• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

on-line UPS or balanced power supply?

Status
Not open for further replies.

Les Jones

Well-Known Member
Most Helpful Member
You do not say what you are trying to achive. I suspect you are havinig a problem with hum or noise on audio equipment. The two diagrams on your first link show the power from the substation. The transformer shown will be is the substation (It will be one of the three windings on a three phase transformer.) It is unlikely that a separate earth wire is run from the substation to your house. The earth and neutral are probably connected together where the cable enters your house and this point will also probably be bonded to your gas and water pipes. (Assuming they are not plastic.) and possibly a ground spike. Although there will probably be a difference of potential between the substation earth and the earth in your house there will be very little potential between the earth wire in your house and the earth in your environment. I think adding a UPS will cause more problems as there will be radiated interference from the high frequency switching circuits in the UPS.

Les.
 

ronsimpson

Well-Known Member
Most Helpful Member
I did some reading on balanced power supplies
From that; all problems including my back pain are all from the power line.
I think most audio equipment really does not care if the power is balanced or not.
Keep current off the ground wires.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
What I read while somewhat true, seems to be a lot of propaganda. I used ONEAC power conditioners (It's not a UPS) for over 25 years. These are not isolation transformers either. This
video, but wasn't as good as a live demo from the manufacturer that sold me on the conditioner. It's not really a surge suppressor either, but it really cleans up the grounds.

I have their module that lets you examine the AC power, but I have been too busy to try to hook it up

One I started to use it, computer problems went away. I was left with two problems, power supply and mechanical (fans and disk drives). So, when a Macintosh Centris 650 system was installed, it ran 17 years, same hard drive with only a floppy replacement and cleaning the fan and motherboard from dust. The system was still operating. We used these on three of our production test systems. One of the systems was identical in parts, acted as a spare and "portable" system.

I put an ISOBAR surge suppressor after the conditioner. Powervar has some comparisons for the ISOBAR conditioner too. The POWERVAR/ONEAC are available cheap on ebay.

My audio system has a 500 W AC sine wave voltage regulator on it. I would consider the ONEAC/Powervar for my UPS backed up systems at home.
 
My house is single phase (like most free standing single houses in Australia), so I get live and mains. In the meter box then is the split between ground (the green yellow) and neutral. Think there is still a connection to the earth spike. But now RCDs are required, so I guess if I have a balanced power supply there will be some current onto the ground which is not on the neutral. So they wil trip all the time. Plus I am a bit worried, with a balanced power supply both wires have 120 V on them, not one is 0 the other 240.
The UPS would make some more or less messy sinewave and a ground and would be galvanic separated from the grid plus maybe have brownout/blackout protection? If the UPS has a high "sampling rate" the noise on top of the 50Hz sinewave would be way outside the audible spectrum?
Yes, there is trouble with hum.
The ONEAC demo, how did he measure that, maybe its a recording itno the osci, looks to repetitive. Plus you never get proper earth to the osce, there is always lots of noise if you zoom in.
 
Last edited:

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
In the US, resisdential is fed by single phase something around 9 kV . This is stepped down to the residence to 240 V center tapped (120-0-120)
So, our Neural and ground is boded to earth at one place for the residence. That's the reference for the residence.

The 120 VAC outlets in the residence come from one of these split-phases. So, we end up with L1, L2, N and ground. 240 feeds stuff like electric water heaters and ranges.

I believe Austrailia has 230 V, 50 Hz with essentially a 0V 230V transformer.

RCD devices are made from toroidal transformers, so for 120 VAC, the HOT and N paths are wound together, so that they cancel. Another winding amplifies the difference. That's basically how they work. They, themselves don't need a ground to function. An inadvertent path to ground triggers them, because the current in the neutral wire differs by a few mA than that of the hot wire.

If we were designing electrical distribution in today's age or right before LED/CFL lighting was common, we might do it differently. It would be wise to wire every outlet home run, with a clean and dirty ground. Now, one might have DC distribution in the home.

I need some time to research the gizmo they likely used. I likely have one.
 
I see, current at centre tap is zero. And the RCD sees the primary winding of the transformer anyway. The transformer just has to be perfectly symmetrical.
Then the problem is if I plug CD players and the amp on the other side, where to connect the signal ground to.
 

spec

Well-Known Member
Most Helpful Member
Hi CS,

My house is single phase (like most free standing single houses in Australia), so I get live and mains.
Your mains supply is the same as the UK, though I think you mean, 'live and neutral' rather than 'live and mains'.
Yes, there is trouble with hum.
Can you explain what is producing the hum: HiFi system, TV, computer... ? Is it hum on an audio signal or is it a hum from some other equipment: air conditioning, cooker, vacuum cleaner... ?

