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1/14/2021 RMS PM Hardware User Manual 31 of 54
will only remain closed for about 3 seconds. The pre-charge sequence must complete
before this time or the inverter will declare a fault condition and open the pre-charge relay.
The pre-charge circuit should be fused with a small fuse appropriate to the wire used. Since
the pre-charge current is generally very low, approximately 0.5 amps in the example below,
small wire can be used (recommend 18 AWG). A 5 amp fuse would be appropriate for this
wire.
Sizing Example:
A typical application could have a maximum DC bus voltage of 320 volts. If a 600 ohm
resistor were chosen this would result in a power dissipation of 171 watts. This is within the
short term rating of a 50 watt wire-wound resistor. The internal capacitance of the controller
is approximately 500uF. It takes approximately 3 time constants before the controller will
close the main contactor, thus in this example it will take 0.9 seconds for the pre-charge to
complete.
Cascadia Motion can provide the following parts if needed. Reference the following:
• Pre-charge Relay (30A, 12V COIL): p/n 77-0026 for DX inverters
• Pre-charge Relay (50A/1000V, 12V COIL): p/n 77-0034 for DZ inverters
• Pre-charge Resistor (600 ohm 50W): p/n 53-0006 for DX inverters
• Pre-charge Resistor (1K ohm 100W): p/n 53-0008 for DZ inverters
• Pre-charge Fuse (5A 500V): p/n G1-0013-01 for DX inverters
• Pre-charge Fuse (5A 1000V): p/n G1-0015-01 for DZ inverters
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