Coil Winding Trouble

We have an exhibit at our local science museum that is a 3-4' 1" diameter tube
with about 150' of wire wrapped around 8" of one end. First 75' were wound, and
then another 75'. An LED is connected across the wires. When a cow magnet is
dropped down the tube, the LED lights momentarily. Some time ago someone
deliberately broke the exhibit. I had to unwind the last 75' to make some
repairs. When I try the new configuration out, the LED doesn't light. I'm sure
the connections are correct. At least a continuity check at the leads shows a
connection. I would think if 1/2 the wire is wound the opposite way from the
other 1/2 that maybe no current would appear. Is that right?
--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

"I know that defies the law of gravity, but, you see, I never
studied the law of gravity." -- Bugs Bunny

Web Page: <home.earthlink.net/~mtnviews>

 

At this point in time, my best suggestion is, unwind the broken 75', and
wind it back the other way, and see what happens.

In the interim, please do some googling on basic electricity and magnetism.

Good Luck!
Rich

 

If the two halves are in series, that is correct. The wire has to all
wrap around the magnets the same way, since each turn makes a
contribution to the total voltage.

Have you checked the LEDS to make sure they have not been damaged?

By the way, another neat magnet - generated current demo is to drop a
neodymium iron boron or samarium cobalt magnet down a copper pipe not
much larger than the magnet. It falls very slowly because of the
interaction with the magnetic field produced by the high currents that
are generated around the magnet. The forces also keep the magnet away
from the pipe. I even got this to work just rolling a cylindrical
magnet down an aluminum flat strip. It rolled slowly, and when the
magnet got near the edge, the drag forces dropped, that end sped up,
and the magnet was steered away from the edge. It zig zagged all
across the strip as it crawled to the bottom but never went over the
side. An example of a gravity powered mechanical negative feed back
loop.

 

Google? What's Google? Suppose I had virtually no knowledge of electricity
and magnetism. Would you make the same suggestion? Then too I'll bet you've
never seen the inside of my garage and the exciting time I had unwinding the
coil and rewinding it. I'll bet ... Oh, well.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

"I know that defies the law of gravity, but, you see, I never
studied the law of gravity." -- Bugs Bunny

Web Page: <home.earthlink.net/~mtnviews>

 

I tried 5-6 LEDs. Sounds right to me. Thanks. Weather permitting, I think I'll
do the rewinding outside. I just had to check before facing the confines of my
garage again. It takes about an hour in my garage. Alice-in-Wonderland would
feel happy there.

Yes, I'm familiar with those demos. Eddie's currents. I always liked that
guy. Fun stuff.

--
Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

"I know that defies the law of gravity, but, you see, I never
studied the law of gravity." -- Bugs Bunny

Web Page: <home.earthlink.net/~mtnviews>

 

This trick with super magnets works well with flat ones too. Take a
strip of aluminum canted at about 15 degrees from vertical and slide a
washer down it. It will stay on the aluminum and zip down the length
of it. Next, lay a flat super magnet on it and let go. It just crawls
down. It really is a good show. BTW, this is how mechanical
speedometers work.
ERS

 

If you can get to the ends of that half, you can just cut it and swap
the ends.

 

I could have been more specific: http://www.google.com ;-P

Well, notwithstanding "virtually" means "not really", I'd say, of course.
We all have to start somewhere, and as Commander Spock said just before
the thin Vulcan Kirstie Alley ("Mister Savik") drove the Enterprise out of
Space Dock, "For everything, there is a first time."

This is a sucker bet. I've never seen the inside of your garage and don't
expect to. ;-p

If winding coils is giving you pains in the neck, you might need some kind
of spool or fixture to manage the lengths of wire. Once, I needed to wind
a fairly large toroid (1.5" OD) with some teflon-insulated wire. I made
a shuttle out of a stick about 2' long, with notches in the ends. Loaded
it with a passel of wire, and it only took a couple of hours to get it
wound. But winding on a cylinder should be trivial.

If the PITA you're having has to do with getting the exact length of wire
wound on the coil, let that whole idea go. Go by number of turns, and
let the length of the wire be whatever it needs to be. I used to hold
a pencil between my knees to mount the source spool on, but the point
kept sticking into my knee, until I figured out that I should use
something blunt.

When do I get the opportunity to say, "Elementary, ..." ;-P

(what did Mr. Holmes say about the digestive system? "Alimentary, my
dear Watson".)

Good Luck!
Rich

 

It's too late at night here, but a suggestion. Before you rewind try
reversing the end connections of one of windings! Might work?
Logic being that if one coil is reversed in winding direction to the other
reversing connections to one of them MIGHT put the induced voltage back in
series?
Terry in Canada.