Solenoids remaining on.

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Hi

Could it cause a problem if a solenoid like the one below is left on
for several hours or a day? I am trying to invent something where it
supposed to only remain on for a few seconds. However, there is always
a chance that the prototype could fail and that it may remain on.
Could this possibly damage the solenoid or worse still cause fire?

The solenoid I am using is at can be seen by going to http://www.jaycar.com.au
and enterering CAT. NO. SS0901

A description is also below. However the Jaycar site has a photo and
more information.
.
Miniature 12V Solenoid

Square frame unit, Pull type.- Coil resistance 58- 25 watt (maximum).-
Pulling force 100- 600g (25% duty cycle).- Stroke 1.0 - 5.5mm (25%
duty cycle).- Total weight 46g, plunger weight 9g.- Full data supplied
with unit.

Your help is appreciated,
Regards Richard.


Re: Solenoids remaining on.



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You have the datasheet already, haven't you? I got it right from the site
you mentioned. Take some time to read it carefully and you'll have the
answer.

petrus bitbyter



Re: Solenoids remaining on.


Hi

Thank you for your letter. I just read
http://www.jaycar.com.au/products_uploaded/SS0901.pdf

I am not fully sure what the percentages are referring to, however it
appears to indicate the ratio of on time to the total time and that it
would be ok if it is on continuously. However, there would be a limit
if it is going on an off frequently. Is that correct?

The circuit I am using is not a good connection as it is a pressure
plate designed to measure very light weights that vary. So it could be
possible that the circuit is complete and open intermittently, however
the high resistance in the connection may mean that there is often
less than 12 volts across the solenoid. So it would be hard to know
percentages of on time.

What is the worst thing that could happen and what is the likelihood
that the solenoid would remain working ok if it was on for an extended
period and intermittently off like described above?

Your help is appreciated,
Regards Richard.


Re: Solenoids remaining on.


On 16 Mar 2007 16:29:42 -0700, " snipped-for-privacy@yahoo.com"

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http://www.jaycar.com.au/products_uploaded/SS0901.pdf
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You have that backwards. It's saying that you can vary the drive power
to to exert X grams of force for Y percent of the time. If you use it
to exert less force, you can safely leave it on for longer. This limit
is to prevent the coil overheating.
 If your solenoid is the first one on that datasheet, it's saying that
if you're giving it no more than 12V, you can leave it on as long as
you like. (If you check the other columns, you'll see the higher drive
voltages at the bottom, which will give you higher holding strength,
but shorter times you can leave it on for.)

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Give it 12V for as long as you like.

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No problem. Best of luck with your project.

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


Hi

Thank you for your letter.

It looks like the solenoid should work for that project then if it
remained on all the time.

However, I had ideas for another project where a similar but larger
solenoid could be used to pull a vent or louver closed when the sun is
shining on a light sensor. It would be good to keep the sun out of the
window for a couple of hours in the afternoon. Also another sensor
could allow the solenoid to turn on when rain is hitting the window so
that the louver would close.

If I use a solenoid for this purpose it would be pulling a force
continuously for several hours. I thought that I read that the
solenoids may burn out if there is a force on them when they are left
on.  Will this probably be a problem if 12 volts is used or could this
work? If it will work for some force, what force could a similar
solenoid exert continuously?

Another option would be using a motor to reverse like explained in an
earlier thread that I discussed at
http://groups.google.com/group/aus.electronics/browse_frm/thread/ae720342f1c3824c?hl=en
It had the subject of "Motors controlling vents etc."
However, this would be more complicated to do and I am not experienced
in making up electronics. Do you know anyone who could help me do
this?

Your help is appreciated,
Regards Richard.




Re: Solenoids remaining on.


On 16 Mar 2007 18:42:33 -0700, " snipped-for-privacy@yahoo.com"

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Depends on the force, on the solenoid, & on the distance you need to
move the load. If the force is within the continuous rating of the
solenoid, at the rated voltage, no, it's not a problem.

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That's where you need to look at the load graphs on your data sheet,
because all those factors are interdependent. For example; the
solenoid you've been talking about requires 12V to safely stay on
continuously. At 12V, it consumes 2.5W. Referring to the graph on the
right side of the first page, you'll see that 2.5W will pull 150 grams
a distance of 1mm, or 50 grams a distance of 4mm.

