Solenoids remaining on.

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

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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.

Reply to
richardghole
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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

Reply to
petrus bitbyter

Hi

Thank you for your letter. I just read

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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.

Reply to
richardghole

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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.)

Give it 12V for as long as you like.

No problem. Best of luck with your project.

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Reply to
Lionel

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

Reply to
petrus bitbyter

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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.

Reply to
Stephen Robinison

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.

Reply to
richardghole

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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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Reply to
Lionel

Yes, no problem at all.

My pleasure, Richard.

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Reply to
Lionel

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

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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.

Reply to
richardghole

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.

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.

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

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.)

No problem.

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Reply to
Lionel

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

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Your help is appreciated, Regards Richard.

Reply to
richardghole

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 :)

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Regards
Mike
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Reply to
Mike

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...

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Regards
Mike
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Reply to
Mike

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. ;^)

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

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.)

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?

snipped-for-privacy@imagenoir.com

My pleasure, Richard.

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Reply to
Lionel

Hi

Thank you for your letter.

I have been posting messages to the newsgroup by using the form at

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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.

Reply to
richardghole

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.

Reply to
richardghole

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 ;)

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Regards
Mike
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Reply to
Mike

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.

Reply to
richardghole

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.

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Regards
Mike
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Reply to
Mike

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