Re: [EE] Small electromagnet cores?

At 01:51 PM 2025-06-02, you wrote:

Hi, Mike:-

There's sellers for 3mm diameter 'soft iron' and for 1J50 permalloy 
rod on Aliexpress.
The latter is stupidly expensive compared to the domestic price in 
China- it's just that
nobody is bothering to sell it for a reasonable price overseas. There 
you can get
a couple meters of 3mm diameter permalloy for a few dollars delivered 
overnight.

If you happen to have a friend in Shenzhen getting them to chop it up 
into short
lengths and put it in a package for shipment might be an option if you want a
material that's got a _datasheet_ and is characterized for magnetic 
properties.

Soft iron:
https://s.click.aliexpress.com/e/_oE8kZe0

Permalloy:
https://s.click.aliexpress.com/e/_okGhroo

The latter type 1J50 is a about a 50:50 Ni-Fe alloy that is hydrogen annealed
to improve the magnetic characteristics such as permeability.

You can get similar material to the 1J50 off the shelf at electrical 
steel suppliers
in the US such as Carpenter and Fry (with different numbers) but they 
don't generally
carry small diameters-- 3/16" is about the smallest and IME they 
don't tend to be
enthusiastic about tiny orders even for exotic materials.

But I'd give a cheap steel screw, nail or threaded rod a try first 
and see if it's
good enough. In the US, McMaster sells 3mm threaded steel rod cheaply:

https://www.mcmaster.com/98861A040/

Best regards,
Spehro Pefhany


>Hey all-
>
>I'm trying to make a flip-dot display like this one:
>https://hackaday.com/2021/05/29/3d-printed-flip-dots/
>
>I'm having a hard time with the electromagnet component of the project. OP
>used 3mm threaded rod, and it seemed to work okay per his videos, but it's
>not working for me at all.
>
>I'm relatively sure the problem is in the permeability of the core.
>Stainless steel is not a great magnetic field conductor. I'm looking for
>something better.
>
>Lots of searching has led me nowhere. I'm thinking of trying a nail next;
>I'm wondering if anyone has any better ideas for a core? NB- I've seen the
>"soft iron core" that Amazon sells; it's a bit expensive for my taste ($16
>for 200mm; I would need four of those rods to complete the project).
>
>Mike
>--
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