hall sensor magnet

[garyParticipant @gary44937]

is it ok to mount the ignition magnet direct to a steel cam gear or do i need to fix it to a plastic disc first. gary

[garyParticipant @gary44937]

[Roderick JenkinsParticipant @roderickjenkins93242]

In my experience it will work fine installed in a steel gear.

Rod

[not done it yetParticipant @notdoneityet]

Posted by gary on 27/04/2023 19:51:47:

is it ok to mount the ignition magnet direct to a steel cam gear or do i need to fix it to a plastic disc first. gary

I doubt it, but depends on how it is mounted. Best if not out of balance, for a start?

I, personally, likely wouldn’t just fix it to a plastic disc, either. Of course it might depend on the plastic disc…

[SillyOldDufferModerator @sillyoldduffer]

The tachometer magnet on my lathe attaches directly to the metal with no plastic because that would weaken the grip. However the magnet is mounted in a flat bottomed pocket about 1mm deep and of slightly larger diameter. The pocket stops the magnet sliding sideways should the spindle stop or accelerate suddenly.

Dave

[JasonBModerator @jasonb]

No doubt about it mounting to a steel part makes no difference whether it is holding itself to the surface, placed in a hole or stuck to the surface or in the hole with teh glue insulating it.

If in doubt try sticking a disc or cylindrical magnet to a bit of steel and then offer up another piece of steel and low and behold the magnet will attract the steel. Do the same with the opposite pole of a magnet and they will repel each other

[Robert Atkinson 2Participant @robertatkinson2]

A hall effect sensor will work better if the target magnet is attached to a magnetic surface. It concentrates the magnetic field. Use an adhesive to keep it in place.

Robert.

[Maurice TaylorParticipant @mauricetaylor82093]

Hi, Does a Hall sensor need a magnet to trigger it ,a a Hall crank sensor uses a toothed steel disc.

Maurice

[Mike HurleyParticipant @mikehurley60381]

Whatever you attach it to, beware the polarity! They work one way, but not the other. Test first before fixing permanently in place!

Regards Mike

[John HaineParticipant @johnhaine32865]

Posted by Maurice Taylor on 27/04/2023 21:44:43:

Hi, Does a Hall sensor need a magnet to trigger it ,a a Hall crank sensor uses a toothed steel disc.

Maurice

I think the crank sensor have a built-in magnet, the toothed disc creates a magnetic circuit with varying reluctance.

[Joseph Noci 1Participant @josephnoci1]

Posted by Maurice Taylor on 27/04/2023 21:44:43:

Hi, Does a Hall sensor need a magnet to trigger it ,a a Hall crank sensor uses a toothed steel disc.

Maurice

Hall Crank sensors, and indeed many such sensors in industry, have a magnet installed with the hall sensor in the housing. The magnetic field is such that the hall sensor is not activated till a tooth of the sense disc aligns – the magnetic field is then concentrated at that location and the hall sensor activates. No external magnet needed here.

Hall sensors are available that sense the North or the South magnetic pole, and if it is the raw sensor, ie, the hall device itself, as opposed to a custom molded ,fit-one-way device, simply flipping the hall sensor over will correct an incorrectly mounted magnet.

Also, base hall sensors ( the raw sensor) are available in many different gauss sensitivities, and also in toggle or latching mode. Low Gauss sens aids using small low energy magnets, even a worn out button Eclipse magnet works fine, but they have lower noise immunity as well. Toggle mode means the sensor de-activates when the magnet leaves the area. Latching mode – the sensor latches 'on' when the 'on' magnetic pole approaches, and to turn it off the pole must be reversed.

Last, hall sensors are also analogue – give out a voltage proportional to the strength of the magnetic field or digital, ie, on/off…

[garyParticipant @gary44937]

thanks for the replies guys, gary

[Chris Evans 6Participant @chrisevans6]

Posted by Mike Hurley on 27/04/2023 22:30:47:

Whatever you attach it to, beware the polarity! They work one way, but not the other. Test first before fixing permanently in place!

Regards Mike

Plus one for the heads up re polarity, I found this out when I built an ignition system for a three cylinder Triumph.

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