Strictly, power (for AC):
P = VIcos(phi)
That means that 480VA only equals 480W when there's a resistive load because that's when cos(phi) = 1.
As for isolated shaver outlets being rated at 2A, no, they aren't. The socket may safe for 2A, but the transformer supplying it isn't. Look at the size of a 480VA transformer then look at the size of one supplying a shaver outlet. Shaver isolating transformers are good for 20VA; about the load of a shaver...
Attempting to draw 2A from an isolated shaver outlet will cause a fire.
P = VIcos(phi)
That means that 480VA only equals 480W when there's a resistive load because that's when cos(phi) = 1.
As for isolated shaver outlets being rated at 2A, no, they aren't. The socket may safe for 2A, but the transformer supplying it isn't. Look at the size of a 480VA transformer then look at the size of one supplying a shaver outlet. Shaver isolating transformers are good for 20VA; about the load of a shaver...
Attempting to draw 2A from an isolated shaver outlet will cause a fire.
TugaTweaker,
I'm interested in your experience, I had a thread asking this same question but got no replies : http://www.diyaudio.com/forums/showthread.php?s=&threadid=116106
Do you mean the supply is better when running off batteries or when connected to the mains? Did you ever try running your equipment from the UPS in battery mode? Any sound differencies?
What power is the UPS? What power equipment are you running it off?
As I said in the thread I can get a APC server UPS - should be powerful - 4 outlet plugs at the back - can't find the model no. on it, inside or out! It has 4*12V 7aH SLA batteries
I'm interested in your experience, I had a thread asking this same question but got no replies : http://www.diyaudio.com/forums/showthread.php?s=&threadid=116106
Do you mean the supply is better when running off batteries or when connected to the mains? Did you ever try running your equipment from the UPS in battery mode? Any sound differencies?
What power is the UPS? What power equipment are you running it off?
As I said in the thread I can get a APC server UPS - should be powerful - 4 outlet plugs at the back - can't find the model no. on it, inside or out! It has 4*12V 7aH SLA batteries
Could be that being a Hi-fi show the guy demonstrating his gear wanted to avoid any public liability issues that may result from having equipment on show that was not isolated. If you have need for a large amount of power as well, then the use of the industrial site isolation transformers might be the cost effective way of doing it. Wherever the public are liable to come into contact with powered equipment it makes sense to have it all fully isolated for safety reasons alone.
In these situations the earth is normally left disconnected so equipment supply filters would not be performing as expected. I understand that earths are allowed on building sites using 110V equipment, in which case the center tap of the transformer is earthed so that the potential is reduced to a less hazardous 55V. My own thoughts however lead me to avoid earths of any kind on the outputs of isolation transformers, that way any likelihood of a current path through a person to earth is negated. Using two such transformers as he did, enhances further the safety aspects should the insulation of one transformer break down, which is very unlikely anyway due to the special way such safety transformers are constructed.
In these situations the earth is normally left disconnected so equipment supply filters would not be performing as expected. I understand that earths are allowed on building sites using 110V equipment, in which case the center tap of the transformer is earthed so that the potential is reduced to a less hazardous 55V. My own thoughts however lead me to avoid earths of any kind on the outputs of isolation transformers, that way any likelihood of a current path through a person to earth is negated. Using two such transformers as he did, enhances further the safety aspects should the insulation of one transformer break down, which is very unlikely anyway due to the special way such safety transformers are constructed.
EI core type isolation transformers block dc, and by virtue of a significant amount of leakage inductance are also quite effective at removing some line noise and high voltage transients.
I have a 230V British market Sony SACD player which I initially powered off of a 240V circuit in my entrance panel. Subsequently I tried an industrial control transformer to step up the 120V from a standard mains outlet to 240 for the player. Interestingly the player sounded much better powered from the transformer rather than directly from a 240V circuit fed from my panel. This was very unexpected to say the least, and I repeatedly switched back between the two and asked a couple of friends over to comment. They apparently heard the same things I did with no pre-conceived notion that this should be the case. (I didn't tell them what I was doing.)
