Primary voltage regulators for boatanchor life

[W7TFO]

Has anyone tried a ferroresonant job like those from Sola to keep things even and make that elusive 117 Volt line for the old gear?  Most of them have taps to select the output Voltage.

They seem to be RF quiet, fairly efficient if kept loaded close to the design rating, and available reasonably on the used market.

73DG

[K5UJ]

A few months ago, actually around 6 months ago, I grabbed a Sola on eBay that my employer had up for sale.  I don't think anyone else bid on it.  The one I got was a little one, rated at 4 A 120 v. with two outlets on the panel.  I didn't know much about it at all but it was listed as a "power conditioner" and the price was only around $25 so I thought I could check it out and if I didn't have any use for it I could give it away or something and no big loss.  I opened it up to clean it out and was met with a transformer looking thing with odd taps and a couple of oil caps.  That plus the wiring and sockets was all there was to it.  I blew it out and plugged it in and tried it out.  It hummed, and gave off a lot of heat and I checked the v. and read 125 v.  I looked back inside and did not see any way to adjust the v.  No unused taps, or rheostat or anything.  While that was high, I'll tell you something, it held it at 125.  I put it on a variac and moved the line v. from 100 up to 140 and the output v. hung right there at 125.  I have no idea how that "ferroresonant" jazz works, but I'm disappointed mine is high.  I finally concluded a few windings must have shorted out to each other or something.  I have always used buck transformers and don't really know if I need it.   it would be interesting to look at the output waveform with it fed by some choppy source like a generator or inverter and see how much cleaning up it does.   I considered feeding a buck transformer with the Sola to get it down to 115 but it seems kind of ridiculous and inefficient. 

[KE6DF]

I have a small one -- 250 VA.

Probably too small for boatanchors except perhaps a receiver.

It was stripped out of a transmitter and was used to regulate the filaments for a traveling wave tube.

I figured that when I get around to building a medium/large transmitter, I might use it to regulate the input to the filament transformer.

[w3jn]

The only bad thing about those Sola regulators is they make an incredible racket.  You'll need to mount it in another room separate from your radio shack if you want to keep your sanity.

[WD5JKO]

    The Sola constant voltage transformer embrace Ferro-resonant technology. This is neat, and has many applications.

    They work by having the primary and secondary windings separated on the core with a third winding in between that is paralled with a large AC oil type capacitor. This additional LC circuit is designed to saturate at a predetermined flux density. This is where the peak of the AC wave is lopped off resulting in a squarish wave with normal sine wave rise and fall times.

    So the output voltage is fixed, but might be coaxed to shift a bit if the capacitance is changed. The L-C usually stores about 4X the KVA of the unit, and since the inductor is a saturating reactor, you could say that a Ferro-resonant transformer has nothing to do with resonance! We seldom apply the term resonance to an L-C circuit where the L component is non-linear.

    Since we have a lot of energy circulating, and the core saturating every half line cycle, the core losses are high, making heat come from within the core. Also the circulating current is also high, causing high I^2*R losses in the wiring of the saturating inductor. Therefore a 1 KVA unit might consume 200 watts unloaded, and that loss is pretty constant up to rated output meaning the % efficiency at rated load is ~ 80% and drops at lower than rated load. For example, a 200w load on a 1KVA Sola still has 200w loss, so efficiency is 50% at 200w load.

    Although the Sola may have constant RMS voltage from zero to rated load, the clipped peaks are at a much lower level than an equivalent sine wave source. So applications that rely on the peak to be 1.414 times the RMS will not work right.

Jim
WD5JKO

[k4kyv]

I have experienced all those problems with Sola CVTs.  I used to run one in the loft to get the noise out of earshot.  It ran so hot I was afraid of fire, and mounted it in an elaborate metal enclosure with thermal isolation away from all combustibles.

I use one now with my 75A4.  It is a small unit, about 3" X 3" X 4", rated for around 75 V-A, just barely enough to run the receiver.  It was originally used to run a desktop computer in an office environment, and is whisper quiet.  I can hear a buzz only if everything in the shack is turned off. It appears to be af a more modern design and evidently designed to be quiet, since it would be used in the office environment.  I have used it for years.  The problem I was having was that the receiver would drift with small line voltage changes, even with regulated +HV due to variations in filament voltage. The CVT cured the problem.

You have to be careful when working with those things.  The resonant coil that the capacitor connects to runs at hundreds of volts, and can give a nasty shock if you contact its terminals or the capacitor.  Circulating current in that coil is what saturates the core and limits the output voltage.

I have found that some solid state devices are freaked out by the square wave and simply won't run off the power supplied by a CVT.

[WD5JKO]

    So the output voltage is fixed, but might be coaxed to shift a bit if the capacitance is changed.

    Thinking about this some more, what I said above probably will not work. Back around 1980 I worked in a Lab where an engineer was designing Ferro-resonant transformers. I remember him playing with adding and subtracting laminations in the magnetic path where the saturating coil is located. I believe this changes the portion of the BH curve where the slope changes, and therefore changes the RMS output voltage.

    Changing the capacitor value does change the amount of energy circulating in the core however, and will effect the voltage regulation more so than the output voltage.

   The demand for EE's like that guy are not great these days. Last I saw him he was managing a public campground. 

Jim
WD5JKO

[Opcom]

    So the output voltage is fixed, but might be coaxed to shift a bit if the capacitance is changed.

    Thinking about this some more, what I said above probably will not work. Back around 1980 I worked in a Lab where an engineer was designing Ferro-resonant transformers. I remember him playing with adding and subtracting laminations in the magnetic path where the saturating coil is located. I believe this changes the portion of the BH curve where the slope changes, and therefore changes the RMS output voltage.

    Changing the capacitor value does change the amount of energy circulating in the core however, and will effect the voltage regulation more so than the output voltage.

   The demand for EE's like that guy are not great these days. Last I saw him he was managing a public campground. 

Jim
WD5JKO

I bet the RV outlet voltage is well-regulated.