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Newbie here. I've got this old line interactive type UPS which cannot drive any inductive load. I suspect the issue is with inverter side of the cct as there is no issue when the commercial supply is on. The load is just below 1A AC and I'm guessing a simple low pass filter might help. Just going through a hard time with designing one by myself as I'm not much familiar with filter so it would be a huge help if someone can give me a hand with the designing part. Here are the requirements. Frequency: ~50Hz AC voltage: ~230V AC current: <1A

Thanks in advance!

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  • \$\begingroup\$ LPF will not help an inductive load \$\endgroup\$ – Sunnyskyguy EE75 Apr 11 at 4:25
  • \$\begingroup\$ What happens with the inverter when you try to drive the load? What does this mean: "there is no issue when the commercial supply is on." What is the commercial supply? In what way is it connected to the inverter when there is "no issue?" \$\endgroup\$ – mkeith Apr 11 at 6:01
  • \$\begingroup\$ @mkeith No any strange observations other than a noise, voltage also seems to be normal. Commercial supply means the actual 230VAC 50HZ power supply we get from the grid. This is a line interactive UPS so the inverter is inactive when grid supply is available. Only changing to active state via a relay when it is unavailable. \$\endgroup\$ – Komee Apr 11 at 8:03
  • \$\begingroup\$ @SunnyskyguyEE75 Only a guess because I have observed a lack of a filter in inverter circuit. \$\endgroup\$ – Komee Apr 11 at 8:04
  • \$\begingroup\$ @komee the surge current on inductive loads starts at Vp/DCR Ohms not 1A an this is often 5* rated current. So a LPF does not help DC resistance but an ICL rated for Vac 1A will limit Current on start \$\endgroup\$ – Sunnyskyguy EE75 Apr 12 at 17:32

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