Variable Isolation Transformer - Isolation, Day 30

Teardown of a variable transformer, which provides a variable voltage and isolation. Single phase 1x250V @ 3A.
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#electronicscreators

[@KaizerPowerElectronicsDk]

Reverse engineered schematic: highvoltageforum.net/index.php?topic=1271.0

[@simontay4851]

That PCB is very interesting. Its a fast resetable electronic fuse with adjustable current. Ive always wanted to build a similar circuit for when im working on something that keep blowing its fuse (like a SMPS or audio amp). i wouldn't waste as many fuses and could save money and time buying new ones. Please could you reverse engineer that PCB and post the schematic on your website. Thanks.

[@KaizerPowerElectronicsDk]

I can not promise that it will be any time soon, but you can find similar schematics by searching for "reset-able electronic fuse", but many of those are for low voltages and the mains versions I saw did use a relay.

[@KaizerPowerElectronicsDk]

reverse engineered schematic: highvoltageforum.net/index.php?topic=1271.0

[@iganas88]

Hey Mads, great short video! I have exact same transformer, which died after plugging in a potentially fried switch mode power supply. What would be your guess as to which part failed?

[@KaizerPowerElectronicsDk]

Hi Ignas. I reverse engineered the schematics: highvoltageforum.net/index.php?topic=1271.0
I think you should look at the power resistor used for current sending and the transistor switch the relays.
Is the transfor itself damaged?

[@CliveChamberlain946]

I prefer this transformers roller contact over my original wiper-style 5 amp Variac. It seems like it would wear less the copper over time and use.

[@KaizerPowerElectronicsDk]

Carbon rollers have less wear over time, but are very sensitive to high peak current that could make it spark and burn dents in it.

[@leozendo3500]

Very interesting how they get around with two layers of windings stacking on top of one another with the correct geometry for variable transformer. Also the insulation needs to stand mains voltage++

[@simontay4851]

Just a piece of plastic between the windings should be enough. They might even have a custom moulded piece that the secondary is wound onto.

[@NiHaoMike64]

Most likely it just uses Kapton or Mylar tape between the windings just like most transformers.

[@selectronic001]

Seeing two sets of small TR/Relay/Power Resistor, i am wondering if one set is the over-current protection you described that affects the Secondary winding, and the other is an inrush-current limiter connected to the Primary winding....
Otherwise why the two sets of parts?

[@KaizerPowerElectronicsDk]

I am in the proces of reverseengineering the PCB and will make a Update about how it works.

[@gammaleader96]

Interesting, thanks for showing the inside.
I thought it might not be possible to wind a variac in such a way that the secondary winding is on a single layer for the movable contact to work.
But definately a pretty interesting construction.
Oh and nice to see something made in Denmark, I don't see that very often.
Greetings,
Michael

[@SeanBZA]

Much more expensive though, you basically are winding 2 very tall toroidal transformers, with there then being an internal plastic set of half shells ( to get your robust isolation requirements, plus to handle the load of the rolling wiper) that you carefully wind the secondary over. Has to be oversized to allow for the heating of the primary side, which is why it is not so common, probably cheaper to have a second transformer to do isolation, and will probably use less copper overall. But will be more compact over the 2 transformer solution.
Interesting it is rated for 400Hz operation, so the core is a very thin tape wound high quality silicon steel band, or even a permalloy type of material, both of which are not cheap.
I have an isolated variac as well, though it is only from 0-12VAC, as I repurposed a 115VAC 5A 400Hz variac, and drive it from a 12VAC 50VA toriodal light transformer. V.Hz product works out almost perfectly there, and reuses an otherwise unusable variac.

[@Hatmager]

Bagside. Det er nok fordi det IKKE er oversat. Prøv at læse det på dansk ;o)

[@KaizerPowerElectronicsDk]

Du har ret, det er dog kun normal og bagside der er dansk, resten er på engelsk, der blev jeg snydt af migselv :)