Hi guys
During a recent test run of my setup - Cat 0.5 driving a ST5 head, I noticed a problem. I was getting 88V on each leg. My ST has a AVR, so I removed the "voltage sense leads" and voltage came back up to 125V. The AVR is still in the loop, but I suspect is just passing the Z winding voltage through. I origninally had not planned on ordering one with an AVR at all. It was just a surprise that it was in there.
My questions are:
1) Is 125V (@60.5HZ) too high? - No Load
2) If I turf the AVR, How do I lower the voltage? Or do I even need to?
If it safe, I will run it in it's current config.
Thanks for your help!
Your AVR isn't hooked up right, or is defective, or you'd never see 88V. If you post a link to the AVR manual, or scan and post the manual's AVR hookup schematic page, perhaps we can help get you sorted out.
It sounds like the AVR isn't needed if you can maintain that voltage (minus normal droop) under load.
From my understanding of these ST AVRs, they can only reduce the z winding voltage (or current, I don't remember which) to bring the output voltage down, not bring it up. 125V at 60.5 Hz seems about perfect to me.
Edit- 1/4/2010 Bschwartz is right, and I was wrong- there are some new AVRs which regulate the Harmonic output. It's a very poor way to do an AVR on an ST head, but they are being sold cheap. What they will do is reduce the no-load overvoltage. Read the rest of the thread for more.
An AVR shouldn't be hooked to the harmonic winding of an ST head. If Bantor did that, that's why his output voltage was so pathetic (88v). The AVR gets hooked to the 120 or 240VAC output, and uses that for excitation. Since the harmonic winding distorts the AC waveform on the ST heads, this is a good thing; AVR controlled heads will have a much better looking waveform.
If Harmonic regulation is good enough for your needs, great. You can adjust the overall voltage higher by adding some capacitance after the bridge diode. You can adjust it lower by adding a dropping resistor in series with the harmonic before the bridge. You can't fix the voltage droop with load, that's just the nature of the (primative) beast.
Quote from: BruceM on December 21, 2009, 01:03:13 PM
An AVR shouldn't be hooked to the harmonic winding of an ST head. If Bantor did that, that's why his output voltage was so pathetic (88v). The AVR gets hooked to the 120 or 240VAC output, and uses that for excitation. Since the harmonic winding distorts the AC waveform on the ST heads, this is a good thing; AVR controlled heads will have a much better looking waveform.
If Harmonic regulation is good enough for your needs, great. You can adjust the overall voltage higher by adding some capacitance after the bridge diode. You can adjust it lower by adding a dropping resistor in series with the harmonic before the bridge. You can't fix the voltage droop with load, that's just the nature of the (primative) beast.
Bruce do you have a suggestion on a good AVR, or a schematic of a home grown?
I just read about that in Bill Rogers book, I would like to add one to my 12kw and drop the Z winding.
Thanks
Bill
Never mind Bruce I found it in another thread!
Thanks
Bill, I don't have a design for the ST-12. That's a big beast, and the simple AVR I did for the ST-3/5 uses a very simple push button start (no 12V supply needed) that isn't OK for the ST-12.
There are some commercial AVR products out there...
Bruce, you said "An AVR shouldn't be hooked to the harmonic winding of an ST head."
I believe on my ST, the AVR is wired to the harmonic winding. It also connects to the 240 (or 120 depending on the version) output of the generator. The AVR measures the output and reduces the throughput of the harmonic winding to lower the voltage output if it gets above the set point. I don't know if it has the ability to raise the current/voltage to raise the output if it starts to drop too low. These aren't the highest tech AVRs on the market.
Quote from: BruceM on January 03, 2010, 09:50:46 AM
Bill, I don't have a design for the ST-12. That's a big beast, and the simple AVR I did for the ST-3/5 uses a very simple push button start (no 12V supply needed) that isn't OK for the ST-12.
There are some commercial AVR products out there...
OK thanks Bruce.
bschwartz, The typical ST stock harmonic winding doesn't have any (or not much) extra excitation current to be down-regulated, so on those ST heads, trying to regulate the harmonic output would be disappointing, at best.
There's a bunch of ST manufacturers, so it's possible that one put some extra turns on the harmonic, and then offered a basic AVR to down regulate it. But it's never been reported anywhere before. It would be great if you had some documentation on yours and could post it...it may be something new in the world of ST generator heads.
I don't have any documentation, but this is what I have.
http://cgi.ebay.com/ST-STC-Automatic-Voltage-Regulator-AVR-1-or-3-Phase_W0QQitemZ150394075298QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item23042f78a2
Quote from: bschwartz on January 03, 2010, 05:33:58 PM
I don't have any documentation, but this is what I have.
http://cgi.ebay.com/ST-STC-Automatic-Voltage-Regulator-AVR-1-or-3-Phase_W0QQitemZ150394075298QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item23042f78a2
bschwartz,
That AVR is driven off of the 220 volt outputs of the alternator, it's not driven by the Z winding...
Daryl
Why is it in series with the windings as opposed to bypassing them?
Quote from: bschwartz on January 03, 2010, 08:05:24 PM
Why is it in series with the windings as opposed to bypassing them?
That will teach me not to expand the picture and take a close look at the diagram... :o
You're right, it appears to sample the AC output and then regulate the field via the Z winding...
It's better than just a Z winding for regulating, but not near as good as one that regulates off of the rectified AC output...
I wonder if the Z winding is modified in your ST5 vs. what we have in a standard ST5 with just a resistor ?
Sorry for the confusion !
Daryl
Guys, I just bought a new 12kw st head from Tom @ Central Georgia Generator and it has an AVR built in. What the heck it was the same price with or without. Would it help to post what I got in the way of paperwork? On second thought, I think Tom has documentation posted online.
