 times faster :( and use 4 times as much energy :(
(these differences assume the same 12V supply is used to operate it)

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yes, you'd have to take all the wire off it. cut it into 20 equal
pieces parallel them all and wind them back on, after this modification
you'd need to use 12V AC to operate it. (or you could just replace the wire
with wire with having 20 times the cross-section of the original wire)

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after the specifications are finalised, an hour shopping for the parts
an hour or two to assemble and test.

this is not including the rain and sun light sensors.
Jasen

Re: Solenoids remaining on.


Hi Jason

Thanks for your letter.

What time or cost would be involved to make get the rain and sun light
sensors to work for the louver?

So are you indicating that a washing machine solenoid is not just one
wire wrapped around in a coil or that it is best to have several
parallel wires wrapped around instead of one? I thought all solenoids
had only one strip of wire wrapped around.

What do you mean by the "aluminium tube will slow down the response
rate of your solenoid" are you indicating that there would be less
pulling force in aluminum than plastic?

I also wound about 2 meters of the thin wire around a plastic straw
and it did pull a nail. I then wound the wire around an aluminum pipe
about the same diameter and it also pulled the nail with about the
same force.

However, the bigger pipe has not worked yet. Probably because the
weight is heavier and I have not yet wound enough wire. I plan to try
to wire a single strand of wire around the pipe that is maybe 100
meters long. Would that work or do you suggest winding several shorter
strands of the wire around the pipe in parallel. It is important to
note that I do not want to get the solenoid to get too hot if it is
left on. I could leave it one all the time. Would it be possible to
make a solenoid to perhaps pull 2 kg over a say 2 inches and remain on
all the time that the vent is open?

Your help is appreciated
Regards Richard




Re: Solenoids remaining on.


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I've not worked with a rain sensor before, but light sensors are easy to
work with, rain's a bit trickier, probabkly 2 hours tho get them playiung
nice with the rest of it

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one wire many times around, or many wires fewer times around the magnetic
strength is the same (but at different input voltages)

to make the 240V solenoid work on 12V at the samee strength you need to
make the wire 20 times shorter and 20 times fatter (cross section), you
can do that by buying a new fatter wire or by recycling the old one.

looking at the catalog picture of SS-0904 you'd need to drill out a few
rivets to get the bobin out and after rewinding it replace them with new
rivets (or bolts)

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The peak strenght will be the same, but the aluminium will resist the
changes. softening the the onset and ending of the pull.

never use an aluminium tube for the core of an AC solenoid,
it'll act like a short-circiuted transformer (probably catch fire)

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For maximum strength, figure out how short a piece you can use without it
overheating and use many of that length. (not quite that simple because
you'll be packing them closer together so the heat will be more
concentrated.

For a solenoid the strength is determined by the number of turns and the
current that flows through them, longer wires have proportionally higher
resistance so while you gain more turns you lose bu having less current.
and come out about even. (see Ohm's law)

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2Kg x 2",  it's good to finally have some figures.

Something like Jaycar YM2734 with a 1 inch lever on the end of the
shaft looks, to me, like a better solution.
It'll have atleast 4.8Kg of force on the end of that arm....
(more atthe start and end because the angle is less)

because at the end of the stroke the crank will be in line with the motion
the motor won't slip when the power is off.

840mW is less power than a solenoid is likely to need too.

Bye.
   Jasen

Re: Solenoids remaining on.


Hi Jason

Thanks for your letter.

I could not find YM2734 on the Jaycar site. Are you sure that is the
correct number?

Do you think that a washing machine solenoid would be stronger than
the one at STOCK-CODE: SS0904?


Your help is appreciated
Regards Richard


Re: Solenoids remaining on.


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It was two years ago (paper catalogue) ...
looks like they changed the code

  YG2734

http://jaycar.com.au/productResults.asp?FORM=KEYWORD&keywords=yg2734

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To me SS0904 looks like a WM solenoid.
the solenoid changes the gear in the gearbox from stir to spin and/or
operates the brake neither of these things needs a very stroong solenoid

5cm is a long stroke for a solenoid

Bye.
   Jasen

Re: Solenoids remaining on.


Hi Jasen

The site states that SS0904 has a stroke of 15mm. Do you know of a
solenoid that has a stroke of 5cm or do you think that SS0904 is about
the strongest solenoid that could be purchased?

Thanks for the link to the motor. I have looked at that motor before
and am thinking of getting it. It is just a matter of getting the
reverse and forward circuit to work. I thought that a strong solenoid
could save some of the electronics. However it would have to be strong
enough.

Your help is appreciated
Regards Richard


Re: Solenoids remaining on.


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no.


I'm sure bigger and stronger are available, I have no idea where to get one
though,  personally I'd use the motor.

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You don't need to reverse it, use a 2.5cm crank and you only need to drive it
in a single direction, the trick then is stopping at approximately the
right time :)

Bye.
   Jasen

Re: Solenoids remaining on.


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Older type Simpson washing machines ie 30 years or older had very strong
solenoids on them, but theyre few and far between these days.
The Jaycar solenoids are not much different to the ones fitted to WM
The only thing different are the mounts.

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