Fancy a guess at my next project?

[Bigman80]

This is a 750va Toroidal. [emoji6]https://uploads.tapatalk-cdn.com/20180117/16f66e539d4231a8619589b11b025b0b.jpg

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[struth]

an electric shock machine for your bubble bath;)

[walpurgis]

Pass?


More likely a valve power amp if you need 750v.

[Firebottle]

I don't think Oliver has progressed to 750V projects (yet?) :eek:

It's 750 VA.

[Bigman80]

Lol, yep, typo!!!

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[Bigman80]

It going to back a Balanced Mains Unit. Made into an old BT distribution block. Nothing fancy, just working and doing a good job hopefully!

In an unexpected move, I found a whooshing noise on my rig and put it down to some sort of electrical problem somewhere but by chance yesterday, I remover the powerline adapter for the Internet and the background whoosh disappeared. Further experiments today have shown that the more things I turned off around the house, the better my noise floor has got SO looks like a BMU may be ideal.

Toroidal came from Airlink for £77 and a couple of 10A MCB for £4. The BT box is a gift so I may have quite a good solution for under £100!!

[struth]

ive got a bt transformer dist block lying in a cupboard.. weighs a ton.

[Gazjam]

Orgasmatron?

[Bigman80]

ive got a bt transformer dist block lying in a cupboard.. weighs a ton.The TFmer that came out of the BT donor unit was a monster!!!!

[Bigman80]

Orgasmatron?[emoji23]

[struth]

The TFmer that came out of the BT donor unit was a monster!!!!

that'll be same as mine then...lol

[Ammonite Audio]

A soft start module of some sort would be a good idea with a transformer of that size.

[walpurgis]

The power transformer in my Audio Concepts P300 Legend power amp was so big the whole amp shook when turned on and went 'boing'!

http://i68.tinypic.com/24eaohc.jpg

[Ali Tait]

Just fit a big NTC on the input.

[Bigman80]

A soft start module of some sort would be a good idea with a transformer of that size.Oooh good point!

[Bigman80]

Just fit a big NTC on the input.NTC?

[walpurgis]

A soft start module of some sort would be a good idea with a transformer of that size.

I was browsing 'soft start' modules on ebay the other day. There seem to be quite a selection from Chinese sellers.

[Bigman80]

I was browsing 'soft start' modules on ebay the other day. There seem to be quite a selection from Chinese sellers.A link would be welcome Geoff!

[walpurgis]

A link would be welcome Geoff!

Didn't save any mate. A quick browse under 'soft start' should bring 'em up.

[Bigman80]

Didn't save any mate. A quick browse under 'soft start' should bring 'em up.[emoji106]

[DSJR]

Not sure you'll need *all* the extras suggested - my BMU is totally benign on switch-on and no 'boooiiinnnggg' at all (mine has an earlier transformer and hums on and off at different times of day, which the later production doesn't do I discovered), but I'd suggest that if the case is a metal one, the safety features as Airlink do on their own complete units would be a good idea.

[Ali Tait]

NTC?

I needed one on mine as it tripped the CU every time, but mine is 3kva. You may well be fine without one. Try it first and see.

An NTC is a thermistor which limits current inrush when you turn the thing on, so stops it tripping the CU breaker. You will probably be fine without one though, given it's 750va.

[Gazjam]

Fitting a DC Blocker to mine, its in the next room from my listeneing area, but cant help that buzzing has to be putting some crap on the line somewhere...

[Bigman80]

I needed one on mine as it tripped the CU every time, but mine is 3kva. You may well be fine without one. Try it first and see.

An NTC is a thermistor which limits current inrush when you turn the thing on, so stops it tripping the CU breaker. You will probably be fine without one though, given it's 750va.Ah I see. I'll have a chat with Alan and see what he thinks. Anything that improves it chances of fault free usage will be beneficial

[Bksabath]

NTC thermistor is way to go but if you want fault free you also need a timer and relay to take it out of the circuit NTC go really really hot
and if you got space certainly a DC blocker ( I have bridge diode and big low voltage ELT capacitors) can help getting buzzzzzzzz of transformer.

