Loading/charge time of an electromagnet

[losbellos]

Hej Guys,

Did anyone see anywhere an equation to this?
If nothing else then a loading time formula for solenoid would do.

Thank you!

 

[berkeman]

Did anyone see anywhere an equation to this?
If nothing else then a loading time formula for solenoid would do.

What is loading time in the context of an electromagnet? Do you mean the time to ramp the current up to max?

 

[yungman]

Here is the time constant of L https://www.electronics-tutorials.ws/inductor/lr-circuits.html

How fast depends on the output impedance of the driver of the magnet ( treated as inductor). The higher the impedance, the faster it is. I designed a government project controlling a magnetic that is over 50A and settle in less than 1sec to 100ppm ( don't remember the exact number, it's fast) I used a few giant MOSFET as current source to get the highest output impedance, it worked like a charm.

 

[losbellos]

I meant when the electromagnet reaches the designed load. Let's say it was designed to have 2 ams and 50 volts.
How long does it take to reach the operating magnetic field strength?

 

[losbellos]

see my answer above, a DC electromagnet that has 2 amps some hundred turns and a iron core. How long does it take for the electromagnet to reach the maximum electromagnetic field strength B.
Just turn the electricity on and how long does it take to get it up and running.

 

[yungman]

As I said, it depends on the source impedance. Read the link I gave you. Put it in another way, if you DC source has very low impedance, it will take a long time.

 

[berkeman]

a DC electromagnet that has 2 amps some hundred turns and a iron core. How long does it take for the electromagnet to reach the maximum electromagnetic field strength B.

How big of an iron core? 10cm? 1 meter?

What gauge wire (so what is the total wire resistance)? Do you have a datasheet for this electromagnet, or did you build it?

 

[yungman]

Magnet is just an inductor, measure the inductance and you'll know. If you use like a conventional bench power supply ( low output impedance), it will be show. We cannot give you an answer because it depends on what you use to drive the magnet. Use the formula in the link to calculate.

If you need it fast, we can talk more, like I said, I designed a magnet controller that run really fast. It was a huge magnet used in mass spectrometer to detect Krypton to verify the INF treaty in the early 90s.

 

[losbellos]

Impedance is related to AC its a resistance type that relate to AC. Why would I even think on it?

It is a DC electro magnet:

R = 10.4 Ohm
I = 2.0 A
U = 20.8 V

By the way I know that is in the microseconds to milliseconds range

 

[berkeman]

Impedance is related to AC its a resistance type that relate to AC. Why would I even think on it?

Because you are asking about the charging time constant. That's where the inductance value L comes in...

 

[berkeman]

https://www.electronics-tutorials.ws/inductor/ind53.gif

https://www.electronics-tutorials.ws/inductor/ind53.gif

 

[losbellos]

No I am asking about the time requires to load/charge the electromagnet this means how long doest it take until the electromagnet's field builds up from zero...

 

[berkeman]

No I am asking about the time requires to load/charge the electromagnet this means how long doest it take until the electromagnet's field builds up from zero...

See the graph in my post #11 above...

How big is the electromagnet physically?

 

[losbellos]

Well, its like m shape and it size is like 15cm * 10cm * 15cm. Its charging less than in a 0.001 sec. I don't have better equipment to measure smaller time, so I need the calculus... The winding is on the the middle leg of the iron core.

 

[berkeman]

Here is an inductance calculator that may help you come up with a good inductance number for your coil:

https://rimstar.org/science_electronics_projects/coil_design_inductance.htm

 

[losbellos]

Its 51.

 

[losbellos]

You know I don't believe in this, since the charging time must be related to the velocity of the light the coil length and some pretty complex evaluation that relates to the volume of the iron core.. As the electricity goes in it the field already exit from it and the charge propagates toward the iron core too.
I don't really see the point in this.

 

[berkeman]

Its 51.

51 what?

You know I don't believe in this, since the charging time must be related to the velocity of the light the coil length and some pretty complex evaluation that relates to the volume of the iron core.. As the electricity goes in it the field already exit from it and the charge propagates toward the iron core too.
I don't really see the point in this.

I'm not seeing your confusion. Have you worked with electricity much in the past? How about inductors and capacitors in circuits?

 

[yungman]

No I am asking about the time requires to load/charge the electromagnet this means how long doest it take until the electromagnet's field builds up from zero...

Did you read what I posted, the time depends on the impedance of the power supply + the 10ohm of the internal resistance. Do some calculation using the time constant formula.

If you don't know how to calculate or you don't know the output impedance of the power supply, just use a scope to measure it. Put a 0.1 to 0.5ohm resistor in series on the low side and measure how long it takes for the voltage to settle across the resistor. That is the time for the current to to settle to the highest point.

 

[losbellos]

Hej Thanks,
But you know its very weird. There is this impedance you writing about that is related to the change of voltage and ampere in a coil.

However this change doesn't refer to the fact that the electricity is actually charging the magnet the same way. And it is also related to AC not DC.
The impedance of your power supply... if there is an impedance(R) in it then that impedance is in the system... The bigger it is the voltage is the bigger and the ampere is less. I=U/R , R=U/I The amperes is the work capability of the power. This is what is charing and electromagnet... So this impedance of the power supply is usually very low because the number of turns and size etc inside the power supply.
And so on.

Please someone else some other answer please?

 

[jim hardy]

Please someone else some other answer please?

See the graph in my post #11 above...

here it is again ...

https://www.electronics-tutorials.ws/inductor/ind53.gif

Magnetic field is proportional to current "I" so will follow the upper graph

so if you're sure L and R are what you said, 51 and 10.4 ,,
then τ (pronounced " tau " ) = L./R = 4.9

 

[berkeman]

here it is again ...

https://www.electronics-tutorials.ws/inductor/ind53.gif

Magnetic field is proportional to current "I" so will follow the upper graph

so if you're sure L and R are what you said, 51 and 10.4 ,,
then tau = L./R = 4.9

So assuming the OP's inductance calculation was in MegaHenries for L=51MH, that would make the time constant 4.9MegaSeconds. Got it.

 

[jim hardy]

Got it.

As you said, "51 what?"

 

[eq1]

There is this impedance you writing about that is related to the change of voltage and ampere in a coil..

Losbellos,
Are you familiar with Ampere's Law? It basically says the amount of magnetic field is proportional to the amount of current in the wire. So if you can answer how fast the current ramps up you can also answer how fast the magnetic field ramps up. See the link below for more information on Ampere's Law.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/amplaw.html#c1

However this change doesn't refer to the fact that the electricity is actually charging the magnet the same way. And it is also related to AC not DC.

When you flip the switch to turn on your device the voltage and current have to transition from zero (off state) to their resting or DC, values (on state). This transition is an AC event.

 

[arydberg]

It might be easer if you looked at charging a capactor first . It is easier to understand. Charging an inductor is similar except the current replaces the voltage on a capacitor. Most inductors tend to charge very fast.