Dangerous SCR MAIN AC Voltage Regulator.

**BobL** · 12th August 2021, 03:54 PM

A couple of years ago I bought two of these 4000W? SCR voltage regulators to have a bit of a play around with.
At $12 ea I figure I did not have much to lose.

Screen Shot 2021-08-12 at 12.20.13 pm.jpg
4000W 220V SCR Electric Voltage Regulator Dimmer Motor Speed Controller | eBay

The build was to say the least "flimsy" with the surrounding Al enclosure being particularly light weight.
They also did not have an earth connection so I added my own and luckily I did.

I tested one out with a variety of electric motors and it did indeed work all the way up to 4000W but I only left it there for a few seconds so I don't know how long it would maintain this for.
Like most SCR control the motors were pretty gutless at low speeds - I expected that.
I assumed the second one was the same so I did not test it and put the units away in my parts cupboard.
Earlier this week I looked for them to see how well they would control the speed of a small fan.

I only found one and it was not the same unit I had tested back when I first got them.
I don't know where that one is - probably buried in the pile of stuff in my electrics cupboard.

Any way connected the second one up - turn it on BANG! nice fat sparks. and the circuit breaker blew.

Opened it up and immediately could see scorched "short" marks on the Al casing in a number of places.
Case.JPG

Flip the circuit board and it shows where the soldered joints or tracks were touching the enclosure and where some circuit tracks have been blown off the board.

Cboard.JPG

The arrow on the lower right shows where the metal circuit board support was in contact with a nearby circuit track.
The upper left arrow shows a similar thing.

Anyway - love the sticker "QC passed"

I guess you get what you pay for - as I say, lucky I had earthed it.
Now I need to find the other one and see how close to the wind I sailed with that one.

**Bohdan** · 12th August 2021, 04:58 PM

Originally Posted by BobL

Anyway - love the sticker "QC passed"

It passed their QC but that may have only been to see if it actually got soldered.

**droog** · 12th August 2021, 05:51 PM

The QC Passed will be for the circuit board, run up to check operation after assembly of the circuit board, a standard process in electronic assembly lines.

The board would then be installed into its frame / case etc.
A final QC should be performed on the unit but any sticker will be on the outside of the unit.

Depending on where those tracks are in the circuit it may be no damage to the components and simply copper vaporised from the circuit board, replace with some stiff copper wire and test.

Of course if you are not trained or comfortable working on lethal voltage then just put it in the bin.

**BobL** · 12th August 2021, 08:21 PM

Originally Posted by droog

Depending on where those tracks are in the circuit it may be no damage to the components and simply copper vaporised from the circuit board, replace with some stiff copper wire and test.

None of the individual components look damaged and there was no acrid smell that comes from component damage - might just give it a go - thanks. BUT I'll be putting it in an insulating type enclosure before testing.

**BobL** · 15th August 2021, 05:41 PM

Originally Posted by droog

Depending on where those tracks are in the circuit it may be no damage to the components and simply copper vaporised from the circuit board, replace with some stiff copper wire and test.

Well I managed to fix it but I'm not putting it back into its original box. Might 3D print a custom box for it.

**droog** · 15th August 2021, 08:28 PM

Originally Posted by BobL

Well I managed to fix it but I'm not putting it back into its original box. Might 3D print a custom box for it.

Did the same many times in the past while in that part of the industry.
A sheet of insulation between the circuit board and the chassis was the most common commercial solution.

**BobL** · 15th August 2021, 09:38 PM

Originally Posted by droog

Did the same many times in the past while in that part of the industry.
A sheet of insulation between the circuit board and the chassis was the most common commercial solution.

The chassis is too flimsy for my liking - I'm going to put it inside a plastic box.

**BobL** · 17th August 2021, 06:47 PM

Here we go,

3D printed box

Enc.JPG

3D printed glands too
Black&orange.JPG

The original had a fan but it seems like it has died - have to snoop around in my bibs and bobs to see if I can find another one.

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