[Elecraft] Power-surge!

[Jim Wiley]

At least one manufacturer (Tripp-Lite / Isobar) advertises that if your 
equipment is damaged from a power surge when powered thru their device 
they will repair or replace it for free.   I use their surge suppressors 
for my computers, and have never had a problem, although they tend to 
make a horrible "bang!" on those occasions when they are killing a surge. 


Also, I wrote up a small item for the Glowbugs list that concerns using 
Amperite thermal delay relays to automatically cut off power for 30 
seconds or so when one of those one-second outages happens.   Here is 
the gist of that post.  You should be able to gleam sufficient 
information from the text to see what is happening, and how you could 
use the idea to your advantage.  The original post was concerned about 
how to get around contact bounce with thermal delay relays, which open 
and close relatively slowly.  A suitable delay relay is an Amperite 
115NO30 (115 volt heater, normally open contacts, 30 second delay) which 
I believe is available from eBay or various surplus dealers, typical 
price: less than $20.00.   The usual disclaimers apply. 


_________________________


The solution to the "contact chatter" issue is to use the thermal relay 
to activate a conventional relay that has the same coil voltage as the 
thermal relay heater.  Use a set of contacts on the conventional relay, 
in parallel with the thermal relay's NO contacts to latch the 
conventional relay closed.

This has several advantages.  If wired correctly, this allows the 
thermal relay to be "de-powered" almost immediately after closure, thus 
effectively preventing heater burnout from prolonged activation, and the 
delay relay is aways ready for another cycle, instead of having to wait 
for it to cool down.   The same SPDT contact set that uses its 
normally-open side to  "latch" the conventional relay can, from the 
normally-closed side,  control heater power for the thermal relay.

If you use a DPDT conventional relay, then the set of contacts not used 
for latching and controlling the thermal relay heater can be used to 
switch the actual power load, avoiding the problem of burning the 
contacts of the expensive (and increasingly rare) thermal relay.

The latching relay will drop out instantly on power off, so the cycle 
always starts fresh on each power on, no matter how long (or how short) 
the "off" period has been.   I use this basic circuit in most of my 
power control systems, including multiple-outlet AC boxes, typically 
with a 30-second or so delay.   In the event of a momentary power 
outage, the latching relay drops out at once and makes sure that 
sensitive items (hard disks, high-voltage power supplies, etc.) have 
completely spun-down or discharged before being re-energized.  Has saved 
me any number of problems,  and with a little more thought, allows 
remote control of power to whatever item(s) are being activated. 
_________

_________________________


- Jim, KL7CC



JIM DAVIS wrote:
> To the "Elecraft Crew",
>
> Many thanks for building into the K3 to sense when the AC power is not there and "shut-off" 
> completely!
>
> I say this because earlier this morning here locally there was a PG&E power outage. Initially the 
> juice went off and then just a few mil-secs the power tried to come back on, which would mean 
> there'd be
> a huge power surge to follow! I had my finger on the Astron-50m to switch the rig off but I did'nt
> have to really do that, in that the K3 sensed the power cut-off and "shut down" immediately. 
> Everybody knows what "power-surges" can do to our solid-state rigs, and eventhough most of our
> power-distribution strips SUPPOSEDLY have protection against such occurrences I've found that NOT 
> all
> of them are cracked up to what they advertise!!!
>
> Many thanks for saving our "BABY!"
>
> Jim/nn6ee
> S/N 2406
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