3 Phase power supply


Recently I came in the possession of a relatively small 3 phase transformer. It weights approx. 50 kg, so provided the possibility to build it in a 19" rack.

It's heavy, no doubt about that! But still can be moved to other locations, if needed.

The schematic is almost identical to the "small 3 phase power supply" which is described here. The only difference is the single phase rectification instead of the dual phase. (one diode stack instead of two per transformer tap). This is due to the much higher AC voltage provided by the secundairy of this transformer.

The power supply in its construction phase. On the left hand side of the bank of capacitors the PC boards with measuring circuits can be seen.

The PC board at the bottom contains the resistor chain for high voltage sensing and voltage measuring. The circuit on the left contains the over-current sensor with high voltage opto-coupler connection to the protection circuits.











At the front the various relays are located. The "big" relays in the 380V Ac lines are controlled by the 12 V DC relays.


Note the modified 3 phase 5 pin connector.

This connector does not protrude on the outside, thus preventing any damage to it. The same principle applies to the 10 kV high voltage connector, which can be seen in the right hand corner.









The finished power supply. Note the plexiglass board on which the 3 diode stacks are mounted.

This provided good insulation and does not obstruct the view to the underlying components.












The power supply during the various tests.

The 3 phase variac reduces the input voltage, if needed.












Another view of the finished power supply.













The power supply is built in a very compact way. The idle current of the transformer and the various bleeder resistors produce at least 100W of heat just in the stand-by mode of operation.

The total dissipation will only rise when the power supply is used while transmitting.


Hence the two blowers in the cover. The bottom plate of the cabinet is made of meshed aluminium, provinding a good airflow.









The modified 3 phase cable connector.

Left the original one, on the right hand side the modified connector.













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