Post by thread:Inductive kickback diodes, etc.

>>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)

>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 ==================================================================

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

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}> 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). 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

> 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€LLEKS (in A-Z letters: "HALLEKAS") SE-277 35 KIVIK, SWEDEN .....mrtKILLspam@spam@iname.com ______________________________________________________________

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

On Wed, 28 Oct 1998, Dwayne Reid wrote: {Quote hidden}> 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. 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