earth magnets

[JUDWAK]

i have said there is a lot os risk involed in this

[blackpoolsparks]

25mm tails (the stuff that feeds your house) is rated at 125 Amps.
It costs 2.50 per metre + Vat.
you'de struggle to get a 200 meter drum into the back of the Surf and in any case you'de never get it rolled back up again.

Now,
you haven't calculated in voltage drop and I cant be bothered at the moment, but I would assume on a length of 200 meters you would end up with millivolts at the other end. So you may need to rethink it.

Not much more I can say as don't know what you're building

[JUDWAK]

this bit
an elclectro magnet
but its quite big

[JUDWAK]

and judgeing by what you just said blackpoolsparks
i gone realy wrong some were

[blackpoolsparks]

OK, now we're getting somewhere.

Do you want to build an electromagnet utilising the power produced from your Surf/ alternator?

[JUDWAK]

yes
but i may need to raise and drop the volts by some sort of controle
like a dimmer switch type thingy mi bob

[blackpoolsparks]

OK
Go back 10 steps.

What material are you using for your core?
how heavy do you anticipate the things you're picking up to be?
What shape will the things you're picking be?

[JUDWAK]

i want to pick up everything metal or magnetic
the clear the way so i can sweap the area with other things that the metal would get in the way of

the core i can get in any size
i was thinking 6ft high and 5'' in garth soft iron bar

my mate sells iron bar gurders and stuff

[JUDWAK]

but when i worked out the size of wire i went compleatly wrong somewere

[blackpoolsparks]

sorry george,
I have to keep popping in and out as i'm making tea for my kids, i'll be back on properly later tonight

[JUDWAK]

sound mate thanks very much

[blackpoolsparks]

OK.I'm back

To save all the short posts, I'm going to tell you everything I know about electromagnets, and its not a lot, and I hope I'm not teaching you to suck eggs.

3 ways to increase the power of an electromagnet.

1. Increase the current (amperage) - power is equal to the square of the current multiplied by the resistance of the material, and the strength of the magnetic field is directly proportional to the current passing through the electromagnet, the field strength will increase at the square of the increase in electrical power entering the electromagnet. This will remain true until the electromagnet is saturated and the field strength levels off.
As you are limited to the current supplied by the alternator, that is constant. That is unless you install a more powerfull alternator.

2. Increase the number of turns on the coil - The strength of the magnetic field is directly proportional to the number of turns in the electromagnet's coil, so adding double the number of turns will double the field strength. Again, this will remain true until the electromagnet reaches its saturation point and the field strength levels off.
One way of doing this is by using a twisted pair of conductors

3. Increase the metal core mass - The magnetic field strength is directly proportional to the permeability of the core material, so doubling the permeability will double the magnetic field strength---up to the point where the material is saturated.
So, instead of iron, use a ferrite rod. Ferrite rods concentrate magnetic fields.

Other considerations:
* Don't design a simple nail and coiled conductor shaped magnet, try using the traditional horseshoe shape or a round shape.
** Remember, the only power consumed in this electromagnet will be due to the resistor you've created (the windings) and this will be dissipated as heat, a lot of heat, and whats a magnet's arch enemy? heat.

This is copied from the tinternet:
When any magnet gets hot enough, the magnetism goes away--this includes natural magnets as well as electromagnets. Magnetism appears when all the atoms in a material line up--electricity can do this, which is how electromagnets are produced. Atoms act as tiny magnets, but they usually point in all different directions so the magnetism of the atoms cancels each other out. When something like electricity causes the tiny atomic magnets to line up, a substance becomes magnetic. In most electromagnets, if you take away the electricity, the atoms revert to their disorganized state. Natural permanent magnets keep their atoms lined up without the electricity. In either case, heat causes the atoms to jump out of alignment. The exact conditions differ for every material, but at some point the temperature becomes high enough to destroy the magnetism

Thats why electromagnets have a duty cycle.

So, I know it dosent answer your original question as to what size cable to use, but it might get you thinking as how to achieve your goal.

[BigBobE]

i have tried a couple of cable size calculator for you george and the current and length your trying to run is not feasible....

can you shorten your dc source.... say 100m????



For reference, the voltage drop for other sizes are:

1mm˛ - 44mV/A/m
1.5mm˛ - 29mV/A/m
2.5mm˛ - 18mV/A/m
4mm˛ - 11mV/A/m
6mm˛ - 7.3mV/A/m
10mm˛ - 4.4mV/A/m
16mm˛ - 2.8mV/A/m
25mm˛ - 1.75mV/A/m

[Apache]

So even with 25mm cable, you drop 70V over 200m? Starting with 12V, thats a tough call!

George, what you're planning aint gonna work. You need to start with kV rather than V, so you need smaller cross section cable to get the same power at the magnet. I doubt this is feasible.

[blackpoolsparks]

So even with 25mm cable, you drop 70V over 200m? Starting with 12V, thats a tough call!

George, what you're planning aint gonna work. You need to start with kV rather than V, so you need smaller cross section cable to get the same power at the magnet. I doubt this is feasible.

unless he uses step-up transformers along his length of cable