Balanced 240V AC mains supply, simply does it

[Reid Malenfant]

I'm sure Ali will be interested in this one so i thought i'd get something up here now with a full test coming soon. However i trust my judgement having previously been involved in set up & testing of rather large 3 phase power supplys & battery chargers, 100KVA+ anyone?

I recently purchased two 3.3KVA site transformers, to be specific these ones here! I'll be honest & say that when i popped the top off i was cursing rather a lot as i didn't think i'd be able to do what i wanted, some thought led me to the conclusion that things couldn't be better as the transformer is "potted" up so will make less noise.

Here goes with the internal pictures...





I'll attempt to make this simple so everyone can understand, if anyone has any questions then for gods sake ask as we are dealing with voltages & currents that can kill here

Unfortunately like everything in this world these days the 3.3KVA rating isn't continuous, there is a nice label on the side saying that continuous rating is 2/3 of the peak. So each transformer will do 2.2KVA continuously, please remember you'll need 2 of these things to get your balanced mains so in reality you'll end up with a 4.4KVA or if you like 4.4KW balanced mains supply. The peak will be 6.6KVA, & i'm sure it'll be able to supply this for more than a few minutes - how deaf do you want to be

Anyway, heres how to go about it... First up don't have the transformer plugged in when operating on it!!! To get to where we want to go isn't really hard at all. Firstly cut the two earth leads that dive down into the potting compound, i'd suggest you leave about 5cm length just in case you ever decide to use the thing for it's intended purpose That way a terminal block can be employed to reconnect as per standard.

Having cut the earths you'll have a 110/120V secondary with no earth reference. So find yourself a single block of terminal block & reconnect the earth from the mains that comes from the mains input plug to the earth that connects to the output sockets. Now get yourself a 30Amp terminal block... Disconnect the red & blue leads that come from the potted up transformer (there are 2 of each) & connect both reds into one part of the block & both blues into another terminal.

At this point in time you can toss a coin & decide which terminal you are going to connect the earth to, it doesn't matter, red or blue However please take note of which one you connect it to! The reason being is that on the second transformer you do everything just the same, except you connect the earth to the wire colour that you didn't on transformer number one

If this all appears to be a tad complicated don't worry, i'll be back tomorrow with pics of the completed article & a pretty scope trace & voltage readings to show you what is going on

Obviously both transformers will need to be mounted in a strong case to prevent little fingers doing what they do. I'd suggest some nice 18mm MDF. A couple of mains sockets on the side & you are pretty well sorted. Frankly i'll leave anyone who wants to tackle this to sort out the aesthetics themselves

Back tomorrow, cheers for now More details to follow...

[The Grand Wazoo]

Can I take the opportunity to express to all who may be interested in this that if you don't know EXACTLY what you're doing then you shouldn't even think about this.

I struggle with the wisdom of this even being allowed to remain visible to all and sundry. Remember, it's not just us regulars (who I think pretty much all have some common sense between our ears) who can read this.

[The Vinyl Adventure]

i wouldnt have the first clue what it even is, never mind trying to emulate it ...

[colinB]

Its a balanced mains innit

[John]

Whilst I find Mark Article Fascinating I also agree with Chris Do not do this unless you seriously know what you doing. This could be lethal

[Dave Hewitt]

Hi
See Airlink Transformers web page regarding balanced mains supplies,seem cheap enough.
Dave.

[Alex_UK]

I agree Chris/Hamish etc - when I saw this thread there was a "whooshing" sound - I just hope it was the sound of the idea going straight over my head and not someone reading this thread going up in smoke... PLEASE OBSERVE ALL WARNINGS, PEOPLE!

[anthonyTD]

hi all,
a true isolating transformer has a seperate primary and secondary, in this case 240v primary, 110v or 55+55 secondary this type of transformer is used mainly for plant tools on site for added safety. what mark is describing when done properly will work, unfortunetly i too strongly recommend that unless you are absolutely sure you understand what your doing and the consequences if you dont then i would leave well alone. however i understand that this thread will be of interest to those who are capable and competent enough to investigate the advantages that may be apparent folowing its correct implimentation.
A...

[Reid Malenfant]

Indeed, i'm sure i might have made it known not to attempt this unless you feel confident in what you are doing & that you can hopefully read, & follow instructions.

These will be comprehensive enough & in reality you'll need at least a mulimeter that can read 240V AC, ohms could be handy to, to check things are correct before you even think of powering any of this up....

If you have a multimeter you'll be able to do this, if you don't then i wouldn't attempt what i will do! You need to test certain things simply because you can't guarantee everything is the same all of the time. I'll explain this better when i post again When i'm a little more sane... drinkinone.gif rofl.gif


Like tomorrow Well hopefully...

[Barry]

Hi all,
a true isolating transformer has a separate primary and secondary, in this case 240v primary, 110v or 55+55 secondary this type of transformer is used mainly for plant tools on site for added safety. What Mark is describing when done properly will work, unfortunatly I too strongly recommend that unless you are absolutely sure you understand what your doing and the consequences if you don't then I would leave well alone. However I understand that this thread will be of interest to those who are capable and competent enough to investigate the advantages that may be apparent folowing its correct implimentation.
A...

+1

To confirm Ali's (Tait) comment, both of the secondary lines must be fused. And, strictly speaking, both being phase lines, ought to be coloured brown.