Discussion of AC mains isolation transformers

[asdf1000]

I've just ordered a CABAC Power-Mate: POWER MATE 10A | CABAC

 

There are $20 ones at JayCar but I wanted something built well (this is built in Australia) and will last. Right now is definitely not the only time I'll be interested in my system's overall power consumption. This one is pricey at $170 but I've heard it's well built and accurate enough so should be a good investment for years to come.

[asdf1000]

Hi guys, I've borrowed a power meter while I wait for my own to arrive. Plugged in my PS Dectet power board into the power meter with my pair of 1600watt subwoofers and 350watt integrated amp and microRendu plugged into the power board. Cranked up the music to louder than normal.

 

Apart from my ears still ringing, the other interesting thing is the meter shows 0.7A of current being drawn but a power factor of 40-42 (fluctuating).

 

Can someone help me to understand what these figures mean? And how do I convert this to the amount of current being drawn, to size an appropriate iso transformer?

 

Just as a sanity check, I went to the kitchen to test it with a kettle and it showed 8.7A with power factor of 100.

[asdf1000]

Just as a follow-up:

 

Can I use this: Power Factor = True Power / Apparent Power

 

Therefore: Apparent Power = True Power / Power Factor = 0.7 / 0.42 = 1.75A = current to be used to size an iso transformer?

 

Allowing for even significant measuring equipment error, if I'm using < 3.5A then it sounds like my 8A (2.5KVA) Elgar Iso transformer should be fine.

 

Voltage at the wall here is ~ 249 Vac

[asdf1000]

Yes, you're on the right track.

 

Power factor is always is equal to or less than 1.00. So Power Factor = True Power / Apparent Power and

 

Apparent Power = True Power x pf and

 

VA (apparent power) = Volts x Amps

 

Watts = Volts x amps x pf

 

If your load is 0.7A at 0.42 pf at 249V, then the Watts = 249 x 0.7 * 0.42 = 73.2 Watts.

 

The ISO transformer in this case is a minimum 73.2 Watts / 0.42 pf = 174VA.

 

If the pf can be improved even to 0.8, the size of the ISO transformer can come down 73.2 / 0.8 = 91.5 VA. Power factor can be improved using a combo of mainly capacitance and inductance. BUT. No free lunch here, possible resonances between the load and the power factor correction gear can occur. The load has harmonics which usually add voltage and also resonate with the frequency of the LC filter, which the capacitor tries to support, so an over voltage occurs. If the load decreases, then too much capacitance can makes things worse as well. Oversizing a capacitor bank can attract harmonics from other appliances in the house or your neighbour.

 

In audio case, it is simpler and less painful to buy a bigger ISO transformer.

 

BTW, you buy electricity in kW, not VA, eg. $0.25 / kWH, not kVA per hour.

 

The kettle 8.7A at 1.00 pf 249V = 2166 Watts.

 

The ISO to supply the kettle (silly but for exercise only) VA = 2166 /1.00 = 2166 VA

Thanks so much. I was worried a 2.5kVA iso transformer @ 249Vac could be an issue (undersized) since I thought my pair of subwoofers and integrated might get close to 10A. But today's measurement and your calc of <100 watts consumption by my gear is awfully low. That's a good thing I guess !

 

Just another question. If a 2.5kVA iso transformer itself has a power factor of 0.8, then it's good for 2.5 x 0.8 = 2kW = 8.3Amps.

 

If someone accidentally put a 10A fuse on the inlet of the iso trans (or they thought it should have a 10A fuse on there despite my above calc) and the iso trans had a 9A load applied.... what would happen to the iso transformer? And what could happen to the gear connected to it?

[asdf1000]

An ISO transformer doesn't have pf. The load does.

 

Inrush currents and protection on larger transformers can be an issue. There are ways to get it right, but not tonight Josephine.

Thanks mate. So a 2.5kVA iso transformer is actually good to provide a full 2.5kW of power?

[asdf1000]

Yes, if the load is a kettle pf of 1.00

 

Ok I get you now all depends on the load. Took a minute to finally click.

 

But from a safety perspective, a 2.5kVA iso transformer in my place can have up to 2500 VA /249 A = 10.04 A of current pass through without damage to the iso trans? Obviously it would need to have a 10A circuit break though (here in Australia). But a full 10A can pass through without damage to the iso trans?

 

I previously (wrongly) assumed there was a power factor needed to convert kVA to kW which is why I thought perhaps a 2.5kVA iso trans wouldn't be able to supply up to a full 10A current, if required.

[asdf1000]

Many people in typical domestic situations vastly overestimate amplifier power requirements !

 

Me included - until I actually measured the consumption today. This entire thread has been a good learning curve for a muppet like me ! :-)

[asdf1000]

A typical average listening level in many Aussie lounge rooms is likely to be in the vicinity of 1 or 2 watts !

