Choosing the Right Magnetic Switch for Your Project
The magnetic switch is a wonder tool for designers who would like to turn a circuit on and off based on proximity. The Shiny Clutch and Aromatherapy Sachet in our book Switch Craft are two examples. However, buying the right magnetic switch can be tricky at times.
To cut a long story short: If you'd like to turn something OFF when the two halves of your switch are apart, buy the NORMALLY-OPEN (NO) type; to turn something ON when the two halves are apart, buy the NORMALLY-CLOSED (NC) type. This is the textbook definitions of NO and NC. For unknown reasons, there are some companies classifying their magnetic switches against the grain. Their NC switches turn things OFF when the two halves are apart, while NO does the opposite. This is why even some salespersons are confused as well. Therefore, before purchasing any magnetic switches, read the product descriptions carefully.
The readers of Switch Craft know that we recommend mini (low profile) NC switch for Shiny Clutch and Aromatherapy Sachet. To help you quickly locate the item, we searched the Web and found some options for you:
RadioShack
No introduction necessary.
(Catalog #) 55016278
Digi-Key
It's a site for engineers and may look a bit intimidating. But it does provide the largest selection and the most detailed info. Click on "Datasheets" to view switch dimensions and technical drawings. We like these two pairs:
(Part #) CH406-ND + CH412-ND
(Part #) 59140-040-ND + 57140-000-ND
Minute Man Electronics
This is one of those contrarian places that label NO and NC in reverse. So look for "low profile normally open magnetic switch" on their site. Note the $20 minimum.
(Philmore #) 30-17054
If all this NO/NC talk makes your head spin, or you simply want a switch that can be reuse for a different type of project later, there is the 2-in-1 magnetic switch that combines NO and NC (its technical nomenclature is "SPDT"):
Digi-Key
This was the only place where we managed to find mini NO+NC magnetic switch.
(Part #) CH409-ND + CH413-ND
(Part #) 59150-030-ND + 57150-000-ND
(Part #) 59145-030-ND + 57145-000-ND
It's much easier to find regular-sized NO+NC type switch. If that is fine for your purposes, you may get one from the following sources:
RadioShack 55016279
Minute Man 30-10072
All Electronics MS-7
You may have noticed that many security equipment vendors also sell magnetic switches. However, some of them do not supply detailed technical specs for their merchandises. Unless you are obsolutely sure about the item, or can return it easily, think twice before buying.
Since inventories change over time, the product numbers and links listed above may become obsolete sooner or later. Please leave us a comment if any links stop working. Should you find other stores selling mini magnetic switches, feel free to share it here too.
Share / BookmarkAdded April 10, 2009 14 comments »
Posted by Fang
Comments
For those catalogs which sell magnetic switches individually as two pieces, presumably the end user can use her own magnet for the non-wired side...?
Wednesday, April 15, 2009 - 14:30
Yes, Dorion that is correct. Though there are many types of magnets with different strengths and I suggest testing the contact with your magnet to make sure you get your desired effect.
For example, if your magnet is really strong it may require the two parts (magnet and switch) to be 1” away from each other before closing the circuit and having the light come on, while if its weak, it will only take a few mm. Either is fine as long as it fits your needs. Hope this helps!
Friday, April 17, 2009 - 10:38
Can you wire these switches in a series or something so that you need to connect like 3 magnets to 3 separate switches to complete the circuit and have a switch activate, or like a hidden passageway opening?
Friday, August 21, 2009 - 01:55
Sure you can do that. Many security systems are wired that way. Usually, you'd want all switches to be of the same type—either NC or NO. However, if you are truly planning a super secret "hidden passageway" (your own Batcave?), you may consider mixing NC and NO switches. Thus, only you and your butler would know the secret combination (e.g.: on-off-on) that can open the door.
Sunday, August 23, 2009 - 00:47
Love this site and thanks for making real what I thought were fantastical ideas....But where does one by conductive thread in NYC?
Friday, September 11, 2009 - 14:34
@brunchbabe: We always bought conductive thread online therefore can't really give you any local recommendation. However, since fencers sometimes use conductive thread to repair their lamé, you may try calling the fencing equipment sellers in NYC. I found three via Google: International Fencers Supply, Blade Fencing, and Physical Chess. Not sure if they carry it though.
It is also possible to extract conductive thread from some anti-static wrist straps. But it's hardly worth the price just to get a scant bit of thread. All things considered, buying online may just be the easiest. Check out these two links:
http://members.shaw.ca/ubik/thread/index.html
http://www.google.com/products?q=conductive+thread
If you do find it in NYC, please drop us a note. We'd love to know.
Saturday, September 12, 2009 - 11:43
Is a switch made with the magnet built in the switch so you only need to come in proximity to steel to change the normal condition?
Thursday, November 19, 2009 - 13:28
@anonymous guest: A magnetic switch usually comes in two halves—one wired and one not wired (see images above). The wired half is the actual switch itself, and there is no magnet in it. The magnet is in the half without wire; it is called an "actuator." Therefore, the switch's condition is changed when it comes in proximity to magnet not steel.
Thursday, November 19, 2009 - 22:20
I need a stong cylinder type 1/4" or 5/16" round magnetic switch that operates to the closed postion when it comes in contact with steel
Tuesday, January 19, 2010 - 06:55
@guest on Jan 19: We are not aware of any magnetic switch that senses steel. There might be some but we simply can't think of any. However, do an online search for information regarding "inductive proximity switches." They may be what you are looking for.
Wednesday, January 20, 2010 - 12:30
Is there an NC switch which opens when AC current (110V) is fed to it?
Thursday, April 22, 2010 - 20:32
Household AC power through magnetic switch? That scares me. Yes, you may find industrial-strength magnetic switches out there, but I wouldn't want to create a circuit where AC power travels around. It'd be safer to isolate the AC power to only a small part of your circuit and use DC in other parts.
For example, I'd run DC through the magnetic switch and have it trigger a solid state relay that controls the AC current.
That said, if you know what you're doing, don't let me stop you. Try mouser.com or digikey.com for switches that suit your needs. Be sure to read the product datasheets.
Friday, April 23, 2010 - 11:18
Is there a kind of switch that has three positions depending on the polarity of the magnetic actuator? Meaning there would be two "on" states (one for a "North" magnet and one for a "South" magnet) and an "off" state when no magnet is present?
Thursday, April 29, 2010 - 14:41
You may want to look into the "Hall effect sensor." It can differentiate polarity while the typical magnetic switch only detect proximity. More info here:
http://www.electronics-tutorials.ws/electromagnetism/hall-effect.html
http://www.hexy.name/blog/2010/04/19/magnetic-polarity-indicator/
http://www.kerrywong.com/2009/12/05/a-hall-effect-magnetic-field-polarit...
Thursday, April 29, 2010 - 17:38
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