Turning off electromagnet

cypressfalls Robert
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Turning off electromagnet

Post by cypressfalls Robert » January 24th, 2010, 12:59 pm

This is a disscusion for the task to shut off power to an electromagnet and drop a mass

-the obvious one is just to turn a switch off
-a little copmlicated one we used was to lift up a ball that connected two sides of a alluminum foil wall with wires connected to both walls, to open the circuit, it was pretty much a switchlike apparatus.
Other ideas....

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Re: Turning off electromagnet

Post by LukeThomas » January 26th, 2010, 5:34 pm

SPDT relay, have the coil connected to the NC pin, and the positive to the common pin and the other end of the coil to ground, when the relay is activated it will turn the circuit "off", thats if you need two separate or isolated power supplies, if not, just use a spdt limit switch, and wire it the same.
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cypressfalls Robert
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Re: Turning off electromagnet

Post by cypressfalls Robert » March 23rd, 2010, 10:47 pm

What is the most amount of weight anyone has been able to pick up/hold in place with their electromagnet?

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Re: Turning off electromagnet

Post by starpug » March 24th, 2010, 3:45 am

cypressfalls Robert wrote:What is the most amount of weight anyone has been able to pick up/hold in place with their electromagnet?
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Re: Turning off electromagnet

Post by fleet130 » March 24th, 2010, 8:43 am

shut off power to an electromagnet and drop a mass
There's a more complicated discussion here.
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!

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Re: Turning off electromagnet

Post by Breaking Yaytz » March 27th, 2010, 11:39 am

If I have a momentary push button that is normally open, how would I use it to turn off an electromagnet? I tried to use it to create a short circuit, but it didn't work.

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Re: Turning off electromagnet

Post by andrewwski » March 27th, 2010, 12:19 pm

Use a relay. Wire the electromagnet to the relay's normally closed pins, then run current through the pushbutton switch to the relay coil - when you push the switch, it'll pull the relay the other way and the electromagnet will shut off.

However, it would only be momentary, as once you release the switch the relay will flip back the other way and put power to the electromagnet. You could create a more complex circuit that would use the pushbutton switch to permanently turn off the electromagnet until reset with another switch, but it's much more trouble than it's worse - just get a non-momentary switch if that's what you need to accomplish. In which case you don't need the relay either.

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Re: Turning off electromagnet

Post by fleet130 » March 27th, 2010, 6:29 pm

Regular on/off switches can take a lot of force to operate. It can be difficult to find a switch that van be turned on/off by a previous action. Lever switches (sometimes called micro-switches) are often used because they can be actuated with very little force. Unfortunately they are momentary contact switches that will turn off/on again if the force that actuated them is removed. A relay can be used to make a latching circuit that will keep the circuit closed even if the actuating force is removed.

The following circuit does just the opposite. It uses a momentary contact switch and relay latch to turn off a circuit.

In the 1st drawing, the open contacts of S1 prevents the electromagnet from being energized.

In the 2nd drawing, S1 has been turned on and current flows through the normally closed contacts of the relay to energize the electromagnet and attract the object.

In the 3rd drawing PB1 is pushed, closing its contacts which energizes the relay coil to open the normally closed relay contacts. This de-energizes the electromagnet, causing the object to be released.

In the 4th drawing, PB1 has been released, opening the path for current to flow to the relay coil, however, the normally open relay contacts are now closed and provide current to keep the relay energized and the electromagnet turned off.

The circuit can be reset to its initial state at any time by opening S1.

Image
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Re: Turning off electromagnet

Post by Paradox21 » March 28th, 2010, 10:07 am

I just use a simple on/off switch with some weights attached to the lever to make it easier to trigger. It is very sensitive actually, anything more than blowing on it will make it trigger. Relays clutter up my device with wires really quickly. At the moment I use 2 of them and I feel like I have wires flying everywhere. The on/off switch approach is very simple but takes some tinkering to work just right. If you can't get it to work though, the relay is definitely the best way to go.
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Re: Turning off electromagnet

Post by fleet130 » March 28th, 2010, 2:39 pm

2 relays? Wait until you get a hundred or so. Then you'll have wires EVERYWHERE!
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!

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