how should I connect an isolation trafo for 230 V operation

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andre tchmil

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Jun 4, 2004
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I have a IMO isolation trafo that I would like to connect.
Connections on Primary are 0/ +5% / 400V / -5%
Secondary are 0 / 230 V

How to connect for a primary of 230V AC and secondary of 230 V

Should I make a bridge between the 400V and -5 % on the primary ?
 
Doesn't look like an isolation TX... isolation implies just 1:1.

What they call a 'verhuistrafo' here could as well do 220V - 110V etc (OK, 230/115 these days).

Your TX sounds more like some 230/380 affair. What do you want to do with it ? Don't make that short on the primary.

Bye,

Peter
 
[quote author="andre tchmil"]want to make an isolation/split trafo with it , to make my AC line more silent for Guitar amps etc
Here are the specs of the thing.
http://users.telenet.be/ccr/68645.pdf


it's the 500VA type , 230V[/quote]

To be honest, if you have indeed the 400/230 type it seems only of use if you want to 'starve' guitar-amps the EvH-way, so run them on lower mains voltages. At least I recall that variac story being for lower voltages, not higher. You should then feed the 230V mains to the 400V and feed the obtained 230*230/400 to the amp.
Don't use it the other way around, unless it's for amp thats amplifying a monkey-grip-style kind of guitar :twisted:

But I highly doubt this is what you're after. Can you swap it for a 230/230 model ?

You could of course involve a second TX to make up for the lower 'secondary' but it'll become less elegant.

And first of all, I'm not sure if/why using such a TX would silence your AC. There are other approaches for silencing, a topic of its own. I hope others can chime in on this.

Bye,

Peter
 
[quote author="andre tchmil"]Hm, ok thanks.
Seems I can put this baby back into the closet :green:[/quote]
I'm afraid so, but let's hope others have better news.
What kind of noises are you actually trying to get rid of ?
 
I had my tech putting parallel caps on the mains on my first studio. Helped to filter out the fridge and other parasites in the mains.

We needed to replace these caps every year or so (could have been bad capsbrand) but the results were not that bad.
These days we have 3 times 240 V coming in. We use 2 of these for about everything except the studiocritical stuff. The leftover source of 240 is used for studiogear only. I also have a "scheidingstrafo" but it just didn't do any good to the sound, and it blows some fuse when taxed a little more then average... I have bypassed this trafo after a few blown fuses...

Andre, you should try to get 3x230V (mine is really 3x 240 most of the time) from Electrabel, and avoid on one phase all domestic and other stuff. How did you do all those cool productions without this?? :wink:

Just my 0,02 ? btw.

Cheers,
Tony
 
Tony.
I have a very very big Isolation trafo on my mains for over 18 years with good results.
I have a second smaller overdub room now, and thought to use that spare trafo as well.
3X230V here , so no worries.
 
yep, it appears as if yours is bigger :green:

However try for your small room to put some capacities across the mains, you be surprised how clean mains can be...
 
> isolation trafo that I would like to connect. Primary ... 400V Secondary ... 230 V

OK, Euro-Power basics.

First: this transformer can not be connected for 230:230. However it may be able to give an isolated 230V supply, depending how your house is wired. See first drawing.

Small houses get a single circuit, one side grounded, the other side 230V hot to ground.

Long power lines are much more efficient as 3-phase power, so for more than one house on the block, it gets cheaper to use a 3-phase transformer and connect houses to all three hot legs equally (more or less). Each house gets 230V to ground, single-phase. This directly runs 230V lamps, computers, and cookers.

When you have a big house, or a big load (industrial machinery) a single 230V line has to be very fat to carry the current. As Tony in Hellgium says, "These days we have 3 times 240 V coming in." See second drawing. (Other houses or offices may get the same 3-phase line, which means you may get crap from the welding-shop next door.)

230V-400V-230V.gif


OK, if there is 230V to ground on each leg of the 3-phase line, what is the voltage from one leg to another leg (an un-grounded load)? Not 230*2= 460, but 230*(square-root of 3)= 398V (call it 400V). Why square-root of 3? Each leg is neither in-phase nor completely out of phase with another, they are all 120 degrees apart.

Therefore if you connect the 400V side of your transformer to two hot legs of your 3-phase 230V line, you will get 230V on the other side. If you have heavy-duty appliances, you may have seen 400V un-grounded circuits.

(In US terms, this is similar to a 240V stove that has ungrounded heating elements bridged across both hot legs of our 120V/240V split-phase power. It is more like the 208V that I get here at work where we do have 3-phase 120V power inside the building, but US homes almost never get 3-phase power.)

However I really wish you would ask an industrial electrician to guide you. If you do it wrong, it can really bite you: electrocution, or burn the house down. In the US, a derived voltage like this has pages of Code requirements, including some non-optional Grounding requirements (which make true isolation difficult).

> put some capacities across the mains

That rasises a point. A floating transformer can reduce common-mode garbage, but will not reject differential mode garbage. Most crap is a combination of both.
 
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