9v solenoid: large or small?
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9v solenoid: large or small?

by paulcj2 on Fri May 03, 2013 5:01 pm

I have two questions about your solenoids.

I'm creating a project to pull a string when a cat enters a door to cause the door to close behind her. The door is a standard screen door with a standard door closer. I want to prop the door open with a small stick, attach a string between it and one of your 9v solenoids. I'm building a circuit to activate the solenoid when the cat crosses a laser beam. I'm modifying the project shown here: http://www.youtube.com/watch?v=zQK1kTh57Fk to activate the solenoid instead of a camera, as shown in the video. I also want to activate an audio alarm, so I know when the door has been closed.

My first question is which of your 9v solenoids do you recommend:
The small one at: http://www.adafruit.com/products/412
Or the larger one at: http://www.adafruit.com/products/413 ?

My 2nd question is how do I need to modify the project in the video to work with your 9v solenoid?
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Re: 9v solenoid: large or small?

by adafruit_support_bill on Sat May 04, 2013 5:37 am

A couple of problems there. First, the stroke on both of those solenoids is relatively short (small = 5.5mm. large = 10mm). That is not a long enough to close a door. Second, these are 24v solenoids. While they will work at 9v, the force at that voltage is very small.

For operating a door, you would be better off with a gearmotor or heavy-duty servo. Here's an example of a small door operated by a servo:
http://www.adafruit.com/blog/2012/12/11 ... -citizens/
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Re: 9v solenoid: large or small?

by tastewar on Mon May 06, 2013 9:50 am

Don't believe the OP was looking to directly close the door. Door has a closer but is being propped open by a stick between door and jamb; attach string to stick; use solenoid to pull string to remove stick; closer will close door now that it's not propped open.
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Re: 9v solenoid: large or small?

by adafruit_support_bill on Mon May 06, 2013 10:02 am

use solenoid to pull string to remove stick;

That might work. But probably not at 9v. At that voltage, they do not have much force.
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Re: 9v solenoid: large or small?

by paulcj2 on Wed May 08, 2013 1:06 pm

Thanks for the tip that this solenoid really works on 24 volts. Now the question is how best to provide that power. This is a small, short-term rig, so I really don't want to buy 2 12 volt car batteries and wire them in series. What low cost solution do you recommend?

By the way, a 9 volt battery didn't move the plunger at all.
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Re: 9v solenoid: large or small?

by tastewar on Wed May 08, 2013 1:19 pm

Does it have to be battery? If not, I'd think that for a solenoid just about any 24vdc power supply/transformer would work. Product page claims 250ma required. eBay would be one possible source; here's another (didn't check shipping cost...) http://www.ispsupplies.com/categories/Power-Supplies/WiFi-Boxes-Low-Cost-24-Volt-DC-Power-Supply.html?gdftrk=gdfV25486_a_7c1893_a_7c7138_a_7cPS_d_24V_d_1A
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Re: 9v solenoid: large or small?

by adafruit_support_bill on Wed May 08, 2013 3:10 pm

A 9v battery has too much internal resistance to deliver that kind of current. The solenoid probably isn't even seeing 9v from the battery.

We do have 8xAA battery holders : http://www.adafruit.com/products/449
These will give you plenty of current at 12v with alkaline batteries.

A cheap transformer will do the job too - as suggested by tastewar.
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Re: 9v solenoid: large or small?

by paulcj2 on Wed Jun 05, 2013 1:08 pm

Thanks for all the help. I ended up using the 24v DC converter/power supply. It worked very well with the solenoid pulling on one end of a stick holding the door open. I had to work on the door to get it to close and latch properly. Attached are pics of the final rig (overview, & control center), plus a pic of my cat Stella, safely at home.
Attachments
overview.jpg
Overview
overview.jpg (47.43 KiB) Viewed 505 times
stella.jpg
Stella
stella.jpg (64.28 KiB) Viewed 505 times
contro_center.jpg
Control Center
contro_center.jpg (106.45 KiB) Viewed 505 times
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Re: 9v solenoid: large or small?

by adafruit_support_bill on Wed Jun 05, 2013 3:01 pm

Looks great! Thanks for posting.
And be sure to post Stella up on Cats of Engineering too! :D
http://www.adafruit.com/blog/2013/06/05 ... -update-3/
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