Discussion of AC mains isolation transformers

[octaviars]

7 minutes ago, Cornan said:

There is no toroidal transformer in that spot AFAIK, so I guess there is more to it than just toroidal transformers. LED-lights (popular these days) for example?

 

Well I dont really know but I suppose all depends on the transformer but the only thing a DC offset on the powerline will do is saturate the core of a big transformer and mainly larger toroids. A small DC mA on the AC line will not affect a small transformer as the resistans is to high in the winding that is ohms law so no magical stuff going on there and a SMPS will not be affected by it.

 

Of course today there are much more stuff going on in a house that can affect the AC sinus wave, every object that in some sort alters the sine wave like dimmers, frequencydrives and so on can do this but it is not a constant problem and it can vary during the day so not easy to judge how much problem there is without looking at the actual sinewave.

[Speedskater]

I think that the main reason for transformer buzz & hum in US residential areas is high line voltage. Many small production, legacy or boutique hi-fi components were designed for 110V, 115V, or 117V power lines. US line voltages have been creeping upward. NEC and UL now spec 125V and I sometimes see the line voltage approaching 127V at home.

* * * * * * * * * * * * *

So the question is, does the transformer buzz/hum 24 by 7 all year?  In a residential area there are very few devices that run 24 by 7 capable of causing DC offset. Nor does line voltage stay at one voltage. Over a typical month, I see periods with line voltage as high as 127V and as low as 116V.

[zilch0md]

4 hours ago, Forehaven said:

Thanks for the help guys.  I bought a 1kV Elgar, model HIT .001R

 

Sounds like I'm kind of screwed with the noise.  Unfort. I live in a 1905 built home, with old....circa 60's?...wiring.  Plus, I live on a street surrounded by lg multi residential bldg's.  

 

Are there actually IT's that are silent??

 

My 500VA Topaz 19095-32 is also pretty close to silent.  I have to put my ear close to it to hear anything.  It is not a toroidal transformer, though.  Then again, there are some people out there with noisy Topaz transformers (i.e. John S.) 

 

I really think the quality of the incoming AC mains power is a big factor, no matter what type of transformer you are using - and that incoming quality can fluctuate throughout the day.  

 

There are are a lot of people out there who have silenced noisy transformers that are inside their various audio components, just by inserting a DC blocker ahead of the their A/V systems - here in the States, too, not just elsewhere.  See the reviews of the relatively affordable Emotiva CMX-2, which is more than just a DC blocker.  It's the people who had noisy transformers who are writing the most positive reviews of the CMX-2 - so, I'm pretty sure it does a good job of DC blocking, even if it only does a fair job of CM or DM noise reduction.

 

If I had a noisy transformer, even a noisy Topaz, I would try putting the CMX-2 in front of it.  I definitely would not put anything like this (containing MOVs for surge protection) in between my Topaz and the power strip into which all my gear is plugged.  Surge protectors, if really needed, should be placed ahead of the Topaz - which is exactly where you want a DC blocker, too.

[Speed Racer]

My 2.5kVa Topaz was a bit noisy until I converted it to balanced power. It went from noisy and hot to silent and cool.

[One and a half]

1 hour ago, zilch0md said:

 

My 500VA Topaz 19095-32 is also pretty close to silent.  I have to put my ear close to it to hear anything.  It is not a toroidal transformer, though.  Then again, there are some people out there with noisy Topaz transformers (i.e. John S.) 

 

I really think the quality of the incoming AC mains power is a big factor, no matter what type of transformer you are using - and that incoming quality can fluctuate throughout the day.  

 

There are are a lot of people out there who have silenced noisy transformers that are inside their various audio components, just by inserting a DC blocker ahead of the their A/V systems - here in the States, too, not just elsewhere.  See the reviews of the relatively affordable Emotiva CMX-2, which is more than just a DC blocker.  It's the people who had noisy transformers who are writing the most positive reviews of the CMX-2 - so, I'm pretty sure it does a good job of DC blocking, even if it only does a fair job of CM or DM noise reduction.

 

If I had a noisy transformer, even a noisy Topaz, I would try putting the CMX-2 in front of it.  I definitely would not put anything like this (containing MOVs for surge protection) in between my Topaz and the power strip into which all my gear is plugged.  Surge protectors, if really needed, should be placed ahead of the Topaz - which is exactly where you want a DC blocker, too.

The Topaz/Elgar/Xentek is an effective surge suppression in itself. Absorbs a 6000V spike to some mV value, so any MOV or device like it just adds nuisance currents and is redundant.

 

Noisy transformers fix often is to tighten the four large bolts on the frame when the Transformer is warm to hot. These devices are years old and with transport the nuts loosen.  Check this by examining the paint on the nuts, if it's cracked, then they are loose.

[sandyk]

Cornan

There is another possible cause for toroidal transformers buzzing under heavy continuous loading.

It has to do with high peak rectifier currents.

Please check your PMs.

Alex

[Cornan]

6 hours ago, sandyk said:

Cornan

There is another possible cause for toroidal transformers buzzing under heavy continuous loading.

It has to do with high peak rectifier currents.

Please check your PMs.

