>>quoting>>
Depends on circuit and timing - if you place the back "anti-spike"
diodes directly across the relay coil, when the relay opens the
current will "circulate " through the coil and diode until the energy
dissipates. With low resistance in the circuit this can slow the
relay release time (time constant is L/R where L is coil inductance).
If you place a resistor in series with the diode the energy will
dissipate faster due to higher R and the relay will turn off more
crisply. This affect can be significant in some applications. The
"downside" is that the voltage spike will rise to "IR" above the
supply voltage (I is relay current, R is total resistance including
coil and resistor). The diode forward voltage drop complicates all
this only slightly.
<<me<<

The way to make a relay drop fastest is to allow it to
allow its kickback voltage to rise (the higher it rises
the faster it will decay).  Rather than letting all that
energy go to waste, however, I wonder if in some appli-
cations where power consumption is an issue it would be
practical to have that energy feed into a capacitor which
could then supply useful energy later on?

Another idea I was pondering, for cases where it's necess-
ary to hit a coil briefly with a fair amount of power (e.g.
electric locks, etc.) would it be practical to use the act-
uator coil along with a decent-sized cap as a switching sup-
ply to charge up the cap, and then dump all the cap's energy
into the coil?  Since electric locks and similar devices need
a fair amount of power but have a long time between actuations,
it would seem like it should be possible to use a much smaller
battery than would otherwise be required.  Does anyone know if
this is practical?


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