Not so many years back, a 30W per channel amplifier was considered adequate in many Pommy homes.

In fact, I have never been able to use my 15W/Ch. into 8 ohms Class A amplifier (30W Class AB into 4 ohms) at anywhere near it's maximum power into speakers of 87.5dB/1W @ 1 metre sensitivity at home. It's far too bloody loud in a room about the size and width of a master (large) bedroom or for that matter, in a typical Aussie lounge room.

Many of our American cousins appear to have listening rooms far larger than most Aussie homes do, judging by the amplifier ratings they often mention of >700W per channel. They mustn't have neighbours right next door to them ?

Very true. I feel silly and embarassed having mentioned my pair of 1600W subwoofers and 350W integrated. But I literally had no idea up to now, what my actual consumption is. I'll never mention those figures again ! ;-)

[asdf1000]

Hi Ted,

I'll cover the general question first, specifically where do you need the isolation transformer? It is there to provide external world noise suppression and surge suppression to a simple power strip with no filtering or surge suppression. THAT strip is used to provide extremely low AC mains impedance to help decrease the sonic degradation from leakage currents.

 

IF everything is plugged into the same simple strip you can only have one device to provide surge and noise suppression. The only way you can have more than one outside world suppressor is if you have two or more power strips, and that blows away the advantage from having the single simple power strip, you now have a higher impedance between groups of devices.

 

Remember the single strip is to decrease the degradation due to existing leakage loops, if you don't have any leakage loops you don't need the single strip stuff. So if you have a digital source powered by an LPS-1 and the DAC is also powered by a LPS-1 (either separately or VBUS from say a microRendu) and you are going directly into a power amp, then you can't have a leakage loop through the poweramp since the only thing connected to it has all ITS leakage loops blocked.

 

As to your specific existing power conditioner, IF it has nothing between outlets, just wire, then you can use it as is. IF it has anything other than wire between outlets (all three connections, a common ground is not sufficient), then you could use the existing conditioner as an outside world filter and plug a separate simple power strip into one of the existing outlets. This keeps the low impedance and gives outside world filtering. Something like the Topaz is actually a much better filter than what you have, but yours is much better than many others, so it is certainly all right to use it, you don't HAVE to switch to the isolation transformer approach.

 

I think it is a really good idea to make a diagram of all the audio equipment, power and signal connections, include any digital connections etc. From this you can trace connections and see where you have leakage loops through power supplies and come up with an approach to minimize the affects due to these. Make sure you include paths through power strips, power conditioners etc, they are part of the loops.

 

John S.

 

Hi John, if I had 3 power outlets fitted to the iso transformer, and had double adapters in each, giving a total of 6 outlets, would that be the same as having a single strip with 6 outlets - in terms of impedance between devices.

 

Seems hard in Australia to find a well built power strip with no filtering, circuit breaker etc etc

[asdf1000]

The chain should look like this:

Iso transformer output -> portable rcd 30mA -> standard 6+ standard plug board with no suppression devices.

Have the power amp and pre amp close to the cable end and the sources can follow whatever you wish.

 

Try to find boards that are 4x 2 instead of 6 x 1.

 

This is the hard part to find here in Aus: standard 6+ standard plug board with no suppression devices

 

John S mentioned, no filtering, no switch, no circuit breaker.

 

So I have the option to fit 3 outlets on the iso transformer output. I can then add a double adapter to each (which only has wiring, no filters) giving a total of 6 outlets. Will that achieve the same impedance between devices as a single strip with 6 outlets?

 

And what would be the role of the portable RCD after the iso transformer? Especially if I had a 10A switch/fuse at the iso trans input?

[asdf1000]

Even Bunnings?

 

Yeah, they all have surge protection, or a circuit breaker, or both. If you know if any without switch/surge protection/circuit breaker, let me know because I've looked everywhere. Possibly only Elsafe can make a power distribution board, but that would have to be a custom make.

 

What's the advantage of having an RCD between an iso transformer and your gear, compared with the RCD in the home's meter box (which @esmit is also asking above I think)

[asdf1000]

Even Bunnings?

 

Also regarding impedance between devices, can anyone help me with this: I have the option to fit 3 outlets on the iso transformer output. I can then add a double adapter to each (which only has wiring, no filters) giving a total of 6 outlets. Will that achieve the same low impedance between devices, as a single strip with 6 outlets would?

[asdf1000]

As promised, here is the reason to install an RCD/GFCI.

Thanks for that. Might just stick with a single outlet on my iso trans and add one of these: Clipsal - 951 - Twin Switch Socket Outlet, 250V, 10A, 2 Gang, Circuit Identification, Safety Shutter, White Electric

 

And then add one of these to the RCD's outlet: https://www.racklink.com.au/products/5190dd8de387edcd65b49245

 

with the option of no circuit breaker, no switch and just a short 1m lead.

