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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 12th Nov 2018, 11:27 pm   #1
Bazz4CQJ
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Default Ferroresonant Cnst V transfmer; Faults?

I have one of these units which is a Cetronic Reguvolt. It has not been used for years, but I ran it up on my Variac a few days ago and it is not working. Vout increases greatly in the Vin range of 200-250, whereas it should be within 3%. I used a 1kW fan heater as a load.

From what I can find on the internet this units are pretty simple http://www.powerqualityworld.com/201...oresonant.html but I'm not sure what the implications are for serviceability.

I wonder if anyone has any experience of servicing them and what the specs of the capacitor are? This is an obsolete unit and I've not been able to get info about it from Cetronic. It is so very heavy that even standing close to it makes my back hurt .

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Old 13th Nov 2018, 12:20 am   #2
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Default Re: Ferroresonant Cnst V transfmer; Faults?

I have looked at the graph in the link you have provided and guess that it is working correctly.
I would just check the capacitor.
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Old 13th Nov 2018, 12:51 am   #3
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Default Re: Ferroresonant Cnst V transfmer; Faults?

My tests results are attached. There's major volts loss. According to the info on the unit, the output should stay within 3% of 240 volts with an input ranging from 192(-20%) to 264V(+10%), percentage is relative to 240V.

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File Type: pdf Cetronic Test.pdf (16.4 KB, 25 views)
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Old 13th Nov 2018, 12:56 am   #4
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Default Re: Ferroresonant Cnst V transfmer; Faults?

Have you checked the capacitor?
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Old 13th Nov 2018, 1:04 am   #5
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Default Re: Ferroresonant Cnst V transfmer; Faults?

Is the meter reading affected by form factor? ISTR that the output waveform from these devices can get somewhat squared off compared to the input and shape presumably changes with input voltage as the degree of saturation changes.
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Old 13th Nov 2018, 2:21 am   #6
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Default Re: Ferroresonant Cnst V transfmer; Faults?

No, I haven't checked any component yet. To open it up I think that I will have to support it in such a way that both end plates can come off and then the single metal plate that covers the top and the two sides slides away.

Ah, waveform; forgot about that!!! I remembering Wrangler warning me it wouldn't suit my Avo163 valve tester as the output is 'distorted' sinewave, and I did once look at it on a scope and it is "irregular". I was just using an Avo8 to look at the output. Mmmm... how do I deal with that

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Old 13th Nov 2018, 6:57 am   #7
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Default Re: Ferroresonant Cnst V transfmer; Faults?

If you plug a light bulb in to it, it greatly reduces to rate of change of lumens out-v-voltage, but doesn't meet 3% and is well down on output. So, it works to some degree, and perhaps it is the aged capacitor that's letting it down?

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Old 17th Nov 2018, 6:52 pm   #8
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Default Re: Ferroresonant Cnst V transfmer; Faults?

There's not much else to go wrong, to be honest! They are "Ferro-resonant"
!

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Old 17th Nov 2018, 7:48 pm   #9
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Default Re: Ferroresonant Cnst V transfmer; Faults?

It probably has a paper resonating capacitor. And we all know what happens to paper capacitors, given enough time...

The value is fairly critical. Ferroresonant transformers work well, but they are critical as to supply frequency. So, thinking laterally, they'll be similarly critical as to capacitor value (given the frequency is correct). You may have to replace the capacitor with a biggish-but-slightly-too-small polypropylene AC-rated capacitor, with a few smaller ones in parallel to bring it up to the ideal value.
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Old 17th Nov 2018, 8:08 pm   #10
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Default Re: Ferroresonant Cnst V transfmer; Faults?

Thanks for the inputs. That unit is such a pain to work with. It has no handles, it's the size of three shoe boxes side by side and is pretty much full or iron, except for the cap!

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Old 17th Nov 2018, 11:34 pm   #11
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Default Re: Ferroresonant Cnst V transfmer; Faults?

I may be speaking out of turn here, and certainly out of my depth, but does the design/operation principle of these things make assumptions about the input mains source, i.e. a "low" (as in neglectable) source impedance whereas the variac output impedance is non-negligible, so as to upset the transformer's output impedance, or alternatively perhaps to de-tune it?

Clutching at straws, but intrigued as to mechanisms that might impair effective operation!
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Old 18th Nov 2018, 1:03 am   #12
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Default Re: Ferroresonant Cnst V transfmer; Faults?

It aught to be opened up if only for the usual safety checks.
There might be a mass of dead spiders in there for all we know.
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Old 18th Nov 2018, 2:14 am   #13
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Arrow Re: Ferroresonant Cnst V transfmer; Faults?

Just for what it's worth, during the period 1972 - 1982 (approx.) I was employed by a company who manufactured, sold & serviced photo-type setting equipment. Many of their photo-type setting machines were a mix of technologies: electronics, mechanics and optics. They were big and heavy! It was usual, when they were installed at a customers, for them to be powered from a CVT. (IIRC, these CVTs were manufactured by Claude-Lyons). Working as a technician, in the test dep't., we also used CVTs. One quiet day, just out of interest, I took the covers off one to see what was inside and trace the circuit. In essence (and, yes, from memory), that circuit was essentially the same as shown in the link in post #1.

If memory serves me right, I do recall that there were two types of CVTs: one type, primarily designed to suppress transients and R.F. noise, regulation being of a secondary function, and the other type the 'opposite', so regulation was the primary purpose. Ours were of the latter type.

And yes, heavy they certainly were! Ours were mounted on substantial pieces of 4" x 2" which, in turn, were mounted on four very strong castors. Still took a fair amount of 'manipulation' though, dragging them around the test dep't. floor.

If you do find that the cap.is defective, drop me a line with the required capacitance and working voltage. I might have something suitable.

Al.
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Last edited by Skywave; 18th Nov 2018 at 2:24 am.
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Old 19th Nov 2018, 1:01 am   #14
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Default Re: Ferroresonant Cnst V transfmer; Faults?

@ Turretslug re Variac; using a 100W filament bulb as CVT load, that gives a light-meter reading of 7600 lux when the CVT is connected directly to the mains supply compared with 7400 lux when the CVT is fed via the Variac (8amps) set at 240 volts. I didn’t check the mains voltage at that moment. So, in that particular test, the Variac “effect” could well be measurement error?

@ Skywave; thanks for that insight on the use of 4 by 2” Al. I’m glad it’s not just me being weedy. Let me get back to you re the caps.


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