On Fri, 15 Oct 1999 06:18:13 -0600 Harrison Cooper writes: > But now a client has 380VAC 3 phase, and demands (I hate that!) to > use only > 220VAC single phase for all control voltages. If it's a standard Y type of service, then there is already 220 V available from either of the phases to neutral. If there are only 3 phase wires and ground installed, you'll need to have a neutral wire brought from the circuit panel to your equipment. Do not cheat and return neutral current through the ground wire. If it isn't practical to add a neutral wire, then a transformer could be used. > > I can find sources on 380 to 110 transformers, but can't seem to > locate > anything that will take 380 to 220, in either a control or > buck-boost. All > I need is about 250VA. I'm pretty sure such a transformer is made, there are ones with multiple taps on both sides for this sort of application. Look at Newark's catalog. You need a regular transformer, not an autotransformer. Using an autotransformer, part of the control circuit would be 380V or more above ground, which isn't very safe. If worst comes to worst, there are lots of tricks possible with transformers. One is to use two transformers. It would seem obvious to connect them in sequence (380 to 110 then 110 to 220), but it is probably better to use two 380 to 110 units, connecting the primaries in parallel and the secondaries in series to develop 220. (If you connect the secondaries out of phase in series, you get approximately nothing). Also it is possble to use a transformer at less than its rated voltage and the ratio of voltages will stay the same. For example if you can find a transformer designed for 480 to 277 volts, this usnit used with 380 V input will produce about 220V output. In this case, it is necessary to oversize the transformer since you are using a higher current through the windings for the same VA output. ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: http://dl.www.juno.com/dynoget/tagj.