This article describes a simple circuit which can be used for pulsing an electromagnet. The IC 555 once again becomes the central part of the circuit. Let's learn the making procedure of this simple adjustable electromagnet circuit for varying the magnetic power of an electromagnet.
Introduction
The circuit was requested by Mr.Jason, one of the followers of this blog. Though I'm not sure of the application needs, the circuit probably can be used for controlling the average magnetic power of an electromagnet or rather the circuit may be considered an adjustable electromagnet circuit.
The circuit involved is quite basic and has been already employed in many applications, explained in my earlier posts. Here the application is quite similar to the earlier ones, that is controlling the output load through a series of varying pulses or through PWM method.
Circuit Description
The mark/space ratio can be appropriately adjusted using the shown configuration, which in turn can be used for varying the response of the output load.
Here the output load is an ordinary homemade electromagnet, connected via a power transistor TIP 122.
The power of the electromagnet is at the maximum level when the pot is set for achieving high mark levels than the space levels and vice versa for reducing the magnetic effects of the electromagnet.
The electromagnet may be procured ready made or can be hand made at home using suitable lengths of enameled cooper wire wound over a magnetic core, like an iron nail or rod etc.
The diode connected across the electromagnet protects the transistor from back emf fluxes of the electromagnet.
The circuit may be powered with voltages between 5 and 12, but the current must be appropriately rated, otherwise the circuit will fail to operate.... if a battery is used, make sure it's rated at least at around 1 AH.
Once powered, this adjustable electromagnet circuit will enable smooth adjustments of the attached electromagnet's magnetic field from zero to maximum.
Circuit Schematic
Aqib Ahanger says
swagatam sir…. i have a 3 cable setop boxes… one has got a signal dropping problem which autimatically shows no signal after two or tgree minutes i have to switch on n off the supply of it then it worrks again n vice versa… another one shows on indicator but diesnt gives video out put at oll.. or like it doesnt takes the signal out put. .
Aqib Noor
Electronic n Electrical Technician…
Swagatam says
I am sorry Aqib, i have no idea regarding signal processor units because these normally work with extremely sophisticated and complex circuits..
Brett Buckley says
Making a micro controller based project and my project is a crane that will also have an electromagnet for picking up objects, would this circuit work for that?
Swagatam says
the 555 section might not be required for your application, just feed the MCU output to the transistor base for controlling the EM.
TTGB says
Could an LED display be added to this to visibly display the intensity of the magnetic field as it changes?
Swagatam says
you can add an LED in series with the transistor base, this will enable the required indications…
Gustavo A. Díaz says
Hi! I was about to make something like this, since i need to test the speed sensor of my motorcycle (or modify the mileage, since i've buyed a new gauge that start from 0KM) but in a fast way (using high hz/Khz in the output of 555). So pulsed needed to simulate the wheel spining. This will work right? Thanks!
Swagatam says
Yes, it will work in that way as it would effectively simulate the pulses acquired from a rotating wheel.
Anonymous says
Hello,
Can i modified this circuit to have a 5v regulated output using a 5.6 zener diode and totally remove the pot.?
how it is possible? I dont want to use a circuit built around a 7805 IC/LM317 bcoz the use of heat sink makes the circuit bulky.
i want to use 12v input from a car. Thank you.
Swagatam says
Where would you put the zener???
Add a 220uF cap across the base/ground of tip122, abd adjust the pot to get the desired voltage at the collector of the transistor……..
Jonathan McIntosh says
Hi there. I came across this page while looking for some ideas while building an electromagnet for my son's science project. My needs are slightly different, and I was wondering if you could help/comment. We are making a home-made electromagnet. What we have experimented with so far does not give us a very strong magnet. So far, we have simply wrapped a coil on an iron core (bolt) and attached to an AC power source. We wrapped one bolt with perhaps 1000 turns of a very fine wire, so the inductance would be very high and it could be attached directly to 110V ac 60hz (a little bit dangerous if there is a short…). But, inductance was so high that the strength of the magnet was not that great. Even so, it heated too quickly. On another bolt, we wrapped heavier gauge wire but far fewer times, maybe 150-200 windings, then connected it directly to 24V AV 60hz (step-down transformer from 110V AC 60Hz) Again, not very strong, but not as much heat generated. Then I began thinking about how to build a circuit to get better strength. Clearly we cannot connect it directly across a DC power source without blowing the power source. For example, putting an AC-to-DC 4-diode bridge on the 24V AC step-down transformer would be bad. But, put a resister in series with the coil and it should be OK. Then also, I was thinking one should have a diode across the coil in reverse, so that when the power is turned off the diode can take the current from the coil, preventing high-voltage sparks across switch gaps. (I'll call thei the "reverse diode") Then, if one wants the magnet to die quickly when the power is shut off, put a resister in series with this reverse diode. Next, if one wants to "pulse" the magnet, change the first resister (in series with the DC current) into two resistors, and put a push-button switch across one of these two resistors: once in steady state with most of the voltage across the resistors, push the button to short across one of the resistors, thus pulsing a voltage across the coil. You don't want the energy you put in to the coil with such a pulse to be dissipated quickly when the push-button comes up – it would be dissipated in the resistor in series with the reverse diode. So, the resistor in series with the reverse diode should be shorted-out except when the power switch is thrown. But, all this is pretty simple-minded stuff. I'm sure someone with a better feel for electronics, esp. what could be done with a few transistors and IC circuits, could do a much better job. Can you help?
