Discussion of AC mains isolation transformers

[jamesg11]

Hmmm ... is the 'explosive' risk exacerbated or ameliorated in 240V circuits?

[Speedskater]

13 hours ago, jamesg11 said:

Hmmm ... is the 'explosive' risk exacerbated or ameliorated in 240V circuits?

Higher voltages bring higher dangers.

But in the US type system, the 240V is line to line. Either line is still 120V to ground.

[zilch0md]

Thank you, Alex and John, for putting this one to bed, so to speak. I was on the fence, in ignorance.  :-)

[Abtr]

Hi all,

 

I tried the following, audio-grade, toroid, balanced 240VAC, 900VA iso-transformer: Amplimo ZN1902S (https://www.toroidal-transformer.com/shop/high-end-audio/audio-safety-transformer/709/audio-scheidingstrafo-900va.html).

 

It has an electrostatic screen between primary and secondary windings (to be connected to earth potential) which largely eliminates the capacitive coupling between primary and secondary windings. The specs don't state what the value of the residual capacitance exactly is, but according to my own noise measurements it performs quite good.

 

Furthermore, the secondary winding of this iso-trafo can be connected in balanced (common) mode, with the center tap connected to Earth. Here in the Netherlands we have wall power that has one phase connected to Earth. This transformer can change that to balanced (line to line) power which may be advantageous as stated e.g., here: http://www.equitech.com/articles/enigma.html

 

In my system, this transformer (connected in balanced mode), sounds awesome. I think it may be the solution to all my AC power problems..

    

[Iving]

This TOPAZ manual told me one or two things I didn't know, even being familiar with this thread. In case anybody else might find it useful: http://www.surplussales.com/Transformers/Pdfs/tp-91092-31_N.pdf

[Middy]

18 minutes ago, Iving said:

This TOPAZ manual told me one or two things I didn't know, even being familiar with this thread. In case anybody else might find it useful: http://www.surplussales.com/Transformers/Pdfs/tp-91092-31_N.pdf

I wish it said how to get them cheap in the UK. ..

[Iving]

1 hour ago, Middy said:

I wish it said how to get them cheap in the UK. ..

Sent PM!

[Speedskater]

That paper was written over three decades ago. Things do change, like rules about capacitors and ground rods.

[Iving]

19 minutes ago, Speedskater said:

That paper was written over three decades ago. Things do change, like rules about capacitors and ground rods.

 

There was much else that interested me. Please do expand your remarks for our benefit.

[tapatrick]

4 hours ago, Middy said:

I wish it said how to get them cheap in the UK. ..

Hi Middy

I managed to get a 1Kva Topaz and shipped to UK for just over £200. Because they are so heavy the shipping is a lot but seller used the eBay shipping partner scheme so if you can make use of that it helps a lot. 

[Ralf11]

"The common circuit for the "DC blocker" is a diode bridge made out of high voltage diodes. The bridge conducts during most of the AC waveform except for the the volt or so around 0V. Some high value low voltage electrolytic caps are placed across the bridge such that they only see the voltage +- the diode drop (a volt or two). These caps pass the portion of the waveform around zero and block the DC near zero. Since the frequency is very low (50/60Hz) and the current is high it needs very high value caps."

 

I always buy my organic flour from the mill on the other side of the Wheatstone bridge

[Speedskater]

On 7/27/2017 at 9:42 AM, Speedskater said:

That paper was written over three decades ago. Things do change, like rules about capacitors and ground rods.

Capacitor Rules:

Capacitors connected to the AC power line must follow the safety rules. (this includes isolation transformer secondaries) Across the power line to line it's type "X" and for line to ground it's type "Y".

 

I'm not getting into DC blockers.

Be back later.

[jamesg11]

A la John S's observations on devices having having there own inherent 'noise', is this relevant to the iso transformer in any way?

[Speedskater]

After further thought about the capacitors in a DC Blocker.  Because the electrolytic capacitors in a DC Blocker are neither connected line-to-line nor line-to- ground, the "X" & "Y" type safety rules don't apply.

However that doesn't mean that connecting electrolytic capacitors to an AC line is completely safe! Over voltage or reverse voltage can cause an electrolytic capacitor to explode!  So when trying out a DIY DC Blocker, stand well clear of the unit.

[JohnSwenson]

19 minutes ago, Speedskater said:

After further thought about the capacitors in a DC Blocker.  Because the electrolytic capacitors in a DC Blocker are neither connected line-to-line nor line-to- ground, the "X" & "Y" type safety rules don't apply.

