Vintage laboratory stabilised AC Power supply - Page 1
Forum section: electronics / projects

author: 001
author_rank: Super Contributor
timestamp: November 25, 2017, 12:34:52 pm
content: I grab nowday Vintage laboratory stabilised AC Power supplyIt IS NOT a "automatic variac" and it IS NOT a "ferroresonance buzzer"It is very tricky circuit for me (see attachments)It use vacuum diode as RMS detector and transistor amplifiers to magnetise special winded chockes to + or - voltage at the outputoutput is stabile 220VAC up to 10%THD +/-2% tolerance at +/-20% mains deviation. warming-up time is 1 HOURIs it usable? What THD is ok to go with common 50Hz transformers?Thanx!

author: capt bullshot
author_rank: Super Contributor
timestamp: November 25, 2017, 01:07:11 pm
content: Looks really interesting, would like to get my hands on one ...Can you post some photos?As long as it works, it's usable I guess. 10% THD would be not a big deal for a normal mains transformer. I don't know of a particular THD limit for 50Hz transformers, but I've heard of blown up small 50 Hz transformers when using a cheap 12V to 230V inverter with rectangular output waveform. That's far away from 10% THD.

author: oldway
author_rank: Super Contributor
timestamp: November 25, 2017, 01:09:10 pm
content: The voltage regulator uses two saturable inductors to control the output voltage.This type of circuit works on the principle of phase control and is similar to the operation of a triac.This operating principle is not very good because it generates a lot of harmonics.There is also a filter (probably H3) to reduce them.Before looking in detail at the drawings, I immediately thought in Russian technology .... seeing the indications in Cyrillic, my first impression was confirmed.Is it usable? If it works, why not? It should be checked if the output voltage is not too distorted and the filter H3 is still working.Be aware !!!! if you check the output voltage, DO NOT CONNECT THE OSCILLOSCOPE DIRECTLY TO THE OUTPUT because this regulator is not isolated.It is necessary to use a small isolated transformer 220V / 12V for example and to connect the oscilloscope on the low voltage winding of the isolation transformer.

author: 001
author_rank: Super Contributor
timestamp: November 25, 2017, 01:31:23 pm
content: Yes it worksI can adjust output voltage with pot on the front panelBut what the way to eliminate additional harmonics? Can I use some inductor?Is it critical to have 10% THD mains when You do voltage and current readings on common 50Hz transformers?

author: oldway
author_rank: Super Contributor
timestamp: November 25, 2017, 02:08:49 pm
content: The first question you need to ask yourself is whether you really need a voltage stabilizer ....As for harmonics, there are no specific rules, it depends essentially on the application.If you use the voltage for measurements, the harmonics change the rms value and a voltage with more than 3% of THD is not recommended.Effectively eliminating harmonics requires a very expensive filter with series inductance and LC resonant filter in parallel.The current flowing in the 50Hz parallel filter should be about 10x the rated current of the voltage stabilizer ...The filter will be huge, very expensive and will dissipate a lot of power.This is what we used in Mc Murray Bedford's fast thyristor inverters.