Swagatam says
Hello,
An electromagnet will never work with an AC, simply because an AC consists of current that alternates from positive to negative and back to positive continuously, therefore the electromagnet would also generate corresponding north pole and south pole field nullifying the effects completely.
You will need to power the coil from a DC source, may be through a transformer after rectifying the AC with the help of a 4-diode bridge as you suggested.
If the coil current consumption is within the transformer rating then nothing is bad, the coil can be connected directly to the source.
You may use Ohms law to find the resistance or the current of the coil:
R = V/I, where V and I are the voltage and current of the source.
Measure the R of the coil with a DMM and solve the formula, keeping modifying the turns until the current (in the formula) reaches below 1/2 the transformer rating.
mist says
the spike discharge diode, if used with a AC supply, will short out half of the AC supplied to the coil. This will effectively give a half wave DC supply – a very wasteful and very HOT way to get DC but it will operate.
A better plan, if you're supplying AC, is to used 2 or 4 diodes, to set up a "bridge rectifier" and use the output of that, through a current limiting resistor, (and also recommend a large smoothing capacitor). This will provide the DC to the coil, and then another diode (reverse connected, of course, not to short out the DC supplly!) to act as spike protection.
If you use a transformer, it will have to be BEFORE the bridge rectifier. As transformers only work with varying current.
Another point is to consider the thickness of the wire. thin wire is for low current, high frequencies, where the high frequency travels along the surface on the wire. So they use a wire with lots of surface area.
However, the more current you wish to push through the windings, then the thicker the wire will have to be.
Also the more windings the more back EMF, which causes reluctance, and also the more pure resistance from the wire, both of which reduce the current flow, and create heat.
Heat will also soften the insulation around your wires, and the more heat there is the more resistance will occur, which will cause more heat….
And! the higher the voltage (and the softer the insulation) the more likelihood of the voltage penetrating through the insulation and causing internal shorts. These destroy the transform or coil and will have to be rewound or get a professional to do a specialist repair.
Swagatam says
Thanks for the info!
However here the output to the electromagnet is not an AC, it's a pulsating DC at high frequency. The back emf from the coil does not have any influence on electromagnetism anyway so the inclusion of diode won't affect the results.
The idea here is to vary the current through the electromagnet by applying the desired amount of On-time or OFF-time pulses, so that the average power to the coil can be controlled.
John Nordstrom says
Would it be possible to modify this circuit using an optical or magnetic sensor so that when a periodic physical event occurs the electromagnet would be pulsed?
Swagatam says
Yes it would be possible, if the 100K preset is replaced with a couple of opto-couplers.
Jason says
got it working but the tip122 is getting hot pretty quick
Jason says
thanks a bunch working on this now
Jason says
Just a quick question about the tip122 which pin goes where with it?
admin says
Thanks for the correction Jason. EM pumps (as I described) are producing rotating magnetic fields however in the paranormal mix, nothing is certain. Therefore many different systems have been employed that "may" produce the desired results. Some persons swear by spinning magnets, other people swear by random generated electromagnetic fields, and yet another group believes such fields inhibit paranormal activity all together. Who (if anyone) is right is very open to interpretation.
Jason says
Admin, The spinning magnets make a magnetic field not a electromagnetic field. I make a few different things for paranormal investigations and the above will work well for it.
admin says
In the paranormal world I.E. Ghost hunting, The common belief is that spirits feed off of Electro Magnetic Fields. So called EMF pumps are often used to produce these fields. The current method employs a 9 volt battery, a small dc hobby motor and a natural earth magnet glued to the shaft of the motor. As the magnet turns a rotating magnetic field is produced. See image [IMG]http://i47.tinypic.com/2qbuah0.jpg[/IMG]
The down side of this design is the vibration / noise sometimes generated by the dc motor.
The ideal solution is to build a simple motor-less design. I am not an engineer so I ask you this question is your design capable of producing the same kind of field?; and could you expand on the design or implementation of a electromagnet capable of achieving said, goals.
Rspene smit says
What do you make the EM out of that would work best, wrap the red copper on an Iron Nail or sometype of Ferrite piece and if so, exactly what would i look for to purchased for it, thanks.
Swagatam says
you can use an iron bolt and wind some 200 turns of 0.5mm magnet wire….but with an iron as the core make sure to reduce and fix the frequency of the IC 555 anywhere between 50 and 500 Hz not above this
Jason says
Thanks so much I will make this on Monday.