Quoting Sean Breheny : > Do you guys have actual test data showing improved life with the zener o= r > tvs instead of a simple diode? Every relay I've seen which had an > integrated diode used a simple switching diode. Also, usually the current > required to keep the relay closed is only a tiny fraction of that require= d > to make it close so only a small portion of the coil current decay is > relevant to the actual speed at which the contacts open. On top of that, > usually relays are designed so that the magnetic circuit is broken before > the electrical circuit - and once the magnetic circuit starts to open the= re > is a positive feedback effect which causes the attractive force to drop > very rapidly. In sum, I would be very surprised if the type of diode made > much difference to the contact life, except for reed relays. I thought th= at > the usual reason for wanting the field to collapse faster was to make the > delay from open signal to actual open circuit shorter for system reasons. The magnetic circuit breaks (and inductance drops rapidly) just before =20 the contacts open because there is compliance in the contacts, so the =20 force from the field slows them down just at the very worst time. You can read these app notes, for example, but there are otehrs. http://www.te.com/commerce/DocumentDelivery/DDEController?Action=3Dsrchrtrv= &DocNm=3D13C3264_AppNote&DocType=3DCS&DocLang=3DEN http://www.te.com/commerce/DocumentDelivery/DDEController?Action=3Dsrchrtrv= &DocNm=3D13C3311_AppNote&DocType=3DCS&DocLang=3DEN "It is normal industry practice to test relays and subsequently establish performance ratings without coil suppression" Song Chuan says; http://www.songchuan.com/en/Technical-Infomation.pdf 12. Relay Coil Transient Suppression The use of a single diode in parallel with the coil for transient suppression causes longer contact release time. On power relays, longer release time may reduce relay life. For longer contact life, use a zener and diode, a capacitor and resistor, or only a resistor. Using a zener or clamp to a higher voltage is, however, harder on the =20 transistor so examine the SOA specs. You can also use a resistor + a diode per coil. Pick the resistor to =20 give you the desired voltage at the nominal coil current. Eg. 12V + a =20 diode drop above the 12v supply voltage for a 200mA relay would be 12/0.2 =3D 60 ohms and th= e transistor would see a peak of 24.7V or so, nominally. --sp > On Dec 18, 2017 2:36 PM, "Spehro Pefhany" wrote: > > > >> >> The diode across the coil method isn't the best either, if you care how > quickly the relay opens. >> Slow opening can result in contact welding. >> >> The best method is a Zener from Collector/Drain to ground. Set the Zene= r > voltage a bit below the transistor VCE/VDS rating. >> This speeds up the collapse of the current in the coil by as much as 3x > > Dave is right, this will help get rated life out of the relays. They are > *not* rated with diodes directly across the coils. You may be able to use > one TVS or Zener (total) and one diode per relay. > > Spehro Pefhany > >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .