Author: "Wolfert, William R." <WWolfert@columbuspolice.org>
Date: Wed, 28 Jan 2009 09:20:59 -0500
Gentlemen I'm putting together a switchbox for a phased array. I had many spdt relays on hand so I'm using them. 2 relays per antenna will work fine. The array is an 8 circle (for 80m, hung off the t
I can answer the diode question. It is generally good practice to put a diode across the relay because of the inductive spike when turning it off. I have seen the spike go 3-4X the input voltage. If
--Original Message-- Actually, the relay manufacturers (e.g. Tyco, P&B, etc.) recommend NOT using the diode across the coil, because it reduces relay life and changes actuation speed. Depending on wh
I had never heard of that before. The ULN2003 is a seven darlington switch and has the diode built in. Also MOSFETS usually have the diode built into the switch for the diode in parallel with the swi
Yah, but...they also recommend the diode AND resistor/zenner/varistor/MOV/ reverse bias..., or some combination. IOW they too recommend the diode, just not the diode by itself. Nearly all DC relays a
First question: Why do you want to put a diode across the relay coils? Are you driving the relays with something that is transient sensitive? If you're just driving them with a mechanical switch, etc
Neither had I, but several other relay manufacturers say the same thing, as do the reliability folks in aerospace. I'd venture that the ULN part was designed to match what folks were doing with discr
This discussion of relay reliability and switching speed is irrelevant for a relays in a phased array that should never be hot switched. The spike suppression components don't need to be outdoors, th
This reminds me of an incident when I worked at Sanders in Nashua NH. An EE thought he'd play a joke on me: "Here, hold the ends of this coax. I've got to measure the resistance... It's a little less
Across relay coils I recommend using a zener rated at at least 3 watts and preferable at more than that. Look for one with a high current surge rating. The reason being that lightning can sometimes i
I told myself not to enter this endless discussion. However the above comment got my attention. I fully agree with the statement especially when it comes to engineering Car batteries. They are the m
Protection for "remotely located relays" (out at the antenna) In the case where the relays are remotely located (at the end of a long control cable) I use absolutely nothing. The cables were about 18
The reliability issues in the Tyco ap note aren't tied to whether the contacts are carrying current. Indeed. _______________________________________________ __________________________________________
Carrying current IS the whole issue. If they were not carrying current then it does not matter how fast the contacts close or open. The goal of the applications note was to minimize the contact arcin
If you're not hot-switching does it change the answer to what the issue is? Dick, K6KR --Original Message-- From: towertalk-bounces@contesting.com [mailto:towertalk-bounces@contesting.com] On Behalf
I think they're talking about the "control contacts", while the life issue is the "controlled relay". i.e. the residual flux making the relay sticky, etc. ____________________________________________
Jim, Did you actually read the app. note? It very clearly indicates that the reliability issue is due to contact welding caused when high levels of DC current are interrupted in the normally open con
Indeed. I'm looking for a copy of another relay life apnote that talks about the contact life issue in lightly loaded situations (the RF array) where they address the close/open speed (and whether DC
Yes, I think that is good advice, Jim. Relays seem pretty simple and innocuous on the face of it, but when you dig into the details (as the Tyco app note demonstrates) you start to find out that ther
Answer at bottom. This thread has morphed into several distinct lines (hot switched and cold switched) with answers to one line easily confused with the other and none addressing the subject "relay l