 

Thoughts?

[asdf1000]

You do realise that this is meant to normally be the rear panel of a 1 Unit rack case such as the attached from Altronics ?

H5031 1U Black Aluminium Front Panel 19" Rack Case - Altronics

 

It has it's power lead on the same surface as the outlets though. Behind the furniture it wouldn't be visible at all.

 

And it's the only type of board I can find with no circuit breaker, no switch, no filters.

 

Wouldn't work? Apart from the visual aesthetics, any other issues with using it to plug Hi-Fi into?

[asdf1000]

Forget double adapters, their connections are too sloppy. There's nothing on the Australian market that does what we need to do.

 

You mentioned an electrician that is re-working the Elgar when it arrives? I thought to use standard 4 Way Outlets and a mounting block.

Put two of these back to back, and wire via shielded power cable to the RCD. A fire resistant timber perhaps would jazz it up. The joining wires can be short, there are only three, so impedance is not an issue.

 

[ATTACH=CONFIG]30450[/ATTACH] Available here

 

[ATTACH=CONFIG]30451[/ATTACH] Available here

 

This is what I made before standardising on Oyaide and Furutech Euro standard plugs and sockets, there's nothing much for AU style even from Furutech only one or two models, that's it. Euro gear is rated for 230V and it stops anyone else using a vacuum cleaner out of the system. Choices.

 

Never use NEMA 120V plugs and sockets on 230V systems. You don't pressurise a tyre rated maximum at 30psi and you put in 60psi?

 

[ATTACH=CONFIG]30452[/ATTACH]

 

Very nice! You're a lot handier with this stuff (and qualified) than me. But yes, my Elgar has arrived ! And I just dropped it off today with a gentleman (who also makes some pretty well known amps here in Oz) to 'do up' for me. But he won't be working on it till next week.

 

I'll scrap the idea of double adapters.

[asdf1000]

The 3m lead would not be shielded.

Noted. I can ask them to put an IEC socket instead of a lead and use my existing shielded power cable.

 

They're pretty open to customisations. Any other issues with using this type of product for my/our application? Apart from the looks of course

[asdf1000]

Sure it would work. I do like Garry's suggestion though.

 

Are you from Melbourne ? If so, you may mean AKSA from DIY Audio who makes Aspen amplifiers ?

If this is the gentleman, please say hello to Hugh from me !

 

Alex

Yes, I'm in Melbourne. Earle from Weston Acoustics is helping me out. One of the nicest people you could ever meet ! First time meeting him today.

 

For anyone interested, here is a John DARKO review: Weston Acoustics Troubadour integrated | DAR__KO

[asdf1000]

You do realise that this is meant to normally be the rear panel of a 1 Unit rack case such as the attached from Altronics ?

H5031 1U Black Aluminium Front Panel 19" Rack Case - Altronics

Also, there other rack mounted PDU's I had seen before that had the inlet power lead on the opposite side to the outlets, which would make for awkward cable routing on the ground. But this particular one (made in Oz) has the inlet lead and outlets on the same face. So on the ground it would look like a typical powerboard, with the addition of a couple mountain plates/flanges on the ends.

 

I think that's the only downside? Provided I can get an IEC socket to use with my shielded power cable.

[asdf1000]

I received the second network isolator today and connected that. In addition, I have recently purchased two power strips without filtering, surge suppression, etc. These strips take IEC inputs. I'd had old MIT Z-Cords feeding them, but thinking of avoiding filtering, yesterday I substituted two ordinary Tripp-Lite IEC cords. So I've got the strips plugged into the wall with these cords, a couple of the network isolators (inexpensive b/c bought used), a couple of small (about 5" cube) inexpensive iso transformers, and the LPS-1. I had this combo together for the first time tonight and just had time to listen to a few songs, not too loud because my wife had gone up to bed.

 

The sound is effing amazing. Effortless clarity and beauty. All the nuances, all the little differences in the way things are recorded, even from track to track on the same album...I'm loving it.

Very nice. Which power strips if you don't mind me asking?

 

 

Sent from my Blackberry DTEK50 using Tapatalk

[asdf1000]

Not Jud, but IIRC, he may have ordered one of these based on John's recommendation.

 

Audio Catalog

 

They are very nicely made and the price is hard to beat. But I think they took a long time to arrive.

 

Another decent no-filter-element, heavy-duty USA power strip series is this one from TrippLite.

 

12 Outlet Vertical Power Strip 120V 15A 6 ft Cord 5 15P 36 in (PS361206) | Tripp Lite

 

Attractive extruded aluminum housing, outlets that grip like crazy, and a 14awg cord. The linked 12-outlet version is $41.

Very nice indeed. Thanks for that. Looking forward to getting my Elgar back next week and hooked to my system.

