Re: DC relay latching voltage

On 2024-08-25 11:52 a.m., Don Y wrote:

On 8/25/2024 8:30 AM, John Robertson wrote:

<https://www.te.com/commerce/DocumentDelivery/DDEController?
Action=srchrtrv&DocNm=13C3311_AppNote&DocType=CS&DocLang=EN>

Is there an index to these useful Application Notes?

No idea.  I'm just leaning on lessons learned decades ago and searching for
documents that would likely confirm those issues.

I only found this when I searched for "application notes":

https://www.te.com/en/products/relays-and-contactors/relays/
intersection/application-notes.html

And did you happen to write some of them by chance?

No.  I don't publish anything "for general consumption"; only specific
issues for specific audiences.  Not enough time in the day to do the
things I *want* to do while considering "optional" efforts.

Don't kill yourself worrying about this sort of thing for a pin table.
You're likely not as concerned with durability.  The board's already
(likely) designed.  And, it's already got an established (tolerable?)
level of EMI.

Actually the 2nd link you provided that speaks of Coil Suppression with
DC relays pointed out that the zener and regular diode in series had a
drop -out time of almost the same as an unprotected coil, but the EMI
was limited to the zener's rating along with the diode voltage drop.
What is interesting is if you have a regular diode across the coil it
takes around 5 times as long to decay. That may actually matter in
pinball games - one could get snappier coil action with the zener/diode
combination (or zener across the driver transistor - skipping the
regular diode as mentioned in the note) and folks may be able to notice
that. Hmm, 1.9ms vs 9.8ms - can humans detect that when playing
considering that for the most part 100ms is considered 'instantaneous'?
I may have to set up a game and see...

"Many engineers use a rectifier diode alone to provide the transient
suppression for relay coils. While this is cost effective and fully
eliminates the transient voltage, its impact on relay performance can be
devastating. Problems of unexplained, random "tack welding" frequently
occur in these systems."

Rather, it should be seen as a counter to the "old saw" that you *just* use
a recirculating diode without considering the consequences.  Just like
considering how to *drive* the coil based on how it will be used.

[Remember the "pull in" coils and "end of stroke" (EOS) switches on flipper
solenoids?]

Oh, yes, we constantly deal with them, and pitted contacts on the EOS
switches in our shop. Would zener diodes across the contacts help reduce
pitting?

John :-#)#

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