I just checked, he does, hope this helps.
http://www.centralgagenerator.com/documents/documents.php
Ron.
Thank you bschartz, for posting the info on the "harmonic regulator" type AVR. I never would have believed that an AVR designer would be so ignorant as to do such a thing- but now it's clear that at least one has.
The $50 AVR wiring diagram and ebay ad text does indicate a Z (harmonic) winding connection.
This defeats most of the benefits of an AVR on an ST head. Normally an AVR does not use the harmonic, which results in significantly improved waveform. (Current flowing on the harmonic winding in an ST head causes a characteristic distortion of the AC waveform, known as the "harmonic hump".) For the smaller heads (ST-3 and ST-5), with a decent AVR (not using the harmonic) you can also expect some flicker reduction, as the excitation is powerful enough to compensate for the compression stroke voltage droop.
Using the harmonic as excitation on ST heads with too low a voltage under load (Z winding not providing sufficient excitation), you'll have to add some capacitance after the bridge to try and boost the loaded voltage. This $50 AVR device can only reduce the harmonic excitation.
The only benefit of this device is that no-load overvoltage will be eliminated. If you were expecting the other benefits of an AVR, you'll be disappointed. For example, my washer and other appliances "growl" when run off of the ST-3 with harmonic excitation, but are quiet and cool on my AVR which does not use the harmonic windings at all.
I could not find any documentation on Central Georgia Generator's AVR. I hope it is not another "harmonic regulator".
I'm not smart enough to make heads or tails of the leaflet that came with my 12kw.
Would it help to open the doghouse an snap a pic?
Ron
Ron,
There was good documentation on the standard ST wiring, just nothing on the AVR for the ST-12.
So no, doghouse photos would not help.
If there were better documentation on the $50 AVR, it might be possible to reconfigure it to NOT use the harmonic for excitation. Harmonic (Z winding) peak voltages are quite high- over 350 volts with a sudden surge load (measured on an ST-3). Depending on their circuit design, a transformer on the ST output might replace the harmonic, and improve performance. But I'd want to see more than just their hookup diagram.
BruceM
Good news, I just got off the phone with Tom Osborne at Georgia Generator.
Tom's $59 AVR has been tested to run off of 120V (no harmonic) excitation, for some of his customers with old ST's with failed harmonic windings. This would be ideal for the ST-3 and ST-5 heads. (120V is perfect for excitation for these heads.) Tom even offered to send me one to test, but I'm just not well enough for that right now. If someone else with an oscilloscope and some interest would like to do an evaluation for the forum, I'd be glad to provide phone support.
Tom is going to be adding the wiring diagram for the 120V excitation. The harmonic is not connected, instead 120V is connected to the AVR excitation inputs. If you are operating your ST head at 240V, then I recommend that you use a step down transformer for the excitation. It should be at least 350VA. You can run it off of one N-hot leg of the ST output, but I wouldn't (I don't like growling STs). The voltage sense can be one leg (N-L1), though again using a very small step down transformer would regulate the total voltage, instead of just one leg.
Bruce M
Bruce do you think this AVR will do my 12KW?
Mine is 80 volt dc and think 6.4 amp, I'll check the amp draw tomorrow.
Thanks
Bill
WGB, Yes, I think so. Tom's number is on his ebay store (Georgia Generator), call and make sure. 478-457-5524 cell
Needless to say, I have no idea of the quality or durability of these units, and Tom has been unable to get schematics or other documentation for repairs. At $59, you can't complain too much about that.
Bruce
Well the AVR on my 12kw sure is an itty bitty feller. With some luck "size doesn't matter" ;D
Ron
I just wish Tom had been able to get a bit more documentation on his AVRs- I normally wouldn't recommend a product so poorly documented but I don't see a lot of other choices and at least the price is a bargain.
On the ST12, for example, 240V external (non harmonic) excitation would result in better regulation and a cleaner AC waveform. I'd be surprised if the harmonic (Z) excitation for a surge load wasn't well over 500V. (It's over 350DC peak after the bridge rectifier for a stock, harmonic excited ST-3.) So in theory, an AVR which can handle the harmonic excitation on the ST-12 should be able to cope with 240V. But I'm reluctant to recommend anything when I have zero information on the design... there isn't even a crappy user manual in pseudo-english.
Another oddity in these AVRs is that at least one seems to be switching excitation on the AC side via SCR's or Triacs. (The unit is doing series regulation of the harmonic before the diode bridge.) This saves some cost but may cause some regulation performance problems. Triacs and SCR's can turn on at any time, but can only turn off when the AC current goes to zero. This could lead to issues with a change in excitation source waveform.
On the ST-12, I guess what I'd do is capture the peak DC voltage of the harmonic, after the bridge diode. If it's 400 volts or better, then I'd try the AVR with 240V excitation, with no costly loads attached.
I'd put a slow blow inline fuse in the line to the field coil, on any of these units, just to protect the ST from a failure.
Are there other sources for reliable AVR's and bridge diodes ? Or do I go to the parts bin at digikey.com and kit my own up?
Bridge diodes are plentiful and everywhere, including Digikey, Mouser, Alliedelec, Jameco, etc.
AVRs suitable for ST heads- I'd like to see some other sources, I'd be happy to at least scrutinize the documentation. Anybody seen them???
I wish I knew what my sine wave looked like.
My bottom of the line 12kw ST came with what looked like a AVR.
The first time I spun her the unit smoked literally.
I just slammed a bridge on it, flashed the field, I was up and running.
At 59 to 61 hz I'm in mid 125 volt per leg, no growling or any problem that I'm aware of.
I think I want a AVR from what I've been reading.
Anyway I talk with Tom at GG today, great guy!
I think I'll try one just to see what how it does.
I'll put a fuse before the field.
I know I'm rambling just put in a 16 hour day.