Demagnetized magnet for electronic throttle, help!

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EddySPalm
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Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Nov 26, 2017 6:15 am

So I bought this off of Ebay,
https://www.ebay.com/itm/152139721746?u ... noapp=true

and decided the sleekest way to get a proper length cable on there was to desolder the one that came with it, and solder onto a new one. Job done, or so I thought... Apparanetly neodymium magnets don’t like all that heat, so mine got demagnetized. As far as I can understand, there is no simple way of remagnetizing it.

So, I’m looking for a new magnet, and there are heaps out there, godd stuff! But mine measures 24x4x3mm and so far I haven’t found an exact match.

So now I’m wondering what dimensions I might get away with deviating a little from:
- the 24mm measurement runs the length of the cables travel/stroke. I wouldn’t dare going shorter, but maybe 25mm could work? that might help a whole lot!
- the 4mm is the one that fills the slot it sits in. So obviously I cannot go larger, but would it hurt to go slightly (say 1mm) smaller, If I find no other way?
- the 3mm dimension is the build height, up against the pick-up/sensor, and I won’be changing that.

Then a final question: how much does the force of the magnet have to say? Because I have no way of knowing the now long gone force of the demagnetized magnet... I tried reaching out to the seller, and he has never even opened up one of these throttles, and he can’t source magnets separately...

One way of solving this whole thing would of course be to buy a whole new throttle, and removing the magnet before doing the whole cable change over again...
2017-11-24 21.37.45.jpg
2017-11-24 21.37.45.jpg (247.25 KiB) Viewed 198 times
Thanks for any advice :mrgreen:
Last edited by EddySPalm on Nov 27, 2017 6:07 am, edited 1 time in total.

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fechter
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Re: Demagnetized magnet for electronic throttle, help!

Post by fechter » Nov 26, 2017 1:36 pm

Can you post a picture of the magnets inside?

There are different configurations commonly used, so need to know the arrangement. The hall sensors are all pretty much the same.
You might be able to replace the magnets. I've used the ones from an old Sonicare toothbrush head before.

The trick is to get the right active range for the travel. You can test this with a voltmeter (or just run the motor) while setting up the magnets.
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Re: Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Nov 27, 2017 6:08 am

Thanks Fechter.. Just updated the thread with a picture.
The sensor sits in the opposite side plastic housing, and unfortunately I don't have a picture of it.

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Re: Demagnetized magnet for electronic throttle, help!

Post by fechter » Nov 27, 2017 10:34 am

I see.

I don't know how you overheated the magnet. It seems pretty far removed from the sensor. But some can lose it as low as 80C.

In that configuration, I would guess one end of the magnet is north facing the sensor and the other end is south facing the sensor and it changes gradually in between. If you have another small magnet or compass, you might be able to test this. This configuration might be hard to duplicate.

Even if the magnet was overheated, I would expect it to still have enough residual magnetism to give some kind of response. You can test the hall senor by feeding it 5v and measuring the signal line with a voltmeter. With no magnets around, it should read 2.5v. With any small magnet, putting one pole over the sensor should drive it below 1v and reversing the pole should drive it to around 4v. Maybe the hall sensor went bad, not the magnet....
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Re: Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Nov 27, 2017 4:41 pm

I was desoldering the cable from the brass piece that the magnet is glued to, so temp was well over 1800 degrees C... And the magnet is completely dead by the "feels of it", but I can try and see if I can get some sort of response from the sensor anyway.

The sensor was well out of the way when desoldering the wire, so nothing wrong with it :-)

Just for the record, I have not tried/tested the whole assembly ever, not before nor after the desoldering/resoldering operation. All I've done is noticing that the previously very strong magnet has lost its magnetism after being exposed to all that heat, and declared it dead.

Is the assembly/function a little unclear still? I can take more photos if you'd like!

Thanks a lot for testing procedures, I will get right on to that, though I am fairly sure that my magnet is dead beyond resurrection, and I need advice with regards to what dimensions I can live with as compromises for the original ones.

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Re: Demagnetized magnet for electronic throttle, help!

