AVR restoration, need some detective work...

[Zozew]

Hey there,

First im not an electronics wizard just a tinkerer that likes to fix things, so please be patient with my ignorance

I have an AVR that uses a toroidal transformer and a Servo motor to stabilize the voltage. Now if it was new all would be well, but this sad little thing has seen some battle and i thought as a small learning project i would try and restore it. I know i could buy a new one but i just feel it would make me happy to get it working again.

So...i did some research on different types of AVR and a usual diagram is the one below

Mine however lookes like this

I know the servo circuit part of the AVR doesn't work (motor works fine on 12v) so it's basically just upping or lowering the voltage if I move the arm over the coil. So the boosting and Bucking seems to work. (I've omitted the "safety circuit" and some switches and Voltmeters in the diagram for simplicity)

Now to the help part...

The person i got it from had made some fixes to it just to make it work so i don't know for sure if he has changed how the wiring was and im trying to understand and if i can, fix it of course.

The Safety circuit below only had one input from the secondary coil from the big transformer at about 15v and then strangely it had the phase AC wire (direct from mains) wound once around the right side pillar of the small transformer and then it went to the big transformer primary winding. I'm trying to understand if it is just some anchor point for the cable he used, or it actually does some sensing that way? when powering on the AVR the relay switches on after a few seconds and the LEDs show its on, so it seems the delay/timer works and displays it ok on the leds

Now the servo motor control circuit i think is broken or not very happy. One of the limit switches was broken in half (ive photoshopped in the missing right one)
This circuit also only had one input from a secondary coil and it was just around 2v which must be either wrongly changed by someone or used as something else i totally dont understand. I did try and use the Safety Circuits input on this as i guess they use the same rectifier components an it uses the voltage difference to somehow control the servo....what i am trying to find out is.... does it, the circuit make any sense or did the previous owner just jerry-rig it to statically raise the voltage and moved around the inputs for some reason..? what do you think?

I've ordered a new motor driver IC and the other as well just in case. I only got 8v on the BA6208 output when it had 12v powering it so maybe it somehow blew..

Anyhow if you have come this far , thank you for giving me your time and hope you have a great New Years EVE 2020!! If you have any insight at all please let me know anything would be helpful.

thanks

Andy

 

[dr pepper]

A single turn around a core is a classic current transformer, though I dont know why this thing would need one,

 

[Zozew]

Interesting... This is how the wire was wrapped.. Not around the central core but the side... Is thst how it works? Also the transformer in the photo only has one winding... Would that have some sensing function?

This board has a 2 pole (?) relay so i guess it has some over and under voltage sensing and shuts off the output or input..

 

[Nigel Goodwin]

A VERY long time ago, the company where I worked used to have two small cable TV systems - to provide broadcast TV signals where reception was poor to non-existent, and the repeaters etc. were all valve based - the sole exception was on the Matlock system where it incorporated 625 line TV, down-converted from UHF to VHF, and this used transistorised down-converters.

Anyway, when it was originally installed (before my time) they had endless trouble with it, and were essentially running round every day altering the gain of the repeaters. Eventually they decided that it was due to mains voltage variations, and they bought and fitted voltage stabilising transformers - and these totally cured the voltage related problems.

I've never understood how they worked?, but they were entirely passive, and consisted solely of transformers, inductors, and capacitors.

Now a variable transformer, moved by a servo, that I CAN understand

 

[Zozew]

Well in the Phillipines where I'm right now the mains can be really bad.. Going from 220v in the morning to 150v in the evening, so AVRs are always in demand that's also why I would like to make this one tick... Or rather turn automatically again.

1, The way mine has mains coming in on the arm and out on the tap... Is that supposed to be like that?

2, The 2 secondary windings both are at 1.5ohms but one gives around 15v the other 2v... Sounds strange.. Right?

Any ideas...

 

[dr pepper]

Nige there is such things as constant voltage transformers, they have no visible moving parts.

And looking at that wire no its not being used as a current transformer, prbably just as you say mechanical securing.

 

[Nigel Goodwin]

Nige there is such things as constant voltage transformers, they have no visible moving parts.

I know, we had a number of them at work - but from what Zozew said, his mains variations are probably far beyond their capability.

 

[ChrisP58]

A VERY long time ago, the company where I worked used to have two small cable TV systems - to provide broadcast TV signals where reception was poor to non-existent, and the repeaters etc. were all valve based - the sole exception was on the Matlock system where it incorporated 625 line TV, down-converted from UHF to VHF, and this used transistorised down-converters.

Anyway, when it was originally installed (before my time) they had endless trouble with it, and were essentially running round every day altering the gain of the repeaters. Eventually they decided that it was due to mains voltage variations, and they bought and fitted voltage stabilising transformers - and these totally cured the voltage related problems.

I've never understood how they worked?, but they were entirely passive, and consisted solely of transformers, inductors, and capacitors.