Any one got a look at the crap the gas/electricity smart meter put on your mains ?

[Bigman80]

NTC thermistor is way to go but if you want fault free you also need a timer and relay to take it out of the circuit NTC go really really hot
and if you got space certainly a DC blocker ( I have bridge diode and big low voltage ELT capacitors) can help getting buzzzzzzzz of transformer.

Any one got a look at the crap the gas/electricity smart meter put on your mains ?Cheers mate,.

I have a DC blocker that can go in there already. Would it need one though? That is a question I don't know the answer to

[Bksabath]

22519225202252122518
If transformers Buzzzzzzzzz you need one If they don't U don't need one If you don't need one it does not hurt
One wonder how much crap smart meters for gas and elect throw in the mains ? then one my need a filter...
My big hammer approach (
Litlle trafo and psu to power up big trafo and after delay switch on the relay that close the circuit on the 2 NTC in series note glass ceramic beads on NTC vires
Most probably it could have been done whit just a couple of transistors if one had a clue on what it was doing, but hey it has been working for 10 years whit not a single problem so...
Still I would really like to know same one that can teach me a bit more about electronics
view of the F5 PSU 25 Watt :D mono-blocks not in picture
view of DC suppression The 25 A bridge diodes are on the back of ELT PCB and sneaky peak at a Shafner filter

[Ali Tait]

Have a DC blocker fitted to mine also, sourced a big 30A NTC from Airlink. Worked fine for the last five years or so.

[Stratmangler]

It going to back a Balanced Mains Unit. Made into an old BT distribution block. Nothing fancy, just working and doing a good job hopefully!

Really?
What's this BT distribution block you're on about?


In an unexpected move, I found a whooshing noise on my rig and put it down to some sort of electrical problem somewhere but by chance yesterday, I remover the powerline adapter for the Internet and the background whoosh disappeared. Further experiments today have shown that the more things I turned off around the house, the better my noise floor has got SO looks like a BMU may be ideal.

As you've found out, the crap that powerline adapters kick out onto the mains can cause audible artifacts.
Which is why I bang on about running proper ethernet cable.
Would it fall on deaf ears if I suggest running ethernet cable as well as building your BMU?

[Bigman80]

Really?
What's this BT distribution block you're on about?



As you've found out, the crap that powerline adapters kick out onto the mains can cause audible artifacts.
Which is why I bang on about running proper ethernet cable.
Would it fall on deaf ears if I suggest running ethernet cable as well as building your BMU?It will NOT fall on deaf ears mate and is something I am looking into but routing a cable to the necessary Destination is a veritable nightmare!

I'll try and find a pic of the BT Distribution box. It's perfect for its new job.

[Bigman80]

It's similar to this https://uploads.tapatalk-cdn.com/20180118/2b62b38634b9be83eab35b55fc80bd62.jpg

[Bigman80]

It's similar to this https://uploads.tapatalk-cdn.com/20180118/2b62b38634b9be83eab35b55fc80bd62.jpgThe standard unit isn't suitable for audio. Too noisy!!!!!

[Stratmangler]

Thank goodness for that!
That case is from an overvoltage protection unit.
They used to fit them on PBX equipment to protect it from power spikes on the mains, because quite a lot of their PBX gear had a propensity to turn its toes up permanently if it was hit by a power spike.

Some folk use them as supplied as power conditioners.
That's not what they were designed to do.

The case will be fine, as long as you follow safety regs, and I'm sure Alan will give you correct advise on that front.

[Bigman80]

Thank goodness for that!
That case is from an overvoltage protection unit.
They used to fit them on PBX equipment to protect it from power spikes on the mains, because quite a lot of their PBX gear had a propensity to turn its toes up permanently if it was hit by a power spike.

Some folk use them as supplied as power conditioners.
That's not what they were designed to do.

The case will be fine, as long as you follow safety regs, and I'm sure Alan will give you correct advise on that front.Yep, that's exactly what I read about those units. It will be 100% up to regs as there are two little fellas in our house (3&5) that'll mess with everything and I'll be taking no chances with their safety.

[RothwellAudio]

In an unexpected move, I found a whooshing noise on my rig and put it down to some sort of electrical problem somewhere but by chance yesterday, I remover the powerline adapter for the Internet and the background whoosh disappeared. Further experiments today have shown that the more things I turned off around the house, the better my noise floor has got SO looks like a BMU may be ideal.

Sorry for being a numpty, but what's a powerline adaptor?

[Bigman80]

Sorry for being a numpty, but what's a powerline adaptor?It transfers your internet signal around your house using the mains wiring. It's so you have a wired connection everywhere. Very clever but dirties the mains badly IME
https://uploads.tapatalk-cdn.com/20180118/cb9bfcedc1bb67385349c58b4bb2d818.jpg

[sq225917]

Best soft start I've seen is from sonny at mirand. Not cheap but it does the biz and is super flexible. Don't touch the Chinese crap, recycled parts, dodgy specs. Not worth the risk IMO.

[Bigman80]

Best soft start I've seen is from sonny at mirand. Not cheap but it does the biz and is super flexible. Don't touch the Chinese crap, recycled parts, dodgy specs. Not worth the risk IMO.Thanks. I will look into it.

[Blueflash]

Yep, that's exactly what I read about those units. It will be 100% up to regs as there are two little fellas in our house (3&5) that'll mess with everything and I'll be taking no chances with their safety.

I take it that you are having the Primary 230v and the Secondary wired 115v - 0, 115 - 0 with the Red and Orange wires connected together and connected to earth which will give you balanced 230v.

For safety you really need a double pole 30ma RCCB on the output otherwise if a fuse blows on the "Live" side you will still have 115v from "Neutral" to earth. I would recommend a Hagar 263U which is a 63A capacity but will trip both poles in a fault situation.

[Bigman80]

I take it that you are having the Primary 230v and the Secondary wired 115v - 0, 115 - 0 with the Red and Orange wires connected together and connected to earth which will give you balanced 230v.

For safety you really need a double pole 30ma RCCB on the output otherwise if a fuse blows on the "Live" side you will still have 115v from "Neutral" to earth. I would recommend a Hagar 263U which is a 63A capacity but will trip both poles in a fault situation.Cheers Alex.

[Barry]

I take it that you are having the Primary 230v and the Secondary wired 115v - 0, 115 - 0 with the Red and Orange wires connected together and connected to earth which will give you balanced 230v.

For safety you really need a double pole 30ma RCCB on the output otherwise if a fuse blows on the "Live" side you will still have 115v from "Neutral" to earth. I would recommend a Hagar 263U which is a 63A capacity but will trip both poles in a fault situation.

Good advice - and supports my comments made on another BMU thread.

However the current rating of the RCB fitted to the output should not exceed that of the transformer itself, so unless the transformer has a rating of 14.5kVA, the 63A rated breaker you mention is quite inappropriate, as it will only provide protection against differential currents but not for non-differential currents that exceed the current rating of the transformer.

A 750VA transformer can only supply an in-phase current of 3A, so the double-pole RCB ought not have a current rating much greater than that.

[Blueflash]

Good advice - and supports my comments made on another BMU thread.

However the current rating of the RCB fitted to the output should not exceed that of the transformer itself, so unless the transformer has a rating of 14.5kVA, the 63A rated breaker you mention is quite inappropriate, as it will only provide protection against differential currents but not for non-differential currents that exceed the current rating of the transformer.

A 750VA transformer can only supply an in-phase current of 3A, so the double-pole RCB ought not have a current rating much greater than that.

16A is the lowest that the RCCB`s go down to so whatever is fitted will not be suitable for short circuit protection unless you have over 3680 VA so choose the one with the better internal connections. I chose the 63A for it`s 10000A breaking current capacity for minimal contact resistance.

For the short circuit protection you can then use a 2 pole MCB with the correct rating for the transformer, they go down to 2A.