 

Sent from my Blackberry DTEK50 using Tapatalk

[asdf1000]

Thanks, Alex. I ordered two of them, and they are indeed nicely built. They did take a while to arrive, because I selected the cheapest shipping method, surface from Hong Kong to the eastern US. You can have them shipped as fast as you like, but they are substantial so the speediest methods may be relatively expensive.

Thanks, i sent them an email enquiry.

[asdf1000]

Yes, you're on the right track.

 

Power factor is always is equal to or less than 1.00. So Power Factor = True Power / Apparent Power and

 

Apparent Power = True Power x pf and

 

VA (apparent power) = Volts x Amps

 

Watts = Volts x amps x pf

 

If your load is 0.7A at 0.42 pf at 249V, then the Watts = 249 x 0.7 * 0.42 = 73.2 Watts.

 

The ISO transformer in this case is a minimum 73.2 Watts / 0.42 pf = 174VA.

 

If the pf can be improved even to 0.8, the size of the ISO transformer can come down 73.2 / 0.8 = 91.5 VA. Power factor can be improved using a combo of mainly capacitance and inductance. BUT. No free lunch here, possible resonances between the load and the power factor correction gear can occur. The load has harmonics which usually add voltage and also resonate with the frequency of the LC filter, which the capacitor tries to support, so an over voltage occurs. If the load decreases, then too much capacitance can makes things worse as well. Oversizing a capacitor bank can attract harmonics from other appliances in the house or your neighbour.

 

In audio case, it is simpler and less painful to buy a bigger ISO transformer.

 

BTW, you buy electricity in kW, not VA, eg. $0.25 / kWH, not kVA per hour.

 

The kettle 8.7A at 1.00 pf 249V = 2166 Watts.

 

The ISO to supply the kettle (silly but for exercise only) VA = 2166 /1.00 = 2166 VA

Just ran the same test with the better quality Power-Mate power meter which arrived Friday afternoon.

 

I needed ear muffs to go to louder than normal listening volumes.

 

I got similar figures to the reading I took last week. RMS current approx. 0.7A, and approx. 180VA.

 

So there will be no issues with my 2.5kVA 0.0005 pF Elgar when it's finally hooked up to my system. This once again confirms that a lot of people over-estimate the power consumption of their gear (I was one of these people until I now have some measured figures).

 

Turns out I don't get anywhere near the specified maximum power consumption of 1100W for my integrated amp !

 

All of my amplification is Class D by the way (the power amp section of my integrated and the subwoofer sections of my powered speakers) apart from the Class A pre-amp section of my integrated. And my speakers are rated at 93db sensitivity too.

 

I most definitely could have got away with a 1.0kVA iso trans so I quite obviously may have over-sized it. Good to know I have head room though if I add a power hungry projector in future to the system ! Their typical consumption figures (not max consumption) are ~300-400W

[asdf1000]

My recommendation is to use a simple power strip with NO filtering or surge suppression, the Topaz does it much better than what will come in almost any power strip. I plug EVERYTHING into thepower strip. This dramatically cuts down on the impedance between boxes, significantly lowering noise generated by leakage loops.

 

John S.

 

Hi John, just a quick clarification/question on an earlier recommendation of yours.

 

If you have a power strip which has no filtering between the outlets but does have a circuit breaker and on/off switch at the inlet, is this inlet protection of the power strip going to contribute to increasing the impedance between the outlets/boxes on this one power strip?

 

And thus contribute to increased noise generated by leakage currents?

 

Assume this powerstrip is plugged into a high isolation transformer like the Topaz (an Elgar in my case).

 

Does your Tripp Lite power strip have a circuit break at it's inlet? And on/off switch?

 

Many thanks for your help again

[asdf1000]

Just wanted to open up my question to John above, to all here also

 

If you have a power strip which has no filtering between the outlets but it does have a circuit breaker, is this inlet protection of the power strip going to contribute to increasing the impedance between the outlets/boxes on this one power strip?

 

And thus does the circuit breaker contribute to increased noise generated by leakage currents?

 

I'm finding that even the custom powerstrip makers are hesitant to custom make me a powerstrip without a circuit breaker - this is fair enough too - safety first.

 

John mentioned the Tripp Lite but I can't find any of their models that don't have a circuit breaker, so I'm assuming the circuit breaker doesn't contribute to increasing the impedance between outlets?

 

Appreciate anyone's help/clarification

 

Many thanks in advance :-)

[asdf1000]

Not if it is the bimetallic strip type.

For a brief description in reasonable English, check this site.

 

Miniature Circuit Breaker or MCB | Electrical4u

 

Thanks for that. Are those bimetallic strip types found in $30 powerstrips, like the Tripp Lites? Or only in more expensive power strips?

 

ANd would you say the $30 circuit breakers found in Australia (like HPM, Jackson) are of the bimetallic strip type? If not, what type are they typically?