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'Inductive kickback diodes, etc.'
1998\10\27@130357 by John Payson

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>>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?


Attachment converted: wonderland:WINMAIL.DAT 3 (????/----) (0001BE75)

1998\10\27@155414 by Andy Kunz

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>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?

Electronic Speed Controls for full-size and model cars use the technique.
It's called "Regenerative Braking" but it works fine at partial throttles
as well.

>battery than would otherwise be required.  Does anyone know if
>this is practical?

Yes, I've used this technique for pole-mounted addressable taps for cable
tv systems.  Works quite nicely, provided you let the cap charge.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\27@174323 by Dwayne Reid

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John Payson wrote:
>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?

Bang on, John!  I've done this and it works.  Actually firing (opening) the
lock is a teeny bit more complicated and you want the electronics to be near
the lock so that you are not running EMI radiating wires everywhere, but it
works.

dwayne


Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1998\10\28@110920 by Peter L. Peres

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On Tue, 27 Oct 1998, John Payson wrote:

> 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

Not quite. If it has enough Q it will cause other problems. The best way
to get rid of the energy is, as with any generator, to load it with a
resistive load R = Zo. Ok, there are other tricks using a negative power
supply and other magic. Many of these techniques are used in high
performance stepper motor drivers (hint, hint).

> 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?

Not to do with relays, but the Vertical Deflection output circuit in most
TVs uses just this method to obtain a recovered voltage > Vdd that is used
to steer the upper transistor better (base bias). The energy to be
recovered from a relay is too small to be useful, but it will flash a neon
indicator etc if properly applied.

{Quote hidden}

This is practical but not in the way you seem to think. The energy
required to open a lock is usually too large to mandate capacitor storage
(locks run from 5 Watts to almost no end - 100 Watts for largish units is
not impossible - and they need to be ON for at least 2-3 seconds. 0.5
sec is minimum).

However, lots of electric vehicles and even hard disks use recovered
energy from spinning down motors to drive emergency brakes, locks and the
like.

Peter

1998\10\28@131020 by Morgan Olsson

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> 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).

As high as the coil and driver permits

If driver is a transistor, open collector, then a zener between c and e is
nice and easy.  Zener voltage= slightly lower than c-e breakdown.

/Morgan
       Morgan Olsson                   ph  +46(0)414 70741
       MORGANS REGLERTEKNIK            fax +46(0)414 70331
       H€LLEKS    (in A-Z letters: "HALLEKAS")
       SE-277 35 KIVIK, SWEDEN         .....mrtKILLspamspam@spam@iname.com
______________________________________________________________

1998\10\28@134528 by Dwayne Reid

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Peter L. Peres wrote:

>> 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?
>
>This is practical but not in the way you seem to think. The energy
>required to open a lock is usually too large to mandate capacitor storage
>(locks run from 5 Watts to almost no end - 100 Watts for largish units is
>not impossible - and they need to be ON for at least 2-3 seconds. 0.5
>sec is minimum).

Hmm . . . on the lock that I did this with, the solenoid needed MUCH more
energy to pull in than it took to hold it in.  I was able to charge a
largish cap to 30 or 40 volts, dump that into the solenoid to cause it to
pull in, then use the normal 12 volts to hold it in.  As I mentioned
earlier, the switching was slightly more complicated but it did work.  Its
been years since I did this - I don't remember the details exactly.  But I
used the solenoid coil as the inductor to get the high voltage onto that cap.

dwayne


Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1998\10\29@132139 by Peter L. Peres

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On Wed, 28 Oct 1998, Dwayne Reid wrote:

{Quote hidden}

Ok, it should work. What I'd like to know is how far this can be taken to
be able to drive a 12 V automotive solenoid lock with energy taken from
3.6V NiCds, without using a drawer full of caps. It also occurs to me that
when you release capacitor energy into a coil the resulting waveform is
NOT dc while the caps are polarized. This has some serious implications on
the driver components.

Peter

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