Re: [CAD_CAM_EDM_DRO] Re: floating aluminium

> I take it electrons have to move through some
> resistance to produce a magnetic field.

Nope. Current simply has to flow. In a coil, say in a stepper motor
(to get back on topic) what matters is the amount of current flowing,
and the number of turns in the loop. The important parameter is the
product "ampere turns". In other words, one amp flowing in a two turn
winding generates the same field as two amps flowing in a single turn
winding.

The resistance of the wire may be quite different in these cases,
and in fact is really only important for two reasons:

1) Any resistance the current has to flow through will result in the
generation of heat in the windings. This represents a power loss, but
it also makes the motor get hot (induced eddy currents flowing in the
core when AC or chopper drive is used also generate heat, so the core
is made of seperate laminations to reduce eddy currents).

2) The resitance of the coil, in combination with its inductive
reactance determines what type of driver will be necessary to power
it, especially if it is to be switched on and off rapidly.

Let me also make another comparison. A 10 ohm carbon resistor with an
ampere flowing through it will consume 10 watts of power, but produce
very little magnetic field as the circuit topology is perhaps a large
single turn "winding". However take some copper wire and form it into
a coil of many turns to get a winding of 10 ohm resitance, push the
same ampere of current through it, and you will get a substantial
magnetic field.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT