The drawing at the left illustrates an inductor with a series resistance
and switch combination connected to a battery. The time required for the
current to rise to 63.2% of the maximum value after the switch is closed
is the ratio of inductance to resistance (L/R). The graph below illustrates
the changing current of a 1 Henry inductor which has 1 ohm of resistance and
is connected to a 1 volt battery. The current will increase from 0 to
632 milliamps in 1 second of time which is the ratio of inductance to
resistance (L/R) = 1 second. The maximum value of current is determined from
ohms law, or I=E/R = 1 volt / 1 Ohm = 1 amp. The calculator below can be
used to determine various other points along the graph or the inductance
and resistance needed for other situations. Four known values must be entered
to solve for the unknown. For example, the instantaneous current of the
1 Henry/1 Ohm inductor below after 3.5 seconds of time is found by entering
1000 in the maximum current field, 1 in the resistance field, 1000 in the
millihenrys field, and 3500 in the milliseconds field. Only one field should
be blank or set to 0 before each calculation.

Inductor Current With Respect To Time

Instantaneous Current = Maximum Current * ( 1 - e ^((-Time * R) / Inductance))