This fellow wants to make an electromagnet....

[jim hardy]

Following is a conversation that was started by a fellow tinkering with a MOT
which can be very dangerous
but to his credit he DID remove the deadly high voltage winding(at least he said he did).
It belongs in a thread
so I'm moving it here



------------------------------------------

1. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108278
   shantanu23
   
   
   0 / 0
   Hi,
   
   Case 1:
   I took out the secondary winding of a microwave transformer and kept the Primary winding in the transformer core. Now when i Connect the primary winding to the mains (220V) AC supply. the fuse blows.
   Case 2:
   But when I connect a 50watt electric bulb to the circuit in series to the coil the circuit is closed and works fine but NO ELECTROMAGNET gets created here.
   
   Why doesn't the Case 1 work. Isnt the inductive resistance created by the Primary winding enough. What can i do so that I am able to produce Electromagnet along with a 220V Ac Supply.
   
   Please help.
   
   Regards,
   
   shantanu23, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108278 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108278
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2. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108281
   The Electrician
   
   
   877 / 54
   shantanu23 said: https://www.physicsforums.com/goto/convMessage?id=108278#convMessage-108278
   Hi,
   
   Case 1:
   I took out the secondary winding of a microwave transformer and kept the Primary winding in the transformer core. Now when i Connect the primary winding to the mains (220V) AC supply. the fuse blows.
   Case 2:
   But when I connect a 50watt electric bulb to the circuit in series to the coil the circuit is closed and works fine but NO ELECTROMAGNET gets created here.
   
   Why doesn't the Case 1 work. Isnt the inductive resistance created by the Primary winding enough. What can i do so that I am able to produce Electromagnet along with a 220V Ac Supply.
   
   Please help.
   
   Regards,
   Post a thread in the Electrical Engineering forum: https://www.physicsforums.com/forums/electrical-engineering.102/
   
   asking your question. Post a picture there of the transformer as it looks now that you have removed the secondary.
   
   The Electrician, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108281 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108281
   https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/reply?m=108281
3. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108409
   jim hardy
   
   
   5,957 / 932
   Science Advisor
   https://www.physicsforums.com/account/upgrades
   i agree with Mr Electrician post it on the thread.
   
   Sounds to me like one of two things:
   1. the primary winding is damaged
   2. you removed the wrong wimding and are applying line voltage to the 2 volt coil(big wires) that's intended to power the magnetron's heater
   
   We need to see what it is that we're asked to diagnose.
   
   "Never trust a computer with anything important."
   jim hardy, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108409 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108409
   https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/reply?m=108409
4. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108423
   The Electrician
   
   
   877 / 54
   jim hardy said: https://www.physicsforums.com/goto/convMessage?id=108409#convMessage-108409
   i agree with Mr Electrician post it on the thread.
   
   Sounds to me like one of two things:
   1. the primary winding is damaged
   2. you removed the wrong wimding and are applying line voltage to the 2 volt coil(big wires) that's intended to power the magnetron's heater
   
   We need to see what it is that we're asked to diagnose.
   He says "No electromagnet gets created here". ?
   
   How does one create an electromagnet out of a microwave oven transformer? Or any transformer, for that matter?
   
   A transformer has a closed magnetic path, but an electromagnet needs an open magnetic path. One might disassemble a standard transformer with E and I laminations. restack it without the I lams, and have the ends of the E lams just open. Then you would have an "electromagnet". Now imagine what would happen if you apply rated AC voltage to the primary! Blown fuse.
   
   I'm concerned that he may have done something like that, trying to make an "electromagnet".
   
   The Electrician, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108423 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108423
   https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/reply?m=108423
5. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108432
   shantanu23
   
   
   0 / 0
   The Electrician said: https://www.physicsforums.com/goto/convMessage?id=108423#convMessage-108423
   He says "No electromagnet gets created here". ?
   
   How does one create an electromagnet out of a microwave oven transformer? Or any transformer, for that matter?
   
   A transformer has a closed magnetic path, but an electromagnet needs an open magnetic path. One might disassemble a standard transformer with E and I laminations. restack it without the I lams, and have the ends of the E lams just open. Then you would have an "electromagnet". Now imagine what would happen if you apply rated AC voltage to the primary! Blown fuse.
   
   I'm concerned that he may have done something like that, trying to make an "electromagnet".
   
   shantanu23, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108432 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108432
   https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/reply?m=108432
6. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108433
   shantanu23
   
   
   0 / 0
   Thats right @The Electrician.
   
   I removed the I laminations from the microwave transformer and kept the Primary Winding in the E laminations of the microwave transformer.
   
