# Low power magnetic hold and release mechanism

## Explanation of the idea:

With the inductor and magnet combined, ferrous metal objects can be held without any power indefinitely. To release the metal object the magnetic field holding it up needs to be temporarily cancelled out. This happens by pulsing current through the inductor which generates a magnetic field separate to that of the magnet. These two magnetic fields are of the opposite polarity meaning the inductors field cancels out the magnets field. The inductor only has to be powered long enough for the item to drop which I haven’t measured but its probably somewhere in the hundreds of milliseconds lets say around 100 milliseconds at a guess. This means you can hold an object for potentially a very long time (months, years maybe I dunno!) and expend a relatively small amount of power releasing it compared to if you’d used an electromagnet to hold the thing up which required a constant power source.

Or you could disregard the above explanation and look to this meme for guidance:

## 18 thoughts on “Low power magnetic hold and release mechanism”

1. Fascinating. I’m curious about the air gap – it looks quite large! As a matter of interest, is the air gap required? Is it that the inductor can’t overcome the intensity of the permanent magnet at very close range?

This got me thinking. It seems like it could be important to get the solenoid current just right to cancel the field of the permanent magnet, but not generate a strong enough field to continue holding the object. It would be interesting to get a magnetometer under this thing to see what the resultant field is at different current values.

Ted

1. wattnotions says:

Without the airgap the LED just stays stuck to the magnet. From a physics point of view I don’t really understand why the air gap changes things, I would have thought the magnetic field intensity from the inductor and magnet would fall away at the same rate the further you move away from them. Another problem I noticed is if you try to hold heavier items the air gap needs to be reduced but this unfortunately also means that a stronger field is needed from the inductor to make the thing drop. After this video I tried to use a 5c coin but couldn’t get it to work with the inductor I had. To try and hold heavier things, I tried loading the magnet with an object that was very slightly under the maximum weight it could hold ( I had an alligator clip holiding a bag and just kept adding weight to the bag until I found the point that was too much and used the last weight it could succesfully hold) at this point where the magnet is just barely managing to hang on, a pulse from the inductor can drop what I’d estimate was somewhere around 70-100 grams. The magnetometer idea would be cool to try out I’d be interested to see the results of that!

2. I’ll see if I can root out a magnetometer in Kevin St and maybe we could set up an experiment some time over the next couple of weeks?

Ted

1. wattnotions says:

Sounds good. Drop me an email whenever you manage to find one and we’ll organise a time.

3. zaptac says:

The technical term for the idea is “electropermanent magnet”. E.g. google is using them to snap the modules of the upcoming mobile phone platform “ara”.

4. Dilek says:

Hi,

We need to install this setup for our student project urgently to release 20 gr x 20 parts from different locations of our platform. Could you please send all the necessary equipment needed to generate this setup. We couldn’t understand clearly the parts that you used in video. Could you please explain us step by step the installation procedure, necessary materials, necessary voltage levels, batteries, and software etc.

Thanks.

1. wattnotions says:

I’m in work right now, I’ll respond to this later today.

Shane

2. wattnotions says:

The inductor used was 100mH. The voltage applied was 20V and the inductor draws about 0.1 Amps from this. The neccesary materials are a neodynium magnet, an inductor and a power source. This power source could come from a battery depending on your application. The same goes for software that is totally application specific I would think.

Best of luck with it,
Shane

5. TomCircuit says:

The permanent magnet + electromagnet combination is the heart of the “latching relay” which uses a spring, rather than gravity, to do the work of pulling the armature away from the permanent magnet. The relay stays open until the electromagnet is used to assist the PM to pull the armature in. These relays were used in huge quantities by the telephone industry before fully electronic switching, and are great for projects that are battery powered (no need to run coil current continuously). Thanks for the video to demonstrate this effect!

1. Thanks for the info, using a spring in an interesting idea!

Shane

6. Dilek says:

Hi,

Thanks for your information. I will try to obtain necessary parts to obtain this setup. I have talked with a magnet company and asked them whether we can depolarize neodynium magnet or not. They told me that the depolarization is not possible with neodymium magnet. However as we see in your setup it is possible, isn’t it? To carry 20 gram, what should be the diameter and thickness of the magnet. Do you have any suggestion? Thanks for your help and advices.

7. Ginina Grinceri says:

I need a switchable mechanism of release for a tractor that i am putting a magnet on so all the things i collect will fall off easily

8. V Stone says:

anyone know where one could buy one of these on the internet/ any data sheets for existing products?

9. Maria says:

From where i can read out more about it. Do you have any suggestive readings?