Questions about ST head operation and wireing

[mobile_bob]

GE makes an option card that fits inside the watthour meter head i referred to in the test equipment post
it can be programmed to open or close a set of relay contacts for any number  of faults, over and under voltage being one.

i don't have one of them yet, but i think i will be looking to get one and then report back

bob g

[Crumpite]

Bob,

Those meters are sounding better and better all the time !

Crumpite

[sailawayrb]

However you elect to do this, you may want to consider that just simply opening contacts on low/high voltage threshold exceedance won't work well for STs because the voltage variation from normal load changes can be significant.  You don't want to load shed everything whenever you fire up your microwave.  Just opening contacts on threshold exceedance may result in having to use thresholds that violate your objectives for doing this in the first place.  The $60 Magnecraft device allows you to open the contacts only after the threshold has been exceeded for X seconds.

[mobile_bob]

Bob, makes a good point

i remember talking to GE a year or better back, and i think the option card can be programmed for
a time function as well, but
if not Bob's solution would be much better in my opinion.

guess more digging is in order to find out if the over/under voltage can be programmed with a time out variable

most loads wouldn't be damaged by a 5 second low, but a 5 second over voltage might be a problem?
so i guess the question becomes can they be set with differing timeouts.

bob g

[Crumpite]

Bob, makes a good point

i remember talking to GE a year or better back, and i think the option card can be programmed for
a time function as well, but
if not Bob's solution would be much better in my opinion.

guess more digging is in order to find out if the over/under voltage can be programmed with a time out variable

most loads wouldn't be damaged by a 5 second low, but a 5 second over voltage might be a problem?
so i guess the question becomes can they be set with differing timeouts.

bob g

It depends a lot on your control system.
With relay logic the cost of a time delay relay will negate the value of the option card.
With computer control the cost of an X second delay loop is nothing...
Different strokes for different folks !

I'll be using computer control as much as possible, so it's a viable option for me.
Crumpite

[sailawayrb]

I'm a big fan of computer control systems as well.  I use my home automation control system (Omni II that is 8080 based) shown in my previous link for many things listeroid/ST related in addition to controlling my house.  Most recently I used it for automated load shedding of various house circuits feed by ST.  For example, microwave circuit is disabled whenever AC circuit is actually ON, but AC circuit is disabled during normal meal times.  It works well since it knows latitude of house and thereby knows daily sunset/sunrise times.  That in addition to knowing inside/outside temps, status of house appliances including thermostat settings/schedules, getting real time data from internet, and the status of genset allows doing things well beyond the scope what most folks need, could afford, and perhaps even envision. Automated loading shedding will be used for our next passive solar/hydro powered home.  However, for emergency shutdown and other critical control aspects, I still prefer simple relays and KISS control schemes...and fail safe without requiring any electrons to accomplish it.  Or in the words of control design engineers, I prefer a simple, robust inner loop for the critical control functionality and a separate outer loop for the more advanced control functionality that is not safety critical.

[Crumpite]

I'm a big fan of computer control systems as well.  I use my home automation control system (Omni II that is 8080 based) shown in my previous link for many things listeroid/ST related in addition to controlling my house.  Most recently I used it for automated load shedding of various house circuits feed by ST.  For example, microwave circuit is disabled whenever AC circuit is actually ON, but AC circuit is disabled during normal meal times.  It works well since it knows latitude of house and thereby knows daily sunset/sunrise times.  That in addition to knowing inside/outside temps, status of house appliances including thermostat settings/schedules, getting real time data from internet, and the status of genset allows doing things well beyond the scope what most folks need, could afford, and perhaps even envision. Automated loading shedding will be used for our next passive solar/hydro powered home.  However, for emergency shutdown and other critical control aspects, I still prefer simple relays and KISS control schemes...and fail safe without requiring any electrons to accomplish it.  Or in the words of control design engineers, I prefer a simple, robust inner loop for the critical control functionality and a separate outer loop for the more advanced control functionality that is not safety critical.

8080's - I still remember some of the op-codes, my first computer was a SOL-20...

Nice system, I'd like to try something like that myself someday, although on a much simpler scale.
Active load/generation management with complete data capture is my ultimate goal.
We'll see if I get it all done by the time I'm in a wheelchair sucking on my gums. 

What are you using to control the AC power ?
Relays, SSR's, X10 or whatever ?
I'm just curious as I haven't seen what I'd consider cost effective solutions for small load switching in the home.

I've spent the majority of my life repairing, modifying, designing and programming  industrial and lab control systems, and I hear what you say about simple robust safety systems.
With proper engineering you *can* have computerized fail-safe systems, but you'd better know what you're doing !

In my case, it's cheaper to do it with skull sweat and a simple micro-controller system.
I'm disabled and don't have much money but do have a lot of time, so my designs are skewed that way.

I miss being able to throw money at a problem for a quick solution sometimes though. 

Crumpite

[sailawayrb]

Yeah, 8080 is very old tech now, but they are rock solid and no need for bloated, unreliable MS OS...  I spent first half of my career designing control systems for ICBMs, cruise missiles, helicopters, wind tunnels, and commercial airplanes.  I don't think in Laplace transforms anymore, but I use to

I used solid state relays (SSRs).  Something like these:

http://www.virtualvillage.com/40a-ssr-solid-state-relay-for-ac-devices-003602-009.html?utm_source=googlebase&utm_medium=shcomp

I think I got 50 of them for about $80 on ebay a few years ago.  They do need to be mounted with thermal paste directly to a metal panel and the panel has to have sufficient area for cooling.  My home automation system can tickle the SSR inputs with 12VDC and the SSR outputs can handle 240VAC/50A.  Mine have outputs that are NC and they are mounted in a sub-panel directly behind my transfer switch.  You could probably find electro-mechanical ones cheaper, but I like the flexibility of having variable input DC voltage and the high reliability of the SSRs (i.e., no moving parts or contacts that could start arching). 

I wouldn't recommend X10 for a 6/1 ST load shed system.  X10 isn't 100% reliable on grid power and it's much less so on 6/1 ST power...too much noise and not well defined zero crossing points where the X10 protocol is transmitted.

[rcavictim]

That darn little light and the on/off switch is a little weird and if I had not read up on them before I got an ST head , it could have gotten me killed,
or at least made me say "sugar" when I turned it off to connect or disconnect something.
Chalk it up to cultural differences, I guess.
Ron

P.S. Why do my italics not turn off? I assumed that what one types between the brackets would be italicized, not everything that is typed thereafter. See, even the modifications that are posted are in italics

That might be because everything you have to say is important!