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10-07-2012, 12:03 AM #1
480 input 240/120 output control transformer wiring mystery
In transfomer below, I presume I can achieve 480 volt input and get both 240 and 120 output, yes ? If so, how exactly ? The wire configeration chart seems a bit odd....can anyone explain it better ?
(The thumbnails are double posted but can't get "delete" function to work on the extra two)
10-07-2012, 04:03 AM #2
Looks fairly straightforward, you have 2x240 Volt Primary input windings and 2 x 120 Volt Secondary output windings. So for 480 V input the two 240V primaries are in series and to get the 120 Volt output the two secondaries are in parallel. One of the USA 3 phase voltages is 480V?, you can run a single phase transformer off two actives of three phase which looks like what they are doing here. My 415 volt stick welder works that way with a single 415V input winding connected to two active wires.
The only reason the wiring diagram is so specific about the connections, is so the phasing of the windings is correct, if you get the two 120V secondary windings in parallel and out of phase the voltages will cancel the magnetic field of each winding and you'll get zero volts out and the same goes for the 240V primary windings
10-07-2012, 09:43 AM #3
I hear ya SAG but I really just need to know exactly which "X" wires are connected together to achieve both 240 and 120 outputs, then what 2 wires (or combination of wires) do I connect to for 240... and what to connect to for 120 ? I don't need theory here, I need the numbers.
I mean, the way it's printed for all voltages except 120/240 is pretty straightforward. But for 120/240 I just don't get it. Do you literally wire X2, X3, X4 all together ? That makes no sense....and even if so, then what ? Output lines X1 X2 X4 ....which combination is 120 and which is 240 ?
Or is X2 to X4 connection really part of the 120 only configuration ?
Such a muddled printing.... It would have helped if they had put lines in to separate which connections were for what voltage to make it absolutely clear. As it is, involves some guessing.
10-07-2012, 10:25 AM #4
Primary: Tie H2 & H3
- apply 4XX V onto H1 and H4
Secondary: Tie X2 & X3
- find 2XX V between X1 and X4
- find 1XX V between X1 or X4 and the X2+X3 tie (which has been made into a center-tap)
120 V can be pulled off either X1. X4 side to X2+X3. Or some of each. The effective 'center-tap' now serving a similar function as the neutral of US std 240 /120 split-phase. It is otherwise NOT 'the' neutral, however.
Apologies for the sloppy lines...
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10-07-2012, 10:47 AM #5
As an aside, this transformer, being an enclosed potted type is not really typical of what would be used in a machine tool cabinet. But I noticed that no one seems to make a standard single phase under 1 kva, 240 x 480, 120/240 transformer in open style. All of the open style seem to be 120 or 240 on secondary, but never both voltages on secondary. I wonder why that is ?
10-07-2012, 11:04 AM #6
Improvement in clarity is an artifact. I took a 'screenshot' of your post (already 'enhanced' by your camera), smacked the lines onto it with an 'Inkscape' virtual felt-tip marker.
W/R 'potted'. The market for so called 'dry' transformers finds them hanging outdoors or 'barely' indoors on shed or garage walls all-too often. Most are filled with sand and a plastic resin as much to keep insects and vermin from nesting as to keep water out, yet still transfer 'some' heat safely.
The truly 'open' ones are still available, just not as commonly stocked.
10-07-2012, 01:16 PM #7
The "control" transformers are quite available, Hammond HPS (Hammond Power Solutions) makes a lot of them.
As for teh 120/240 vs 120 OR 240, there is NO difference. For 120/240, you wire the X2 and X3, etc just as for 240V, but you get the voltages as Thermite has mentioned. Current is the 240V current for ANY winding, so you get better usage if loads are balanced vs the "neutral" (the X2-X3 connection.).
Since it IS a neutral if you call it that, you can ground it (in fact you are supposed to for some purposes) if needed.