Alex

 

Thanks Alex! Interesting read! ?

[One and a half]

10 hours ago, Speed Racer said:

My 2.5kVa Topaz was a bit noisy until I converted it to balanced power. It went from noisy and hot to silent and cool.

Is your model the 0.005 pf or 0.0005 pf? If the voltage symmetry is really close, there's no need for the Equitech.

[Speed Racer]

10 minutes ago, One and a half said:

Is your model the 0.005 pf or 0.0005 pf? If the voltage symmetry is really close, there's no need for the Equitech.

 

It's a 91002-31 so it is .0005pF. The unit offers 146dB of common mode noise reduction and 60dB of normal mode noise reduction.

[One and a half]

2 minutes ago, Speed Racer said:

 

It's a 91002-31 so it is .0005pF. The unit offers 146dB of common mode noise reduction and 60dB of normal mode noise reduction.

Thanks for that. Presume if there's more garbage on either side of the line, the transformer would 'absorb' more, has to go somewhere and that's heat. If the wiring was changed to balanced, there's less common mode noise to remove then.

[spacexpert]

OK I'm back in Topaz country.  My new 750VA unit arrived, this time with jumpers included.

This one is a little worse for wear, but I guess you shouldn't judge an IT by it's outsides.

It's outputting around 247V and it is quiet.  No load attached yet, I just wanted to do a heat test and...

After 1 hour, it is skin temperature.  Barely warm to touch.

 

Phew!  Looks like a keeper.

 

Now as for this "earth leakage circuit breaker"... is this a simple job?  I'd like to have this thing wired nice and safe. 

 

[oneguy]

Very nice! My new old stock 1.8 kVa (MGE 91018-32T) was waiting for me when I came home on Saturday. The exterior looks great but I unfortunately can’t check it out operationally since it came with a twist lock plug. I just ordered an adapter plug but I have anothe 7-10 days before that arrives. 

[One and a half]

1 hour ago, spacexpert said:

OK I'm back in Topaz country.  My new 750VA unit arrived, this time with jumpers included.

This one is a little worse for wear, but I guess you shouldn't judge an IT by it's outsides.

It's outputting around 247V and it is quiet.  No load attached yet, I just wanted to do a heat test and...

After 1 hour, it is skin temperature.  Barely warm to touch.

 

Phew!  Looks like a keeper.

 

Now as for this "earth leakage circuit breaker"... is this a simple job?  I'd like to have this thing wired nice and safe. 

 

Depends on how the output is wired, balanced or SE.

 

Glad to hear that the heat is contained, the other transformer is clearly faulty. 

[Speed Racer]

1 hour ago, oneguy said:

Very nice! My new old stock 1.8 kVa (MGE 91018-32T) was waiting for me when I came home on Saturday. The exterior looks great but I unfortunately can’t check it out operationally since it came with a twist lock plug. I just ordered an adapter plug but I have anothe 7-10 days before that arrives. 

 

Do you know how it is wired? 240v or 120v?

[One and a half]

If the Topaz output is balanced, ie 120-0-120 (60-0-60) with the centre tap earthed, then use this RCBO. This RCBO is a 2 pole device, since there are two wires above ground with different potentials to ground. By different potentials I mean direction, one is 180 degrees out of phase with the other.

 An RCBO is a combined circuit breaker plus an RCD (GFCI) in the same package. The 6A rating is about the smallest available in current rating. In the event of a leakage current to earth or imbalance btween the two hot conductors, or current drawn is greater than 6A (double the output of the 750VA transformer, then the breaker will trip. There are ways to detect excess current with an adjustable overload, but more on that a lot later. Still working on protection systems for transformers much to do still.

 

If one of the outputs is earthed, there's a different RCBO to choose and it's a LOT cheaper, since they make them by the millions.  A portable one is fine, like this one but it's only an RCD and doesn't have the thermal protection. 

 

 

 

[Speed Racer]

7 minutes ago, One and a half said:

If the Topaz output is balanced, ie 120-0-120 (60-0-60) with the centre tap earthed, then use this RCBO. This RCBO is a 2 pole device, since there are two wires above ground with different potentials to ground. By different potentials I mean direction, one is 180 degrees out of phase with the other.

 An RCBO is a combined circuit breaker plus an RCD (GFCI) in the same package. The 6A rating is about the smallest available in current rating. In the event of a leakage current to earth or imbalance btween the two hot conductors, or current drawn is greater than 6A (double the output of the 750VA transformer, then the breaker will trip. There are ways to detect excess current with an adjustable overload, but more on that a lot later. Still working on protection systems for transformers much to do still.

 

If one of the outputs is earthed, there's a different RCBO to choose and it's a LOT cheaper, since they make them by the millions.  A portable one is fine, like this one but it's only an RCD and doesn't have the thermal protection. 

 

I wired mine as follows:

 

Input:
Hot (black) to H1
Neutral (white) to H4
Jumper H2 to H3
Ground to chassis

Output:
Hot 1 (black) to X1
Hot 2 (white) to X4
X2/X3 center tap connected to chassis ground and outlet ground.

 

That means I need the less expensive RCBO or the RCD because the output is earthed, correct?