 Bear in mind that you'll likely need levers to move something a
larger distance, so you'll need to do the maths to multiply the actual
mass of your gizmo by the amount of leverage, to work out how much
force your solenoid will need to exert.

 On the plus side, it generally requires less force to hold something
in place than it does to get it moving, so a common trick is to
over-voltage a solenoid briefly (eg; 24V for 1/2 second) to move the
actuator, then drop to the continuous safe voltage (12V) to keep it in
place afterwards.

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For experimental purposes, you might find it simpler to use a servo
motor of the type used for model aircraft or cars.

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What sort of money can you afford to spend on the project, and what
part of Australia are you in? (Reply by email if you like.)

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No problem.

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


Hi

Thank you for your letter.

I am from Tolga, on the Atherton Tableland behind Innisfail which is
about to have the anniversary of Cyclone Larry that devastated our
region.

Where can I get a servo motor? I am about to make an order from
Electus Distribution or Jaycar so please let me know if they have any.

How much money could it cost to make an automatic vent like described?

What is your email address? Mine is on my websites linked to
http://www.advantagein.com/overview.htm

Your help is appreciated,
Regards Richard.



Re: Solenoids remaining on.


snipped-for-privacy@yahoo.com says...

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Dont need a servo unless you want proportional response.

A simple flip flop arrangement with two solenoids or if you can balance
weights then just use one, dead easy, useful to learn about springs too...


--
Regards
Mike
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Re: Solenoids remaining on.


[posted & emailed]
On 16 Mar 2007 21:46:10 -0700, " snipped-for-privacy@yahoo.com"

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Well, it was a Usenet post to this public newsgroup, in fact. I take
it that you've enabled Googles "Email me stuff from this group"
option? There's nothing wrong with that, but you need to be clear
about whether you're communicating via email vs a public newsgroup, or
you could cause yourself terrible embarrassment. ;^)

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Well, I'm in Melbourne, which might make things a bit difficult.

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Check the Jaycar website, cat #'s YM2760-YM2766. Mind you, they're
$25-$40 apiece, so you'd better make sure you're clear on how to drive
them before handing over the dosh. (Fixed drive voltage, angular
position set by a PWM signal.)

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Mm. Some questions:
1) How much force would it take to move the vent?
2) How far does it need to move?
3) How do you intend to power the device?
4) Do you want it to close when the sun's between certain angles, or
just when it's shining on the window?
5) How much do you care about the rain detector thing?
6) And this one's really important, considering your location: How
mechanically minded are you?

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snipped-for-privacy@imagenoir.com

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My pleasure, Richard.

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


Why not use a windscreen wiper motor/gearbox.  12 v operation, end stop
switch already built in, probably more torque than necessary, easy to get
and replace from motor wreckers.

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Re: Solenoids remaining on.


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http://www.jaycar.com.au/products_uploaded/SS0901.pdf
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The solenoid has a duty cycle of 25%. which means it is only rated to be
energised for 25% of the time. The off time is needed for cool down.
A lower supply voltage may allow that time to be extended, but it is
hard to say.
The worst thing that can happen is that you will cook the solenoid.
Bottom line, use it in your application and keep an eye the solenoid for
a few hours. you might be able to determine if it will survive or fail.

Re: Solenoids remaining on.



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Wrong, you did not see the datasheet at all or could not read it. It says:
Duty cycle 100% (continuous), max. on time infinite, power dissipated 2.5W
at 20C, ampere turns 389 at 20C, voltage 12V. The other colums show the
reduction of the values at higher voltages. You can drive this thing with
38V if you need to but only with a duty cycle of 10% max. and an on time of
7s max. As with all electronics you'll have to make sure the components can
get rid of the heat they dissipate. That's why most PCs have those noisy
vents.

Meanwhile that's not to say it will be wise to keep the solenoid on if you
don't need to. Components don't like to be driven to their limits.
Datasheets can be conservative but some others are - let's say - too
optimistic. But there should be no reason to find a solenoid like this fried
when it has been on for some hours. If you nevertheless want some extra
safety, lower the voltage (and hence the power dissipation) by one or two
series diodes.

petrus bitbyter



Re: Solenoids remaining on.


