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Joined: Jul 2004
Posts: 5
F
fiddler Offline OP
Junior Member
Hi Guys, I need a few clarifications..please

help.[A] A stepdown transformer is used in

a 240 volt area that's notorious for low

voltages.The output needed is 110/120 V..

can a Voltage stabilizer be used with the

transformer and should the secondary of

the transformer be grounded ? [B] Is it

necessary for my computer UPS to be plugged

into a grounded outlet ?

Thanks for any input.

Joined: Jul 2002
Posts: 8,407
Member
Hi there fiddler!,
Welcome to ECN. [Linked Image]
Regarding your question on a step-down Transformer, I suppose you could use a voltage stabiliser on the output, but finding a suitable type for that level of voltage, would be a different story.
For safety reasons the UPS should be plugged into a Grounded outlet.
As far as grounding the secondary side of the Transformer goes, unless anyone else here says otherwise, I'd advise against it.
Hope this helps. [Linked Image]

Joined: Sep 2002
Posts: 1,498
C
C-H Offline
Member
Intuitively, I'd be inclined to answer yes to [A]. But not to jump to conclusion, maybe there is risk of unwanted interaction between the step down transformer and the voltage stabiliser. (Inrush current?)

If the voltage is low but stable, you can use a step down transformer with other voltage levels to compensate for the undervoltage and omit the voltage stabiliser, e.g. a 220V to 127V transformer. The prerequisite for this is that the voltage is reasonably stable or your equipment will let the smoke out as soon as the voltage rises. [Linked Image]

Joined: Jul 2004
Posts: 5
F
fiddler Offline OP
Junior Member
Thanks for your welcome Trumpy , however I have been around for a while with just a few postings.

Point taken on the UPS grounding. I noted your usage of 'suitable' and this rings some bells..lots of domestic Nippon Voltage
stabilizers here ..240/110..110/240.. what it now comes down to is'suitability 'as
there are lots of sad stories on their usage.
While not willing to give your reasons against grounding the transformer output on
Post do you mind sharing same with me at
helpinghands42@yahoo.com..Thanks.

C-H , thanks for your imput..it has led me back some 40 years to ohms law and as I got
out my pencil and moved around the equation E=IxR I discovered that if the voltage goes
up with resistance remaining constant then the current also goes up. This brings me
to your emphasis on 'Voltage stability'.This may be the reason for problems encountered
with the usage of transformer plus voltage stabilizer.Please add any other factor you
you consider important. Thanks

Joined: Aug 2001
Posts: 7,520
P
Member
Personally, I would ground the secondary of the transformer, then you have a supply with the same characteristics as a normal 120V system. You certainly want to run a ground onto the EGC which goes to the UPS/computer, otherwise the filter capacitors are likely to result in a substantial touch-potential on the cases.

Joined: Sep 2002
Posts: 1,498
C
C-H Offline
Member
Paul, what happens if it is an autotransformer?


[This message has been edited by C-H (edited 10-26-2004).]

Joined: Aug 2001
Posts: 7,520
P
Member
That possibility occurred to me as well. If it's an autotransformer then the output is already grounded via the incoming supply neutral.

Obviously you would not then put a separate bond to earth or you would have a parallel neutral/ground connection.

Joined: Jul 2002
Posts: 8,407
Member
Good call C-H!. [Linked Image]
Most Voltage Stabilisers that I've been associated with, have been of the Auto-Transformer type.
However, I can't say that I like the idea of the A-Transformer, there are Regulations here that limit thier use to 5% of input voltage, for safety reasons, one of them being, if there is a short-circuit in the Primary/Secondary winding, the output load recieves full Primary voltage.
Another thing that I must ask, are these Transformers made for continuous duty?, as they would be supplying a computer system.
Heat build-up in a transformer is usually thier biggest killer.

Joined: Jun 2002
Posts: 159
L
Member
hi trumpy,
open circuit on secondary will lead to primary voltage being imposed on secondary.
What about just using a double wound tx with any secondary pole earthed (but kept separate from building earth) to provide for filter caps.Relatively common arrangement to prevent protective conductor currents.


regards

lyle dunn

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