Without trying something I would not be quite so quick to dismiss it, there may be (actually is) a sound technical basis for using transformers this way, and in fact transformers can be constructed to have relatively high leakage inductance and low interwinding capacitance for this application. Adding electro-static shielding between the windings also helps by interfering with capacitive coupling between them.
Modern mains are extraordinarily noisy, and it would not be surprising to find spurs out to a couple of hundred MHz on circuits shared with computers, TVs, and other modern electronics. (Just to name a couple.) Industrial estates in the vicinity can also seriously pollute the power in surrounding areas, not to mention your neighbors if they share a distribution transformer with you..
The line filters in most modern appliances are there solely to comply with the EU conducted EMI directives, they do little if anything to help the sound, are largely ineffective at relatively low frequencies, (probably below a couple of hundred kHz) often they may provide a measure of transient protection for distant lightening strikes and load dumps, but I wouldn't count on that..
I have a 230V British market Sony SACD player which I initially powered off of a 240V circuit in my entrance panel. Subsequently I tried an industrial control transformer to step up the 120V from a standard mains outlet to 240 for the player. Interestingly the player sounded much better powered from the transformer rather than directly from a 240V circuit fed from my panel. This was very unexpected to say the least, and I repeatedly switched back between the two and asked a couple of friends over to comment. They apparently heard the same things I did with no pre-conceived notion that this should be the case. (I didn't tell them what I was doing.)
Without trying something I would not be quite so quick to dismiss it, there may be (actually is) a sound technical basis for using transformers this way, and in fact transformers can be constructed to have relatively high leakage inductance and low interwinding capacitance for this application. Adding electro-static shielding between the windings also helps by interfering with capacitive coupling between them.
Modern mains are extraordinarily noisy, and it would not be surprising to find spurs out to a couple of hundred MHz on circuits shared with computers, TVs, and other modern electronics. (Just to name a couple.) Industrial estates in the vicinity can also seriously pollute the power in surrounding areas, not to mention your neighbors if they share a distribution transformer with you..
The line filters in most modern appliances are there solely to comply with the EU conducted EMI directives, they do little if anything to help the sound, are largely ineffective at relatively low frequencies, (probably below a couple of hundred kHz) often they may provide a measure of transient protection for distant lightening strikes and load dumps, but I wouldn't count on that..
Large EI core transformers have a nice advantage for filtering; they have a limited bandwidth and tend to filter out a lot of mains borne garbage. Add additional filtering and it would be better. I've posted before on the great benefits we found using this approach in a temporary RF facility I worked in years ago. The Tx's we used then were huge for their rating, maybe a 60L enclosure/5kVA lump. These were designed to run at low temps and to deal with large overloads, hence were a tad over engineered. Cheap on the surplus market at the time too.
Drag it back up TTT!
Anyway, I recently added in a UPS to the hifi gear. I think it improves things a bit, but its not huge. However, one major thing is that I did have a hum in a phonostage - not huge, but there when the volume was high. That is gone now since I added in the UPS. Worth it for that alone.
I know that doesn't exactly fit with the rest of this thread (isolation Tx), but its close!
Fran
Anyway, I recently added in a UPS to the hifi gear. I think it improves things a bit, but its not huge. However, one major thing is that I did have a hum in a phonostage - not huge, but there when the volume was high. That is gone now since I added in the UPS. Worth it for that alone.
I know that doesn't exactly fit with the rest of this thread (isolation Tx), but its close!
Fran
Possibly another parallel idea with this thread. I have a mains voltage with around 2.8% total harmonic distortion. The spectrum follows a fairly consistent decaying curve, with harmonics measurable out to the 41st (using an AEMC 3945 meter). Visually, the waveform is flat-topped, due to the vast quantity of electronic equipment connected to the pole mounted transformer (shared with about 5 other homes).
Next project amplifier is a 300B PP AC-heated amp, and this flat topping didn't have me excited. Figured I'd be dealing with more IM distortion or hum issues than if I had a nice clean sine wave for heating. So I purchased a used Sola MCR ferroresonant regulator to try and clean up the sine wave. The claim is that the regulator has "harmonic filtering" properties.
