Technically speaking you would install it directly on the relay coil leads. It may seem like semantics, but if you had a cutout switch or other electronics between the power supply and the relay, the diode needs to be as close to the relay as possible electrically.
BTW, I have only send a few thousand or so of those. I used to work for the local telco in old electro-mechanical telco offices (#5 X-BAR & STEPxSTEP). Almost every relay in those places had a reverse current shunt diode on them... Lyle ----- Original Message ----- From: "Rajeev Sharma" <[EMAIL PROTECTED]> To: "Asterisk Users Mailing List - Non-Commercial Discussion" <[EMAIL PROTECTED]> Sent: Sunday, October 10, 2004 8:14 PM Subject: Re: [Asterisk-Users] POTS failover relays (was Vonage, PSTN, 911, and hardware question) > OK... so what you're saying is that I put a diode across the power supply input legs for the DPDT > relay, right? > > (sorry, i'm not the best person at electronics...) > > Greg Hill wrote: > > On Sun, 10 Oct 2004, Rajeev Sharma wrote: > > > > > >>Yeah, thanks, I was thinking of doing something similar to that. > >>Actually, I was gonna spice a cable in my computer's power supply and > >>use that. Why? Because if it's on a UPS, then the switch will throw at > >>the same time as the computer looses off. I dunno, I might not even use > >>a UPS, just a surge protector, but I'll see. Thanks for the idea. > > > > > > I was going to suggest this, but didn't because it's (slightly) more > > involved. Due to the physics of a relay (that it's constructed with a coil > > of wire), there is some inherent inductance. When you try to interrupt the > > current to an inductor, the voltage across it spikes. This is considered a > > Bad Thing in sensitive electronics like a computer. This isn't really an > > issue with the wall-wart power adapter, because there isn't likely to be > > anything terribly sensitive in there (and they're cheap to replace in the > > event of failure). > > > > In a sensitive computer environment, you should include a reverse-biased > > diode in parallel with the relay's coil. This diode, because it's > > reverse-biased in normal circuit operation, won't conduct any current. But > > when power is lost, the voltaged induced by the inductor will forward bias > > the diode, and the voltage spike will be clamped by the diode rather than > > going out into other components via the power bus. Most any common diode > > will work fine (1N4148 small-signal diode, 1N4001/2/3/4 rectifier diode, > > etc) for this purpose. > > > > Greg > > > > _______________________________________________ > > Asterisk-Users mailing list > > [EMAIL PROTECTED] > > http://lists.digium.com/mailman/listinfo/asterisk-users > > To UNSUBSCRIBE or update options visit: > > http://lists.digium.com/mailman/listinfo/asterisk-users > > > > > > > _______________________________________________ > Asterisk-Users mailing list > [EMAIL PROTECTED] > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users > _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
