relay coil inductance

Given the 12 V figures, and the difference in core mass between the two form factors, I would say that it is decidedly easy to contend that it IS beyond the realm of possibility to get that level of flyback from a 3.3 Volt stimulus into a tiny, low mass, low turns count, open ended coil..

100 ohms was a "generic" rough "ballpark" value which you should very well know; so if you dislike 100 ohms, then use 50 ohms already!

=A0 =A0 =A0 =A0 =A0...Jim Thompson

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SAYS THE MAFIOSOS FUCKTARD

YOU THINK YOUR TORN UP ANUS IS A THING THAT PLEASES

YOU ARE SO DELUDED IT ISN'T EVEN FUNNY ANY MORE

I AM PROTEUS

you can probably come close to that with just the right RC snubber (just enough for critial damping)

Since capacitors larger than around 30pF are forbidden, I chose my approach... which works perfectly, by the way ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

=A0 =A0 =A0 =A0 =A0...Jim Thompson

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The capacitance isn't the only thing making the field continue after the contacts open. The eddy currents in the core are also at work. The contacts start to open when the field going through the bit of iron that can move drops below some value. Some relays are made with an effective shorted turn on purpose to keep the back EMF within reason.

I know the effect is real. I assume that lowering the SRF down to nearer the time frame of the decay of the eddy currents causes the field at the point where it matters to fall below that magic value a little sooner because the current in the coil is backwards at just that instant.

=A0 =A0 =A0 =A0 =A0...Jim Thompson

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See my answer to J. T.

I will have to spice model it to see if I can show the effect in a model some time.

BTW: I think it won't happen in an AC relay The shading ring would mean that you have to get two fields to drop at the same time that are decaying at wildly different rates. Matching two parameters with only one knob is unlikely.

related.

What complicates things is that L is changing, usually severely, with time, as the armature moves. Less for reeds than regular relays.

This would be a bear to Spice.

John

related.

Not for us pro's ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I have, it doesn't, for the cases I've tried. Your statement has to be incorrect, if you meant it to apply to all cases of a cap across the coil. Perhaps you have a specific example in mind?

Ed

=A0 =A0 =A0 =A0 =A0 =A0...Jim Thompson

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You can model the mechanicals and use a "bv" to make the inductance effect. It would be more complex than just the Rs and Ls.

Perhaps though, I could just ignore the changing inductance because that happens after the mechanical bits start to more. So long as the field is less than saturation, I could just use linear parts. Unfortunately, I believe that most relays use no more metal than they absolutely need and hence are always near saturation at least.

=A0 =A0 ...Jim Thompson

d.

Yes, I qualified it elsewhere as being a small specific value. You need to use one that only lowers the SRF by just enough to line the minus wing up with the right time.

related.

One could go a little bit faster than open-circuit unsupressed, but it wouldn't be worth the considerable trouble. The point is to get rid of all armature magnetization as fast as possible.

The shunt capacitance thing might just work.

John

related.

Prove it. I don't think so.

It would be interesting to compare unsuppressed versus reverse biased (low impedance) until current reaches zero.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

=A0 =A0 =A0 =A0 =A0...Jim Thompson

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You never really get rid of it all. It just has to drop to a low enough value. You are right it isn't ever likely to be worth the bother however since at best the effect is small and one could just buy a different relay.

related.

Riskier is to find the voltage that closure occurs at on say 50 units. Just a tad over that threshold voltage is where you want your drivers to fire at.

Then, release will be as immediate as one can physically make it as the closure plate will detach even before the voltage drops to zero.

In such a case, one could design a "soft release" in the driver pulse signature that negates any back-emf spike since there is no high slew rate fall-to-zero stimulus removal, which is the cause of the spike to begin with. The soft release will not slow the relay much if at all, because it is already close to losing its closure.

Perhaps they should design a relay that has a coil to close it, and a coil to aid in turn off velocity, and soak the back emf as well.

Likely too expensive, but I wonder if there are any piezo stack actuated relays out there...

All IC designs are "custom". Duh!

related.

Cool. 5% won't pull in at all, and 25% won't pull in when the temperature goes up. Great idea.

No. There's a huge pullin-dropout hysteresis that makes your concept not work.

Dual-coil latching relay.

John

And, Jim designs them, with the help of some of the members here at A.B.S.E., and I imagine some of the students at the University. ;-))) ( ducking )

Bill