Round electromagnet for cuffs...need advice

Ideas and instructions how you can make your own bondage toys.
Post Reply
malesub22pa
*
Posts: 1
Joined: 17 Feb 2021, 15:42

Round electromagnet for cuffs...need advice

Post by malesub22pa »

I am working on a cheaper version of the Magbound.

I currently have this:
https://amazon.com/gp/product/B07JL1Q4V ... UTF8&psc=1
and plan to power it with this: https://amazon.com/gp/product/B074HQ722 ... UTF8&psc=1

Are there power concerns with this? I plan to use a smart plug to set a timer. I'll attach them to cuffs, but is there any safety concerns with the electricity? Can the magenet itself be safely touched? I'll wrap up that green connecter with electrical tape, but I just want to make sure I am not going to electrocute myself.

I have heard of heat concerns as well, but this seems to be well made and not generating much heat as best I can tell.
User avatar
Shannon SteelSlave
Moderator
Posts: 6530
Joined: 03 Feb 2019, 19:49
Location: New England, USA

Re: Round electromagnet for cuffs...need advice

Post by Shannon SteelSlave »

Welcome to Bound Anna, Malesub
Bondage is like a foreign film without subtitles. Only through sharing and practice can we hope to understand.
A Jedi uses bondage for knowledge and defense, never for attack.
I am so smart! I am so smart! S-M-R-T!....I, I mean S-M-A-R-T!
👠👠
User avatar
kinbaku
*****
Posts: 5050
Joined: 10 Jan 2020, 20:26
Location: Belgium

Re: Round electromagnet for cuffs...need advice

Post by kinbaku »

Welcome malesub22pa.

Since there is only 12 V on the side of the magnet and it only draws 0.5 A (6W / 12V), the chance that you will be electrocuted is very small. :wink:
Only with the transformer that previously supplies 1 A and thus supplies 12 W (12V x 1A) to the magnet, the magnet can become too hot.
Also note that only 80% pulling power for only 7 minutes is guaranteed by the manufacturer at that 6W power. After that, the magnet gets too hot and loses its attraction.
I would put a flyback-diode in parallel - negative to plus - at the green connector screws, so that the magnet coil cannot draw wrong current.

I previously bought myself a 5V magnet with a 25 N (~ 2.5 kg) force of attraction last week for use with my arduino to keep the key of my handcuffs out of reach. I also bought this at the same time. Only 2 W (5V x 400 mA).
lj
Moderator
Posts: 2255
Joined: 14 Oct 2008, 18:22
Location: East Anglia, UK

Re: Round electromagnet for cuffs...need advice

Post by lj »

the vital piece of information is "duty cycle 50%"

the snag with "duty cycle" is that there is no mention of timescale. 50% duty cycle applies to "one day on:one day off" and one microsecond on:one microsecond off". The duifference is that the microsecond version simply equates to a continuous supply of half the maximum current, whereas the day version would possibly melt the coil !!!!

Without actually trying the magnet, you won't know how hot it will get in the time you anticipate using it.

Unfortunately this is typical sales technique, aimed at the uninformed (ie most people). It's a bit like the tiny computer speakers sold as "200 watts" which is true for about 1 millisecond of a peak signal, but are actually 3 watts continuous rms signal.

The only safe component for the job is one with 100% duty cycle.

edited to add:
you could use a 6v supply instead of 12v, this would reduce the current by 50%, so the magnet could now be running at 100% continuous, but of course with a reduced holding power
be a switch, double the fun :-)
rmcingle
***
Posts: 224
Joined: 13 Jul 2010, 17:28

Re: Round electromagnet for cuffs...need advice

Post by rmcingle »

I agree with the other posters.

The diode is a good idea. "coils" are 'inductors' and an inductor has a characteristic of not allowing current to change rapidly. When the supply shuts off the 'inductive kick' could damage the power supply. Not a safety issue, but you might be surprised when the power supply quits working. If you want to protect the power supply get a 1N4000 diode. I just checked, and you can buy these off Amazon. Course, you have to buy a pack of 20! The diode will connect directly to the two leads of the magnet coil. The diode will have a band at one end: that needs to tie to the positive side. Note that now it is important to observe polarity.

I am also concerned about the 50% duty rating. Get one, try it. If it gets too hot to touch, you will have to do something else. Getting too hot might be very uncomfortable/painful, and it could damage the coil. If it doesn't get too hot to have against your bare skin, then it would probably be okay. Like LJ said, you could get a lower voltage power supply and have it work just fine without getting as hot. It may only have half the holding power, but you may find that even 50 pounds is enough to hold you if you can't get a 'jerk' motion.

You may find that one problem with this is that the wires between the magnet and power supply will be easily within your reach. it will be very tempting to just pull on the wires and pull the plug out of the wall. You could protect against that, to some degree, by using a heavy duty power cord and tying it to some anchor point that is out of reach.

Good luck!
R. Mc.
OrgasmAlley
****
Posts: 515
Joined: 18 Nov 2012, 17:43

Re: Round electromagnet for cuffs...need advice

Post by OrgasmAlley »

I agree with things others have posted. I use a similar magnet in a latch-based electromagnetic cuff system I sell, and from the experience designing them I can say that:

1 - The strength ratings are pretty optimistic, by my tests, and are generally overstated by at least 20%.
2 - Even at a 20% discount, the strength rating is only valid for a dead-straight pull and a substantial, very flat steel plate. If the plate can angle, reduce strength by 50% or more.
3 - This magnet gets quite hot. In my case, the entire lock body is milled from aluminum billet and snugly fits the magnet to effectively transfer heat. There's also a 30x30mm fan... because I want it to be capable of holding indefinitely.
4 - Duty cycle is all about heat, and they're typically rated using a 10 minute period. It probably doesn't cook itself in 5 minutes, but I would guess melted wire insulation within 10.
User avatar
Gregovic
****
Posts: 1119
Joined: 26 Mar 2016, 21:31
Location: Netherlands

Re: Round electromagnet for cuffs...need advice

Post by Gregovic »

Duty cycle is also about voltage. At the rated 12 volts it's 50%, at 9 volts, it'll last a LOT longer. (The 50mm ones I have don't seem to get over hand warm at 9v. So I'd trust those specific ones not to burst into flames when run at 9v continuously.)
How may I serve you? *Curtsey*
OrgasmAlley
****
Posts: 515
Joined: 18 Nov 2012, 17:43

Re: Round electromagnet for cuffs...need advice

Post by OrgasmAlley »

Yes, that's certainly true.

In my case, I wanted the cuff device to be as compact as possible. The next magnet up (this 110# one, I think) increased the dimensions of other parts -- particularly the billet -- in an unacceptable manner. Running the one I'm using (55# maybe?) at a lower voltage would not draw in the strike plate from the required distance.

In this case, I think the 110# magnet is probably already or marginal strength for the application, although I haven't tested this configuration.
Post Reply