Can I just say that if you are trying to resolve a problem it is best to separate the problem, the cause, and solution: first establish what the problem is and then find a cause, then find a solution.:)

By the way, there is normally a simple solution to hum problems.

spec
 
Last edited:

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
We have to sort out the communication issue.

I see, current at centre tap is zero.
.au doesn't have a center tap. Your AMP might have a center-tapped linear supply.

And the RCD sees the primary winding of the transformer anyway.
I read primary as the high voltage side of the distribution, in the neighborhood or probably 9 kV. It should not be there. If we are talking about the primary of the AMP then yes, but it MAY see other stuff too. There's a distinction of Whole house RCD's vs outlet RCD's.

The transformer just has to be perfectly symmetrical.
.au doesn't have a center-tapped distribution transformer. Even if we talk about the US, a room may see only one side of the mains distribution, The amplifier may isolate that.

Then the problem is if I plug CD players and the amp on the other side, where to connect the signal ground to.
Is this speculation or the problem we are trying to solve? We have some apples/oranges issues here to solve first llke defining the problem and defining the terminology at least within this space.

Consumer equipment makes "sacrifices" to make stuff cheaper. The RCA phono plug was one of those sacrifices. Professional stereo equipment uses XLR connectors and a balanced signal. Today we use fiber to get 5.1 or 8.1 consumer stereo.

We FORCE the house reference to be the house's zero V point when we bring power in. Our water fixtures also see this same zero point. The ground in the outlet is only supposed to see faults, but it may be used for communication like a real RS232 serial port.

Ground loops in audio can be eliminated. They can cause hum.
 

nsaspook

Well-Known Member
Most Helpful Member
When I built my home theater room I decided to provide power to the room using it's own sub-panel that was powered from a 240 transformer circuit from the main panel to create a 120 0 120 separately derived power system with it's own neutral/ground connections only for the room to eliminate ground loops. One 120 leg was dedicated to AV circuit power while the other 120 leg was for lighting and general power circuits. Just having a transformer or UPS on one device does very little to to improve electrical power quality or the noise floor from hum.
 
all devices have to be behind the balanced supply or the UPS. Seems to work (see omage). UPS has the advantage, it makes 240V. In Australia there are plenty of brownouts and blackouts. Plus the actual voltage is 250V and more.
 

Attachments

Les Jones

Well-Known Member
Most Helpful Member
I don't see why you think a balanced supply will help. Other than the capacitance between the primary and secondary of the transformer there is no electrical connection. Also in reasonable quality transformers there is a foil screen between the primary and secondary which eliminates this capacity coupling. With older audio equipment that had an earth wire there were always earth loops formed as the earth on the mains leads was in parallel with the earth of the signal leads. There could also be small currents on the earth wire due to the current though capacitors in mains input filters if fitted. (These normally have a capacitor to earth from neutral and live as well as one between live and neutral. More modern filters tend not to have a capacitor from live to earth as the accumulated current from a number of filters may cause RCDs to trip.) More modern equipment tends to have double insulated tranformers and do not require a mains earth so this eliminates ground loops and reduces hum problems. You need to treat hum and noise pickup as two separate problems.

Les.
 
I am worried the whole thing swings at 50Hz and thats why I cannot get rid of the hum. Put it all on star ground, its not helping. Have to find some time and connect the amp secundary to a lab power supply, see what happens then.
Just in case, it will be a struggle to get cast double insulated transformers with shield and all that in Australia I guess. Its pretty light on suppliers for electronic components...
 
if feed DC in fom a lab power supply its all quiet, but as soon as I plug the power cable into the housing, the noise is back. Its not actually a pure 50Hz hum, more a scratching noise, 50Hz with lots of over tones. The housing has a ground connection, one of these 3 pronged ones like PCs.
Suppose thats why the osci would not show anything, hangs on the same messy ground.
 
