Hi Everyone, I need some collective wisdom here on Power Supplies.
I am thinking of getting an Airlink Transformers - Standard Balanced Power Supply and am dwelling on the 10K and 15K VA models, to feed my dedicated CU.
I’m sure that 10K VA is more than sufficient to power my system with clean and low impedance current.
Question: would the 15K VA better the 10K option in any way?
Opinions and experience most welcome 
Stefano
Have you spoken to Airlink? They are a helpful and knowledgeable bunch.
Yes, I have.
They weren’t conclusive on this point but were very helpful in clarifying a few other aspects.
It’s always amusing trying to find a sparky that’s willing to do our hifi devilry… one today literally didn’t know what I was talking about i.e. wiring a balanced power supply to a CU, and advised me to go to “hifi specialists”. Another one, yesterday, is concerned that my 100A DNO isn’t enough to cope with the 65A of the 15k VA version, and wants to measure my power consumption before “deciding”.
Airlink told me it’s more than adequate.
Anyway, I don’t want to overkill uselessly and hence this ask to the community.
Hi, can I as why you are looking to install a balanced main transformer in? In these days of sky high electricity bills, then such a transformer will be consuming electricity all the time… if necessary then perhaps a price worth paying… but hence the reason to ask. Also it is worth confirming the power loss and quiescent current draw from the manufacturer. I would see if when installed it can easily be by passed if necessary.
Transformers can be great things, but efficiency is not one of their strong cards.
As far as power draw… it is the inductive change current rather than the steady state that is crucial… albeit steady state has to be factored. When you turn on a big transformer such as in a power amp, there is a short burst of very high current. MCBs in your consumer box will have a delay built it to stop this surge tripping them… but you should check your balanced transformer can handle this surge load… and it might require a larger transformer than initially seems necessary.
AC and inductive loads are a lot more involved that simple DC powersupplies 
That should be absolutely minimal. In all the power supplies I’ve tested, a wattmeter isn’t even sensitive enough to even register any current until something downstream is turned on. But yes, always worth checking. From what I read current high energy prices are the norm and the past 40 years of cheap energy was the anomaly.
As to capacity, ultimately your electrician will install it so you need to confer with them. I’ve always gone by the, at the same current rating as the circuit or higher rule.
At a guess I’d suppise an average 10KVA balanced transformer (so much larger than what I measure with a wattmeter) might lose 10-20w on heat and noise.
They will be consuming current… even though no load on it. Sure it might only amount to £75 per year at current prices… but worth knowing. Its the current I would measure so as not to mislead with with power factor.
Interesting articles recently in the press of phantom loads from standby powersupplies etc adding to the households bills.
A good tutorial on residual losses etc. https://eepower.com/technical-articles/transformer-losses-and-efficiency/#
Shows example of 15 amp transformer consuming 38 watts of standby (no load) waste through losses.
Hi Simon, simple answer is cleaner current feeding my system and elimination of transformer hum, which in the evening can be rather loud.
Thanks for the tip on power loss and quiescent current draw; have emailed the questions.
Any idea if 15K is “better” than 10K VA?
Stefano
Yes I’ve read the same things. They crop up every few years when energy price increase any amount or there has been aclimate meeting. I’d counsel anyobe to not take the claims as truth until they spend $20 on a wattmeter and see what is really burning through their bills.
The classic (utterly false) claim is that your phone SMPS charger is wasting 25 quid a year and alk such things must be turned off at the wall. So everyone does it. A few months back I profiled everyghing in the house. A few surprises let to me shaving 30% off my bill but wall wart chargers? Nup. When a phone or whatever isn’t connected, my 0.01w resulution wattmeter measures 0.00. It’s daily cost calculator reads 0. I suspect many articals a regurgitating myths from the 90s.
Thanks I hope the balanced transformer resolves your dc offset… it should… albeit there other methods as well that are more efficient if indeed you have DC offset… a loud typically wavering rasping sound from a large Naim toroidal transformer is usually a typical indication.
Yes 15 kVA is ‘better’ than 10 kVA. In fact you want to get the largest you can, which normally means it presents the lowest source impedance to your power amps. That is what you need for your amps, including Naim amps, to operate at their best.
To be honest the acid test on small SMPS is do they feel warm, even slightly, when in standby, if so switch off at the wall… they are wasting and consuming power.
I think a lot of people just don’t realise how much energy is wasted in their home.
We have instilled the discipline of switching off SMPS and transformers that do feel even tepid in standby… and yes it has made a difference to the house bill… I was personally surprised.
To the OP, have you confirned DC offset? It’s one of several possible causes of hum and statistcally less likely than overvoltage. I’d definitely see a doctor before taking prescription meds… if you know what I mean.
Hi, I haven’t confirmed it with any tool, but let me say it has all the symptoms
I will however check the voltage this evening when it’s most audible.
Is there a way to eliminate specifically DC offset before the dedicated CU? i.e. some form of filter to be placed before the CU ?
Yes of course. An isolating transformer can be fitted between the meter and a second smaller CU.
Eliminating it before every circuit in the house though would require a massive one rated for the total CU. Waste of time, space and money though. Stick to a dedicated circuit.
When I spoke with the Engineering Director at Airlink, he said a good start point would be to add up the transformer size (in VA) of all your system’s supplies, then double it to choose the size of BPS.
For us, this meant that circa 3kVA would have been fine but as it was only £50 more to go for 5kVA, we went for a 5kVA one, primarily due to its lower impedance.
Hope this helps, BF
Thanks BF, it does.
I think that the 15K model would be overkill and that the 10K model is MORE than sufficient, giving the lowest impedence that one could probably appreciate on my system.
In the uk typically a radial should be protected with no more than a 16 amp MCB.
So assuming peak mains of 250 volt… then power is 4kVA… so if you double to protect for inductive surge loading then you get 8 or nearest up is 10kVA which should be fine.
The 15 kVA will given a lower source impedance but for a cost… and very much diminishing returns.
Of course you could reduce the power of your balanced radial but inviting potential compatibility issues in the future.
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