Jump to content

What to use to precharge the inverter capacitors?


John
 Share

Recommended Posts

1 hour ago, John said:

As the title says are there any suggestions on the specifications of the resistor to reduce the inrush current when starting an inverter?

Hi John, are you planning to build an inverter from scratch? if not, then you do not to build any circuit to protect the inverter when you switch it on. Just connect it according to the installation manual and you will never go wrong. if it pops when powering ON, take it back to your supplier for warranty repairs or exchange 😀

Link to comment
Share on other sites

@hoohlocCharging the inverter's internal capacitors through a resistor is just a safety measure to prevent possible failure of the capacitors and other components in the DC circuit. Using a 100W 230V incandescent light bulb, as @Chris Louw suggested above, will prevent the capacitors from failing because of extreme inrush current and the subsequent hassle of disconnecting the inverter for a warranty claim. My inverters are out of warranty so won't do me any good. The inrush current of LFE batteries can be a few hundred amps so why take the chance that something may fail. 

Link to comment
Share on other sites

13 hours ago, ebrsa said:

The inrush current of LFE batteries can be a few hundred amps

Or indeed a few thousand amps. Inrush current is hard on the contactor or fuse contact that makes the initial connection. If you're making the final connection by hand, there is the danger of flash injury, burns from copper snot, damage to contacts or fuse casings, and the cost of new underpants 🩲🥴

I use high pulse power rated aluminium clad resistors, and a circuit that automatically shorts it out after a suitable time, so I never get lazy. Around 3.3 Ω and 50 W continuous / 1250 W pulse is good for 50 V systems. That limits the in-rush to some 15-18 A, depending on the battery voltage, and will pre-charge two 5 kVA inverters in less than a second.

I note that some packaged LFP batteries (e.g. Pylontech) may automatically limit the current to a manageable value for a short period of time (e.g. 1C for the battery), thereby automatically performing a reasonably graceful pre-charge. For a single US2000 Pylontech, that's about 50 A. I have no idea how hard that is on the internal MOSFETs, which have to dissipate half of the energy stored in the capacitors. If you have a lot of Pylontechs in parallel, as you eventually are likely to, the current limit will still be very harsh on contactors, fuse holders, etc.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...