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[SOLVED] Basic transformer question

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Zak28

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I am not familiar with power transformer operation and wanted to see if its permissible to hookup this transformer as shown in the image blow.

s-l1600.jpg


hookup.png

Greatly appreciated.
 
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First of all, I'm have no idea why you would want to hook it up like that: 115V in, 133V out. Secondly, with a 2 milliohm resistor on the output you'll draw about 66000 amps, which is slightly more than the transformer can handle.
 
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    Zak28

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First of all, I'm have no idea why you would want to hook it up like that: 115V in, 133V out. Secondly, with a 2 milliohm resistor on the output you'll draw about 66000 amps, which is slightly more than the transformer can handle.

To isolate from power grid. Transformer core would magnetise more at higher currents.
 

Then get an isolation transformer. No need for 6 windings
 
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Then get an isolation transformer. No need for 6 windings

Because I cannot find one which is 1:1 voltage, made for 125v residential and 750-1KVA rated.
 

Hi,

There's something wrong with your values.
I assume the 2mOhms value is wrong.

There are two major formulae you should already know:
Ohm's law:
R = V / I

And calculating power:
P = V x I (for DC or AC_with_pure_resistive loads)
And if you have sinusoidal AC combined with a complex load (when a capacitance or inductance is involved with the load)
P = V x I x cos(phi)

There should be a lot of 1:1 transformers. You may use one with a (slightly) higher voltage rating.

Let's do some calculations:
If you want V = 125V with P = 750VA...and a pure resistive load..
Then use formula P = V x I to calculate I
--> reorganize the formula to get I = P / V
I = 750VA / 125V = 6A
This is the upper limit for your transformer...and this causes 750W at 125V.

Now that you have V and I you are able to calculate R:
R = V / I = 125V / 6A = about 21 Ohms.
But you speak about 2mOhms... there is a deviation factor of more than 10000!

--> Please rectify your specifications.

Klaus
 
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Hi,
There should be a lot of 1:1 transformers. You may use one with a (slightly) higher voltage rating.
bout 2mOhms... there is a deviation factor of more than 10000!

The 2 mills of resistance is the esr accross the cap because transformer is going to charge a cap which will constantly be discharged thus very low resistance accross secondary coil. Please let me know were I may purchase 1:1 125v US residential isolation transformers.
 

Do you want to use An Tech inc (1000VA) transformer ?

You should parallel primary and apply 125V (50Hz or 60Hz) and parallel secondary and add one more tapping to get 125V @ 9A ( Due to load the output voltage will reduce – (low load regulation) for compensating this voltage drop you can add 12v tapping )
Tapping.png
 

Hi,

The 2 mills of resistance is the esr accross the cap because transformer is going to charge a cap which will constantly be discharged thus very low resistance accross secondary coil. Please let me know were I may purchase 1:1 125v US residential isolation transformers.
Then this 2mOhms are just true at the very first moment of swtich ON.
Even after 1us you will have higher ohmic transformer load.

Maybe there is a rectifier involved...additionally increasing load resistance value...

--> We need to see (a draft) of your circuit.

If one ignores rectifier loss and capacitance loss ... then the transformer only needs to supply the power (energy) that is drawn by the load connected to the capacitor.

Please let me know were I may purchase 1:1 125v US residential isolation transformers.
First you need to know your load specification.
Then the voltage and frequency of your mains grid. (I doubt it is 125V)

Isolation transformers for every usual mains voltage and frequency are widly available.

Klaus
 

The 2 mills of resistance is the esr accross the cap because transformer is going to charge a cap which will constantly be discharged thus very low resistance accross secondary coil.
Sorry but that does't make sense. ESR by definition is a series resistance not a parallel one and in any case why are you connecting a capacitor as the sole load across a transformer? If you mean the capacitive reactance is 2m at 60Hz it implies the capacitor value is 1.326 F. Good luck trying to find one of that value rated at 125V AC !

Brian.
 

The cap is "constantly discharged"??? You mean shorted? I don't think so. You need to specify your circuit in more detail, you can't just model a capacitor as a 2 millohm resistor.
And I'm fairly confident that any 1:1 transformer rated for 115v will work equally well at 125V
 
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