large & efficient electro magnet

[therian]

Im building pulse motor, after construction small scale I decide to make large one, I will hand wound 2 km of thin wire to create electromagnet it a lot of wire to do manually so I want to make most efficient magnet from first time.
The question is what is more important , coil bobbin length or thickness , should my coil be tall or short and fat, I will use 1 inch diameter iron rod.

Formula from wiki
B = (N I)/L


* N is the number of turns of wire around the electromagnet
* I is the current in amperes
* L is the length of the magnetic circuit
* B is the magnetic field in teslas


show that fat coil will be more efficient (less L) but personal experiment show opposite result , long coil stop moves compass needle from 7 cm when thick coil twice shorter of same wire length stop move needle only from 4 cm away




Another question should I wind many wires together and then connect them (in series or parallel) or single wire is more efficient



maybe picture will explain better what I mean.

[Melanie]

All you ever wanted to know...

http://info.ee.surrey.ac.uk/Workshop...ils/force.html

Wiki I would not trust.

[therian]

Thank you that was very useful information

just one more question, can I have an advice how to safety connect digital scope to read the coil, I have 100x probes but they home made and really noisy so I want to use 10x one and voltage might exceed them and I don't know what will happen to scope then.

[Melanie]

and I don't know what will happen to scope then

You will destroy it. A coil with the kind of inductance you are winding will probably have an emf of a few kV... most modern scopes only have a 50v tollerance.

Use your probe set to 10:1 and use a Resistor divider chain of another 10:1. If the Bottom Resistor is 1M it won't load the circuit. That should give you a 5kV operational tollerance.

[Luciano]

Hi,

Pulse motor evolution. (Moto-perpetuos made in Seattle USA).


(Make sure your PC speakers are on).

Best regards,

Luciano

[Melanie]

Yeah, right... more like moto-preposterous...

Would be more meaningful if he showed CURRENT-IN versus CURRENT-OUT as well as the voltage which on it's own is irrelevant.

What he's trying to make you believe is that his Power-Input, less frictional losses, less conversion losses, less electrical losses, is still a NET GAIN?

[christopherh]

I learnt so much through these threads. thanks every one for enhancing my knowledge by sharing your posts.