Inverter Pre-charge circuit

[Old Timber guy]

Hi this is Rick
I'm new here and enjoying many hrs of reading past questions and posts. I have read everything I can find about pre-charging the inverter before connecting to battery. I believe I may have damaged or destroyed my 3 year old Giandel PS-3000KAR inverter, (for lack of knowledge on pre-charging)? My system is for emergency and hobby. My heating system is a pressurized wood boiler which needs constant power to circulation pumps, should we have an outage. Secondly we have freezers etc that are nice to keep running should the outage occur in the summer.

Anyway here is the problem, and the dumb question. Every component can be isolated by breakers, fuses, and battery switches. When the batteries are fully charged I generally turn off the panels first, then the battery from the CC, and sometimes I switch off the batteries from the inverter. The battery switch is rated for 600 amps, so I wasn't worried about an arc, but I never considered the in-rush on the inverter. I also use the battery switch to go back and forth between 2 battery banks, all of this successfully for 3 years. I have a new inverter, and I'm attempting to repair the old one with 24 new mosfets. The pre-charge circuit I'd like to include before installing the new inverter will use a light bulb as suggested by many. I'm planning to place it permanently wired into the system, choosing the bulb method as a visible confirmation of this often repeated action. Here's the dumb question: Should the pre-charge be needed every time I switch off the inverter, or only when I disconnect and reconnect the battery? Is it even advisable to leave the battery connected to the inverter for long periods of idle?

I will be posting a future inquiry on troubleshooting an inverter if I'm unsuccessful after replacing all the mosfets. This is the only suggested repair from Giandel tech, I can't find a schematic on the inverter or anyone that has made a repair?
Thanks for any help! Rick

 

[Hedges]

Precharge any time inverter's capacitors have been allowed to discharge.

My inverter has a circuit breaker which disconnects the battery input; that would let capacitors discharge.
It also has a front panel control to start and stop inverter operation. That doesn't discharge capacitors.

If there is voltage present across a switch which has been opened, precharge before closing the switch.

 

[JoeHam]

It can take many hours for the capacitors to discharge if everything is off but you’re better safe than sorry.

Fortunately there has been a little bit of discussion on the forum about how to handle the issue :

Search results for query: Pre charge

diysolarforum.com

 

[TacomaJoe]

I thought that pre charge was to protect the BMS.

 

[Mattb4]

...Here's the dumb question: Should the pre-charge be needed every time I switch off the inverter, or only when I disconnect and reconnect the battery? Is it even advisable to leave the battery connected to the inverter for long periods of idle?

...

Not sure about your Giandel but many mobile inverters On/Off switches control only the output and not the DC input. So turning them off does not interrupt battery voltage and your capacitors stay charged. If you disconnect the battery and the inverter is on you drain the capacitors. Thus the next time you reconnect the battery it will have to charge them back up. Being off the capacitors likely retain charge unless there is a internal power demand such as a power available light.

Leaving the battery connected to the inverter slowly drains your battery. More so if inverter is on. If you do not intend to use power from the inverter for some time having a DC breaker inline between battery and inverter to shut off can help preserve battery charge.

At least that is how I sus it out.

 

[upnorthandpersonal]

I thought that pre charge was to protect the BMS.

The BMS will shut down due to an over-current situation. It doesn't protect the BMS: it makes sure the BMS doesn't step in to protect the battery. It can also trip your breaker etc. without the pre-charge.

 

[Old Timber guy]

Thank you for the response, I did read many of these but must not have worded the search in a way that came up with all of these, I'll read further before asking any more questions.
Rick

Not sure about your Giandel but many mobile inverters On/Off switches control only the output and not the DC input. So turning them off does not interrupt battery voltage and your capacitors stay charged. If you disconnect the battery and the inverter is on you drain the capacitors. Thus the next time you reconnect the battery it will have to charge them back up. Being off the capacitors likely retain charge unless there is a internal power demand such as a power available light.

Leaving the battery connected to the inverter slowly drains your battery. More so if inverter is on. If you do not intend to use power from the inverter for some time having a DC breaker inline between battery and inverter to shut off can help preserve battery charge.

At least that is how I sus it out.

Thank you, I suspected that there was only a pre-charge needed when the battery is disconnected, not required when inverter is shut off. In my case of primarily using the system for grid power down times. I'm going to install a (push button with a bulb) pre-charge circuit before my new inverter. Thanks again!