Effective electromagnet setup?

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mymy42
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Effective electromagnet setup?

Post by mymy42 »

Hello,

I remember having seen some discussion about that and hints but couldn't find anymore.

I'm thinking of using electromagnets, I saw a lot of them on internet.

What I failed to find, is the right metal piece that will be in contact with the magnet...

Electromagnets (for door at least) have a round design and I remember discussion about the design of the piece that makes contact - sorry I can't put a name on it! - in a way that :
1. It place it self in a good position from the magnet
2. Its design doesn't allow side movement that would require less force to unbind.

I struggled to find the right piece (if any) that would have the right shape to face the electromagnet and have an eyebolt or whatever allowing to attach a chain/rope/cuff.

Thank you!
lj
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Re: Effective electromagnet setup

Post by lj »

I suggest you put "electromagnets" into the "search" box at the top right of the page. There are over 250 hits, so have a look at these. There are certainly threads discussing the use of door and similar electromagnets.
be a switch, double the fun :-)
MrKnottie
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Re: Effective electromagnet setup?

Post by MrKnottie »

this is what I got, but I've haven't tested it out yet (I still have to see how warm the magnet gets, and other safety stuff).

https://www.amazon.co.uk/gp/product/B017R2F9HW
https://www.amazon.co.uk/gp/product/B001MSHOLC
https://www.amazon.co.uk/gp/product/B00B3RLE9U
https://www.amazon.co.uk/gp/product/B00JY5YQFM

although I admit the bolt might not have been long enough, I did manage to get it attached, you could then zip tie the base magnet to something fixed. I have an ardinuo controlling a relay on this to make a random release time, but I also got a timer plug just in case the ardinuo failed.
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sweh
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Re: Effective electromagnet setup?

Post by sweh »

MrKnottie wrote:this is what I got, but I've haven't tested it out yet (I still have to see how warm the magnet gets, and other safety stuff).
Warmth is something that worries me a lot (stuff catching fire maybe my biggest fear when I'm immobilised; eg vacuum bondage... will the vacuum cleaner catch fire 'cos there's not enough air flow to cool it down?). The electromagnet I've got became pretty hot, and I'm not sure why (perhaps lack of power from the DC adapter so the magnet didn't switch to "closed" mode?).

In theory door electromagnets should be safe (they hold doors closed between 6pm and 6am every day!) so I don't know why my one got hot :-(
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ruru67
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Re: Effective electromagnet setup?

Post by ruru67 »

sweh wrote:
MrKnottie wrote:this is what I got, but I've haven't tested it out yet (I still have to see how warm the magnet gets, and other safety stuff).
Warmth is something that worries me a lot (stuff catching fire maybe my biggest fear when I'm immobilised; eg vacuum bondage... will the vacuum cleaner catch fire 'cos there's not enough air flow to cool it down?). The electromagnet I've got became pretty hot, and I'm not sure why (perhaps lack of power from the DC adapter so the magnet didn't switch to "closed" mode?)
The door magnet should be fine. They typically pull about 500 mA at 12V - which works out at about 6 watts. The metal case of the magnet will easily dissipate that into air (which is a lousy conductor of heat - wood for example will drain heat away five times as fast). Basically, the thing might get a little warm, but it won't get "ouchy" hot, let alone dangerously so.

It's possible for a fault to cause very localised heating in wires; that typically requires some kind of damage (and remember these things are used all the time in situations where they're going to get abuse), but if that really worries you, put a 1A fuse in series with the thing.
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Sashauk
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Re: Effective electromagnet setup?

Post by Sashauk »

I use a similar set up of two electromagnets and I have never noticed them getting particularly hot.

I use one of these to control the release time http://www.ebay.co.uk/itm/New-DC-5V-Mul ... 3f6fbd8bc2 which you can program for anything between 1 second and 99 hours. I have mounted it in a case so I can see the counter count down but sometimes it's more fun not know how long there is left.
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Sashauk
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Re: Effective electromagnet setup?

