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Running Electromagnets

Bruce Baker

New Member
I thought I would attach a pdf so it would explain better what I'm trying to do.
I have a 12 volt 29 amp DC converter to power electromagnets. Of course the higher the amps the more powerful the magnetic coils. It seems that this is too much amperage for a reed switch or hall sensor to operate?
So Maybe I need someone to tell me what type of sensor I need for quick response time to fire electromagnets by north pole magnet and could put it after the electromagnets and reduce the amperage for whatever sensor would be best, by using resistors?

Bruce
 

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dr pepper

Well-Known Member
Most Helpful Member
I think reed switches respond to north & south.
An electromagnet holding/pulling power is set by its electrical power rather than just current.
Depends how fast you need to switch, if 10mS is ok then a hall effect sensor controlling a relay via a transistor sould work, and you'd probably get your n & s pole discrimination with the right hall sensor, also dont forget a hooge electromagnet is going to give one heck of an inductive kick, the mosfet will need protection.
If you want really fast response then a hall sensor driving a fet is the way to go (if the magnet is Dc).
How many volts & amps is the actual electromagnet.
If your using some kind of voltage converter then for speed you'd run this all the time & switch its o/p.
Is this a free energy project?
 

Reloadron

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Most Helpful Member
Saw your other post on hall effect switches. No, you won't find a hall effect switch which will handle 30 Amps. You may also want to consider an electro magnet is an inductive load. Depending on the magnet be it AC or DC about all a hall effect sensor will do is, depending on type, sense the magnetic field strength.

So assuming you have a 12 VDC electro magnet which draws 29 or 30 amps what exactly are you trying to do? You can turn it On/Off using a large switch, a relay or contactor, or even a DC SSR (Solid State Relay). Your attached PDF lacks any detail. Your magnet coil is, again, an inductive load so when power is removed the field will collapse resulting in an inductive kick or flyback effect. You need to consider that and add a flyback diode or similar.

I would look towards using a 40 amp 12 volt coil automotive relay to switch your electro magnet On/Off. You also do not mention any On/Off rate? How many times over a given time period do you want to turn this magnet On/Off? You want good answers you need to be detailed in exactly what you want to do?

Ron
 

Bruce Baker

New Member
Electronics is all pretty new to me to try and solve on my own. I have studies electromagnetism, AC converting to DC along with inverters and 3 D printing which I have a handle on but just can't quite manage the electronics! Forgive my communication in this subject and thank you all for your help!!
12 volts and 29 amps go through the wound coils to make electromagnets. There are 8 magnets on a rotating wheel, I want to turn the magnets on when they oppose another north permanent magnet. Therefore there will be 8, turn on pulses, with each revolution and trying to get the rpms to around 160 rpms.
So, 160/60 = 2.66 2.66/8 = .33 turn on pulses per second if I did the math right!
 

Reloadron

Well-Known Member
Most Helpful Member
This just went from being a simple electro magnet project to a complicated affair. You now have a rotating mass with 8 coils. Actually while I am not sure where you are going with this you would likely do better with an 8 pole stator and rotate your permanent magnets outside the stator. If you are looking to use 8 coils and energize them in a sequence it gets complicated. Let me think on this overnight and hopefully will come back with some ideas,

Ron
 

dr pepper

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Most Helpful Member
Isnt that 2.66 x 8 so around 22hz, or maybe 2.66 x 4 because 1/2 the magnets are south poles so 11hz.
For electronics thats s;ow, but for a relay maybe too much, a solod state relay would be a simple solutiuon, so long as it can switch at that speed.
 

unclejed613

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160/60 = 2.66 2.66/8 = .33 turn on pulses per second if I did the math right!
PRR should be 2.66*8=21.28 pps. you could make it even more efficient if it were AC at 21.28Hz, then you would have the coils pushing and pulling.
 

shortbus=

Well-Known Member
There are 8 magnets on a rotating wheel, I want to turn the magnets on when they oppose another north permanent magnet. Therefore there will be 8, turn on pulses, with each revolution
Won't work if the solenoids(electromagnets) have a steel core in them. As the permanent magnets pass the turned off solenoid they will try to slow down the rotation. It sounds like you are trying to reinvent the BLDC motor. They use 16 pulses per revolution for a an 8 pole motor.
 

Reloadron

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Below is an image of an 18 pole stator. Notice the cores are laminations and not solid. The reason for laminations are as shortbus just mentioned. This is a 30 Amp stator assembly. Magnets rotate around the stator coils and the coils are wound opposing. That means each coil in the rotation is wound in the opposite direction of the previous coil.

Stator 1.png

Stator 2.png


This is a 30 amp 3 phase stator but you should get the idea.

Here is an example of a magnet which could be rotated. The poles alternate N, S, N, S, and so on.

Magnets 1.png

So on a stator if you want alternating magnetic poles you don't turn poles on and off you simply wind the coils in alternating directions.

I have no idea how or why a hall effect switch figures into this?

Also are we looking at 30 amps per coil or 30 amps max total?

Ron
 

dr pepper

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Looks like an outboard alternator ron.
From what I've seen so far this sounds much like a brushless dc motor.
 

Reloadron

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Hall effect switches are normally used to detect the position of the rotor to allow the electronics to switch the windings correctly, and to control the speed.
Yes Nigel I am aware of that. Prior to this thread there was this thread. I am just trying to figure out how things tie together.

Looks like an outboard alternator ron.
From what I've seen so far this sounds much like a brushless dc motor.
Actually a spare stator for my bike. I think it's a 30 amp alternator. Yes, I agree as to it sounding like a BLDC motor but am not sure where all of this is going? Beats me. :)

Ron
 

Bruce Baker

New Member
This is the 3 electromagnets with 4th space for a sensor (north pole) to turn on as each of the 8 magnets pass the coils. DC current will make the coils north pole, will push permanent magnets away.
Sorry, thought pic may help.
 

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shortbus=

Well-Known Member
You seem to be missing the point in this, motors don't just use a single pole to make them rotate. Like Ron said the PM (permanent magnet) poles alternate, N-S-N-S and so on. The solenoids(electromagnets) are situated opposite each other. When a N PM is lined up on one side a S PM is on the other, and the solenoids are made to be similar poles this pushes the PM away and the rotor rotates.

Why not try to explain completely what you are trying to do? That way maybe we can find a link that shows why what you are describing isn't the way you think things work, or we can get a better understanding of your thoughts.

This link shows how both a brushed and brushless motor work. https://electronics.howstuffworks.com/brushless-motor.htm
 

Reloadron

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So the object here is to make a motor?

Below is a hall effect sensor circuit I made years ago. I forget the sensor part number but recall it was Allegro manufacture. It also had 4 leads, Vcc (power) Gnd (ground) and an output for both North and South pole.

HAL2.jpg

HAL3.jpg

Mounted on a piece of nylon the green LED indicates North and the red LED indicates South.

Back to the hall effect sensor. In the last thread I provided a link as to the different types of hall sensors, they all behave differently. I would look for a 3 lead SIP (Single Inline Package) type which has an output go high when a North Pole field is present since that seems to be what you want. I would use the output to turn on a MOSFET to power your coil. This is just based on what you have posted. Choose your hall sensor based in part on magnetic sensitivity thresholds, and polarity. Since you want a North polarity decide sensitivity (distance at which the output changes state) and if you want an active High or Low output. Remember what was mentioned about inductive kick and the need for flyback diodes across the coils.

Personally I doubt I would go about things this way for a demonstration type motor display but it's your project which you seem to have started.

Ron
 

dr pepper

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Most Helpful Member
If I'm right bedini claims that the back emf pulse from its motor coil has more energy than the energy put into it from the power source, therefore its an overunity machine.
I dont think its ever been proved.
Nice to look at though whizzing round.
If the 30 amp coils are on the pic you mentioned it would be more efficient with larger magnets, as the field from the coil will probably dominate that from the magnets.
 

shortbus=

Well-Known Member
Bruce Baker, please keep this out of PM, anything you say should be for all to see.

You say it isn't "free energy", but yet when you do a Google on Bendini generator, every site calls it that. So are they wrong or you?
 

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