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Comment by dotancohen | Hacker News Reader

I've been epoxying a metal plate to the back of my phones for years. I have a hard drive magnet on the dashboard, that I stick the phone to.

It's absurdly strong, much stronger than traditional phone mounts. And I can just grab the phone and go, no fussing with release buttons or whatnot.

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A lot of phones have almost enough metal to stick to a magnet. I bought this car mount a while ago and while it came with metal plates I found that my Nexus 6 would stick to it without anything. I later upgraded to a nexus 6P which weakly stuck, it would kinda hang off the bottom but never fell off.

https://www.amazon.ca/dp/B01AMGFY5M

I was thinking that it would be nice if we could just standardize something as simple as "stick an iron plate in the back of the phone" but I guess now I see that it would be nice if there was some sort of standard for a Qi charging location relative to whatever metal/magnets are there.

Me too!

I used hard drive neodymium magnets for awhile, but recently discovered some incredibly strong magnetic strips with an adhesive backing. This gives me way more positioning freedom for my phone. These strips are neodymium and at least ~7 times stronger than every other magnetic strip. (which all use ceramics).

You can find the magnets I'm talking about on McMasterCarr [1] or just search for "NeoFlex magnets". Besides McMasterCarr, I can only find them from European sellers.

IMHO, anyone buying adhesive magnet strips would be happier buying these, but no one advertises any sort of standardized magnetic strength per area unit. This makes the differences very hard to determine for most consumers. The typical flexible ceramic magnets, like this one [3], support 70g/cm2 [4], while the NeoFlex ones I mentioned support 400g/cm2. ( 800lbs/sqft)

Also many people try to stick magnets to magnets, works works for typical magnets, but that doesn't work well at all for the multi-pole magnetic strips like these. It works just enough that people blame the magnets for being weak, when really they might be quite strong if you just used a thin steel plate instead.

[1] https://www.mcmaster.com/catalog/3651K8

[2] https://www.amazon.com/NeoFlex-Flexible-Neodymium-Magnetic-3...

[3] https://www.amazon.com/dp/B005HYA2SE

[4] https://www.wolframalpha.com/input/?i=12lb+%2F+%281%22+*+12%...

I had one of these in my old car and can't really find a good place to put it in my new car. It's a pity as it was incredibly useful.

Neodymium magnet I think.

I stick the metal plate in a phone case instead of on the phone. Better trade-in value for my phone that way.

My last phone I kept seven years until it now longer worked! Samsung Note 3, the hardware buttons failed, the screen never cracked in 7 years.

I've never left anything to trade in!

Wow. So, the magnetic field doesn't mess with the electronics of the phone?

Wires only pick up current when they’re moving through a magnetic field. Just sitting in one is fine. Although the internal compass isn’t going to work great.

Also people significantly overestimate the amount of current a normal (something you’re gonna encounter in day-to-day life) magnetic field can induce in a wire. There’s a good reason motors are packed with so many windings, you either need an incredibly large magnetic field, or a crap ton of wire, to get an interesting amount of current.

Magnetic field also falls off as 1 over distance cubed. So very very quickly.

The reason for magnetic field strength falling off as 1/r^3 is interesting: the biot-savart law says that magnetic field falls off as 1/r^2 from a magnetic source, but in reality sources tend to be better approximated by magnetic dipoles than magnetic monopoles. A "north pole" is always accompanied by a "south pole", and at distance there are "interaction effects" such that a part of the field strength is "canceled out".

https://en.wikipedia.org/wiki/Magnetic_dipole

https://en.wikipedia.org/wiki/Magnetic_monopole

Ooh that is a really great visual to explain it.

Current also picks up force as it moves in a magnetic field, but it's not like the electrons are going to fall off.

Magnetic fields can saturate ferrites and affect coils, but the slight deviations in few components should be nothing the closed loop circuitry won't handle. You'd need a stronger/closer magnet for that.

Solid state circuits usually have tiny sensitivity to static magnetic fields as opposed to EM waves, which they need to handle gracefully.

It very very likely messes up the magnetometer or even breaks it completely (I've managed that myself).

I've never noticed an issue. And I have used Waze at least three or four times over the years, both with my old Note 3 and now with a Samsung A50, with no issues.

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