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Lifting magnet with "release on power"


#1

Hi, just messing around with some mechanics, and need a magnet to hold something, and only release it when I apply power.

A normal lifting magnet uses power to keep the magnetic field and hold stuff up, but I dont want to spend power on holding.

My plan is to apply power, and then the magnet releases the stuff that it holds.

Whats the name of such a thing?


#2

An electrical door lock works that way, mechanically closed and open when you apply 12vac.


#3

Those are mechanical type locks and energising the solenoid pulls the lock into the open position. It doesn’t use a magnet to hold anything.

I know what Njbuch is after but I have only seen them as electromagnetic and therefore they are in the HOLD position with power on and usually holds a steel plate that is fixed to the door.

Not sure you will find anything magnetic Niels as electromagnetic locks are generally fail safe so need power to keep the hold active.


#4

Hi,
perhaps you can use some ideas from one of my future projects, intended to lift our car across the fence. The car is hold by a permanent magnet which can be moved vertically in a case. To release the car we move the permant magnet away with a lever and an electro magnet controlled by Gadgeteer.
Cheers
Roland


#5

@ RoSchmi - Good luck :wink: the R8 is aluminum :whistle:

But for real, if you don’t want to use power during the “hold” phase then you need a permanent magnet strong enough to hold the object, there are amazing strong neodymium magnets but then how to release… you have to mechanically force it off the magnet…


#6

@ David@ Emrol -
:open_mouth: Ouch! So I can only hope they take it back!
Anyway, perhaps you are right and I’should think of another project.
But seriously: Releasing is done by the electro-magnet on the other side of the lever (see the axis on one third of the distance). Indeed it would be more elegant to use a „tubular solenoid" to force the magnet away from the load.
Do there exist magnets that loose the magnetism with power applied?


#7

Use a permanent magnet and a piece of iron or steel to keep it “closed”. Make an electromagnet out of the iron piece. Place a rubber or plastic material between the permanent magnet and the metal to ensure they don’t touch. They must not touch. Energize the coil in the direction opposite to the pull of the permanent magnet.

The electromagnet cancels out the permanent magnet’s field. This is the basis of a Magnetic Latching Relay.


#8

@ Mr. John Smith -
Ah, interesting. Do there exist commercially available devices of the kind as you described? In the articles I found under Latching Relay the electro-magnet had usually mechanically to overcome a mechanical or magnetic force.


#9

@ RoSchmi, outside the field of latching relays, no. If you are very good however, you can have disk magnet on the inside of an electromagnet so that when the electromagnet is on, the two magnets cancel each other. Again ensure that the magnets don’t touch the metal.


#10

@ RoSchmi, What’s your application again?


#11

Hi again, sorry I have been away…

I have found this supplier http://www.solenoids.co.uk/electromagnets.html which has an SP series that I have a query pending on. Will let you know when I have data…

This should be exactly what I am looking for…


#12

@ njbuch, Whoo hoo dude


#13

Any updates on the device you found? Was looking for something like this recently for my droid.


#14

Hi, I havent gotten a hold of any yet, but I have found several. The most obvious one is http://www.solenoid.cn/en/Product/ZHI-5030.html

But the chinese are really difficult to deal with. They reply emails after 2 weeks, and wants most expensive shipping. Zonhen is a big manufacturer but there is UK and German ones as well. Magnet Schultz is the biggest see fx http://www.directindustry.com/prod/magnet-schultz/power-off-holding-solenoids-19785-664267.html

95% of all holding magnets are electromagnets with holding on power.

I am still trying to get some samples…


#15

Would be so cool if you could just make some uh?


#16

@ njbuch -

I live in the Twilight Zone so I may be way-off base because I do not know what you are trying to do.

How about reversing the current through to coil?

Just a thought!


#17

I am of the type that I would just make one myself, but this idea I have in mind would be something others will be using as well. After that if a “part run” happens I really do not want to make all of them. I am trying to stay with on the self parts that I can buy and have schematics to CAD up.

I am looking for a magnet that will hold a platform in place without power. After applying power I need it to release so the platform can move away. This is all internal mechanisms for R2-D2 that I need secured some times until I use a linear slide to move them to another area.

I have another issue that I have been trying to solve, it involves very tight spaces and need to lock a “lever” that can have a strong load at the far end… basically the ankles of R2-D2. The area inside them is extremely limited.

I have used manufacturing in China and really haven’t had issues and they are MUCH cheaper than anything I can find to be done here in the states… and I have tried and keep trying as I would rather keep the business here. only thing is this is custom parts being milled from my own CAD designs, not parts already done. For those they usually want volume and I can’ seem to get test pieces before any run is done.

I have sent the guys you found earlier a message btu have not heard back from them.


#18

@ Samurai, then buy a CNC mill.


#19

Our local group has a CNC mill, Lathe, multiple CNC routers, and I have small CNC router and a 4.5’x5’ CNC router in the works for the house… but buying expensive things isn’t always the answer, 4 kids @ 4 and under with 2 of them being preemies at the moment. Money and time is worth a lot of money.

What I am looking for is an off the shelf item that I can say to others, go buy this. Another way is to get it working and then figure out how many we need for a run and set up a single large purchase.


#20

@ Samurai, whoops my apologies.