Last edited:

spec

Well-Known Member
Most Helpful Member
if feed DC in fom a lab power supply its all quiet, but as soon as I plug the power cable into the housing, the noise is back. Its not actually a pure 50Hz hum, more a scratching noise, 50Hz with lots of over tones. The housing has a ground connection, one of these 3 pronged ones like PCs.
Suppose thats why the osci would not show anything, hangs on the same messy ground.
If you suspect a bad ground connection, douse the ground thoroghly with a garden hose.

That's what we did on the mobile RADAR I worked on when the signals got a touch noisy, only we didn't use water.:D

spec
 
I think the ground spike is a myth. The ground is pretty dry in summer, the resistance infinite. Plus the voltage on ground really low, so where is it going to go?
Maybe I should put the power supply into a separate box and only feed DC in. Most of time an amp draws a few mA and conducting DC has less resistance than AC, no inductive and capacitive part.
It seems to be higher frequency, I got some 2 way speakers someone threw out, its only in the mid/high driver. In my active speakers it comes out from every driver, must be induced into the amplifiers after the crossover.
Since lab power supplies are switch mode and there was no noise, maybe I go for switch mode. Without any input it drew about 100mA on the DC end
 
Last edited:
I think I found it. Made a special cable and only connected the ground to the housing. Alas, its quiet. Put the 3 pole cable back on, the noise is back. If I leave the amo running and take the earth cable off and put it back on, there are tiny sparks.
So I reckon I put the 240V part into a separate housing. There are 2 options, take the 2 analogue ones with massive transformers or buy 2 switch mode supplies at http://www.shop-audiopower.com/index.php?route=product/product&product_id=108
also could fix up the old crossover, but have to turn them into 24 db or use mini dsp
Switch mode is way faster reacting, the bonus of the lab supply is, the click when I switch on is way less.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You had asked how the voltages were measured in the ONEAC set-up. Here's
http://pdf.textfiles.com/manuals/STARINMANUALS/ETA/Manuals/Power Probe.pdf
the manual of the device.

Your going to need to explain better what's going on. In some respects, I don;t exactly know what we are talking about. Some things that can happen with audio is a simple ground loop.

One of the more complex things I have seen is where the ground pin on a outlet strip raised to 1/2 the supply voltage. In the US, that means about 60 vac. It's easily explainable how it happened. A switch-mode power supply was involved and the "other" device lost it's ground connection. More complex thing can happen when the electrical service has issues with bad connections to neutral.

I've had strange thing happen at home when a ground was not made with a wire-nut. the ground voltages raised.

In one amplifier, I repaired, the power transformer had a major AC leak. Somewhere in the primary, the chassis was connected to ground. The device worked for the most part until you connected other grounded stuff to it.

I know .au has two different plugs, one with a ground and one without and/the coated prong versions. You do need to look at the ground to neutral voltage and if an outlet strip (a device with multiple outlets) is involved, a bad ground connection can create many problems.

I think we need to see some sort of picture.
 
ok, I mean the safety ground, the green-yellow. This meets the blue/neutral at the meter box. There is a connection to the earth spike. But as mentioned, earth spike is useless at 240/0 V.
So, only safety ground to the metal housing, its quiet. Putting the full connection back, L/N/safety ground, the noise is back. So I guess the main transformer (220W) makes the hum and induces it into the housing, even when switched off. As the off switch is single prong, so one end of the transformer could sit on L or N. .au plug is not symmetrical, have to check. So the L end of the transformer should be actually disconnected. But I built it in Europe initially, where the plugs are symmetrical, so did not bother. It did hum back there as well, so its nothing to do with my particular home.

'Buzz' has a sharp edge to it - there is usually a low frequency component, but it has a hard sound that may even be audible in tweeters at times. Buzz is caused by any number of things - input leads close to mains wiring, power transformer or bridge rectifier (and associated wiring), bad or no earth connection, loops (they can cause buzz as well as hum), the list is almost endless."
http://forums.audioholics.com/forums/threads/getting-rid-of-transformer-hum.3879/

hm, ok, its more a buzz. When I run the emps via wht lab power supply, there was a very faint 50z sine tone from the low driver, but that I can live with. Not listening to it wtih 2cm distance. So now, put transformer into separate housing. Power supply needs ceramic caps across diodes (instead film caps). Will pull out the transformer tonight and move it away from the housing, see what happens then. Would a double shielded transformer help, read something about some special shield?

edit: yes, the life wire was connected to the transformer, the switch went to neutral. Took the transformer out and now is quiet, even power cord pluuged in.
 

Attachments

Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top