Electromagnet: Current or Voltage??

[Jasen Betts]

In article <xn0e6vr9x4lrac001@news.east.earthlink.net>, Randy Gross wrote:

John Popelish wrote:

Randy Gross wrote:
John Popelish wrote:


By power, I assume you mean flux.

jpopelish@rica.net

Yes. I'm looking to get maximum flux density. The electromagnet will
only be used in a 12 vdc momentary burst so I need maximum
capability in an instant for an instant.

I'm not familiar with that measure of time, ;-)

Sorry about the ambiguity.

Can you put any number on how long an instant is? I don't understand
if we are talking about a second or a nanosecond.

The width of the coil, including Iron core, is one inch. The length
can be up to one inch. I have 18 awg. magnet wire to wind the coil.

If you can explain more about what you need this flux for, I could
make better suggestions. After that it is a matter of writing and
solving an equation.
jpopelish@rica.net

This is an experiment in Torque.

I'm building a motor from a different point of view. Instead of
rotating the coil in a magnetic field, I'm mounting the magnets
(1"x1/8" NEO disks) on the rotor and spinning the magnetic field.

this is not a new idea, the fans, inside your PC work on this principle...
permanent magnets on the rotor, and and tre field switched eklectronically.

I want to use the coils, mounted in planetary fashion, like spark plugs
in an engine with an adjustable "distributor" (armature) for energizing
the coils mounted on the rotor. When the rotation of the magnets reach
approximately 75 degrees to the coils, The coils (electromagnets) will
energize wrenching the magnets toward 90 degrees but will de-energize
before the poles try to cog on each other.

At this time, I have no Idea what the RPMs will be so time for me is a
best guess. I'm thinking low milli for about 13 degrees of rotation.

13 degrees, (and presumably another 13 degrees with reversed polarity later
on) that's about 7% duty cycle

from my calculations yesterday I wouldn't want to see the motor stall for
more than a few seconds, but once it's running at speed there's be a back
emf that'll reduce the current and stop the electromagnets from frying.

Bye.
Jasen

 

[John Fields]

On Wed, 7 Sep 2005 23:04:46 +1200, Jasen Betts
<jasen-b@free.net.nospam.nz> wrote:

In article <xn0e6vowy1h2yc000@news.east.earthlink.net>, Randy Gross wrote:
vic wrote:

Randy Gross wrote:
John Popelish wrote:


By power, I assume you mean flux.

jpopelish@rica.net

Yes. I'm looking to get maximum flux density. The electromagnet will
only be used in a 12 vdc momentary burst so I need maximum
capability in an instant for an instant.

Current and voltage are linked by this equation :

U = L di/dt + R i

You can't have one without the other.
vic@paris


I think you misunderstood. I know that for a given volt/amp, lets say
12VA for demo., I have a range of choice. I can use 1 amp @ 12 volts up
to 12 amps @ 1 volt. I was just trying to determine where along this
scale I will get the best performance from an electromagnet

all else being equal thin wire 1200 turns and 12V x 1A will get you the same
efficiency as thick wire, 100 turns and 1V x 12A

and, amps
and turns appear to be the answer.

turns take length of wire that means resistance and resistance reduces the
amps. you can't have both.

---
Sure you can. That's why you up the voltage to overcome the
resistance and get the Ampere-Turns where you need it to be.

--
John Fields
Professional Circuit Designer