I believe BornThisWay is doing excellent work towards making his own timer he likes. Amusingly enough, I last used ice years after disassembling the electromagnet release. Have not used either in 5 years, but have considered using another electromagnet recently given my current situation. My favorite is pneumatic latches, but bolting those to something is not discrete.
BornThisWay wrote:It's already worth it. If I wanted to have known release time I could simply connect the transformer to a wall timer.
Perfect timing.JPG
And let's face it, ice isn't an exact timing method as it is.
I would be comfortable using this for real if I used it in this way:
Have two electromagnets, One connected to a battery that you know will not fail even if the timing was unpredictable. The second electromagnet connected to a timer such as the one shown.
If the power goes out (Presto, your keys falls)
If the timer fails and never drops the key (just wait for the battery to die on your other electromagnet)
Regardless of whether I can obtain a consistent key drop from batteries, the variables of key ring weight and residual magnetism are a challenge. But no more predictable than melting ice.
Good ideas. I also like your suggestion about adding more weight, using 3 new identical key rings, and adding a media (electrical tape?) between and then testing again from a previous post. Hopefully, we can get this clarified.
This brings us back back to residual magnetism. I agree with bound_jenny that adding weight or a piece of material between the two will greatly reduce it. In my first post, I mentioned key ring accessories to add weight. Even more keys could do it. Something bulky and soft or glowing may be prefered over more sharp points. Personal preference.
Residual magnetism is the magnetic field that remains after the electricity goes away. Part of this is the metal in the center of the coil; it is a material that concentrates the magnetic force but is not a magnet. It will act like a magnet when in a magnetic field. It also remains like a very weak magnet as long as the field is touching another magnetic object. When the key ring or relay plate gets pulled off, its strength dies. This is half the issue.
The other half is the part being pulled. Steel objects can be magnetized by putting into a magnetic field. If you wipe your heavy duty key rings on a strong magnet north to south, you will likely be able to magnetize them and make them stick to steel plates. More rubs means stronger field until the limit is reached. A key may or may not be enough to overcome the strength of the key ring itself. Every time you stick the key ring to the coil, you could be magnetizing it more. We do not want the magnet to permanently stick in this case.
So, we know what residual magnetism is. What do we want to do about it? There are 3 options: adding space, adding weight, or reducing its effects. The answer is yours to decide.
Adding space reduces the amount of force acting between them by an inverse square law. A single piece of electrical tape over the end of the electromagnet would substantially reduce the holding force of it. I would do the math for you, but my calculator does not like dividing by zero. Odds are good that the coil will still hold a key for basically the same time, but with slightly less enthusiasm. Jenny has a good idea here.
Adding weight was my favorite until 20 keys and a padlock drop on a tender spot. Just like space, this one will fix it easily. What I did was test the stength of the magnet at half to 2/3rds voltage and weight the keys to barely hold here. Doing this will make for nearly instant drops. It can also make for heavy drops. Adding softer and bulkier things are my preference. I got a tobacco cessation stress ball keychain that is a personal favorite. Bright red, easy to find, and personal joke. First thought after bondage: nicotine time. Depending on how much weight is added, the key can drop earlier than a dead battery, but it will still reliably hold to that point except in Japan. Dropping noticeably earlier is better than never.
The last option is to find a way to reduce the residual magnetism. This is where a person tries to reduce the residual magnetism of the coil or try different things to hold against the magnet. Some materials are better magnets than others. Some hold a field better. Iron makes good magnets. Steel almost as well. Some things will attract without becoming a magnet. The armatures of relays are made of metals specially designed to be attracted without attracting. They also have heavy springs. The issue here is cost and shape. Is this something I want falling with my keys?
By using all-plastic and copper coils, I know it will not hold my key ever. I even tested with a magnetic screwdriver to confirm no iron. I modified a handcuff key for this use by removing the tab and pin from it. It became the rod that went in the center. As long as the coil is energized, it stays hard; deenergized, it just drops out. This is my current favorite.
I have also used nails to make a laminated steel object. Basically, multiple pieces of metal all get a weak magnetic field, but they oppose their neighboring fields after the main field leaves and they cancel each other out. Makes it very reactive to electromagnets, but also so they do not interfere. Transformers, electric motors, and generators are made this way using epoxy. How about short (1/2") finishing nails epoxied into a Chapstick lid with a miniature screw eyelet stuck through from the other end? A small, round, inert weight.
At this point, one may ask why do I care? Well, for one, I do not like statistics and chance. For another, I have experience with using these as a release. My tests and months of experience were promising. Then, one day, statistics and chance decided to pay a visit.
My keyring had gotten thoroughly magnetized and would not drop. Tests later confirmed, the keyring was thoroughly magnetized and would no longer drop under the previously tested conditions. Oops. The difference between a magnet holding an extra hour and a extra week is extremely small. May you avoid the experience. Safer that way.