   @jim hardy...I am using the Primary Winding in the 'E' laminations of the microwave transformer core. And when i connect it to the 220 Volt AC mains there must be an INDUCTIVE resistance in the coil to check the current being drawn, which in turn should not allow the fuse to be blown. With a bulb in series the fuse doesn't blows but at the same time no electromagnet gets created.
   
   Is there some thing that i am missing...please guide.
   
   shantanu23, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108433 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108433
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7. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108436
   The Electrician
   
   
   877 / 54
   shantanu23 said: https://www.physicsforums.com/goto/convMessage?id=108433#convMessage-108433
   Thats right @The Electrician.
   
   I removed the I laminations from the microwave transformer and kept the Primary Winding in the E laminations of the microwave transformer.
   
   @jim hardy...I am using the Primary Winding in the 'E' laminations of the microwave transformer core. And when i connect it to the 220 Volt AC mains there must be an INDUCTIVE resistance in the coil to check the current being drawn, which in turn should not allow the fuse to be blown. With a bulb in series the fuse doesn't blows but at the same time no electromagnet gets created.
   
   Is there some thing that i am missing...please guide.
   It's only when the I lams are in place that the inductive reactance is sufficient to prevent the fuse from blowing. I have to leave home for a while, so I'll let Jim Hardy explain more.
   
   The Electrician, https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108436 https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/report?message_id=108436
   https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/reply?m=108436
8. https://www.physicsforums.com/conversations/transformer-getting-short-circuited.78710/message?message_id=108437
   shantanu23
   
   
   0 / 0
   Yes that's right @The Electrician... so how can i create an electromagnet with only E Lams with the primary winding...is there any way to do that with 220 volts AC...thats where I am stuck...Please guide.

-------------------------------

I assume he's removed not only the secondary winding
but the top of the core as well
leaving the magnetic circuit 2/3 iron 1/3 air.

Mr Shantanu
What is it you want to make?

Have you looked up the equations for Inductive Reactance, Xl=2pifL
and inductance L ?

What is it you have done?
Take a photo with your phone, email it to yourself, clean it up with Paint, and use the upload button.

It is rude to ask us to guess .

old jim

 

[shantanu23]

Hi,

@jim hardy and all...i m sorry for keeping you guys guessing. Please excuse my naiveness.

Here is the attached pics of my project.

 

[jim hardy]

I think Mr Electrician probably nailed it in #4

but your picture doesn't seem to be attached.

Are the ends of your Ecore exposed, as Mr Electrician suspects? If so,
...You say you can energize it through a lamp...
...do that..;
then place your I-lamination (or any piece of iron) across those exposed ends.
If you feel vibration you have made your electromagnet.
If the lamp gets dimmer you have also performed an interesting demonstration.

http://powerelectronics.com/content/why-have-air-gap

 

[shantanu23]

i am unable to upload the pics but yes its right i have angle grinded the I Laminations.

 

[shantanu23]

Ok pls check the below thumbnails...i have managed to add them.

 

[jim hardy]

I'm concerned that he may have done something like that, trying to make an "electromagnet".

Just as Mr Electrician surmised - You have made your elecromagnet.

You must control the current through your winding.
That is because your "transformer" is no longer a transformer in the usual meaning of the word
it's an inductor.
When you removed that iron you drastically reduced its inductance.

X_L = 2πfL
I = V/X_L
Applying line voltage across an X_L that's been reduced by several hundredfold gives a lot of current.

I am using the Primary Winding in the 'E' laminations of the microwave transformer core. And when i connect it to the 220 Volt AC mains there must be an INDUCTIVE resistance in the coil to check the current being drawn, which in turn should not allow the fuse to be blown. With a bulb in series the fuse doesn't blows but at the same time no electromagnet gets created.

Is there some thing that i am missing...please guide.
It's only when the I lams are in place that the inductive reactance is sufficient to prevent the fuse from blowing.

Try pulling the I lamination away. You ought to feel it held in place by magnetic force.
You should feel the same thing only weaker when powering the coil through your lamp. The lamp should dim when your I lamination snaps into place.
Try it with a flashlight battery or DC supply capable of a couple amps and detect the magnetism with a toy compass.

Read up on the concepts of magnetic circuits and reluctance.

Thanks Mr @The Electrician !

old jim

 

[The Electrician]

Do you still have the high voltage winding in good enough condition to place it back on the stack of E laminations? It has many more turns of wire and might present enough inductance to be energized from the grid without drawing excessive current. It would be wise to monitor and control the current you apply to whichever winding you use for your electromagnet.

You could use a variac (http://www.bing.com/images/search?q...er&qpvt=variac+variable+transformer&FORM=IGRE) to supply the voltage you apply to windings you place on the laminations.

Start out with the variac set to zero voltage out and turn it up gradually (while monitoring the current to the winding with an ammeter) so the current doesn't become excessive.