The result on the output is still a flat topped sine wave, with a THD of 3.5%. Sad but true. This confirms some of my historical experience with these supplies; they do not put out clean sine waves. However, I noticed that the harmonic spectrum abruptly stops at the 11th: beyond that, complete silence (as measured by the meter). This is encouraging, as is the simple raw regulation characteristic.
Connected the Sola to my preamp, and I believe there is an audible improvement. Blacker background and more clarity in the finer details. Look forward to completing the DHT and see how the heaters like it. Clarification though - these are very high source impedance devices, you don't want to consider them for a power amp - just heaters or preamps.
To add to the DC question, it seems to me that unequal current draw in each half of the rectifier winding will also contribute to a net DC result. So no matter how many xfmrs you have prior to your transformer, it will still experience a degree (though small) of DC. I would expect this is exaggerated in center tapped full wave rectifiers with unequal DCR in each leg of the xfmr secondary. Even adding a resistor to compensate doesn't seem to completely fix it for me - I still measure as much as 0.5V DC. And that's WITH the Sola feeding the system.
Hope in some way this contributes to the discussion. Bottom line is removing higher order harmonics, noise, RF, etc is always a good thing. Now what to do with the 3rd-11th ?
Next project amplifier is a 300B PP AC-heated amp, and this flat topping didn't have me excited. Figured I'd be dealing with more IM distortion or hum issues than if I had a nice clean sine wave for heating. So I purchased a used Sola MCR ferroresonant regulator to try and clean up the sine wave. The claim is that the regulator has "harmonic filtering" properties.
The result on the output is still a flat topped sine wave, with a THD of 3.5%. Sad but true. This confirms some of my historical experience with these supplies; they do not put out clean sine waves. However, I noticed that the harmonic spectrum abruptly stops at the 11th: beyond that, complete silence (as measured by the meter). This is encouraging, as is the simple raw regulation characteristic.
Connected the Sola to my preamp, and I believe there is an audible improvement. Blacker background and more clarity in the finer details. Look forward to completing the DHT and see how the heaters like it. Clarification though - these are very high source impedance devices, you don't want to consider them for a power amp - just heaters or preamps.
To add to the DC question, it seems to me that unequal current draw in each half of the rectifier winding will also contribute to a net DC result. So no matter how many xfmrs you have prior to your transformer, it will still experience a degree (though small) of DC. I would expect this is exaggerated in center tapped full wave rectifiers with unequal DCR in each leg of the xfmr secondary. Even adding a resistor to compensate doesn't seem to completely fix it for me - I still measure as much as 0.5V DC. And that's WITH the Sola feeding the system.
Hope in some way this contributes to the discussion. Bottom line is removing higher order harmonics, noise, RF, etc is always a good thing. Now what to do with the 3rd-11th ?
Ok, I got a Panasonic SA-XR57 HT amp from the US today & I hired one of these step-down isolation transfromers to power it with 110Volt. When I plugged the trafo in it buzzed very loudly - too loud to listen to an amp in the same room. Does this mean there is a lot of DC on the mains or just a badly designed trafo?
So, as luck would have it, I looked through my surplus stuff and found a large 53-0-53 trafo that I had pulled from a dumped HT receiver in the recycling centre. Connected it up - bingo - no buzz - connected amp - perfect. I played amp for about 4 hours & the trafo only got luke warm so I guess it has enough VA for a 7*100Watt amp?
My review of the amp is here if anyone is interested: http://www.diyaudio.com/forums/showthread.php?postid=1446246#post1446246
I'm very impressed with it - I don't know how much of the sound is due to the trafo though!
So, as luck would have it, I looked through my surplus stuff and found a large 53-0-53 trafo that I had pulled from a dumped HT receiver in the recycling centre. Connected it up - bingo - no buzz - connected amp - perfect. I played amp for about 4 hours & the trafo only got luke warm so I guess it has enough VA for a 7*100Watt amp?
My review of the amp is here if anyone is interested: http://www.diyaudio.com/forums/showthread.php?postid=1446246#post1446246
I'm very impressed with it - I don't know how much of the sound is due to the trafo though!
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