Quoting Cedric Chang <cc@nope9.com>:

> I am rewinding a solenoid for the fuel control on a truck injector
> system.
> A slug that is restrained by a small spring is pulled into the
> solenoid to allow fuel to flow.
>
> Since I have a fixed amount of space, I am wondering if it
> is better to have many windings of a smaller gauge wire or
> fewer windings of a larger gauge wire.  I am not worried about
> inductance or ease of winding.
>
> I am seeking the optimum tradeoff between heat dissipated
> by the coil and maximum magnetic field inside the solenoid.
>
> I am guessing that the amount of heat dissipated is inversely
> related to the square of the diameter of the wire ( holding
> everything else constant ).
>
> The B-field seems as though it would also be related to the
> inverse of the square of the wire diameter.  ( divide the diameter
> by two and get 4 times as many windings. )
>
> If I keep everything constant except I vary the current through the
> solenoid, the B-field seems to vary linearly with the current while
> the heat dissipated by the solenoid seems to vary the square
> of the current.  Would this suggest that lowering the current and
> increasing the number of windings would improve the solenoid
> capabilities.
>
> I feel I have made a mistake here somewhere since a gazillion
> windings and nearly zero current would give me the magnetic
> field I want.
>
> Of course there must be some amount of energy required to
> move the slug into the solenoid.

Judging by relay coils, the coil power is going to be fixed when
you need a certain amount of push with a fixed winding window.
Math is left as an exercise. The power might deviate a bit at
extremes of very low or high voltage, but basically DC relays
have the same power over a 4:1 or so range in coil voltage.

Best regards,
Spehro Pefhany


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