# How to measure voltage produced by magnets

Discussion in 'General Electronics Discussion' started by hizuka007, May 15, 2014.

1. ### hizuka007

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May 15, 2014
Good day folks!

I am no electronics guy, but i have some project to make, and I would like to know how to measure the voltage produced by moving a magnet on a coil. I've tried the multitester of my brother setting it to a dc voltage, but when i move the magnet back and forth there is no voltage change...

Thank you

2. ### Harald KappModeratorModerator

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Nov 17, 2011
Welcome to our forum.

A magnet moving through a coil (or a coil moving through a magnetic field) back and forth will create an AC voltage, not DC. You need to move the magnet with some speed, otherwise the induced voltage will be very low (compare to a bycicle dynamo).

3. ### hizuka007

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May 15, 2014
i also tried moving the magnet in one direction by sticking the magnet on a disk then rotating the disk using a battery powered dynamo,.. but still no voltage change, it still 0 volts...
is it necessary to use magnetic wire coil? because im using a single solid wire from a telephone wire... thanks!!

4. ### Harald KappModeratorModerator

11,413
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Nov 17, 2011
A single wire will produce only a very small voltage. wind the wire to a coil. Any kind of wire is o.k., you don't need magnet wire, although you can wind smalller coils due to the very thin insulation of magnet wire.
Rotating the magnet on a disk also produces an AC voltage. You cannot produce a DC voltage using induction because you'd have to constantly change the magnetic field in he same direction which will lead to an infinite magnetic field which in turn is impossible.
Read a bit on induction in the Wikipedia.

5. ### hizuka007

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May 15, 2014
i mean, i used the single wire inside the telphone wire and wind it to a coil....
i tried setting the multimeter to AC but still no voltage produced..

ive attach my test project. forget about the appearance lol

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6. ### Harald KappModeratorModerator

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Nov 17, 2011
This small coil without a core will produce millivolts, maybe even only microvolts.
Also you should orient the coil such that the change in magnetic flux is maximized when the magnet(s) pass the coil.
Add an iron core to the coil to concentrate the magnetic field. and experiment with the orientation of the coil with respect to the magnets.
Use many more turns of the wire to create a high inductance.
Set the voltmeter to AC millivolts.

7. ### hizuka007

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May 15, 2014
I see,. thank you very much! ...so thats why no voltage detected...
and by the way, can i use plastic core instead of iron? so that it will not be pulled by the magnet downwards..

again, thank you

8. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
No, the core needs to be magnetic (not magnetized) unless you can arrange to pass the magnet through the coil, in which case the magnet itself acts as the core.

9. ### hizuka007

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May 15, 2014
but ive seen on some youtube videos demonstrating a coil with a plastic cylinder as a core then passing the magnet inside the cylinder changes the voltage..

and by the way, ive tried the coil of a 220v Relay, it does not produce a volts at all. is it still very little?

sorry for dumb questions, hehe. im no electrician. but i have some ideas that i want to materialize using simple electronics..

thanks!

10. ### Harald KappModeratorModerator

11,413
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Nov 17, 2011
This is exactly what Steve wrote: The magnet is moved inside the coil, the plastic tube is only there to stabilize the windings.
If you have the magnet external to the coil, as in your setup, you need an iron core which will concentrate the magentic field within the coi.

It depends on teh stregth of the magnets and on the way the magnetic field is coupled into the coil. One problem with your setup is that the magnetic circuit (magnet south - coil - magnet north) is not completely contained in a magnetic conductor (iron). When you move the magnet past the coil, only a small part of the magentic field couples into the coil. A lot of the magentic field bypasses the coil as it goes stright from the magnet's nort pole to the south pol without doing work in the coil. For a generator to produce noteable current/voltage you normally create a closed magentic circuit and try to minimikze the air gap between the iron parts of the circuit.
Here is a very basic animated presentation. and here is an instructable.

11. ### hizuka007

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May 15, 2014
I see .. all is clear now..
I will change my setup to a vertical stick lining the magnets verticaly.. i will not use a disk..

Thank you sirs!

12. ### hizuka007

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May 15, 2014
one more thing, can i remove the insulator of the wire when making a coil? because im trying to use a telephone wire as a coil as of the moment.
and whats best, removing insulator or not?

thanks again

13. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
If you remove the insulation from the wire you need to take other precautions that the wire doesn't touch anything (including itself).

In general, the wire *MUST* be insulated except at the very ends where you make an electrical connection to it.

14. ### hizuka007

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May 15, 2014
i see, so its not possible to do so if i wind it on cylindrical object with insulator being removed...

thanks! .. i will return here if i am successful of this project..ehehe

15. ### hizuka007

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May 15, 2014
Good day folks,. this is now my setup, the magnets are place inside the ring as it spin,.. but still I dont get any voltage (DC or AC) at all.
what seems to be the problem?

thanks!

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16. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
That's because the magnet isn't moving *inside* the coil.

You know that thing you wound the coil on? That's inside the coil.

You could spin the magnet near the end of the coil. So that the north and south poles of the magnet alternately come close to it. However you're far better off with a much shorter fatter coil.

17. ### hizuka007

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May 15, 2014
the setup is that the spinning magnets is at the center of a circular coil (attached file).
so i guess there should be at least 1 volt of electricity, but i wont produce one.

i cant put spinning magnets inside the coil, because theres no way to spin the magnets that way..

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18. ### davennModerator

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Sep 5, 2009
you need to rebuild the coil ... as it is its pretty useless .... isn't going to produce any worthwhile results

you would be better off to use that 3M tape roll as the coil former and wind the wire around the outside of the former
and then move the magnet in and out of the former

Now I have only shown 4 turns around the outside of the former for clarity.
But you need hundreds of turns ... at least 300 - 400 to get a significant voltage ( maybe ~ 5V or so)

use a cardboard or plastic tube of 2 - 3 inches in diameter and an inch or 2 wide

cheers
Dave

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19. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
If you really want to rotate the magnet, you'd need to do it this way:

Also note that you'll be generating AC, so a DC meter will show 0V

20. ### davennModerator

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Sep 5, 2009
yup That's another choice

one of my seismometers uses yet another slight variation...

cheers
Dave

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