Hi there fiddler!, Welcome to ECN. 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.
Re: Stepdown transformer & voltage stabilizer#141791 10/25/0403:16 AM10/25/0403:16 AM
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.
Re: Stepdown transformer & voltage stabilizer#141792 10/25/0411:05 AM10/25/0411:05 AM
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 firstname.lastname@example.org..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
Re: Stepdown transformer & voltage stabilizer#141793 10/25/0402:33 PM10/25/0402:33 PM
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.
Re: Stepdown transformer & voltage stabilizer#141794 10/26/0404:26 AM10/26/0404:26 AM
Good call C-H!. 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.
Re: Stepdown transformer & voltage stabilizer#141797 10/27/0401:38 PM10/27/0401:38 PM
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.