# Ways to charge a VERY LARGE capacitor in a 3-phase bridge rectifier circuit

I need to charge two 1500uF-450V capacitors off of a 3-phase 220Vrms-60Hz line using a very robust bridge rectifier (datasheet) as well as both capacitors datasheet (datasheet).

Here's the simulation I performed taking into account ESR of approx $$\63\,m\Omega\$$ for each cap.

WITHOUT the inrush limiting resistor $$\R_2\$$, the inrush current peaks $$\4.2\,kA\$$ in one of the diodes (the max forward surge for each diode is $$\7500 A\$$ for $$\10\,ms\$$) and $$\1.5\,kA\$$ at each capacitor. The duration of both surges is approx 1ms.

The problem is I don't think this kind of surge is good for long-term in the circuit since it might cause tripping of breakers, and it's a very large current so I'm taking the safe path and trying to limit it with an inrush resistor.

The crux of the problem is how to properly design/choose both bypass switches S1 and S2. S1 bypasses the inrush resistor while S2 connects the load R3 to the DC voltage after reaching a reasonably okayish value (200 - 250 V).

I've looked up some solid state relays but most are rated for 40VDC max so it'd not help. Using an IGBT for both switches I think would suffice in my POV however I don't have the time to come up with a PCB or any other additional circuitry at the moment so an off-the-shelf solution would be best here.

Any thoughts on how could I approach that with available solutions?

• On the left side of your drawing, is that Neutral? If yes, it is tied to ground somewhere. Your circuit is also referenced to ground. D2/D4/D6 will be directly across the line, big boom. Oct 26, 2023 at 17:20
• @Mattman944 Circuit ground is arbitrary, and this is a fine reference point for simulation purposes. Oct 26, 2023 at 17:35
• It sounds like you need an inrush current limiter element, or circuit, or capacitor precharge. This is an interesting design exercise, but it sounds like you might not have much design time available; and keep in mind asking for off-the-shelf solutions is discouraged here. Oct 26, 2023 at 17:38
• What are the specs for "charging"? Oct 26, 2023 at 17:40
• @Mattman944 No, it's not neutral. That GND is just for ease of simulation so I could measure voltages with respect to load ground. In the real-world application I won't have a neutral. Oct 27, 2023 at 5:23