However that doesn't mean that connecting electrolytic capacitors to an AC line is completely safe! Over voltage or reverse voltage can cause an electrolytic capacitor to explode!  So when trying out a DIY DC Blocker, stand well clear of the unit.

Right,

the issue is what happens if one of the solder joints on one of the diodes fails, which could happen, the diodes can get hot if a lot of current is flowing through the circuit, which could cause a bad joint to fail, presto, high voltage across the capacitors. BOOM

 

John S.

[Speedskater]

Yep, bad things can happen in a DC Blocker.

Heck, bad things can happen when there are any DIY add-ons to the AC power system.

[One and a half]

About DC blockers...  In dimensioning the diodes, the inrush current of a toroid is considerable especially the "high efficiency" types. 

 

For a 1kva toroidal 230V system under consideration of a DC blocker, the nominal current ay full load pm the primary is 4.3A. Inrush current for 50Hz systems is 60 x for 10ms. 

That's close to 260A which the diode has to survive.  This worked out to be a block style full wave bridge of 35A S1 rating,  so not really sure what's commercially available in DC blockers that cam take this kind of pounding. 

[Cornan]

On 2017-08-01 at 2:23 AM, One and a half said:

not really sure what's commercially available in DC blockers that cam take this kind of pounding. 

 

Except the ATL Hi-Fi DC Blocker trap filter that I use http://www.atlhifi.com/shop/fully-assembled-devices/dc-blocker-trap-filter-assembled-in-case/ there is also the newly released Supra DC Blocker http://www.jenving.com/products/view/dc-blocker-md01-16-eu-3024000378

I have used the ATL version for a while now. It does'nt change the sound signature but do increase SQ in my setup pre a safety IT.

[zilch0md]

Having finally taken the plunge to get a Topaz 0.0005 pF (91095-32), I'm very pleased with the results had vs. the Tripp-Lite is500 I'd been using.  Here's my current setup/guide:

 

[Abtr]

On ‎22‎-‎7‎-‎2017 at 7:32 PM, Abtr said:

Hi all,

 

I tried the following, audio-grade, toroid, balanced 240VAC, 900VA iso-transformer: Amplimo ZN1902S (https://www.toroidal-transformer.com/shop/high-end-audio/audio-safety-transformer/709/audio-scheidingstrafo-900va.html).

 

It has an electrostatic screen between primary and secondary windings (to be connected to earth potential) which largely eliminates the capacitive coupling between primary and secondary windings. The specs don't state what the value of the residual capacitance exactly is, but according to my own noise measurements it performs quite good.

 

Furthermore, the secondary winding of this iso-trafo can be connected in balanced (common) mode, with the center tap connected to Earth. Here in the Netherlands we have wall power that has one phase connected to Earth. This transformer can change that to balanced (line to line) power which may be advantageous as stated e.g., here: http://www.equitech.com/articles/enigma.html

 

In my system, this transformer (connected in balanced mode), sounds awesome. I think it may be the solution to all my AC power problems..

    

 

Well, I think an update is in order here. I found out that the inrush current of this trafo can blow a 16 amp fuse. Hence, I included a 5 Ohm 20W resistor in series with the phase/live mains connection for a slow start. After the trafo core is fully magnetized (in a few seconds) the resistor can be manually shorted with a switch (note that a time delayed 240V relais could do this automatically).

 

I also included a (Rod Elliot) DC filter to prevent saturation of the iso transformer which would degrade its performance. The filter audibly improves sound, which means there is a actually a DC offset component in my AC mains power!

 

Finally, I disconnected the secondary middle tap from primary Earth (which improved sound) and  included an RDC (leakage current breaker) and a warning sign for safety. This power plant as a whole sounds fantastic in my system!

 

[Speedskater]

Most good transformers in most situations don't need a DC blocker.

If there is a DC offset problem, it is caused by things like high-tech lighting systems, appliances, heating & air conditioning systems and motor drives. Most of those items start & stop so the problem will come and go.

[Abtr]

4 hours ago, Speedskater said:

Most good transformers in most situations don't need a DC blocker.

If there is a DC offset problem, it is caused by things like high-tech lighting systems, appliances, heating & air conditioning systems and motor drives. Most of those items start & stop so the problem will come and go.

 

So, just try it.

[Speedskater]

Thinking about it further, why would one think that a good grounding system, wouldn't have a measurable improvement  in the signal-to-noise ratio?

===================

But on the other hand, two different just audible background noises, that measure about the same, could have different subjective ratings.

[Abtr]

Balanced power is not about grounding, it's about noise cancelation, which (obviously) improves the audible/measurable signal to noise ratio.. 

[jamesg11]

What are the relevant specs on the Rod Elliot DC filter?