Now a variable transformer, moved by a servo, that I CAN understand

Probably a ferroresonant transformer.
https://www.sunpower-uk.com/glossary/what-is-a-ferroresonant-power-supply/

 

[KeepItSimpleStupid]

https://www.stacoenergy.com/product...-mechanical/stacoavr#literature_documentation might help under literature.

 

[Zozew]

Good morning lads I see we are on a bit of a time difference,let me be the first one to offer a Happy new year to you all!

Thanks Nigel for your interesting but tangential story about non-mechanical regulators

Anybody have any ideas if what I have should be wired as it is compared to a "regular" AVR with servo ..? or any other insightful thoughts?

Dr Pepper thanks for letting me know as it was doing my head in trying to understand that..

Cheers

 

[KeepItSimpleStupid]

At the very least, you have a autotransformer wired in a buck/boost configuration with a motor and limit switches.

Anny variac (variable autotransformer) should have the wiper fused.

How is the setpoint entered?

Something has to measure the voltage and control it within limits.

With just a window comparator, you might have hunting.

Like was said with it's big brother, when the error is small, you want to change things slowly.

I have a Sorenson ACR500 AC voltage regulator. Specs here: https://www.testwall.com/wp-content/uploads//2015/09/SOREN_ACR200044311.pdf

A ferroresonant transformer is typically noisy and outputs somewhat of a square wave. There is a capacitor across a winding.

 

[Zozew]

This is what I am trying to understand KISS (nice abbreviation) how does it measure/sense the voltage could it be that the leads feeding the servo circuit (all bite to low at 2v) also are used as a sensing circuit depending on the voltage level? The two secondary windings do mirror any changes in voltage ups or drops.. Right?

Thats why I'm so confused when I opened it up and the 2 boards only having inputs from the two secondary windings...

 

[Zozew]

Just for some laughs...

Last one is me finding out what the guy did to the poor variac before.. I did find a winding that broke off, that was under some plastic and measured both secondary windings and they gave me 1.5 Ohms each.. And the main between 6 and 8 Ohms depending on where you measure it before the slider or somewhere on it..

Interestingly on the back of the case there is (was) a 110v socket and on the variac there is a cut/tap at around 4 Ohms... But that cable was just in the air when I opened the case..

Anybody notice the nice label... Think the guy might have had a few too many

 

[KeepItSimpleStupid]

and then strangely it had the phase AC wire (direct from mains) wound once around the right side pillar of the small transformer and then it went to the big transformer primary winding. I'm trying to understand if it is just some anchor point for the cable he used, or it actually does some sensing that way?

It's possible they used the method to implement a current transformer. The"small transformer" only has one winding.

 

[KeepItSimpleStupid]

This https://www.omniphilippines.com.ph/product/avr-1500/ looks similar.

 

[Zozew]

KISS you are totally correct I thought it was the OMNI 1500w AVR... Until I saw the nice spelling of MODEL (Moedl) on the front panel and deducted it must be some copy Mine also lacks the built in fan the branded one has. That leads me to the conclusion more things might be different. But I did however email OMNI customer support a while ago and asked if they would be willing to send me the wiring diagram, although I doubt it...

 

[Zozew]

Dr pepper commented on the photo of the one turn winding and thinks it is most likely just a anchor point.. The previous owner used... But what does a one winding transformer do?

 

[dr pepper]

A one wind or current transformer transforms current.
Say you have a 1000:1 current trans (thats how they are spec'd), and you put 1 amp through the single turn (primary), you would get 1ma through the 1000 turn secondary.
So you transform a high current into a much smaller current that you can process with an electronic circuit, or even just display on a low current ammeter.
There are ac and dc variants, the latter uses some electronics to do the measuring.

That regulator has seen better days, but it might well come back.

P.S. just occurred to me you asked what does a one winding trans do, not a one turn. A one winding core would be an inductor not a transformer.

 

[Zozew]

Yes I thought it would act as an inductor.. But using a transformer core/housing for it, is it like a cheap shortcut..? Or... For some specific reason? Not sure just scratching my head here haha...

The replacement ic's I order are all coming from aliexpress.com so that can take between a few weeks to 2 months.. So until then I'll just do some work on the case, repainting it and making it look nice. Let's just hope I can make it work when I get the parts... With your help of course..

I did see that the previous owner added an extra switch to the front panel and made one of the Vmeters turn on and off... Kinda pointless... Well until let's see when I get the parts...

Until then feel free to grace me with your knowledge I do appreciate it!

Cheers

 

[KeepItSimpleStupid]

I did see that the previous owner added an extra switch to the front panel and made one of the Vmeters turn on and off... Kinda pointless... Well until let's see when I get the parts...

Maybe he used it in a high vibration area. In that case, I would have wired the meter shorted in the off position. A "keeper" of sorts.