Post by Sashauk »

It's probably a time issue. I can see that a strike plate could get hot after being continually powered for days but mine are always cool enough to handle after a bondage session.
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ruru67
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Re: Effective electromagnet setup?

Post by ruru67 »

These aren't the same thing. A normal door latch consists of a latch/bolt, and a strike plate that the bolt engages. With an electric strike, the strike itself can unlatch, allowing the door to open without opening the bolt.

Typically, these are in a "normally closed" configuration, i.e. the strike plate is locked when there is no power. (You can still open the door by unlocking the bolt, e.g. with an override key, which lets you get in if there's no power.) Top open the door, you apply power, and the solenoid unlatches the strike. Normally, the strike is only energised for a short time, either by a card access system or an exit button, just long enough to push the door open - usually five seconds or so.

As such, energising a strike plate for longer is unusual (hence the discussion in the links), and they're normally not designed for that kind of use. The solenoid typically pulls a similar amount of current to a mag-lock, but the metal housing is much smaller and less able to dissipate heat. Even so, while it's likely to get hot if misused like that, it's not going to become fire-starting hot, unless it starts a fire in the wiring. 12v @ 500 mA is still only 6W.
Thub56
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Re: Effective electromagnet setup?

Post by Thub56 »

I have done a little actual testing with two different electromagnets, One is ~50mm diameter and claims 60kg of holding force @11watts, and one which is ~20mm diameter and claims 10KG of holding force.
Both hold more than their rating, given a good solid steel part to hold onto (How much I'm not sure exactly).
Both heat to ~140 degrees F and stay there for hours.(tested with my infrared thermometer) This is uncomfortable to hold, but far from starting a fire. Interestingly, a heat sink, or a 3d printed plastic cup (to prevent the steel part from sliding) did little to change the highest temperature much.
Speaking of the 3d printed cup, it could easily be substituted for by a PVC pipe cap with some holes drilled in it. This can prevent one from sliding the plate off the magnet.
CD Tammy
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Re: Effective electromagnet setup?

Post by CD Tammy »

There are fail safe and fail secure magnetic locks. A fail safe magnetic lock results in the door being unlocked if there is no power. As for heat, the 1511 EMLock that I am playing with, I took off a door that had been in the closed (powered on) position for several years. It was not hot nor was the plate.
rmcingle
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Re: Effective electromagnet setup?

Post by rmcingle »

Hopefully this link will work. One I posted earlier doesn't work anymore . . .

What the below link should take you to is my photobucket account that has pictures of the electromagnet system I use.

I bought the electromagnet used off Ebay, for not much, under $20 if I remember correctly. The magnet is rated for 24 volts DC but I operate it on 12 volts. It still has PLENTY of holding power!

The first picture is of the magnet and plate. Pretty simple. I added the eye bolts to give me mounting options. The second picture is with the magnet holding the plate and how I typically secure it: webstrap closed in the sliding glass door! Simple!

The third picture is the power supply. Overkill, but I had it so I use it. I recommend getting a 12 volt power supply that is capable of 5 amps or so to assure that you don't overheat the supply. You may also note that the power supply is plugged into TWO timers: One is a spring wound timer that provides up to 60 minutes. The second (at the wall plug) is a typical lamp timer, set for several hours. I have had the spring wound timer fail!

The last picture shows it with the rope heading off to my ceiling hook. In use, I would be tied several feet away from the magnet / timers. When the magnet releases I will end up with the slack from the ceiling hook to where the magnet is, which will allow me to reach the key to the cuffs or whatever my eventual release is.

This setup is fairly simple. It has the fail-safe of releasing me immediately if the power should fail. I have been considering adding in a smoke alarm system that would activate a relay that would cut the power, but I haven't gotten around to that yet.

Ron

http://s1231.photobucket.com/user/rmcin ... r%20magnet


Click on the above link to see my pictures
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