CVT/ferroresonant transformer application - Page 1
Forum section: electronics / projects

author: sniper
author_rank: Newbie
timestamp: July 30, 2018, 06:59:12 pm
content: Hi folks,this has gotten a bit longer (and due to ASCII art, certainly wider!) than I anticipated, but please try to bear with me. Right now I'm in need of a somewhat decently stabilized 24V PSU in order to set up an automatic syringe pump array. As I'm currently separated from my huge stash of industrial grade SMPS's by about 200 kilometers, I decided to go through my recently deceased dad's collection of transformers, find one with the right specs and hook up a simple stabilizer circuit in order to obtain 24V @5A.FWIW, I'll probably end up buying a boost converter IC tomorrow and go for the step-up route with a sizable 12V transformer.In similar cases, I tend to select magnetics by size and then establish the voltage/current rating of the promising ones, as they usually don't have a nameplate on, since most of them were salvaged from Cold War era equipment. I immediately noticed a curious looking transformer which is the subject of this question. It's a French made unit, and from what I can tell, quite high quality. Because of the presence of 6.3V as well as HV on the secondary, I'm assuming it's from an oscilloscope or something like that with a CRT. Lots of salvaged T&ME ended up there as my dad worked at a scientific research facility and as an employee, he had the privilege of acquiring the decommissioned Western-made equipment for pennies, which was kind of a big deal on this side of the Iron Curtain.Although I'm not even sure what symbols to use, the winding configuration is:upper cavity | lower cavity110/220V +/-15% |E1 S1 E2 S2 || 5.7Ω | | 6.7Ω | |└~~~~~~┘ └~~~~~~┘ |==================================================================================================================┐┌~~~~~~~~┐ | ┌~~~~┬~~~~~┬~~~~┬~~~~┐ ┌~~~~┬~~~~┐ ┌~~~~~┬~~~~┬~~~~┬~~~~~┐ ┌~~~~┬~~~~┐ PE6.3V .6A | | 3Ω | 63Ω | 9Ω | 9Ω ├---┐ 10V PM 10V 23.5V 20V PM 20V 23.5V 5V PM 5V| 900V C 130V PM 130V CAs you can see, several voltages look quite ideal for a 24V linear PSU, in fact, judging by the wire diameter, both the 10+10V and 20+20V lines would be definitely good candidates for at least 5A. However...I have no idea how to use this thing.I understand that I'm supposed to connect a capacitor in order to saturate the core, but - as you can see - the connections marked "C" are about 1000V apart and that's the point where I'm getting a bit cautious; you know, working with 1+ kV might be fun, but it is definitely no joke... I'd really like to fire up this transformer (not literally though), but my searches turned up either nothing or I had to walk away from a nag screen of an academic publishing house asking for $$$.Are you familiar with this - arguably obscure - type of transformer? Are you willing to walk me through the sizing of that capacitor?Thanks!Gabor

author: edpalmer42
author_rank: Super Contributor
timestamp: July 30, 2018, 07:54:07 pm
content: The first thing to do is look through your dad's stash of big capacitors. You're looking for a big oil-filled capacitor. See if there's one that has the same numbers stamped on it as the transformer - either 613247 or 5. The capacitance value will likely be in the range of maybe 5 - 20 uf and the voltage could be anywhere between 370 and 1000 VAC. One thing to keep in mind is that due to its age, the capacitor is almost guaranteed to be full of PCB oil. You'll have to decide whether you want to use it or find a replacement with the same value and voltage.If you can't find the matching capacitor, you'll have to do some experimenting to find an approximate replacement.Ed

author: sniper
author_rank: Newbie
timestamp: July 30, 2018, 08:38:38 pm
content: Thanks! I probably should've mentioned that I tried to find out if there was a "matching" capacitor (with respect to age, country of origin and value/rating). However, I haven't found the HV caps, only the "regular" ones for 1 and 3 phase line voltage. I'll get the bottom of that tomorrow, but I'm not sure if it's still around.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 30, 2018, 09:04:54 pm
content: In case you're not familiar with them, here's a typical oil-filled capacitor.Ed