Brad Q
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How close can a neo magnet safely be to a Raspberry Pi?

Thu Feb 20, 2020 5:22 am

A little long here but bear with me:

I am on my first Pi (Pi4-4Gb) and have been using it for my daily driver since August. I have a Flirc case and by itself the highest temperature I have ever seen was 77C with an idle in the mid forties (C). Now technically that would be fine, but I was using a wireless keyboard/mouse dongle, so I had heat concerns about it. Have been using computers since the 4k Pet, so I have an extra 120mm fan(12v) on hand and a 5V wall wart to power it. Now it idles as 30-34C and tops out at 46C(still in Flirc case). After a while the dongle went on a short extension cable and later yet a powered USB hub was added. So I like how it performs very much, but it looks bad and the fan slides around a little.

I have looked over a LOT of other cases and have not found one I really liked. So I thought, build your own. So I was thinking of an A frame design with the 120mm fan as the base (legs to space it off the surface for air flow) and the top of the A open to allow air out the top. Then I thought it was going to be a PITA to design and orient all the sockets. So I thought about how often I unplug stuff. Since I added the USB hub, that would be about never. So no external socket arrangement to design, the entire board will be inside the house/case. So just design it up and 3D print it. But all the walls are just basically flats and I would have zero access (without tearing down the case) if something got unplugged(or some other access was needed). So I decided to print a skeletal frame and attach the flats to the frame. Which is where the magnets come in. The idea was to put an eraser diameter neo magnet on each corner of the flats with a matching (inverted) magnet on the frame.

Thanks, any comments would be welcome.

Heater
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Thu Feb 20, 2020 7:24 am

It would probably be quicker and more reliable to fire up a Pi and run some magnets around it to see what happens than to discuss it here.

However: I have done that with a pretty huge neo magnet and a Pi 3 with no observable effect. So I'm pretty certain a few tiny magnets far enough away to be holding the corners of a box together will do nothing. Don't forget that magnetic field strength reduces very quickly with distance. Following the inverse square law or better (depending how you look at it).

I have heard rumors that some people have caused various Pi not to boot up when subject to magnetic field. This is likely cause by saturation of some ferrous component on the board. I'm pretty sure in any reasonable case this is unlikely.

There is nothing like doing the experiment oneself.
Memory in C++ is a leaky abstraction .

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davidcoton
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Thu Feb 20, 2020 10:14 am

Location: 345th cell on the right of the 210th row of L2 cache

StuartF
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Thu Feb 20, 2020 12:41 pm

The idea was to put an eraser diameter neo magnet on each corner of the flats with a matching (inverted) magnet on the frame.
If you want to reduce the chance of magnetic interference on the pi case, use small steel strips instead of magnets on the case.
Keep the magnets on the mounting area.
If you are 3d printing, make a recess for the steel on the inside of the case with a thin wall to the outside ( so the distance between the magnet and the steel is kept small ) and then glue the strip in place. Cover the strip in something non conductive to prevent any possible shorting problems with the internal of the case.

Also, should any ferrous material come into contact with the case, it won't be attracted to it.

Brad Q
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Thu Feb 20, 2020 12:58 pm

To be clear; I am not going to use magnets to mount the board to the case but to mount the flats(walls of the case) to the frame. So the magnets will probably be a couple of inches away from the board. I initially thought about putting long standoffs on one of the flats to mount the motherboard, but that would make cable management more of an issue. Currently I am thinking that I will attach it to the top part that will hold both of the end frames together(not by magnet).

I will have to play with the magnets a little and see how strong the magnet to steel pull is vs the magnet to magnet pull. I suspect that you may be correct that magnet to steel will be plenty. Making sure the flats do not fall off by a casual bump (I am pretty much a bull in a china shop) is important.

After I posted this I installed Freecad to start actually designing this (other than in my head), only to find out that Freecad (including the one in the repo) does not currently work on the Pi4.

Eirikur
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Thu Feb 20, 2020 7:42 pm

KKSB has a case like the Flirc with no plastic insulating panels. It costs more, though. I have not compared them.

Make sure you have the new firmware with the better heat management. My pi 4's are a lot cooler now.

cleverca22
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Fri Feb 21, 2020 12:15 am

from what i know of EM, stationary magnets are perfectly fine, at any strength

the problem only happens if you start moving them relative to the pi (or wires near the magnet)

so its probably fine to use them for mounting

Heater
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Fri Feb 21, 2020 2:27 am

cleverca22 wrote:
Fri Feb 21, 2020 12:15 am
from what i know of EM, stationary magnets are perfectly fine, at any strength

the problem only happens if you start moving them relative to the pi (or wires near the magnet)

so its probably fine to use them for mounting
Not so.

Circuits often have components that are constructed of ferromagnetic materials, transformers, inductors, chokes, They will become "saturated" when subject to strong, static, magnetic fields. When saturated their properties change, specifically inductance, which can cause the circuit they are in to fail.

See article of saturation here: https://en.wikipedia.org/wiki/Saturation_(magnetic)
Memory in C++ is a leaky abstraction .

cleverca22
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Fri Feb 21, 2020 3:12 am

ahhh yeah
i was thinking purely about induced currents in the traces, didnt think about cores getting saturated!

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Burngate
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Re: How close can a neo magnet safely be to a Raspberry Pi?

Fri Feb 21, 2020 10:23 am

Heater wrote:
Fri Feb 21, 2020 2:27 am
Circuits often have components that are constructed of ferromagnetic materials, transformers, inductors, chokes, ...
... of which there are at least four round the PMIC, a couple on the rail labeled 1V05_VLI, eight in the ethernet socket ... and that's only the ones on the schematic

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