[nura]

Hi!
I need a small but powerful magnet. Here is what I plan to do with it.
http://www.team-bhp.com/forum/techni...o-belts-2.html
Post #21
I have some old 4" car speakers. Can their magnets be considered small but powerful? How do I go about removing the magnet from the speaker?
My sincerest thanks in advance for your replies.

[navin]

Originally Posted by nura

Hi!
I need a small but powerful magnet.
I have some old 4" car speakers. Can their magnets be considered small but powerful? How do I go about removing the magnet from the speaker?.

1. I suspect your 4" speaker's magnet wont be strong or powerful
2. The magnet can be removed but these magnets are stuck (tot he pole piece) with a rather strong glue. Some of these glues are NOT waterproof so dipping the magnet in water might loosen the strength of the glue.

Do NOT hammer the magnet or the pole piece ans hammering will drastically reduce the strength of the magnet.

the cheapest way to get a 2-3" donut mqgnet is to buy it. In Mumbai there is a place called Lamington Road where such parts cna be got. I dont know about where you live.

[greenhorn]

I'd say get the magnet from a junked hard disk. they are FAR more poweful

[DerAlte]

Daktar-babu, even a small rectangular ferrite magnet that you can get in stationery shops will also do the job.

[Hashim]

I remember in my childhood I removed magnet from old radio set speaker and played with it. LOL What a good days those were, I would find those small things very entertaining. Anyway you can try putting some drops of thinner (paint solvent) where the magnet is glued to the speaker shell. Use a small hammer and any old knife and tap that place where you have put the thinner, but do it lightly as magnet will break. With little effort it will sure come out.

[Prowler]

The power of the magnet depends on the power handling capacity of the speaker. Car speakers usually have around 20 W rms capacity. Most of them would use Alnico magnets which are powerful enough for your intended purpose - if you can find a small enough magnet.

You can remove the magnet glued to the body of the speaker by immersing the speaker in a bath of thinner liquid.

[nura]

Thanks for all the suggestions. Lazy me will probably pick it up from a shop then.
Do they sell "electronics" in Lamington Road, Mumbai? I guess I will need to look in Chandni in Kolkata.
Is there a simple test to judge the powerfulness of a magnet?

[Sankar]

Originally Posted by nura

Is there a simple test to judge the powerfulness of a magnet?

Stick on to your fridge and try to pull it off Seriously!

Compare this with regular magnets you get at lab supplies etc and compare it with a HDD magnet.

Btw HDD magnets are powerful magnets that you can have for cheap.

[navin]

Originally Posted by Prowler

The power of the magnet depends on the power handling capacity of the speaker.

Incorrect.

Case in point. Dynaudio's 17W75 (and many others from that series).

Extremely high power speaker capable of absorbing 300W (thermal) as long as their Xmax was not tested. but the magnet was not very powerful at all.

The power handling capacity of the spekaer is determined by the design of it's voice coil and to some extent by the design of it's suspension.

[yogeshnaik]

The magnet is in circular ring shape, looks like a tyre. This is glued and sandwiched between two round plates. The bottom plate will have a cylinder at the centre on which the coil runs. It is not easy to remove the magnet if you need to replace. But if you just need it, first you need to remove the diaphram, then using a hammer just tap at the centre on the cylinder. The magnet comes out of the glue but it attracts between the two plates.
Enjoy!

[nura]

Where is an HDD magnet located & how do I get it out? I don't have a wrecked HDD but I might be able to buy one cheap I guess. Is it a doughnut (ring) magnet?

[Sankar]

Originally Posted by nura

Where is an HDD magnet located & how do I get it out? I don't have a wrecked HDD but I might be able to buy one cheap I guess. Is it a doughnut (ring) magnet?

You will need torx screw drivers to open HDD, buy a cheap chinese set for this purpuse.
You can get broken HDDs from your techie friends or from a pc repair shop.

HDD magnet is not round neither does it have a hole. But HDD magnet has a metal base plate attached to it on which you can drill a small hole to pass a wire through. If you're lucky some base plates will have a hole already.

Here's a nice video:
How To Get HDD Magnet - Video

Here's a moronic video:

YouTube - How To Hack a hard drive to get Neodymium Magents

[nura]

Thanks a ton! That was really useful. I already have a set of TORX screw-drivers. Now to locate a kaput hard drive.
BTW how much would the magnet/ base-plate measure across the widest part? I need to drop it into the power-steering fluid reservoir of my Santro.

[Sankar]

Originally Posted by nura

Thanks a ton! That was really useful. I already have a set of TORX screw-drivers. Now to locate a kaput hard drive.
BTW how much would the magnet/ base-plate measure across the widest part? I need to drop it into the power-steering fluid reservoir of my Santro.

That depends on the HDD make & model. But you can be sure of laptop HDDs having smaller magnets than their 3.5" brothers.

The magnet I have is from an old Quantum HDD, the magnet+plate is around 2cms at its widest part.

[nura]

Thanks once again. 2 cms should drop in nicely.