#### MMH

Joined Feb 8, 2013
143
Hello there everybody!!!!

I was thinking of making a Faraday Shake Flashlight. I know how it works, what the materials required are, and all. But I don't know how many turns of insulated copper wire is required and how long the wire should be. I have a wire which is 250.5 ft long and another one 50 meters long. Will either of these work?? And will the hard disk magnets work??

#### wayneh

Joined Sep 9, 2010
17,163
The disk magnet will work as long as the field lines are parallel along the coil's central axis. Mechanically it probably needs to be longer than it is wide, though, so that it stays oriented.

Look up the specs for the gauge wires you have. This will allow you to calculate how many turns and how many meters you can wind into a given volume for the coil. I think you'll want the finer gauge, so that you can get as many turns as possible. This won't allow much current, but I don't think that's a problem in this application.

#### MrChips

Joined Oct 2, 2009
25,919
You will need a lotta turns.

#### Markd77

Joined Sep 7, 2009
2,806
From the 4th google result for "faraday torch" about 150 feet would be enough for a 1/2 inch diameter coil.

#### MMH

Joined Feb 8, 2013
143

Some of the things you said went over my head.

wayneh: "The disk magnet will work as long as the field lines are parallel along the coil's central axis. Mechanically it probably needs to be longer than it is wide, though, so that it stays oriented."-It kinda got over my head. English isnt my mother tongue, so can you write it in a simpler English?

wayneh:"Look up the specs for the gauge wires you have. This will allow you to calculate how many turns and how many meters you can wind into a given volume for the coil. I think you'll want the finer gauge, so that you can get as many turns as possible. This won't allow much current, but I don't think that's a problem in this application."- The 50 metre wire is 30 SWG and the 250 ft wire is 38 SWG.

MrChips: "You will need a lotta turns." Some sites say it is around 300 and some other says that it is over 1500. Which one's true??

Markd77:"From the 4th google result for "faraday torch" about 150 feet would be enough for a 1/2 inch diameter coil."-So, it says that 150 feet would be enough for a 1/2 inch diameter coil or 1/2 inch diameter magnet. Right?? OK, can you tell me where I can get those magnets around the house(if that is possible in a CPU) or is it that I've to but them. I have 4- hard drive magnets and 2-small magnets from old CD-Drive. Can I use any of these to make one??

#### MrChips

Joined Oct 2, 2009
25,919
None of those magnets will do any good. You need the strongest magnet you can get your hands on.

1500 turns is 5 times better than 300 turns.

#### wayneh

Joined Sep 9, 2010
17,163
The 50 metre wire is 30 SWG and the 250 ft wire is 38 SWG
Use the finer wire.

A normal cylindrical magnet has a pole on each flat face, and that is what you want. There are some available with poles on opposite sides of the curved surface. That won't work.

A flat disk may not move smoothly from pole to pole and might become crooked or jammed. So it needs to be a tall cylinder, not a pancake.

As noted, you need a strong magnet for this to work. Bigger is better.

#### MrChips

Joined Oct 2, 2009
25,919
A typical fridge magnet is about 5mT (0.005 tesla).
You will need a cylindrical neodymium magnet (about 1T) and at least 1000 turns to generate about 1V.
And that depends on the area of the coil and how fast you shake the flashlight.

#### MMH

Joined Feb 8, 2013
143

Oh, I forgot to mention that I have a rod magnet which is around 2.275cm in diameter 1.5" long . Will that serve the purpose??

#### Dr.killjoy

Joined Apr 28, 2013
1,196

Oh, I forgot to mention that I have a rod magnet which is around 2.275cm in diameter 1.5" long . Will that serve the purpose??
How strong is the magnet ???

#### MMH

Joined Feb 8, 2013
143
How strong is the magnet ???
It is a neodymium rare earth one. How strong...hmm..... To say the truth, I dont have anything that will measure how much Tesla it is.

#### MMH

Joined Feb 8, 2013
143
By the way, is there anything that can measure Tesla of a magnet??

#### MrChips

Joined Oct 2, 2009
25,919
Tesla is a unit of magnetic field strength.

http://en.wikipedia.org/wiki/Tesla_%28unit%29

The strength or lifting power of a magnet is dependent on the area and distance from the magnet.

You can measure the lifting power of a magnet with a spring scale.

#### MMH

Joined Feb 8, 2013
143

But can anyone tell me why I cant post a new thread??It says:

Server error
The website encountered an error while retrieving http://forum.allaboutcircuits.com/newthread.php?do=postthread&f=6. It may be down for maintenance or configured incorrectly.
Here are some suggestions:
HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.

Can you tell me what I should do to fix it??

#### MMH

Joined Feb 8, 2013
143
So, does that mean there's no way to fix it??

#### MMH

Joined Feb 8, 2013
143
Hello there!!

I decided to leave these things for some time and work with solar cells. I have extracted the solar cell from the Casio fx-991MS. It provides enough electricity to light a 5mm white LED brightly or a 3mm green LED or a 5mm red led(It lighted all of these from the light of a small led flashlight, it is quite dark here and I didn't see the results with the bright sunlight.) I wonder what its(solar cell's) amperage is.Can you tell me an easy way to test it without a multimeter? It doesn't need to be that accurate. Just a hint will do. The whites need 20ma, so does that mean that it is over 20ma??? Thanks.

Last edited:

#### wayneh

Joined Sep 9, 2010
17,163
Can you tell me an easy way to test it without a multimeter?
Yes, go get a multimeter! They are very cheap and will be useful for a long time. Big bang for the buck.

A 5mm LED can be quite bright with as little as 5mA. I'd wager you did not achieve 20mA but that's just a guess. You can be fairly sure you did not hit 30mA, as this might well have damaged the LEDs.

#### MMH

Joined Feb 8, 2013
143

I got the multimeter and it reads an open circuit voltage of 2.85v and a short circuit amp of 28.6ma. Is that it??

#### wayneh

Joined Sep 9, 2010
17,163
Not quite, unless that is with the LED in the circuit. If not, try measuring again with the LED in series with your meter. An LED drops voltage, effectively acting as a resistor to reduce current.

I'm a little surprised your LEDs will light at that voltage.

#### Markd77

Joined Sep 7, 2009
2,806