Inverter Disconnect Switch with Precharge

Inverter Disconnect Switch with Precharge 2022-04-13

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This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on.

26 June 2020 update:
  • At request of a forum member I added a circuit design for 48 volts.
    Warning: I have not built/tested the 48 Volt design.
  • Added comments on how to build the circuit without the PTC thermistor.
28 July 2020 update
  • Expanded on building the circuit without the PTC thermistor. (It is not needed in many (Most?) situations)
8 August 2020 update
  • Updated link to PTC in the parts list.
5 October 2020 update
  • Added slide showing the connections in the four different switch states. (this helps explain how the circuit works)
  • Added label and printing instructions for Perco 8511 switch.
6 October 2020 Update
  • Added discussion of Inverter Disconnect vs Battery Disconnect
28 November 2020 Update
  • Added assembly picture for building w/o the PTC resistor.
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4.86 star(s) 7 ratings

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Excellent made mine with a blue sea switch. No more arcing!
I ordered 100w 20 ohm resistor. Will this work with 48v inverter? 😥
Please post the question to the general discusion board (Flag me with an @FilterGuy)
Thanks for the information! There is some really good stuff in there. One thing that seems to be missing is the timing of the pre-charge. Consider adding information on how to calculate how long the switch should be in the pre-charge before connecting directly.
A simple and elegant "foolproof" solution for someone like me.
The assembled photo was just what I needed to understand how to put this together
Simple solution. Thanks!
Thank you, I built and installed one based on your plans for a 200AH LifePO4 system with 48V and 3KVA inverter. No more sparks :-)
Great design for a vexing problem, thank you very much