Hi

Thank you for your letter.

I probably should have also stated that for this application there
will be nothing trying to pull the solenoid plunger out while the
solenoid is on. It simply is to retract and allow a container to drop
down. Does everyone who read this now agree that this would definitely
be fine if it was on all the time for this application?

Your help is appreciated,
Regards Richard.





Re: Solenoids remaining on.


On 16 Mar 2007 18:01:15 -0700, " snipped-for-privacy@yahoo.com"

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Yes, no problem at all.

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My pleasure, Richard.

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


On Sat, 17 Mar 2007 08:55:07 +0800, Stephen Robinison

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http://www.jaycar.com.au/products_uploaded/SS0901.pdf
[...]
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If you check the table on the datasheet, you'll find that the 25% duty
cycle is when you're driving it at 24V (ie; double the rated voltage).
It states quite clearly that it has an infinite maximum on-time at
12V. IOW, at 12V, you can safely leave it on for as long as you like.

--
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Re: Solenoids remaining on. Add a safety


snipped-for-privacy@yahoo.com says...

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Saw a few other posts but if you want a simple circuit to ensure the
solenoid *cant* stay on, yet be on for long enough to drop some plate
then just put a large capacitor in series with the solenoid and a
resistor in parallel with the capacitor.

Cap something like 10,000uF or more (electrolytic)
Resistor depends on T=RC  (close enough)
Diode across solenoid coil pointing opposite to curent flow.

This way if the transistor (or whatever you have driving the solenoid) fails
for whatever reason then the solenoid will eventually pull out and go off.
Depends on the coil resistance and size of capacitor :)

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


Hi

Thank you for your letter.

I have been posting messages to the newsgroup by using the form at
http://groups.google.com/group/aus.electronics

The small solenoid may not have enough range so I may have to go to a
bigger one detailed below. I never saw any link to a pdf file on the
Jaycar site.

CAT. NO. SS0902

Standard 12V Solenoid

Regular size square frame unit, Pull type, solder tip.- Coil
resistance 24- 50 watt (maximum).- Pulling force 200g- 2Kg (25% duty
cycle).- Stroke 2.0 - 12mm (25% duty cycle).- Total weight 205g,
plunger weight 39g.- Full data supplied with unit.

Do you think that solenoid should be similar where it can be left on
continuously if 12 volts is used and no force? Do you think it could
still work continuously if 20 volts is applied to it and there was no
force pulling it? If this could be done I may still be able to use the
small solenoid as a higher voltage should increase the pulling range.

You do not have to be local to help me make anything. I mostly have
had people not local as it is hard to find someone local who can do
these projects in a small town like this.

I have done little mechanically with motors and not made up circuits
so I would need someone to do it for me. I will try and find out what
force is required for the louver

Your help is appreciated,
Regards Richard.




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


Hi Mike and those interested

Thank you for your letter.

A solenoid would have to be fairly strong to open a louver. Do you
have any suggestions on what solenoid would be strong for the purpose?
I heard washing machine solenoids are strong but they require 240
volts.

With the idea that you had about a capacitor and resistor, I thought
the solenoid may have less chance of going on and pulling in the first
place if the pressure plate used as a switch is not a good contact.
Therefore it would be less sensitive. Would that be so?


Your help is appreciated,
Regards Richard.


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


snipped-for-privacy@yahoo.com says...

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If the cap is large enough you will get a nice current surge to the solenoid
and in any case if you also select a higher voltage - which you can because
it wont stay on - then you will get an even higher surge if the power supply
can handle it.

Best of both worlds and *very* cheap to try.

In fact, I might say, if you value your time, cheaper to try it than go
through news posts after you have an idea what to do from a professional ;)


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


Hi Mike

Thank you for your letter.

Would it also be an idea to use the capacitor and resister like you
described in the other project with the vent? Also do you know any
strong solenoids that work on low voltage that would be capable of
moving a vent or louver?

Your help is appreciated,
Regards Richard.




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