 

Why would you wire it the other way?

[spacexpert]

10 minutes ago, Speed Racer said:

I wired mine as follows:

 

Input:
Hot (black) to H1
Neutral (white) to H4
Jumper H2 to H3
Ground to chassis

Output:
Hot 1 (black) to X1
Hot 2 (white) to X4
X2/X3 center tap connected to chassis ground and outlet ground.

 

This would be how I wired mine as well for 240V.

[Speed Racer]

Just now, spacexpert said:

 

This would be how I wired mine as well for 240V.

 

That makes sense as 240v is balanced  by default.

[One and a half]

9 minutes ago, Speed Racer said:

 

I wired mine as follows:

 

Input:
Hot (black) to H1
Neutral (white) to H4
Jumper H2 to H3
Ground to chassis

Output:
Hot 1 (black) to X1
Hot 2 (white) to X4
X2/X3 center tap connected to chassis ground and outlet ground.

 

That means I need the less expensive RCBO or the RCD because the output is earthed, correct?

 

Why would you wire it the other way?

 

That connection is a balanced connection, Hot 1 and Hot 2 are at 180 Degrees apart. You need a 2 Pole GFCI (RCD).

 

To use the Audio equivalent of an SE (Single Ended), Jumper X1 - X3, X2 - X4 and ground X4 and the shield. This combo still works out the -140db reduction in common mode noise, but doesn't allow any cancellation of noise which a balanced system can.

What it does do is make it compatible with the likes of lamps that switch only the hot. Not that a lamp would be plugged into an audio circuit, but legally the lamp is connected to a designed power system (TN).

TN systems can use a single pole GFCI, although the neutral is connected to the GFCI for the circuit to work.

[oneguy]

36 minutes ago, Speed Racer said:

 

Do you know how it is wired? 240v or 120v?

 

120v

 

http://www.pacificparts.com/vends/mge/images/t1.pdf

[One and a half]

2 minutes ago, oneguy said:

 

120v

 

 

If the Topaz is wired like @Speed Racer, it's possible to use a balanced output of 60-0-60 with noise cancellations as a bonus. By all means work with an electrician if you are uncomfortable as a DIY. They would probably change the receptacle to something that's ex stock and not 10 days.....

[oneguy]

8 minutes ago, One and a half said:

 

If the Topaz is wired like @Speed Racer, it's possible to use a balanced output of 60-0-60 with noise cancellations as a bonus. By all means work with an electrician if you are uncomfortable as a DIY. They would probably change the receptacle to something that's ex stock and not 10 days.....

I am not beyond DIY work but I’d have to open it up to see what is involved. I left the bulk of my tools in the U.S. when I temporarily moved to Japan two years ago. I am also slightly concerned as I have heard that using balanced power for equipment that wasn’t designed for balanced power can have disastrous consequences. I need to get smarter on that. 

[One and a half]

15 minutes ago, oneguy said:

I am not beyond DIY work but I’d have to open it up to see what is involved. I left the bulk of my tools in the U.S. when I temporarily moved to Japan two years ago. I am also slightly concerned as I have heard that using balanced power for equipment that wasn’t designed for balanced power can have disastrous consequences. I need to get smarter on that. 

 

The only devices that complain are line conditioners where they detect a ground that's unexpected. Any AC mains switch needs to be a 2 pole, which for Europe and Japan is a standard and most consumer equipment. Japan uses the TT system of earthing, which very cleanly avoids crap on the ground wire to begin with, since the neutral is referenced to ground wayyyy back at the power station. Top system!!

 

100V though may be too low for the Topaz to work, 20% is a lot on the way down. I would recommend a step up transformer on the line side of the Topaz, 100V to 115V.  That transformer need not be anything special, an auto transformer would do the job admirably and allows for a bit of voltage creep on the output of the Topaz.

[oneguy]

30 minutes ago, One and a half said:

 

The only devices that complain are line conditioners where they detect a ground that's unexpected. Any AC mains switch needs to be a 2 pole, which for Europe and Japan is a standard and most consumer equipment. Japan uses the TT system of earthing, which very cleanly avoids crap on the ground wire to begin with, since the neutral is referenced to ground wayyyy back at the power station. Top system!!

 

100V though may be too low for the Topaz to work, 20% is a lot on the way down. I would recommend a step up transformer on the line side of the Topaz, 100V to 115V.  That transformer need not be anything special, an auto transformer would do the job admirably and allows for a bit of voltage creep on the output of the Topaz.

I already have step up transformer. The power at the base that I live on is 107v so my transformer spits out 127 or 128v. I am trying to verify the frequency though to make sure it’s 60Hz where I live. There are both 50 and 60Hz transformers here.

[One and a half]

9 minutes ago, oneguy said:

I already have step up transformer. The power at the base that I live on is 107v so my transformer spits out 127 or 128v. I am trying to verify the frequency though to make sure it’s 60Hz where I live. There are both 50 and 60Hz transformers here.

Ah ok, all is good, 127V, 5.8% on the 120V... OK.

 

60Hz transformers can run on 50Hz, they get a little warmer. 50Hz Transformers on 60Hz are over fluxed, also get a bit warmer.