Electromagnet powering

Question

Hello all.

I am thinking of buying an 12V electromagnet for various projects.This magnet is a 50mm, 50KG DC magnet.

But before I buy it I need to know how to power it off some 1.5 batteries.Also is there any other cheap way to power it?

So the power - what things will I need ( they need to be cheap, havent got much money) ?

Could I use a transformer that does 1.5 -12V, could I buy a boost converter?

Really, what do you lot think?

Thanks.

14rhb · Accepted Answer

Hi Tom,

Sounds quite like it would need quite a lot of power to maintain that pull (and power is voltage x current). Looking up a typical device on the spec you provided here gives a current requirement of 0.84A - you'd need a bank of 8x AA batteries and they wouldn't last very long. You could get away with rechargables though if you wanted something portable and the electromagnet isn't constantly energised.

A standard 'wall-wart' transformer left over from some other gadget could be repurposed; e.g. the mains transformer, usually black plastic casing, that plugs straight into the mains voltage (240v/115v) and powers things like routers, printers, external lights.

Something with a rated output of 12v-2A perhaps to give you some margin for running continuously. I'd opt for a DC output (as you can use it for other projects) but the electromagnet should work fine on 12v AC as well IMHO. These cheap transformers often don't run at the specified voltage, open circuit they are usually quite a bit higher, but for your application I don't think it would be an issue. Have a tinker and see - keep a check on the current/voltage (if you have a suitable meter) and failing that, ensure the transformer and your electromagnet don't get too hot.

Rod

fmilburn · Answer

Hi Tom,

Your friend is most likely incorrect - see Rod's estimation of the requirements above which are far below what 4 car batteries would deliver.

In order to get meaningful help you will need to better define what your constraints and requirements are. E.G.

Do you want to power it from the wall or batteries
If batteries, how long do the batteries need to last
How are you going to package the device - e.g. electronics and power in a box with magnet connected by wires
Indoors or outdoors
How much do you want to spend
Etc.

14rhb · Answer

Not wanting to ruin an interesting idea but, to get the full pulling force of an electromagnet you'll need to ensure all the magnetic flux couples directly into the ferrous item you are attaching to. A lamppost, being convex, wouldn't work properly with the flat surface of the electromagnet...the air gap would significantly weaken the force below 50Kg. You may still have issues with flat metal plates when the pulling force is tangential to the surface i.e. the magnet will slip.

I also don't think I'd want to be up a lamppost when the battery voltage dropped and the pulling force proportionally so . Saying that, you could build in some cool way of measuring battery capacity and thus warning of impending doom.

p.s. can you not just use a ladder

Rod

jw0752 · Answer

Hi Tom, There is another consideration and that is heat dissipation. Your electromagnets are going to get hot. The other commentators have made really good points about the uncertainty of the strength of the magnets under different conditions. The 50 Kg specification is likely a measurement taken under ideal conditions. Climbing would necessitate a switching off of each magnet so that the next step could be taken. I would guess the best policy would be that any one magnet could support the entire weight. If you climb over 6 feet off the ground you may want to have the fire rescue on speed dial. John

msebok · Answer

Also this hasn't been touched on regarding safety. Typically magnets take more force to PULL an object before releasing then they do with a sliding action. With that said be careful with it.. lol

Fred27 · Answer

Using an electromagnet to climb a lamp post really isn't practical. The only way I can see that this might be possible is if you use permanent magnets in a similar way to you see in the magnetic base of a dial gauge. For instance something like this: https://www.amazon.co.uk/MAGNETIC-BASE-METRIC-GAUGE-INDICATOR/dp/B003W4SFSK This uses a couple of permanent magnets and the "switch" moves one of them so that the magnets can either work together or cancel each other out. They're surprisingly strong, although maybe not quite enough for what you had in mind.

shabaz · Answer

Hi Tom, As many have mentioned, some things are rule-of-thumb and experience-based, and some practicality based on the use-case (since we know that no lamp post is perfectly flat, or perfectly cylindrical), so there can't be a precise recommendation, but from general experience and first-level estimates, it is clear it would not consume 4 car batteries per second. If you actually wanted to derive everything and calculate it all, it would be quite a large exercise - lots of maths and still many things would be severe guesses since not all input information would be available (down to specific material compositions even, to know if it could lift 50kg, temperature rise, etc). It will require experimentation basically.

thotslayer2019 · Answer

Ok so...

I want too make it portable to batteries are a must

How long do the batteries need to last?

Dont know, any amount of time ( more preferably around 1 minute.

I was hoping to have the electronics and batteries in a back pack with the magnet strapped to my hand.

Outdoors is what I am planning my project for -might be a bit crazy but im hoping for this to be a beginner projects into electronics ( use- climbing lamposts/ climbing up low metal objects)

The general costs - I would be willing to pay about £200 for different parts.cannot go over £250.

Thanks!

14rhb · Answer

Hi Tom, May I suggest you spend a small proportion of your funds an a Digital Multimeter ( if you haven't already got access to one ). Something like this Product Link Product Link this could help you understand what is going on in terms of current and voltage as you progress your project. Rod

Electromagnet powering

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