Okay, some more internet sleuthing and measurements of my isolation transformer has confirmed what I have been thinking. To change from a Boosting (+4.3%) configuration to a Bucking (-4.3%) configuration, the following changes are required within the case.
There are two sets of 4 wires, covered in white anti-chafe insulation. On the left side of the enclosure are two blues and two browns, labeled (J18, J15) and (J1x, J11). Each Brown and Blue make up a coil with a number of windings equal to some number ‘N’, each.
On the right side are two orange and two black, labeled (J30, J27) and (J28, J26). Each red and black pair make up a coil with 1.0435N windings each.
Since the intended output is known, the black jumpers are connected as per the manual to make the winding connections in order to get the desired output.
J29 is the “top” end of output coil number 1, routed on board to the Output Line connection
J25 is the “bottom” end of output coil number 2, routed on board to the Output Neutral connection.
When you want 230V output, you short together J31 and J32,
J31 is the “bottom” end of the output coil number 1.
J32 is the “top” end of the output coil number 2.
This effectively creates one “long” secondary coil that has 2.087*N windings.
When you want 115V output, you short together J31-J25 and J29-J32.
This is placing the two output coils in parallel with each other, effectively creating one “thicker” secondary coil hat have 1.0435*N windings (and can handle twice the current).
The beauty of this device is that you don’t need to know the incoming voltage, the device will figure this out for you. So, those same type of connections (making one long primary coil with 2*N windings, or one thicker primary coil with N windings) are being figure out and then made via relays on the control board.
In the central lower section of the control board is a wide-input range offline power supply (runs off AC) and likely some voltage comparators that are used to determine if the input is in the “good” low or “good” high range, and light LEDs and switch relays appropriately.
All that so say, that the reversing the connections of the the toroid transformer will not affect any of the operations of the unit.
So, my research (and years of electrical engineering experiences) leads me to believe that to change this device to be a ~-5% buck configuration, the following wires should be swapped:
J18 ↔ J30
J15 ↔ J27
J16 ↔ J28
J11 ↔ J26
This would result in the wire numbering, from left to right to be:
J30 J27 J28 J26 J18 J15 J16 J11
Normal (Boost) configuration:
Altered (Buck) configuration:
Can anyone confirm or refute these findings?
Mike