ACS800 ABB Drive Precharge Circuit Configuration

The pre-charge is done on the AC side on a stansdard ACS800.

You should not be racking a module in or out with the DC bus powered on - it is a maintenance function not to be taken lightly. But please check with ABB.

After much ginger testing with power on, then double checking what I could, I believe the circuit is a diode bridge, followed by a 32 ohm pre-charge resistor to limit the current, a contact around that resistor to short it out, three 2000uf (420vac)caps in series, with three discharge resistors around each of them (68K, 2 watt each).

So RC discharge time constant is about 42 seconds.

The UDC+ terminal connects to the output of the diode bridge, upstream of the 32 ohm resistor, the UDC- terminal connects directly to the "bottom" of the caps in series.