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'[EE]: 220v Isolated transformer'
2002\12\06@151246 by Tal Bejerano - AMC

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Hi to all
due to the high price for isolated transformer, I thought about an idea....
Is it possible to connect 2 mains transformers (220v->12vac) and connect the
12vac secondary together and have low-cost 220vac isolated transformer?

Regards

Tal Bejerano
AMC - ISRAEL

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2002\12\06@151848 by Rick C.

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I do that all the time.
Rick

Tal Bejerano - AMC wrote:

{Quote hidden}

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2002\12\06@153105 by Tal Bejerano - AMC

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thanks Rick!

Regards

Tal Bejerano
AMC - ISRAEL


-----Original Message-----
From: pic microcontroller discussion list [.....PICLISTKILLspamspam.....MITVMA.MIT.EDU]On
Behalf Of Rick C.
Sent: Friday, December 06, 2002 10:17 PM
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
Subject: Re: [EE]: 220v Isolated transformer


I do that all the time.
Rick

Tal Bejerano - AMC wrote:

> Hi to all
> due to the high price for isolated transformer, I thought about an
idea....
> Is it possible to connect 2 mains transformers (220v->12vac) and connect
the
{Quote hidden}

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2002\12\06@153306 by Bob Axtell

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Yes, I do it quite a bit, but there are losses in the
doubling. If you can, use 24 or 28V transformers,
the losses are less.

And don't expect to be able to draw very much current
out of the secondary.

--Bob Axtell


{Original Message removed}

2002\12\06@154059 by Tal Bejerano - AMC

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Bob

I am aware that it can't deliver large currents
just check if the idea will work.
btw, if I use 12vac/1A secondary how much current I can draw ?

Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

2002\12\06@155518 by Spehro Pefhany

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At 10:39 PM 12/6/02 +0200, you wrote:
>Bob
>
>I am aware that it can't deliver large currents
>just check if the idea will work.
>btw, if I use 12vac/1A secondary how much current I can draw ?

50mA, but the regulation will be twice as bad as with a
single transformer (eg. if the voltage drops 15% from OC
to full load on the transformer, it will drop almost double
that with two). So 25mA would be better from that pov.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2002\12\06@155520 by Bob Axtell

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If the transformer delivers 12V@1A, then it
is delivering 12W. Assuming an 80% efficiency
moving from 12V to 220V, 0.8*12= 9.6W avail.

Since I=P/V, and V=220, and P= 9.6, then
I= 9.6/200A or approx 47mA.

--Bob

----- Original Message -----
From: "Tal Bejerano - AMC" <TakeThisOuTkooterEraseMEspamspam_OUT012.NET.IL>
To: <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Friday, December 06, 2002 1:39 PM
Subject: Re: [EE]: 220v Isolated transformer


{Quote hidden}

> {Original Message removed}

2002\12\06@162026 by Tal Bejerano - AMC

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ok ..I c the point
is the calculation change if the first transformer can deliver large current
(5A) and second transformer is 12v/1A?

Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

2002\12\06@163638 by Peter L. Peres

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On Fri, 6 Dec 2002, Tal Bejerano - AMC wrote:

*>Hi to all
*>due to the high price for isolated transformer, I thought about an idea....
*>Is it possible to connect 2 mains transformers (220v->12vac) and connect the
*>12vac secondary together and have low-cost 220vac isolated transformer?

Yes. The combined transformers will have a rating of only 50% of each for
usual low power (<1kW) transformers).

Peter

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2002\12\06@170539 by Olin Lathrop

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> due to the high price for isolated transformer, I thought about an
idea....
> Is it possible to connect 2 mains transformers (220v->12vac) and connect
the
> 12vac secondary together and have low-cost 220vac isolated transformer?

Sure, but it's somewhat inefficient and limited to the power minimum power
rating of the two transformers.  The result may be a cheap isolation
transformer with a very low current rating.  I would be surprised if you
can kludge two such transformers for the price of an one transformer at
the same overall current rating.


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Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\12\06@170541 by Olin Lathrop

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> btw, if I use 12vac/1A secondary how much current I can draw ?

12V * 1A = 12 watts

12W / 220V = 55mA assuming perfect transformers.  Maybe 40-50mA in real
life.


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Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\12\06@175502 by Spehro Pefhany

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At 11:19 PM 12/6/02 +0200, you wrote:
>ok ..I c the point
>is the calculation change if the first transformer can deliver large current
>(5A) and second transformer is 12v/1A?

The regulation would be better, but you are always limited to the
power handling capability of the smaller of the two transformers.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffspam_OUTspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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