Folks,
I've got a 5kw ST head hooked up to my 6/1 metro.
I took the old flimsy doghouse off today to mount a new more sturdy unit.
To my surprise, the unit I took to be a solid state resistor substitute is clearly marked "AVR" on the side (where you can't see it until you disassemble the doghouse)
What is odd is that the AVR looks to be added on aftermarket, as the wiring is of a completely different style incorporating the use of black plastic tape to insulate the connections.
The AVR uses a couple of wires across the 120v lines (voltage sense and power ?) and it's other two leads are in series between one leg of the rectifier and a line going to the field on the rotor.
Does anyone know how these things work ?
I'd like to have a simple resistor to put in place in case of acts of God (otherwise known as lightning strikes around here...)
Anyone know where to get one and it's value ?
So I started to trace out the wiring so I could document it, and found something else I don't understand:
The little switch that turns the generator on and off is nothing but a switch in series with a small light bulb that lights when the unit is "on"
I looked for online wiring diagrams and found that the switch and light bulb are in series with a small winding in the stator.
Now how does a few mill-amps flowing through a winding turn the generator on and off ?
Thanks in advance,
Crumpite
Yea, the little light didn't make much sense to me. It dosn't turn the gen on or off, the switch just turns the light off, perhaps to keep from burning it out. The little winding powering the light is just to indicate the field is active.
The description of the AVR circuit appears as if it is still in the harmonic winding circuit that powers the field, and it regulates the current flow from harmonic to field to maintain a steady output voltage. My ST-5 dosn't have any resistors in the circuit. It comes from harmonic winding to diode rectifyer to brushes and on to the field. No other parts on mine. Most AVR circuits don't use a harmonic winding for power. They take their power from the main output windings to feed the field. Since yours appears to use the harmonic winding to power the field, It could be that you could disconnect the AVR module and connect the diode output wires directly to the field. I would of course want to check the output voltage before trying to power anything with it wired this way...
Is it an "exciter" circuit...it sounds like a alt/gen light exciter?
Lloyd
Quote from: Lloyd on June 05, 2010, 11:57:58 PM
Is it an "exciter" circuit...it sounds like a alt/gen light exciter?
Lloyd
The exciter on an automotive alternator feeds 12dc to the field to get it started.
This light just lights up from a winding on the stator, no voltage is fed anywhere.
I think that Ronmar hit it on the head, it's there to indicate that you're getting power to the field and that it can generate - no light = no field = no power.
It could be pretty handy in troubleshooting.
As to why the switch is there, it's either to extend lamp life, or just to give you a feeling of control. :)
A bit strange, IMHO.
I've seen serious things written on the exact sequence of switches to throw to make sure you don't loose your residual magnetism.
Any such thing including that little switch on the panel must be just so much pure hokum. :)
I didn't know that you could run without a resistor, everyone seems to mention them, but I did find wiring diagrams that didn't use one.
That's another good thing to know if your AVR craps out just when you need it.The resistor might be another one of those feeling of control things.
Thanks all, my confusion level is a bit lower now !
Crumpite
i have seen the warning about never shutting down an st head with a load attached, because you will lose residual magnetism
and will have to flash the field to get it restarted.
my st7.5 has been shutdown many, many times with the load attached, it is a standard harmonic excitation and never fails to restart
although sometimes it take 15 to 20 seconds to do so.
of those heads that lose their residual magnetism, anyone just spin them up an wait to see if they will come back to life
or do you simply assume they need to be flashed and shut down too soon?
just curious
bob g
I always shut mine down with about a 1200 watt load (battery charger) on it the only time it failed to restart and I lost excitation was when the slip-rings were dirty and I had to clean and flash. Also it has shut down under full load quite a few times overheat e.g. no problems.
Potter
It doesn't seem to be as critical a problem as some think it is. I have had mine shut down a few times (I try not to do it) under load and they fired right up again with no problems. I have also had heads lose the residual magnetism and have tried starting them and running over speed for a few minutes to see if they would come back - it has happened once or twice, but mostly I have had to flash.
The ST's that dont use a resistor are a balance act between harmonic winding and field load needed to get a particular output. I would definitly try it without the AVR before you needed it. It may be that the model with the AVR has a different harmonic winding than the non AVR ST, and won't make useable power without the AVR in circuit.
Quote from: Ronmar on June 06, 2010, 11:32:49 AM
The ST's that dont use a resistor are a balance act between harmonic winding and field load needed to get a particular output. I would definitly try it without the AVR before you needed it. It may be that the model with the AVR has a different harmonic winding than the non AVR ST, and won't make useable power without the AVR in circuit.
I'd be a whole lot more worried about getting, say, 180 volts out, while my appliances fry !
Crumptie
Same concern here. An overvoltage event could be REALLY expensive at my house. I have a Timemark over/under-voltage sensor connected to a shunt trip breaker to protect things.
Chris
On the other hand, I consider it an unlikely failure mode on an AVR and a nearly impossible on a harmonic drive/resistor regulation system.
I *will* have to see how much one of those over-voltage relays cost though !
Crumpite
My ST-5 has an AVR that gets it's power from the 240 (my first got it from one leg 120). It then connects between the field winding and diode bridge. It gets it's power, and voltage input from the 240v and regulates the field. It can be taken out and a high current rheostat installed in it's place. I played with a 10 ohm 150 watt similar to this.
http://cgi.ebay.com/7-5-Ohm-150-Watt-Rheostat-/250560907214?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item3a569807ce#ht_539wt_930
It worked, but I changed to a permanent magnet head.
Another link to look at is this:
http://www.utterpower.com/vreg.htm
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 >:(
Quote from: Crumpite on June 06, 2010, 06:19:07 PM
I will have to see how much one of those over-voltage relays cost though!
Crumpite
Easily under $100 if you roll your own. Here's how I did mine:
http://listerenginegallery.com/main.php?g2_itemId=351
see "Engine Speed and Voltage Protection System 1 & 2".
I was more concerned about "brown out" (low voltage and potentially high current) during 6/1 shutdowns. I wanted to ensure generator disconnect from my house wiring should this occur during an automated emergency shutdown or if I just happened to forgot to manually disconnect the generator using the transfer switch during a routine shutdown.
The heart of the system is a Magnecraft voltage sensor with time delay settable contacts (use 831VS-120A for 120VAC or 831VS-240A for 240VAC):
http://www.bb-elec.com/product_family.asp?FamilyId=225
Oh, that's right, you're the one with the Mil-Spec setup ! :)
That's a little out of my price range but I'm sure I can home-brew one out of parts on hand.
(I'm disabled, no money, lots of time...)
I'm used to industrial grade control systems design.
Crumpite
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
Bob,
Those meters are sounding better and better all the time !
Crumpite
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.
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
Quote from: mobile_bob on June 08, 2010, 05:39:58 PM
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
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.
Quote from: sailawayrb on June 09, 2010, 09:43:17 AM
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
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.
Quote from: vdubnut62 on June 06, 2010, 10:15:17 PM
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! ;)