Post by fechter » Nov 28, 2017 12:12 am

I would test it the way it is and see what happens. Soldering temperature is for sure hot enough to demagnetize them though.

The orientation of the hall sensor matters. If you have a picture of the other half, we can be more certain about things.
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Re: Demagnetized magnet for electronic throttle, help!

Post by Hillhater » Nov 28, 2017 12:40 am

EddySPalm wrote:
Nov 27, 2017 4:41 pm
I was desoldering the cable from the brass piece that the magnet is glued to, so temp was well over 1800 degrees C...
:shock: 1800 C :shock: ...i highly doubt that temp, ...but if so, im surprised there is anything left !
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Re: Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Nov 29, 2017 2:02 am

Hillhater wrote:
Nov 28, 2017 12:40 am
EddySPalm wrote:
Nov 27, 2017 4:41 pm
I was desoldering the cable from the brass piece that the magnet is glued to, so temp was well over 1800 degrees C...
:shock: 1800 C :shock: ...i highly doubt that temp, ...but if so, im surprised there is anything left !
Yeah, well... Did I mention it was silver soldered... So somewhere way above 450 degrees C was needed, and my little Proxxon torch didn't do it (that thing would melt an entire roll of solder in ten seconds...)
So I borrowed a MAPP gas torch from a guy, and at least that did the trick... All I know is the flame reaches 2400 degrees C, so I tried to be a little conservative and said 1800 :mrgreen:

Either way, the solder stayed in place, or at least enough of it, so I didn't have to go out and buy a pack of silver solder cause that sh*t's expensive :O

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Re: Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Nov 29, 2017 2:08 am

fechter wrote:
Nov 28, 2017 12:12 am
I would test it the way it is and see what happens. Soldering temperature is for sure hot enough to demagnetize them though.

The orientation of the hall sensor matters. If you have a picture of the other half, we can be more certain about things.
I will definitely get up a photo of that. Thanks a lot for your help!

I did find (and purchased) some magnets from a German magnet shop yesterday.. one of them is 20x4x3, so perfect in every way except it's 4mm shy of the length I have today. The other one is 25x4x2, so I would say perfect in any way except it will "reach" up to the sensor 1mm shy of the one I have today.

I also found one 25x4x3 which I imagine would be perfect in any way, on Aliexpress, but they are more expensive than the throttle itself, so I'm gonna wait and see if any of the other two will work properly first. I've got all winter, so no rush.

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Re: Demagnetized magnet for electronic throttle, help!

Post by fechter » Nov 29, 2017 9:18 am

See the picture below:
hall_effect_sensor_electric_scooter_cart_bicycle_how_it_works.png
hall_effect_sensor_electric_scooter_cart_bicycle_how_it_works.png (15.12 KiB) Viewed 124 times

This is the closest thing I could find without drawing one myself. You want your magnet to be magnetized axially, along the length. It should work if you stick smaller magnets together as long as they're identical. You need to figure out which end is north and south, which you can do by feeding 5v to the sensor and measuring the signal with a voltmeter, then hold the end of the magnet to the sensor and see which way it goes. Yours might be reversed from the drawing.

With no magnet, your sensor should read 2.5v. With one pole, it will drive the voltage down, with the other pole, it will go up. I suggest using tape or some other non-permanent sticky stuff to get the magnet position right before you glue it with something strong, like epoxy.
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Re: Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Nov 29, 2017 5:07 pm

Fantastic, thank you so much!

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Re: Demagnetized magnet for electronic throttle, help!

Post by EddySPalm » Dec 11, 2017 3:52 pm

Got the new magnets, and would you know they're magnetized the wrong way...

Anyway, I got to test the old magnet and it is completely dead, more or less.

So now the search becomes harder than ever, with the magnets having to be magnetized the right way in addition to being the right dimensions...

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Re: Demagnetized magnet for electronic throttle, help!

Post by fechter » Dec 11, 2017 5:11 pm

If you have multiple smaller (but identical) magnets, you can stack them to get the desired length.

Not sure where you are looking for magnets. One place I've used in the past is Emovendo: http://stores.ebay.com/Emovendo

another one is https://supermagnetman.com/
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